CIVIL

Human anatomy and Physiology words

  Heart


ABCD rules for skin cancer: Carcinoma may become fatal if any of the following conditions exist: A: Asymmetry; the two sides of the pigmented area do not match; B: Border is irregular and exhibits indentations; C: Color (pigmented area) is black, brown, tan, and sometimes red or blue; D: Diameter is larger than 6 mm (1/4 inch).

Abdomen: Portion of the body between the diaphragm and the pelvis.

Abduction: Movement of a limb bone away from the median plane.

ABO-Rh blood types (blood groups): Classification of blood based on the presence or absence of inherited antigens on the surface of red blood cells; ABO blood types (groups) are determined by the presence or absence of A and B antigens; Rh blood types (groups) are determined by the presence or absence of the Rh (D) antigen. Also called blood groups.

Abscess: Localized accumulation of pus and disintegrating tissue.

Absolute refractory period: Period following stimulation during which no additional action potential can be evoked.

Absorption: Process of digestion products passing through the alimentary tube mucosa into the blood or lymph.

Abstinence: Refraining from sexual activity or other behaviors.

Accessory digestive organs: Organs that contribute to the digestive process but are not part of the alimentary canal; include the tongue, teeth, salivary glands, pancreas, liver.

Accommodation: The process of focusing the lens for close vision.

Acetabulum: Cup-like cavity on lateral surface of the hip bone that receives the femur.

Acetoacetic acid: A ketone body produced from fatty acid catabolism.

Acetone: A ketone body produced from fatty acid catabolism; it freely diffuses through plasma membranes and enters the bloodstream. Significant quantities of acetone are found in the blood and urine of people with diabetes.

Acetone breath: When significant quantities of acetone in the blood imparts an ethereal odor to the breath.

Acetylcholine (ACh): Chemical transmitter substance released by some nerve endings.

Acetylcholinesterase (AChE): Enzyme present at the neuromuscular junction that prevents continued muscle contraction in the absence of additional stimulation.

Achilles tendon: Tendon that attaches the calf muscles to the calcaneus (heel bone). Also called the calcaneal tendon.

Acid: A substance that releases hydrogen ions (H) when in solution; a proton donor.

Acid-base balance: Situation in which the pH of the blood is maintained between 7.35 and 7.45.

Acidic: A solution that has a pH lower than 7, and has more hydrogen ions (H) than hydroxide ions (OH– ). Acid solutions taste sour.

Acidosis: A state of abnormally low pH of arterial blood, which is often caused by an increase in the concentration of carbon dioxide.

Acini: Groups of cells in the pancreas that secrete digestive enzymes.

Acne: (1) Inflammatory disease of the skin during puberty. (2) Infection of the sebaceous glands by the bacteria Propionibacterium acnes.

Acoustic: Pertaining to sound or the sense of hearing.

Acrosome: A lysosome-like organelle in the head of a sperm cell containing enzymes that facilitate the penetration of a sperm cell into a secondary oocyte.

Actin: A contractile protein that is part of thin filaments in muscle fibers.

Action potential: An electrical signal that propagates along the membrane of a neuron or muscle fiber (cell); a rapid change in membrane potential that involves a depolarization followed by a repolarization. Also called a nerve impulse if formed in a neuron.

Activation energy: The minimum amount of energy required for a chemical reaction to occur.

Active immunity: Immunity produced by an encounter with an antigen; provides immunological memory.

Active site: Region on the surface of functional (globular) proteins that fit and interact chemically with other molecules of complementary shape and charge.

Active transport: Process that uses transport proteins to move substances across a cell membrane, against the concentration gradient, by using energy provided by ATP.

Acute: Having rapid onset, severe symptoms, and a short course; not chronic.

Adam’s apple: The projection on the anterior portion of the neck formed by the thyroid cartilage of the larynx. Also called the laryngeal prominence.

Adaptation: (1) Any change in structure or response to suit a new environment. (2) Adjustment of the pupil of the eye to changes in light intensity. (3) The decrease in perception of a sensation over time while the stimulus is still present.

Adduction: Movement of a limb bone toward the median plane.

Adductor longus and magnus: Anterior, medial thigh muscles; adduct, flex and rotate thigh. O: Pubis. I: Femur.

Adenine (A): One of the two major purines found in both RNA and DNA; also found in various free nucleotides of importance to the body, such as ATP.

Adenitis: Inflammation of a lymph node or of a gland.

Adenohypophysis: Anterior pituitary; the glandular part of the pituitary gland.

Adenoid: A collection of lymphoid follicles on the posterior wall of the nasopharynx. Also called pharyngeal tonsil.

Adenosine diphosphate: The substance formed when ATP is hydrolyzed and energy is released. Also called ADP.

Adenosine triphosphate: Organic molecule that stores and releases chemical energy for use in body cells. Also called ATP.

Adenylate cyclase: An enzyme that converts ATP into cyclic AMP (cAMP), a crucial step in the regulation and formation of second messengers.

Adipocyte: An adipose, or fat cell.

Adipose connective tissue: Tissue with closely packed cells that have large central fat droplets and peripheral nuclei, and a sparse gel-like matrix with fibers. Functions as an energy reserve, insulation against heat loss, support and protection of organs. Located in hypodermis under the skin, in breasts, around kidneys, behind eyeballs, and widely distributed as body fat.

Adrenal glands: Hormone producing glands located superior to the kidneys; each consists of medulla and cortex areas.

Adrenaline: Hormone secreted by the adrenal medulla that produces actions similar to those that result from sympathetic stimulation. Also called epinephrine.

Adrenergic neuron: A neuron that releases epinephrine (adrenaline) or norepinephrine (noradrenaline) as its neurotransmitter.

Adrenocorticotropic hormone (ACTH): Anterior pituitary hormone that stimulates the growth of the adrenal cortex and secretion of its hormones. Also called corticotropin.

Adventitia: Outermost layer or covering of an organ.

Aerobic: Requiring molecular oxygen.

Aerobic endurance: The length of time a muscle can continue to contract using aerobic pathways.

Aerobic respiration: Respiration in which oxygen is consumed and glucose is broken down entirely; water, carbon dioxide, and large amounts of ATP are the final products.

Afferent: Carrying to or toward a center.

Afferent arteriole: A blood vessel of a kidney that divides into the capillary network called a glomerulus.

Afferent (sensory) nerve: Nerve that contains processes of sensory neurons and carries nerve impulses to the central nervous. system.

Afferent (sensory) neuron: Nerve cell that carries impulses toward the central nervous system; initiates nerve impulses following receptor stimulation.

Afterbirth: The placenta and fetal membranes that are extruded from the uterus after birth.

Ageusia: Loss of the sense of taste.

Agglutination: Clumping of cells in suspension, which settle out of the mixture; induced by crosslinking of the cells by agglutinating antibodies (agglutinins).

Aggregated lymphoid nodules: (1) Collections of many lymphoid follicles in the ileum (Peyers patches). (2) Masses of lymphoid tissue in the vermiform appendix.

Agnosia: Inability to recognize the significance of sensory stimuli such as sounds, sights, smells, tastes, and touch.

Agonist: Muscle that bears the major responsibility for effecting a particular movement. Also called the prime mover.

AIDS: Acquired immune deficiency syndrome; caused by human immunodeficiency virus (HIV); symptoms include severe weight loss, night sweats, swollen lymph nodes, opportunistic infections.

Albinism: Abnormal, nonpathological, partial, or total absence of pigment in skin, hair, and eyes.

Albumin: The most abundant plasma protein; helps regulate the osmotic pressure of blood.

Alcohol: Organic compound that contains hydroxyl groups (-OH) and is usually soluble in water (e.g., sugars).

Aldosterone: A mineralocorticoid produced by the adrenal cortex that promotes sodium and water reabsorption by the kidneys and potassium excretion in urine.

Alimentary canal: The continuous muscular digestive tube extending from the mouth to the anus, which includes the oral cavity, pharynx, esophagus, stomach, small and large intestines, rectum, and anal canal.

Alkaline (basic): A solution that has a pH higher than 7, and has more hydroxide ions (OH– ) than hydrogen ions (H). Alkaline solutions taste bitter.

Alkalosis: A state of abnormally high pH of arterial blood, which is often caused by a decrease in the concentration of carbon dioxide.

Allantois: A small, vascularized outpouching of the embryonic yolk sac that serves as an early site for blood formation and development of the urinary bladder; its blood vessels develop into blood vessels of the umbilical cord.

Alleles: Alternate forms of a single gene that control the same inherited trait and are located at the same position on homologous chromosomes.

Allergen: An antigen that induces an allergic or hypersensitivity reaction.

Allergy: Hypersensitivity caused by exposure to an allergen that, on subsequent exposure, often results in harmful immunologic consequences, such as severe inflammation or tissue damage.

Alopecia: Baldness.

Alpha brain wave: A wave pattern in the encephalogram in the frequency band of 8–13 Hz; found in the awake, relaxed person with closed eyes. Also called alpha rhythm.

Alpha fibers: Large somatic motor or proprioceptive nerve fibers with conducting impulses at rates of 80–120 m/sec.

Alpha helix: The most common type of secondary structure of the amino acid chain in proteins; resembles the coils of a telephone cord.

Alveolar duct: Branch of a respiratory bronchiole around which alveoli and alveolar sacs are arranged.

Alveolar (acinar) gland: A gland whose secretory cells form small, flask-like sacs.

Alveolar macrophage: Highly phagocytic cell found in the alveolar walls of the lungs.

Alveolar ventilation rate (AVR): An index of respiratory efficiency; measures volume of air wasted and flow of fresh gases in and out of alveoli.

Alveoli: (1) Microscopic air sacs that are the actual sites of gas exchange in the lungs. (2) Tiny milk producing, glandular sacs in the breast. Singular is alveolus.

Alzheimer’s disease: Degenerative brain disease resulting in progressive loss of memory and motor control, and increasing dementia.

Amenorrhea: Absence of menstruation.

Amino acid: Building block of proteins and peptides; organic compound containing an amino group, carboxylic acid group, R group, and H atom, all covalently bonded to a carbon atom.

Ammonia (NH): Common waste product of protein breakdown in the body; a colorless volatile gas, very soluble in water and capable of forming a weak base; a proton acceptor.

Amnesia: A lack or loss of memory.

Amniocentesis: A common form of fetal testing in which a small sample of fluid is removed from the amniotic cavity.

Amnion: Fetal membrane that forms a fluid filled sac around the embryo and fetus.

Amoeboid motion: The flowing movement of the cytoplasm of a phagocyte.

Amphiarthrosis: A slightly movable joint.

Amphipathic: A molecule that contains both hydrophilic and hydrophobic regions, such as phospholipids and detergents.

Amphoteric: A compound that contains both an acidic and a basic site; e.g., amino acids.

Ampulla: A localized dilation of a canal or duct.

Amylase: Digestive system enzyme that breaks down starch and glycogen into maltose.

Anabolism: Metabolic synthesis reactions that combine small molecules to build larger molecules, usually with the net absorption of energy.

Anaerobic: Not requiring oxygen.

Anaerobic glycolysis: Energy yielding conversion of glucose to lactic acid in various tissues, notably muscle, when sufficient oxygen is not available.

Anaerobic threshold: The point at which muscle metabolism converts to anaerobic glycolysis.

Anal canal: Terminal portion of the alimentary canal, 3-4 cm long, lined with stratified squamous epithelium; distal portion is surrounded by the internal and external anal sphincters.

Analgesia: Pain relief; absence of the sensation of pain.

Anaphase: The third stage of mitosis in which the chromatids that have separated at the centromeres move to opposite poles of the cell.

Anaphylaxis: A hypersensitivity (allergic) reaction in which IgE antibodies attach to mast cells and basophils, causing them to produce mediators of anaphylaxis (histamine, leukotrienes, kinins, and prostaglandins) that bring about increased blood permeability, increased smooth muscle contraction, and increased mucus production. Examples are hay fever, hives, and anaphylactic shock.

Anaplasia: Loss of structural differentiation, especially as seen in most malignant neoplasms. Also called dedifferentiation.

Anastomosis: A union or joining of nerves, blood vessels, or lymphatics.

Anatomical position: A position of the body universally used in anatomical descriptions in which the body is erect, the head is level, the eyes face forward, the upper limbs are at the sides, the palms face forward, and the feet are flat on the floor.

Anatomy: Study of the structure of living organisms.

Androgens: Generic term for the male sex hormones, such as testosterone and dihydrotestosterone.

Androgen binding protein (ABP): A carrier protein secreted by sustentacular (Sertoli) cells that maintains high high levels of testosterone in the testes, which enhances spermatogenesis in the seminiferous tubules and sperm maturation in the epididymis.

Anemia: Reduced oxygen carrying ability of blood. Hemorrhagic anemia is caused by sudden hemorrhage. Hemolytic anemia is caused by an increased rate of RBC destruction. Pernicious anemia is caused by lack of vitamin B12 or defect of intrinsic factor. Aplastic anemia is caused by defective regeneration of bone marrow.

Anesthesia: A total or partial loss of feeling or sensation; may be general or local.

Aneurysm: A saclike enlargement of a blood vessel or heart chamber caused by a weakening of its wall.

Angina pectoris: Severe suffocating chest pain caused by a brief lack of oxygen supply to the heart muscle.

Angiotensin II: A hormone activated by renin that is a potent vasoconstrictor, stimulates release of aldosterone, and increases blood pressure.

Anion: Negatively charged ion; most nonmetal elements can gain electrons and become anions.

Ankylosis: Severe or complete loss of movement at a joint as the result of a disease process.

Anorexia: Diminished appetite; aversion to food.

Anorexia nervosa: A mental disorder primarily affecting young women, and manifested by extreme fear of becoming obese and an aversion to food, often resulting in life-threatening weight loss.

Anoxia: Deficiency of oxygen.

Antagonism: A situation that occurs when two agents oppose the action of each other.

Antagonist muscle: A muscle that reverses, or opposes, the action of another muscle.

Anterior: Nearer the front part of the body; equivalent to ventral in bipeds.

Anterior fontanel: A diamond-shaped membranous interval in the skull of a fetus and infant; located at the junction of the coronal, sagittal, and frontal sutures, where the frontal angles of the parietal bones meet the two ununited halves of the frontal bone.

Anterior pituitary gland: Anterior lobe of the pituitary gland that secretes the hormones thyroid-stimulating hormone (TSH), adrenocorticotropic hormone (ACTH), follicle-stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), growth hormone (GH), and melanocyte-stimulating hormone (MSH). Also called the adenohypophysis.

Antibody: A protein molecule synthesized by plasma cells derived from B lymphocytes in response to the introduction of an antigen. Antibodies are divided into five kinds (IgA, IgD, IgE, IgG, IgM). Also called an immunoglobulin.

Anticoagulant: A substance that can delay, suppress, or prevent the clotting of blood.

Anticodon: The three base sequence complementary to the messenger RNA (mRNA) codon.

Antidiuretic: Substance that inhibits urine formation.

Antidiuretic hormone (ADH): A hormone secreted by neurosecretory cells in the hypothalamus and stored in the posterior pituitary gland; stimulates water reabsorption by kidneys, causes vasoconstriction of arterioles, inhibits sweat glands. Also called vasopressin.

Antigen (Ag): A substance capable of eliciting an immune response, that reacts with immune cells or antibodies; antigen is a contraction of antibody generator.

Antigenic determinant: The particular site on an antigen that binds to a particular antibody and determines immunologic specificity; many antigens have several different antigenic determinants, and each binds to a different antibody. Also called an epitope.

Antigen presenting cells (APC): Special class of migratory cell that processes and presents antigens to lymphocytes during an immune response; include macrophages, B cells, and dendritic cells.

Antrum: Any nearly closed cavity or chamber, especially one within a bone, such as a sinus.

Anucleate cell: Cell without a nucleus.

Anuria: Absence of urine formation, or daily urine output of less than 50 mL.

Anus: Distal end of digestive tract; outlet of rectum.

Aorta: Major systemic artery; arises from the left ventricle of the heart.

Aortic body: Cluster of chemoreceptors in the aortic arch that are sensitive to changing oxygen, carbon dioxide, and pH levels of the blood.

Aortic valve: The heart valve between the left ventricle and the ascending aorta; it consists of three fibrous semilunar cusps. Also called left semilunar valve, or left SL valve.

Apex: The pointed end of a conical structure, such as the apex of the heart.

Apgar score: Evaluation of an infant’s physical status at 1 and minutes after birth by assessing five criteria: heart rate, respiration, color, muscle tone, and reflexes.

Aphasia: Loss of ability to express oneself properly through speech or loss of verbal comprehension.

Apical: Located at the apex, or extremity, of a structure; opposite of basal.

Apnea: Absence of breathing..

Apneustic area: Part of the respiratory centers; nuclei in the pons that sends stimulatory nerve impulses to the inspiratory area that activate and prolong inhalation and inhibit exhalation.

Apocrine gland: An exocrine gland in which the secretory products gather at the free end of the secreting cell and are pinched off, along with some of the cytoplasm, to become the secretion, as in mammary glands.

Apocrine sweat glands: Sudoriferous glands that open into hair follicles, and develop during puberty in the axilla and pubis; they secrete a viscous milky sweat that supports bacteria growth, leading to body odor.

Apoenzyme: The protein portion of an enzyme.

Aponeurosis: A sheetlike tendon joining one muscle with another or with bone.

Apoptosis: Programmed cell death of certain body cells; cell suicide.

Appendicitis: Inflammation of the appendix (worm-like sac attached to the cecum of the large intestine).

Appendicular: Relating to the limbs; one of the two major division of the body.

Appendix: A wormlike tube attached to the cecum that contains masses of lymphoid tissue. Also called the vermiform appendix.

Appositional growth: Growth by the addition of new layers to the surface those previously formed, as in the growth in diameter of cartilage and bone.

Aqueous humor: Transparent watery fluid in the anterior segment of the eyeball.

Arachnoid mater: The weblike middle layer of the three meninges of the brain and spinal cord.

Arachnoid villus: Berrylike tuft of the arachnoid mater that protrudes into the superior sagittal sinus and through which cerebrospinal fluid is reabsorbed into the bloodstream.

Arbor vitae: The white matter tracts of the cerebellum, which have a treelike appearance when seen in midsagittal section.

Areola: Any tiny space in a tissue. The pigmented ring around the nipple of the breast.

Areolar connective tissue: Tissue with many cell types and a gel-like matrix with fibers. Functions in protection against disease; holds and conveys tissue fluid; wraps and cushions organs. Located under the basement membrane that is attached to epithelium; forms lamina propria of mucous membranes; surrounds capillaries and body organs.

Arousal: Awakening from sleep, a response due to stimulation of the reticular activating system (RAS).

Arrector pili: Tiny smooth muscles attached to hair follicles that cause the hair to stand upright when activated, resulting in “goose bumps.”

Arrhythmia: Irregular heart rhythm caused by defects in the intrinsic conduction system.

Arteries: Blood vessels that conduct blood away from the heart and into the circulation.

Arteriole: A small, almost microscopic, artery that delivers blood to a capillary.

Arteriosclerosis: Group of diseases characterized by thickening of the walls of arteries and loss of elasticity.

Arthritis: Inflammation of the joints.

Arthroscopic surgery: Procedure enabling a surgeon to repair the interior of a joint through a small incision.

Articular capsule: Double layered capsule composed of an outer fibrous capsule lined by synovial membrane; encloses the joint cavity of a synovial joint.

Articular cartilage: Hyaline cartilage covering bone ends at movable joints.

Articular disc: A fibrocartilage pad attached to the joint capsule and separating the articular surfaces of the bones in some synovial joints.

Articulation: A joint; the junction of two or more bones.

Arytenoid cartilages: A pair of small cartilages of the larynx that attach to the vocal folds and intrinsic pharyngeal muscles, which can move the vocal folds.

Asphyxia: Impaired exchange of oxygen and carbon dioxide in the lungs, resulting in hypoxia and hypercapnia.

Association areas: Functional areas of the cerebral cortex that act mainly to integrate diverse information for purposeful action.

Association fibers: Neuron axons that connect different parts of the same hemisphere; short fibers connect adjacent gyri, and long fibers connect different cortical lobes.

Association neurons: Nerve cells located between sensory and motor neurons that govern coordinated activity. Also called interneurons.

Asthma: An inflammatory disease of the lungs; airways become inflamed due to irritation, bronchioles constrict due to muscle spasms, and characterized by episodes of coughing, wheezing, dyspnea, and chest tightness.

Astigmatism: A condition in which unequal curvatures in different parts of the lens (or cornea) of the eye lead to blurred vision.

Astrocyte: A type of CNS supporting cell with a star shape that assists in exchanges between blood capillaries and neurons, and helps to form the blood-brain barrier.

Ataxia: Disruption of muscle coordination resulting in inaccurate movements.

Atelectasis: Lung collapse.

Atherosclerosis: Changes in the walls of large arteries consisting of lipid deposits on the artery walls; the early stage of arteriosclerosis.

Atherosclerotic plaque: A lesion that results from accumulated cholesterol and smooth muscle cells of the tunica media of an artery; may become obstructive.

Atmospheric pressure: Force that air exerts on the surface of th body.

Atom: Smallest unit of matter that retains an element’s properties; composed of protons, neutrons, and electrons.

Atomic mass number: Sum of the number of protons and neutrons in the nucleus of an atom, which determines over 99.9% of the mass, in amu, of that atom. Also called mass number.

Atomic number: The number of protons in an atom, which determines the identity of the element.

Atomic symbol: The 1 or 2 letter symbol used to indicate an element; usually the first letter(s) of the element’s name.

Atomic weight: The average of the mass numbers of all the isotopes of an element.

ADP: The substance formed when ATP is hydrolyzed and energy is released. Also called adenosine diphosphate.

ATP: The universal energy carrier; organic molecule that stores and releases chemical energy for use in cells. Also called adenosine triphosphate.

Atria: The two superior receiving chambers of the heart that are separated internally by the interatrial septum, and their walls are ridged by pectinate muscles; their function is to pass blood to the ventricles; the right atrium receives blood from the coronary sinus, and the superior and inferior vena cava; the left atrium receives blood from the right and left pulmonary veins.

Atrial fibrillation: Rapid irregular twitchings of atrial muscle that results in the cessation of atrial pumping.

Atrial natriuretic peptide (ANP): A hormone released by certain cells of the heart atria; reduces blood pressure and blood volume; promotes kidney salt and water excretion by inhibiting release of renin, angiotensin, aldosterone, and antidiuretic hormone.

Atrioventricular bundle: The part of the conduction system of the heart that conduct impulses from the AV node to the right and left ventricles. Also called bundle of His, or AV bundle.

Atrioventricular node: The part of the conduction system of the heart made up of a specialized mass of conducting cells located at the atrioventricular junction in the heart. Also called the AV node.

Atrioventricular septum: The wall between the atria and ventricles of the heart.

Atrioventricular valves: The two valves that prevent backflow into the atria when the ventricles are contracting; they are pliable and remain open most of the time; the cusps of the valves are attached to chordae tendineae which are attached to papillary muscles in the ventricles; they include the tricuspid valve between the right atrium and right ventricle of the heart, which consists of three fibrous cusps (also called right AV valve), and the bicuspid valve between the left atrium and left ventricle of the heart, which consists of two fibrous cusps (also called mitral valve, or left AV valve).

Atrophy: Reduction in size or wasting away of an organ or cell resulting from disease or lack of use.

Auditory canal: The S-shaped tube that leads to the eardrum. Also called external acoustic meatus.

Auditory ossicles: The three tiny bones serving as transmitters of vibrations and located in the middle ear, called the malleus (hammer), incus (anvil), and stapes (stirrup).

Auditory tube: Tube that connects the middle ear and the pharynx. Also called eustachian tube, or pharyngotympanic tube.

Auricles of atria: Small ear-shaped pouches that project from the superior anterior portion of each atrium of the heart; they increase the atrial volume.

Auscultation: Examination by listening to sounds in the body.

Autocrine hormone: A local chemical messenger that acts on the same cell that secretes it.

Autoimmune disease: Any disorder in which normal tissue is destroyed by the production of antibodies or T cells that attack the body’s own tissue.

Autolysis: Process of autodigestion (self-digestion) of cells, especially dead or degenerate cells.

Autograft: A transplant of tissue or an organ into a new position in the body of the same person.

Autonomic nervous system (ANS): Efferent division of the peripheral nervous system that innervates cardiac and smooth muscles and glands. Also called the involuntary or visceral motor system.

Autonomic (visceral) reflexes: Reflexes that activate smooth or cardiac muscle and/or glands.

Autopsy: The examination of the body after death.

Autoregulation: The automatic adjustment of blood flow to a particular body area in response to its current requirements.

Autosomes: Chromosomes number 1 to 22 in humans; do not include the sex chromosomes.

Avogadro’s number: The number of molecules in one mole of a substance, equal to 6.0221367 x 1023 .

Axial: Relating to the head, neck, and trunk; one of the two major divisions of the body.

Axilla: The small hollow beneath the arm where it joins the body at the shoulders. Also called the armpit.

Axolemma: The plasma membrane of a neuron axon.

Axon: Cell process that conducts nerve impulses away from a neuron cell body.

Axon hillock: The conical area of the neuron cell body where the axon begins and the nerve impulse is generated.

Axon terminal: The terminal branch of an axon that contains neurotransmitters, and makes synaptic contacts with the postsynaptic cell (another neuron, muscle or gland cell).


b (2)

B cell: Type of lymphocyte that becomes immunocompetent in the bone marrow; when properly stimulated by a specific antigen, it can develop into a clone of antibody producing plasma cells or memory B cells. Also called B lymphocyte.

Ball and socket joint: A multiaxial synovial joint in which the hemispherical end of one bone fits into the corresponding cuplike cavity in the other bone, allowing motion in all planes.

Baroreceptor: Receptor that is stimulated by pressure changes. Also called a pressoreceptor.

Basal: Located at the base, or lowest part, of a structure. Opposite of apical.

Basal cell carcinoma: Most common and least harmful type of skin cancer, where stratum basale cells proliferate and invade the dermis and hypodermis, causing tissue destruction.

Basal body: The elongated part of a cell centriole that forms the bases of cilia and flagella.

Basal ganglia: Specific gray matter areas located deep within the white matter of the cerebral hemispheres; contains the corpus striatum which has subcortical motor nuclei involved in regulating voluntary motor activities; regulates initiation and termination of body movements; controls skill learning. Also called the basal nuclei.

Basal metabolic rate (BMR): Rate at which energy is expended by the body per unit time under controlled (basal) conditions: at rest and 12 hours after a meal.

Basal nuclei: Specific gray matter areas located deep within the white matter of the cerebral hemispheres. Also called basal ganglia.

Basal surface: The surface near the base or interior of a structure; nearest the lower side or bottom of a structure.

Base: A substance that releases hydroxide ions (OH– ), or accepts hydrogen ions (H) in solution; a proton acceptor.

Basement membrane: Thin extracellular supporting sheet between epithelium and connective tissue that acts as a selective filter; composed of two layers, the basal lamina and reticular lamina.

Basilar membrane: A membrane in the cochlea of the internal ear that separates the cochlear duct from the scala tympani and on which the organ of Corti rests; it is set into resonance when sound waves are absorbed and activates the hearing receptor cells.

Basophil: Granular white blood cell that releases histamine and other mediators of inflammation; contains the anticoagulant heparin; its granules take up basic stain and turn blueish.

Benign: Not malignant.

Beta brain wave: A wave pattern in the electroencephalogram in the frequency band of 18–30 Hz; found in mentally active people. Also called beta rhythm.

Beta fibers: Nerve fibers that have conduction velocities of 40–70 m/sec.

Biceps: Two headed, especially applied to certain muscles.

Biceps brachii: Superficial, anterior arm muscle; flex and supinate forearm. O: Scapula. I: Proximal radius.

Bicuspid valve: The heart valve closing the orifice between the left atrium and left ventricle of the heart; it consists of two fibrous cusps. Also called mitral valve, left atrioventricular valve, or left AV valve

Bilateral: Pertaining to two sides of the body.

Bile: Greenish fluid secreted by the liver, stored in the gallbladder, and released into the small intestine, where it emulsifies lipids prior to their digestion; it consists of cholesterol, phospholipids, and salts of oxidized steroids and heme.

Bilirubin: An orange pigment that is one of the end products of hemoglobin breakdown in the hepatocytes and excreted as a waste material in bile.

Biofeedback: Training that provides an awareness of visceral activities; enables an element of voluntary control over autonomic body functions.

Biogenic amines: Class of neurotransmitters, including catecholamines and indolamines.

Bipolar neuron: Nerve cell with an axon and dendrite that extend from opposite sides of its cell body; rare neuron type found only in the retina of the eye, the olfactory region of the nose, and the inner ear.

Blastocele: The fluid filled cavity within the blastocyst.

Blastocyst: The conceptus in the postmorula stage with a single layer of outer cells (trophoblast) which encloses an inner cell mass (embryoblast) and a fluid-filled blastocyst cavity (blastocele).

Blastomere: One of the cells formed by the early cleavage divisions of the zygote.

Blind spot: Area in the retina at the end of the optic nerve in which there are no photoreceptors.

Blood: Tissue with red and white blood cells in a fluid matrix. Functions in transport of respiratory gases, nutrients, wastes, and other substances. Located within the heart and blood vessels.

Blood brain barrier: A barrier consisting of specialized brain capillaries and astrocytes that prevents the passage of materials from the blood to the cerebrospinal fluid and brain; reflects relative impermeability of brain capillaries.

Blood capillary: The smallest of the blood vessels and the sites of exchange between the blood and tissue cells.

Blood circulation: The course of the blood from the heart through the arteries, capillaries, veins, and back to the heart; subdivided into three pathways: (1) the coronary circulation that supplies the myocardium, in which blood flows from the ascending aorta, through the coronary arteries and capillaries, and returns through the cardiac veins and coronary sinus to the right atrium; (2) the pulmonary circulation, in which deoxygenated blood flows from the right ventricle through the pulmonary arteries to the capillaries of the lungs, and oxygenated blood returns through the pulmonary veins to the left atrium; (3) the systemic circulation, in which oxygenated blood flows from the left ventricle to the aorta and through the arteries to the capillaries of the body, and deoxygenated blood returns through the veins and the superior and inferior vena cava to the right atrium.

Blood groups: Classification of blood based on the presence or absence of inherited antigens on the surface of red blood cells; ABO blood groups (types) are determined by the presence or absence of A and B antigens; Rh blood groups (types) are determined by the presence or absence of the Rh (D) antigen. Also called ABO-Rh blood types.

Blood pressure (BP): Force exerted by blood against the walls of blood vessels due to contraction of the heart and influenced by the elasticity of the vessel walls.

Blood testis barrier: A barrier formed by Sertoli cells that prevents an immune response against antigens produced by spermatogenic cells, by isolating the cells from the blood.

Bolus: A rounded mass of food prepared by the mouth for swallowing; any soft round mass.

Bone connective tissue: Tissue with osteocytes that lie in lacunae, a hard calcified matrix, many collagen fibers, and highly vascularized. Functions in support and protection, provides levers for muscle action, and stores minerals. Located in bones. Also called osseous tissue.

Bone matrix: The extracellular substance of bone tissue consisting of collagen fibers and ground substance, before the deposition of inorganic bone salts.

Bone remodeling: Process involving bone formation and destruction in response to hormonal or mechanical stress factors.

Bone resorption: The removal of osseous tissue by osteoclasts; can be part of the normal bone remodeling process, or for the maintainance of blood calcium ion homeostasis, or part of a pathologic process.

Bony labyrinth: A series of cavities within the temporal bone forming the vestibule, cochlea, and semicircular canals of the inner ear.

Bony thorax (thoracic cage): Bones that form the framework of the thorax; includes sternum, ribs, and thoracic vertebrae.

Bowman’s capsule: Double-walled cup at a renal tubule; encloses a glomerulus. Also called the glomerular capsule.

Boyle’s law: States that when the temperature is constant, the volume of a gas is inversely proportional to its pressure, and the relationship between initial and final pressures and volumes of a gas is: P1 V1 = P2 V2

Brachial plexus: A network of nerves that supply the upper limb, originating from the ventral rami of spinal nerves C5, C6, C7, C8, and Tl.

Brachialis: Deep, anterior arm muscle; flex forearm. O: Distal humerus. I: Proximal ulna.

Brachioradialis: Superficial, lateral forearm muscle; synergist in forearm flexion; stabilizes elbow. O: Distal humerus. I: Radius. Forearm flexors are anterior to the brachioradialis; forearm extensors are posterior to the brachioradialis.

Bradycardia: An abnormally slow, resting heartbeat or pulse rate, that is under 50 beats per minute.

Brain: The part of the central nervous system contained within the cranial cavity.

Brain death: State of irreversible coma, even though life support measures may have restored other body organs.

Brain stem: The portion of the brain immediately superior to the spinal cord, made up of the medulla oblongata, pons, and midbrain.

Brain ventricle: Fluid filled cavity of the brain.

Brain waves: Electrical signals that can be recorded from the skin of the head due to electrical activity of brain neurons.

Branchial groove: An indentation of the surface ectoderm in the embryo; the external auditory canals develop from these.

Broad ligament: A double fold of parietal peritoneum attaching the uterus to the side of the pelvic cavity.

Broca’s area: Located in the frontal lobe; essential component of the motor mechanisms governing articulated speech. Also called the motor speech area. (Brodmann areas 44, 45)

Brodmann areas: Areas of the cerebral cortex mapped on the basis of cytoarchitectural patterns by the German physician Korbinian Brodmann (1868–1918).

Bronchi: The large branches from the trachea that leads to the lungs.

Bronchial tree: The trachea, bronchi, and their branching structures up to and including the terminal bronchioles.

Bronchioles: Small, branching air passageways inside the lungs, smaller than 1 mm in diameter, with abundant smooth muscle and elastic fibers, but no cartilage in its wall.

Bronchitis: A lung disorder where airways become inflamed, mucus production increases, and coughing brings up mucus and pus.

Brunner’s gland: See Duodenal gland.

Buccal: Pertaining to the cheek or mouth.

Buccinator: Cheek muscle; compress cheek, as in sucking and whistling. O: Maxilla and mandible near molars. I: Orbicularis oris.

Buffer: A solution that resists changes in pH; contains a weak acid and its conjugate base.

Bulbourethral glands: Paired accessory reproductive glands in the male, lying inferior to the prostate on either side of the urethra; that release secretions prior to ejaculation, which contain alkaline fluid that neutralizes acid in the male urethra, and mucus for lubrication. Also called Cowper’s glands.

Bulimia: Episodic binge eating.

Bulimia nervosa: A mental disorder occurring predominantly in young women, characterized by episodic binge eating followed by self-induced vomiting, use of laxatives or diuretics, fasting, or vigorous exercise to prevent weight gain; often accompanied by feelings of guilt, depression, or self-disgust. Also called binge-purge syndrome.

Bulk-phase endocytosis: A process by which most body cells can ingest membrane-surrounded droplets of interstitial fluid.

Bundle branch: One of the two branches of the atrioventricular (AV) bundle made up of specialized muscle fibers (cells) that transmit electrical impulses to the ventricles.

Bundle of His: The part of the conduction system of the heart that conduct impulses from the AV node to the right and left ventricles. Also called the atrioventricular (AV) bundle.

Burn: Tissue damage inflicted by intense heat, electricity, radiation, or certain chemicals, all of which denature cell proteins and cause cell death in the affected areas.

Bursa: A closed sac lined with synovial membrane and filled with synovial fluid that reduces friction in a synovial joint, and is often found over an exposed body part.

Bursitis: Inflammation of a bursa.

Buttocks: The two fleshy masses on the posterior aspect of the inferior trunk, formed by the gluteal muscles.


C

Calcaneal tendon: Tendon that attaches the calf muscles to the calcaneus (heel bone). Also called the Achilles tendon.

Calcification: A process where tissue becomes hardened as the result of deposits of insoluble salts, such as hydroxyapatite; normally occurs only in the formation of bone and teeth.

Calcitonin (CT): Hormone released by the thyroid gland that lowers blood calcium level and inhibits bone resorption; acts as an antagonist to parathyroid hormone (PTH). Also called thyrocalcitonin.

Calculus: A stone formed within various body parts.

Callus: (1) A growth of new bone tissue in and around a fractured area, ultimately replaced by mature bone. (2) Localized thickening of skin epidermis resulting from physical trauma.

Calorie (cal): Amount of energy needed to raise the temperature of 1 gram of water by 1 degree Celsius. Energy exchanges associated with biochemical reactions are usually reported in kilocalories (1 kcal = 1000 cal = 1 Cal = 4186 Joules).

Calyx: A cup-like division of the kidney pelvis.

Canal: A narrow tube, channel, or passageway.

Canaliculus: Extremely small tubular passage or channel.

Cancer: A malignant, invasive cellular neoplasm that has the capability of spreading throughout the body or body parts.

Capacitation: The functional changes that sperm must undergo before the acrosomal reaction can occur, which allow them to fertilize a secondary oocyte.

Capillary: (1) Resembling a hair; fine; minute. (2) A capillary vessel; e.g., blood capillary, lymph capillary.

Capitulum: A small head or rounded articular extremity of a bone.

Carbohydrate: A major class of biological molecules; contains carbon, hydrogen and oxygen with the general formula C(H2O); used as energy stores and structural molecules.

Carbonic acid/Bicarbonate buffer system: Chemical buffer solution that helps maintain pH homeostasis of the blood; contains the weak acid H2CO3 and its conjugate base HCO3– .

Carbonic anhydrase: Enzyme that facilitates the combination of carbon dioxide with water to form carbonic acid.

Carboxypeptidase: A protein digesting enzyme found in the small intestine, formed from procarboxypeptidase that is secreted by the pancreas.

Carcinogen: Cancer causing agent.

Cardiac arrest: Complete cessation of cardiac activity.

Cardiac centers: Nuclei of the reticular formation in the medulla oblongata that regulate the heart; the cardioacceleratory center innervates the SA and AV nodes, myocardium and coronary arteries through the sympathetic division of the ANS; the cardioinhibitory center sends inibitory nerve impulses to the SA and AV nodes through the parasympathetic division of the ANS.

Cardiac conduction system: The system of specialized myocardial conducting cells that transmit electrical impulses to the heart muscle; the impulses are initiated at the sinoatrial (SA) node, or pacemaker, which innervate the atria, then the impulses are conducted to the atrioventricular (AV) node, the atrioventricular (AV) bundle, the right and left bundle branches, and the Purkinje fibers, which innervate the ventricles. Also called conducting system of heart.

Cardiac contractility: A measure of cardiac pump performance; the degree to which cardiac muscles contract and develop increased tension when activated by a stimulus, which is independent of preload and afterload.

Cardiac cycle: The complete heartbeat consisting of systole (contraction) and diastole (relaxation) of both atria and both ventricles, with the intervals in between.

Cardiac muscle tissue: Tissue with branched cells that are striated, mostly uninucleate, and joined by darkly staining intercalated discs; functions to pump blood into the circulation under involuntary control; located in the heart.

Cardiac output (CO): Amount of blood pumped out of each ventricle in one minute, in L/min; CO is equal to stroke volume (SV) times heart rate (HR), according to the formula: CO = SV ⋅ HR.

Cardiac reserve: The difference between the resting cardiac output (about 5 L/min) and the maximal cardiac output ( between 15 – 35 L/min), which depends on the physical condition of the person.

Cardiogenic shock: Shock resulting from decline in cardiac output, usually secondary to serious heart disease, such as myocardial infarction.

Cardiology: The study of the heart and diseases associated with it.

Cardiovascular center: Groups of neurons scattered within the medulla oblongata that regulate heart rate, force of contraction, and blood vessel diameter.

Cardiovascular system: Organ system that distributes the blood to deliver nutrients and remove wastes.

Carina of trachea: The ridge at the bifurcation of the trachea into the right and left primary (main) bronchi.

Carotene: Antioxidant precursor of vitamin A, which is needed for synthesis of photopigments; yellow-orange pigment present in the stratum corneum of the epidermis. Accounts for the yellowish coloration of skin. Also termed beta-carotene.

Carotid body: Chemoreceptor in the common carotid artery sensitive to changing oxygen, carbon dioxide, and pH levels of the blood.

Carotid sinus: A dilation of a common carotid artery; involved in regulation of systemic blood pressure.

Carpal bones: The eight bones of the wrist. Also called the carpus.

Carpus: Wrist bones; arranged in two rows of four bones each. In the proximal row (lateral to medial) are the scaphoid, lunate, triquetral, and pisiform. In the distal row (lateral to medial) are the trapezium, trapezoid, capitate, and hamate. The scaphoid and lunate articulate with the radius to form the wrist joint.

Cartilage: A type of connective tissue consisting of chondrocytes in lacunae, embedded in a dense network of collagen and elastic fibers and an extracellular matrix of chondroitin sulfate.

Cartilage bone: Bone formed by the calcification of hyaline cartilage structures.

Cartilaginous joint: An articulation in which the bones are joined together by cartilage, lacks a joint cavity, and almost no motion is possible; types are synchondroses, and symphyses.

Catabolism: Metabolic decomposition reactions that breakdown large molecules into smaller molecules, usually with the net release of energy.

Catalyst: Substance that increases the rate of a chemical reaction, but is not consumed.

Cataract: Clouding of the eye’s lens; often congenital or age related.

Catecholamines: Epinephrine and norepinephrine.

Cation: Positively charged ion; metal elements can lose electrons and become cations.

Cauda equina: A tail-like array of roots of spinal nerves at the inferior end of the spinal cord.

Caudal: Towards the tail or inferior in position.

Cecum: The blind-end pouch at the beginning of the large intestine.

Celiac plexus: A large mass of autonomic ganglia and axons located at the level of the superior part of the first lumbar vertebra. Also called the solar plexus.

Cell: The basic structural and functional unit of all organisms; the smallest structure capable of performing all the activities vital to life.

Cell differentiation: The diversification of unspecialized cells as they develop different characteristics and become specialized in structure and function. Also called differentiation, or specialization.

Cell division period: One of two major periods in the cell life cycle; involves the division of the nucleus (mitosis) and the division of the cytoplasm (cytokinesis).

Cell inclusions: Insoluble storage materials or metabolic products found in the cytoplasm of a cell, such as glycogen, fat, pigment granules, or crystals.

Cell junction: Point of contact between plasma membranes of tissue cells.

Cell life cycle: Series of changes a cell goes through from the time it is formed until it reproduces itself.

Cell-mediated immunity: Immunity conferred by activated T cells, which directly lyse infected or cancerous body cells or cells of foreign grafts and release chemicals that regulate, the immune response.

Cell membrane: Outer cell membrane composed of phospholipid bilayer with embedded proteins, cholesterol, and surface polysaccharides; encloses cell contents and regulates entry and exit of materials. Also called plasma membrane.

Cell theory: Four concepts that describe all living cells. 1. A cell is the basic structural and functional unit of living organisms. 2. The activity of an organism depends on both the individual and the collective activities of its cells. 3. The biochemical activities of cells are dictated by the relative number of their specific subcellular structures. 4. Continuity of life from one generation to another has a cellular basis.

Cell wall: A permeable structure surrounding the plasma membrane that provides support and protection; found in bacteria and plants.

Cellular respiration: Aerobic catabolic pathway for the production of ATP, in which sugar molecules are broken down and combined with oxygen to produce carbon dioxide, water and energy.

Cellulose: Polysaccharide made from glucose that cannot be digested by most animals; the major structural component of plants.

Cementum: Calcified tissue covering the root of a tooth.

Central canal: (1) A tube running the length of the spinal cord in the gray commissure. (2) A circular channel running longitudinally in the center of an osteon (haversian system) of mature compact bone, containing blood and lymphatic vessels and nerves. Also called an haversian canal.

Central fovea: A depression in the center of the macula lutea of the retina, containing cones only and lacking blood vessels; the area of highest visual acuity (sharpness of vision).

Central nervous system (CNS): The portion of the nervous system that consists of the brain and spinal cord.

Centrioles: Paired cylindical bodies near the nucleus; form the bases of cilia and flagella; they divide and organize spindle fibers during mitosis and meiosis.

Centromere: Area of a chromosome where the two sister chromatids are joined; contains kinetochores that have attachment sites for spindle fibers during nuclear division.

Centrosome: Microtubule organizing center of cells; contains two centrioles.

Cephalic: Towards the head or superior in position.

Cerebellar peduncle: A bundle of nerve axons connecting the cerebellum with the brain stem.

Cerebellum: The part of the brain lying posterior to the medulla oblongata and pons; responsible for coordinated muscle movement, tone, posture, and agility; involved in learning motor skills.

Cerebral aqueduct: A channel through the midbrain connecting the third and fourth ventricles and containing cerebrospinal fluid. Also called the aqueduct of Sylvius.

Cerebral arterial circle: A ring of arteries forming an anastomosis at the base of the brain between the internal carotid and basilar arteries and arteries supplying the cerebral cortex. Also called the circle of Willis.

Cerebral cortex: The outer gray matter region of the cerebral hemispheres.

Cerebral dominance: Designates the hemisphere that is dominant for language.

Cerebral palsy: Neuromuscular disability in which voluntary muscles are poorly controlled or paralyzed as a result of brain damage.

Cerebral white matter: Consists largely of myelinated fibers bundled into large tracts; provides for communication between cerebral areas and lower CNS centers.

Cerebrospinal fluid (CSF): A fluid produced by ependymal cells covering the choroid plexuses in the ventricles of the brain; the fluid circulates in the ventricles and subarachnoid space around the brain and in the central canal of the spinal cord.

Cerebrovascular accident (CVA): Destruction of brain tissue (infarction) resulting from impairment of cerebral circulation. CVA is the third most common cause of death in the U.S.A. Also called a stroke, or brain attack.

Cerebrum: The two hemispheres of the forebrain (derived from the telencephalon), making up the largest part of the brain; involved in conscious thought, perception, intellect, and voluntary muscle activity.

Cerumen: Waxlike secretion produced by ceruminous glands in the external auditory meatus (ear canal). Also called ear wax.

Ceruminous gland: A modified sudoriferous (sweat) gland in the external auditory meatus that secretes cerumen (ear wax).

Cervical plexus: A network formed by nerve axons from the first four cervical nerves.

Cervical vertebrae: The seven vertebrae of the vertebral column located in the neck.

Cervix: (1) Neck. (2) Any constricted portion of an organ, such as the inferior cylindrical part of the uterus.

Chemical bond: A union between the electron structures of two or more atoms or ions.

Chemical energy: Energy stored in the bonds of chemical substances.

Chemical equilibrium: A state of apparent repose created by two reactions proceeding in opposite directions at equal speed.

Chemical reaction: Process in which molecules are formed, changed, or broken down.

Chemoreceptor: Receptors sensitive to various chemicals in solution.

Chemotaxis: Movement of cells toward a chemical substance, such as white blood cells moving toward inflammatory chemicals.

Chiasm: A crossing; especially the crossing of axons in the optic (II) nerve.

Chief cell of parathyroid gland: A cell in the parathyroid glands that secretes parathyroid hormone (PTH); also called principal cells.

Chief cell of stomach: A cell in the gastric glands that secretes pepsinogen, the precursor of the enzyme pepsin, and secretes the enzyme gastric lipase. Also called zymogenic cell.

Choana: The opening from the nasal cavity into the nasopharynx. Also called the internal nares.

Cholecystokinin (CCK): Hormone secreted by enteroendocrine cells in the duodenum that stimulates secretion of pancreatic juice rich in digestive enzymes, and stimulates gallbladder contraction to release bile.

Cholecystectomy: Surgical removal of the gallbladder.

Cholecystitis: Inflammation of the gallbladder.

Cholesterol: Classified as a lipid, the most abundant steroid in animal tissues; located in cell membranes and used for the synthesis of steroid hormones and bile salts.

Cholinergic fibers: Nerve endings that, upon stimulation, release acetylcholine.

Chondritis: Inflammation of cartilage.

Chondroblast: A dividing cartilage-forming cell, derived from mesenchyme, that secretes a cartilaginous matrix and fibers, becomes enclosed in a lacuna, then differentiates into a chondrocyte.

Chondroclast: A giant multinucleated cell involved in the resorption of calcified cartilage.

Chondrocyte: Mature cartilage cell that occupies a lacuna within cartilage matrix.

Chondroitin sulfate: An amorphous extracellular matrix material found outside connective tissue cells.

Chordae tendineae: Tendonlike, fibrous cords that connect atrioventricular valves of the heart with papillary muscles.

Chorion: Outermost fetal membrane; helps form the placenta.

Chorionic villi: Finger-like projections of the chorion that grow into the decidua basalis of the endometrium and contain fetal blood vessels.

Chorionic villi sampling: Fetal testing procedure in which bits of the chorionic villi from the placenta are snipped off and the cells karyotyped. This procedure can be done as early as 8 weeks into the pregnancy.

Choroid: The pigmented vascular middle tunic of the eye.

Choroid plexus: A network of capillaries located in the roof of each of the four ventricles of the brain; ependymal cells around choroid plexuses produce cerebrospinal fluid.

Chromatid: One of the two identical halves of a chromosome found in eucaryotic cells after the time of DNA replication; the two daughter chromatids are joined by a centromere.

Chromatin: Thread-like form of chromosomes in the nucleus during interphase.

Chromosome: DNA with associated proteins; contains genes (hereditary factors); during mitosis it supercoils into a bar-like body that is visible under a light microscope.

Chronic: Long term or frequently recurring; applied to a disease that is not acute.

Chronic obstructive pulmonary disease (COPD): Collective term for progressive, obstructive respiratory disorders; includes emphysema and chronic bronchitis.

Chyle: A milky fluid containing chylomicrons that is taken up by the lacteals in the small intestine after digestion of lipids.

Chyme: Semifluid, creamy mass consisting of partially digested food and gastric juice.

Chymotrypsin: A protein digesting enzyme found in the small intestine, formed from chymotrypsinogen that is secreted by the pancreas.

Cilia: Short motile processes, composed of microtubules; propels material across the cell surface.

Ciliary body: Anterior portion of the choroid that includes the ciliary muscle and ciliary process.

Circle of Willis: An arterial anastomosis at the base of the brain. Also called cerebral arterial circle.

Circular folds: Permanent, deep, transverse folds in the mucosa and submucosa of the small intestine that increase the surface area for absorption. Also called plicae circulares.

Circumduction: Movement of a limb bone in a circular direction so that it describes a cone in the air.

Circumferential lamella: Bony lamella that encircles the outer or inner surface of a bone.

Cirrhosis: Chronic disease of the liver, characterized by an overgrowth of connective tissue or fibrosis.

Cisterna chyli: Large lymph sac that receives lymph drainage from the digestive organs.

Cisternae: Any cavity or enclosed space serving as a reservoir.

Clavicle: Collarbone; extends horizontally across superior anterior thorax; articulates medially with sternum and laterally with scapula. Markings: Acromial end is the lateral flattened end, that articulates with acromion of the scapula to form part of the shoulder joint. Sternal end is the medial conical end, that attaches to the manubrium of sternum. Conoid tubercle is the prominence on the posteroinferior surface, near the lateral end, and an attachment site for the conoid ligament that unites the clavicle to the coracoid process of the scapula.

Cleavage: An early embryonic phase consisting of rapid mitotic cell divisions without intervening growth periods; product is a blastocyst.

Cleft palate: A facial birth defect where a child is born with a separation in the roof of the mouth, or palate.

Clitoris: An erectile organ of the female, located at the anterior junction of the labia minora, that is homologous to the male penis.

Clonal selection: Process during which a B cell or T cell becomes sensitized through binding contact with an antigen.

Clone: Descendants of a single cell.

CNS: The central nervous system; the portion of the nervous system that consists of the brain and spinal cord.

Coagulation: (1) Transformation of a solution into a gel. (2) Blood clotting; process in which blood is transformed from a liquid into a semisolid gel.

Coarctation: An abnormal narrowing of the lumen of a duct, canal, or hollow organ. Also called stenosis, or stricture.

Coarctation of the aorta: A congenital heart defect in which a segment of the aorta is too narrow. As a result, the flow of oxygenated blood to the body is reduced, the left ventricle is forced to pump harder, and high blood pressure develops.

Coccyx: The fused bones at the inferior end of the vertebral column.

Cochlea: Snail-shaped chamber of the bony labyrinth that contains three membranous tubes: the

scala vestibuli, which is filled with perilymph and leads from the oval window to the apex, the

scala tympani, which is filled with perilymph and leads from the apex to the round window, and the cochlear duct, which is filled with endolymph and is a closed tube. The organ of Corti is the receptor organ for hearing within the cochlear duct, which rests on the basilar membrane that is set into resonance when sound waves are absorbed, and these vibrations activate the hearing receptor cells.

Cochlear duct: Closed membranous tube filled with endolymph in the cochlea that contains the organ of Corti. Also called the scala media.

Codon: The three base sequence on a messenger RNA molecule that provides the genetic information used in protein synthesis.

Coenzyme: Nonprotein substance associated with an enzyme; usually a vitamin.

Cofactor: Metal ion or organic molecule that is required for enzyme activity.

Collagen: A protein that is the main organic constituent of connective tissue.

Collateral circulation: Circulation maintained in small anastomosing vessels when the main vessel is obstructed.

Colloid: A mixture in which the solute particles do not settle out readily and do not pass through natural membranes.

Colloid osmotic pressure: Pressure created in a fluid by large nondiffusible molecules, such as plasma proteins that are prevented from moving through a (capillary) membrane. Such substances tend to draw water to them.

Colon: Regions of the large intestine; includes ascending, transverse, descending, and sigmoid portions.

Colony-stimulating factor (CSF): One of a group of molecules that stimulates development of white blood cells.

Colostrum: A thin, cloudy fluid secreted by the mammary glands a few days prior to or after delivery before true milk is produced.

Combination reaction: Chemical reaction in which larger, more complex atoms or molecules are formed from simpler ones. Also called a synthesis reaction.

Comminuted fracture: Bone breaks into many fragments.

Commissural fibers: Neuron axons that connect corresponding gray areas of the two hemispheres. Also called commissures.

Common bile duct: A tube formed by the union of the common hepatic duct and the cystic duct that empties bile into the duodenum at the hepatopancreatic ampulla (ampulla of Vater).

Compact bone: Bone tissue that contains few spaces between osteons (haversian systems); forms the external portion of all bones and the bulk of the diaphysis (shaft) of long bones; is found immediately deep to the periosteum and external to spongy bone.

Complement: A group of blood proteins which, when activated, forms a membrane attack complex that leads to cytolysis of the target cell, and enhances the inflammatory and immune responses.

Complementarity of structure and function: The relationship between a structure and its function; structure determines function, and function reflects structure.

Complementary base: The degree of base pairing between two sequences of DNA and/or RNA molecules.

Complete blood count (CBC): Clinical test that includes a hematocrit, counts of all formed elements and clotting factors, and other indicators of normal blood function.

Compound: Substance composed of two or more different elements that are chemically bound.

Compound fracture: Broken bone through skin; a bone fracture in which a broken bone pierces the skin or comes into contact with an open wound.

Compression fracture: Bone is crushed.

Concentration gradient: The difference in the concentration of a particular substance between two different areas; solutes spontaneously move from high to low concentration (see diffusion) .

Conceptus: The products of conception or fertilization; all structures that develop from the zygote.

Concussion: Traumatic injury to the brain that produces no visible bruising but may result in abrupt, temporary loss of consciousness.

Conducting zone: Includes all respiratory passageways that provide conduits for air to reach the sites of gas exchange (the respiratory zone).

Conductivity: Ability to transmit an electrical impulse.

Condyle: Rounded articular projection on a bone.

Condyloid joint: A biaxial synovial joint in which the joint surfaces are ellipsoidal, allowing two axes of motion at right angles to each other. Also called condylar joint, or ellipsoid joint.

Cones: One of the two types of photoreceptor cells in the retina of the eye; specialized for highly acute color vision in bright light.

Congenital: Existing at birth.

Congestive heart failure (CHF): Condition in which the pumping efficiency of the heart is depressed so that circulation is inadequate to meet tissue needs.

Conjunctiva: Mucous membrane lining the anterior surface of the eyeball and posterior surface of eyelids; acute contagious conjunctivitis is called pinkeye.

Connective tissue: A basic tissue type that functions in binding, support, protection, and insulation; composed mainly of nonliving extracellular matrix with relatively few cells.

Connexons: Hollow cylinders made of transmembrane proteins that connect adjacent cells at gap junctions, allowing chemical substances to pass through.

Consciousness: A state of wakefulness in which an individual is fully alert, aware, and oriented, partly as a result of feedback between the cerebral cortex and reticular activating system.

Contraception: The prevention of conception; birth control.

Contractility: Muscle cell’s ability to move by shortening.

Contraction: To shorten or develop tension, an ability highly developed in muscle cells.

Contralateral: Relating to the opposite side.

Control center: One of three interdependent components of homeostatic control mechanisms; determines the set point.

Conus medullaris: The tapered portion of the spinal cord inferior to the lumbar enlargement.

Cornea: Transparent avascular dome forming the anterior part of the sclera of the eyeball.

Coronal plane: Longitudinal (vertical) plane that divide the body into anterior and posterior parts. Also called a frontal plane.

Coronal suture: Line of junction of the frontal with the two parietal bones.

Corona radiata: (1) Arrangement of elongated follicle cells around a mature ovum. (2) Crown-like arrangement of nerve fibers radiating from the internal capsule of the brain to every part of the cerebral cortex.

Coronary arteries (right and left): First small branches off the ascending aorta that supply the myocardium of the heart.

Coronary artery disease: A condition such as atherosclerosis, that causes narrowing of coronary arteries so that blood flow to the heart is reduced; the result is coronary heart disease (CHD), in which the heart muscle receives inadequate blood flow due to an interruption of its blood supply.

Coronary circulation: The flow of oxygenated blood from the left ventricle, through the coronary arteries and capillaries to the heart cells, and the return of blood through the veins and coronary sinus to the right atrium.

Coronary sinus: A wide venous trunk in the posterior coronary sulcus of the heart that collects the blood from the coronary circulation and returns it to the right atrium.

Coronary sulcus: A groove on the outer surface of the heart that encircles the junction of the atria and ventricles. Also called the atrioventricular groove, or AV groove.

Corpus albicans: A white fibrous patch in the ovary that forms after the corpus luteum regresses.

Corpus callosum: Large commissure that connects the left and right cerebral hemispheres.

Corpuscle of touch: The sensory receptor for the sensation of touch; found in the dermal papillae, especially in palms and soles. Also called a Meissner corpuscle.

Corpus luteum: The yellow endocrine body formed in the ovary at the site of a ruptured vesicular follicle immediately after ovulation that secretes progesterone, estrogens, and relaxin.

Corpus striatum: An area in the interior of each cerebral hemisphere composed of the caudate and putamen of the basal ganglia and white matter of the internal capsule, arranged in a striated manner.

Cortex: Outer surface layer of an organ.

Corticosteroids: Steroid hormones released by the adrenal cortex.

Cortisol (hydrocortisone): Glucocorticoid produced by the adrenal cortex.

Costal: Pertaining to a rib.

Costal cartilage: Hyaline cartilage that forms the anterior continuation of a rib; articulates with the sternum.

Covalent bond: Chemical bond formed when electrons are shared between atoms; nonpolar bonds share electrons equally; polar bonds share electrons unequally, which produces a dipole.

Coxal bones: Hip bones; formed by the fusion of an ilium (superior), ischium (inferior posterior), and pubic bone (inferior anterior); the coxal bones join anteriorly at the pubic symphysis, and join posteriorly with the sacrum to form the sacroiliac joints. Markings: Iliac crest is the hip; thickened superior margin. Iliac spines (Anterior and Posterior) are attachment sites for muscles of the trunk, hip, and thigh. Sacroiliac joint articulation of auricular surface of ilium with the sacrum. Ischial tuberosity is bony projection of ischium; weight-bearing point in the sitting position; attachment site for hamstring muscles. Ischial spine is posterior pointed process of the ischium; attachment site for muscles and ligaments. Acetabulum is lateral cup-shaped socket; articulates with head of the femur to form the ball-and-socket hip joint. Sciatic notches (Greater and Lesser) allows passage of sciatic nerve. Obturator foramen is large oval aperture in the hip bone; allows passage of blood vessels and nerves. Pubic crest is thickened anterior border; attachment site for abdominal muscles. Pubic tubercle is attachment site for inguinal ligament. Pubic symphysis is fibrocartilage that forms anterior junction of the two coxal bones. Pubic arch is the inverted V-shaped arch inferior to pubic symphysis, over 90̊ in females, and about 60̊ in males. Pelvic inlet (brim) is the upper opening of true pelvis; wide oval-shape in females, and narrow heart-shape in males

Cranial nerves: The 12 nerve pairs that arise from the brain.

Craniosacral division: Another name for the parasympathetic division of the autonomic nervous system.

Cranium: Bony protective encasement of the brain and organs of hearing and equilibrium. Also called the skull, or cranial bones.

Creatine kinase: Enzyme that catalyzes the transfer of phosphate from phosphocreatine to ADP, forming creatine and ATP; important in muscle contraction.

Creatine phosphate (CP): Compound that serves as an alternative energy source for muscle tissue.

Creatinine: A nitrogenous waste molecule which is not reabsorbed by the kidney; this characteristic makes it useful for measurement of the GFR and glomerular function.

Cremaster muscles: Bands of skeletal muscle that elevate the testes.

Crest: Narrow ridge of bone; usually prominent.

Cricoid cartilage: The lowermost of the laryngeal cartilages, shaped like a signet ring.

Crista ampullaris: Sensory receptor organ for dynamic equilibrium in the ampulla of semicircular canals.

Cristae: Folding of the inner membrane of mitochondria.

Crossing-over: The exchange of a portion of one chromatid with another during meiosis; it permits an exchange of genes among chromatids and is one factor that results in genetic variation of progeny.

Cryptorchidism: The condition of undescended testes.

Crystals: Large arrays of cations and anions held together by ionic bonds; formed when an element or compound solidifies or is in a dry state.

CSF (Cerebrospinal fluid): A fluid produced by ependymal cells covering the choroid plexuses in the ventricles of the brain; the fluid circulates in the ventricles and subarachnoid space around the brain, and in the central canal of the spinal cord.

Cupula: A mass of gelatinous material covering the hair cells of a crista; a sensory receptor in the ampulla of a semicircular canal stimulated when the head moves.

Cushing’s syndrome: Condition caused by a hypersecretion of glucocorticoids characterized by spindly legs, “moon face” or “buffalo hump” pendulous abdomen, flushed facial skin, poor wound healing, hyperglycemia, osteoporosis, hypertension, and increased susceptibility to disease.

Cutaneous: Pertaining to the skin.

Cutaneous sensory receptors: Receptors located throughout the skin that respond to stimuli arising outside the body; part of the nervous system.

Cyanosis: A blue or dark purple discoloration, most easily seen in nail beds and mucous membranes, that results from an increased concentration of deoxygenated hemoglobin.

Cyclic AMP: Important intracellular second messenger that mediates hormonal effects; formed from ATP by the action of adenylate cyclase, an enzyme associated with the plasma membrane.

Cyst: A sac with a distinct connective tissue wall, containing a fluid or other material.

Cystic duct: The duct that carries bile from the gallbladder to the common bile duct.

Cystic fibrosis (CF): Genetic disorder in which oversecretion of mucus clogs the respiratory passages, predisposes to fatal respiratory infections.

Cystitis: Inflammation of the urinary bladder.

Cytochromes: Brightly colored iron-containing proteins that form part of the inner mitochondrial membrane and function as electron carriers in oxidative phosphorylation.

Cytokines: Hormonelike proteins involved in cell-mediated immune responses, such as interferons, interleukins and lymphokines.

Cytokinesis: Cytoplasmic division that occurs after telophase by splitting a mother cell into 2 daughter cells.

Cytology: Branch of anatomy dealing with the microscopic structure of individual cells.

Cytolysis: The dissolution of a cell by rupture of the cell membrane with loss of cytoplasm.

Cytoplasm: All of the material between the plasma membrane and nucleus.

Cytosine: Nitrogen containing base that is part of a nucleotide structure.

Cytoskeleton: Cell skeleton; network of fibrous proteins; provides cell support and organelle movement.

Cytosol: Viscous fluid portion of the cytoplasm in which the organelles are suspended.

Cytotoxic T cell: Type of T lymphocyte that kills foreign cells, cancer cells and virus infected body cells. Also called killer T cell.

D (2)

Dalton’s law: Each gas in a mixture of gases exerts a pressure proportionate to the percentage of the gas, and independent of the other gases present.

Dartos muscles: Smooth muscle fibers that cause contraction of the scrotum and wrinkle the scrotal skin when the environmental temperature is cold.

Deamination: Removal of the amino group, -NH, from glutamic acid, which produces ammonia, NH, α-keto glutaric acid, and NADH. Also called oxidative deamination.

Decomposition reaction Chemical reaction in which a molecule is broken down into smaller molecules or its constituent atoms.

Deep: Further away from the surface of the body or an organ.

Deep fascia: A sheet of connective tissue wrapped around a muscle to hold it in place.

Defecation: Elimination of the contents of the bowels (feces).

Defensins: Antimicrobial peptides produced by phagocytes, lymphocytes, skin cells, and mucous epithelial cells.

Deglutition: Swallowing.

Dehydration: Condition of excessive water loss.

Dehydration synthesis reaction: Formation of a large molecule by covalently bonding small molecules together, with the loss of water, H2O. Also called a condensation reaction.

Delta brain wave: A wave pattern in the electroencephalogram in the frequency band of 1.5–4.0 Hz; found during deep sleep. Also called delta rhythm.

Deltoid: Triangular shoulder muscle; abduct and rotate arm. O: Clavicle and scapula. I: Deltoid tuberosity of humerus.

Demineralization: Loss of calcium andphosphorus from bones.

Denaturation: Loss of a molecule’s 3-D shape, as weak bonds are disrupted.

Dendrite: Branching cell process that receives nerve impulses and transmits graded potentials

toward a neuron cell body.

Dendritic cell: A type of antigen-presenting cell with long branchlike projections, found in the skin, mucosal linings, and lymph nodes.

Dense irregular connective tissue: Tissue with fibroblast cells, many irregularly arranged collagen fibers and some elastic fibers. Functions to provide structural strength, and withstands tension exerted in many directions. Located in most of the skin dermis, and capsules of organs and joints.

Dense regular connective tissue: Tissue with fibroblast cells, many parallel collagen fibers, some elastic fibers, and dense white matrix. Functions to provide strong attachment of muscles and/or bones, and ability to withstand great tension exerted in one direction. Located in tendons, most ligaments, aponeuroses. Also called white fibrous connective tissue.

Dental caries: Gradual demineralization of the enamel and dentin of a tooth that may invade the pulp and alveolar bone. Also called tooth decay.

Denticulated: (1) Finely toothed or serrated. (2) Having small teeth.

Dentin: The bony tissues of a tooth enclosing the pulp cavity.

Deoxyribonucleic acid: Molecule of inheritance; contains instructions for making all proteins required to build and maintain cells; it has a 3-D structure called the DNA double helix, consisting of two backbones with alternating deoxyribose and phosphate groups, and a pair of nitrogenous bases joined by hydrogen bonds. Also called DNA.

Depolarization: Loss of a state of polarity; loss or reduction of negative membrane potential.

Depressed fracture: Broken bone portion is pressed inward.

Depression: Movement of a bone inferiorly.

Dermacidin: Antimicrobial peptide secreted by sweat glands.

Dermal papilla: Fingerlike projections of dermal tissue into the epidermis.

Dermatology: The medical specialty dealing with diseases of the skin.

Dermatome: (1) Portion of somite mesoderm that forms the dermis of the skin. (2) the area of skin innervated by the cutaneous branches of a single spinal nerve.

Dermis: The layer of skin under the epidermis, composed of a thin superficial papillary region with areolar connective tissue, and a deep reticular region of dense irregular connective tissue.

Desmosome: Cell anchoring junction composed of thickened plasma membranes joined by filaments.

Detrusor muscle: Smooth muscle that forms the wall of the urinary bladder.

Developmental biology: The study of development from the fertilized egg to the adult form.

Diabetes insipidus: Disease characterized by passage of a large quantity of dilute urine plus intense thirst and dehydration caused by inadequate release of antidiuretic hormone (ADH).

Diabetes mellitus (DM): Disease caused by deficient insulin release, leading to inability of the body cells to use carbohydrates.

Diagnosis: Distinguishing one disease from another or determining the nature of a disease from signs and symptoms by inspection, palpation, laboratory tests, and other means.

Dialysis: (1) Diffusion of solutes through a semipermeable membrane. (2) The removal of waste products from blood by diffusion through a selectively permeable membrane.

Diapedesis: Passage of white blood cells through intact blood vessel walls into tissue.

Diaphragm: (1) Any partition or wall separating one area from another. (2) Major muscle of inspiration that separates the thoracic cavity from the lower abdominopelvic cavity.

Diaphysis: The long rodlike shaft of a long bone.

Diarrhea: Frequent defecation of liquid feces caused by increased motility of the intestines.

Diarthrosis: A freely movable joint.

Diastole: In the cardiac cycle, the phase of relaxation or dilation of the heart muscle, especially of the ventricles.

Diastolic blood pressure (DBP): The force exerted by blood on arterial walls during ventricular relaxation; the lowest blood pressure measured in the large arteries, normally about 80 torr (mm Hg) in a young adult.

Diencephalon: That part of the forebrain between the cerebral hemispheres and the midbrain including the thalamus, hypothalamus, and epithalamus.

Differential white blood cell count: Diagnostic test to determine relative proportion of individual leukocyte types.

Differentiation: The diversification of unspecialized cells as they develop different characteristics and become specialized in structure and function. Also called specialization.

Diffusion: Spontaneous movement of a dissolved solute from regions of higher to lower concentration.

Digastric: V-shaped throat muscle; opens mouth; depress mandible; elevate hyoid bone during swallowing and speech. O: Mandible and mastoid process of temporal bone. I: Hyoid bone.

Digestion: Chemical or mechanical process of breaking down foodstuffs to substances that can be absorbed.

Digestive system: System that processes food into absorbable units and eliminates indigestible wastes.

Dilate: To expand or swell.

Dipeptide: A combination of two amino acids united by means of a peptide bond.

Diploe: The internal layer of spongy bone in flat bones.

Diploid: Having the chromosomal number characteristic of an organism, symbolized as 2n; twice the chromosomal number (n) of the gamete; in humans, 2n = 46.

Diplopia: Double vision.

Dipole (polar molecule): Nonsymmetrical molecules that contain electrically unbalanced atoms.

Disaccharide: A carbohydrate containing two covalently bonded sugar monomers, such as sucrose, lactose, and maltose.

Disease: Any change from a state of health.

Dislocation: Occurs when bones are forced out of their normal alignment at a joint.

Dissect: To separate tissues and parts of a cadaver or an organ for anatomical study.

Displacement reaction: Chemical reaction in which bonds are both made and broken; atoms become combined with different atoms. Also calle an exchange reaction.

Distal: Further away from the trunk or the point of origin.

Diuretics: Chemicals that enhance urinary output.

Diverticulum: A pouch or sac in the walls of a hollow organ or structure.

DNA: Molecule of inheritance; contains instructions for making all proteins required to build and maintain cells; it has a 3-D structure called the DNA double helix, consisting of two backbones with alternating deoxyribose and phosphate groups, and a pair of nitrogenous bases joined by hydrogen bonds. Also called deoxyribonucleic acid.

DNA polymerase: Enzyme of replication and repair; assembles a new strand of DNA on a parent DNA template.

DNA replication: Process that occurs before cell division; ensures that all daughter cells have identical genes.

Dominant traits: Occurs when one allele masks or suppresses the expression of its partner.

Dominant-recessive inheritance: Reflects the interaction of dominant and recessive alleles.

Dorsal: Pertaining to the back; posterior.

Dorsal respiratory group (DRG): Part of the respiratory centers; nuclei in the medulla oblongata that generates the basic rhythm of breathing.

Dorsiflexion: Upward movement of the foot that decreases the angle between the top of the foot (dorsal surface) and the anterior surface of the tibia.

Double helix: The secondary structure assumed by two strands of DNA, held together throughout their length by hydrogen bonds between bases on opposite strands.

Down-regulation: Decreased response to hormonal stimulation; involves a loss in the number of receptors and effectively prevents the target cells from over reacting to persistently high hormone levels.

Duct: A canal or passageway; a tubular structure that provides an exit for the secretions of a gland, or for conducting any fluid.

Ductus arteriosus: Fetal heart structure; a fetal vessel connecting the pulmonary trunk to the aortic arch, which acts like a shunt to allow fetal blood to bypass the lungs; it closes after birth, and the fibrous remnants are called the ligamentum arteriosum.

Ductus deferens: The secretory duct of the testis, extending from the epididymis to the ejaculatory duct, that propels sperm by peristalsis during ejaculation. Also called vas deferens.

Ductus venosus: A small vessel in the fetus that helps the circulation bypass the liver.

Duodenal gland: Gland in the submucosa of the duodenum that secretes an alkaline mucus to protect the lining of the small intestine from the action of enzymes and to help neutralize the acid in chyme. Also called Brunner’s gland.

Duodenal papilla: An elevation on the duodenal mucosa that receives the hepatopancreatic ampulla (ampulla of Vater).

Duodenum: First part of the small intestine.

Dura mater: Outermost and toughest of the three membranes (meninges) covering the brain and spinal cord.

Dynamic equilibrium: Sense that reports on angular or rotatory movements of the head in space.

Dyskinesia: Disorders of muscle tone, posture, or involuntary movements.

Dyspareunia: Occurrence of pain during sexual intercourse.

Dysplasia: Change in the size, shape, and organization of cells due to chronic irritation or inflammation; may either revert to normal if stress is removed or progress to neoplasia.

Dyspnea: Shortness of breath and difficulty in breathing.

Dysuria: Difficulty or pain in urination.

 


D (2)

Eardrum: Thin, semitransparent partition of fibrous connective tissue between the external auditory meatus and the middle ear. Also called the tympanic membrane.

Eccrine glands: Sudoriferous glands that open into pores at the surface of the skin, and found on almost all parts of the body; they secrete a watery sweat that cools the body.

Ectoderm: Embryonic germ layer; forms the nervous system and the epidermis of the skin and its derivatives.

Ectopic: Out of place, such as an organ that is not in its proper position.

Ectopic pregnancy: The implantation and development of a blastocyst outside the uterine cavity, such as in the uterine tubes or pelvic cavity.

Edema: Abnormal accumulation of fluid in body parts or tissues; causes swelling.

Effector: Organ, gland, or muscle capable of being activated by nerve endings.

Efferent: Carrying away or away from, especially a nerve fiber that carries impulses away from the central nervous system.

Efferent arteriole: A vessel of the renal vascular system that carries blood from a glomerulus to peritubular capillary.

Eicosanoids: Local hormones derived from arachidonic acid, which include the prostaglandins, leukotrienes, and thromboxanes.

Ejaculation: The reflex ejection or expulsion of semen from the penis.

Ejaculatory duct: A tube that transports sperm from the ductus deferens to the prostatic urethra.

Elastic cartilage: Tissue with many chondrocytes that lie in lacunae, amorphous but firm matrix, and many elastic fibers. Functions in providing support and great flexibility while maintaining shape. Located in the ear auricle (pinna), and epiglottis.

Elastic connective tissue: Tissue with fibroblast cells, many elastic fibers and some collagen fibers. Functions in stretching and passive recoil. Located in the aorta and other large arteries; lung bronchi; some vertebral ligaments.

Elastic fiber: Fiber formed from the protein elastin, which gives a rubbery and resilient quality to the matrix of connective tissue.

Elasticity: The ability of tissue to return to its original shape after contraction or extension.

Electrical energy: Energy formed by the movement of charged particles across cell membranes.

Electrocardiogram: Graphic record of the heart’s electrical activity, displayed as voltage changes over time; the initial deflection of the cardiac cycle is the P wave that represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization. Also called ECG or EKG.

Electrochemical gradient: The distribution of ions involving both a chemical and an electrical gradient interacting to determine the direction of diffusion.

Electroencephalogram (EEG): Graphic record of the electrical activity of nerve cells in the brain.

Electrolyte: Chemical substances, such as salts, acids, and bases, that ionize and dissociate in water and are capable of conducting an electrical current.

Electrolyte balance: Refers to the balance between input and output of salts (sodium, potassium, calcium, magnesium) in the body.

Electromagnetic radiation: Energy form that travels in waves.

Electron: Negatively charged subatomic particle of matter that occupies an orbital around the nucleus; the electrons determine the volume and the chemical properties of the atom; often abbreviated e– .

Electron orbital: One of the volumes of space around the atomic nucleus in which one or at most two electrons are likely to be at any instant.

Electron shell model: Model of electron distribution in which all orbitals occupy a nested series of shells.

Electronegativity: An atom’s ability to attract shared electrons to itself in a covalent bond.

Element: Fundamental form of matter composed of atoms of only one kind (identical atomic number), that cannot be broken apart into a different form of matter by ordinary physical or chemical means.

Elevation: Movement of a bone superiorly.

Embolism: Obstruction of a blood vessel by an embolus.

Embolus: A plug, composed of a detached thrombus or foreign body, transported by the blood.

Embryo: Developmental stage extending from gastrulation to the end of the eighth week.

Embryoblast: An aggregation of cells at the embryonic pole of the blastocyst that forms the embryo and some extraembryonic membranes. Also called the inner cell mass.

Embryology: The study of development from the fertilized egg to the end of the eighth week of development.

Emesis: Reflexive emptying of the stomach through the esophagus and pharynx; also known as vomiting.

Emphysema: A lung disorder characterized by fibrosis of the lungs; alveoli burst and fuse into enlarged air spaces, surface area for gas exchange is reduced, and victims become barrel-chested because of air retention.

Emulsification: The dispersion of large lipid globules into smaller, uniformly distributed particles in the presence of bile.

Enamel: The hard, white substance covering the crown of a tooth.

Encephalitis: Inflammation of the brain.

End artery: An artery lacking anastomoses to maintain viability of the tissue supplied if occlusion of the artery occurs.

Endergonic reaction: Chemical reaction that absorbs energy, such as an anabolic reaction or reduction reaction.

Endocarditis: Inflammation of the endocardium.

Endocardium: Endothelial membrane that lines the interior of the heart chambers, and is continuous with the endothelial lining of the blood vessels.

Endochondral ossification: Formation of osseous tissue by the replacement of calcified cartilage; process for the formation of most fetal bones, and for the growth in length of long bones.

Endocrine glands: Ductless glands that empty their hormonal products directly into the blood.

Endocrine system: Body system that includes internal organs that secrete hormones.

Endocrinology: The scientific study of hormones and the endocrine organs, and the diagnosis and treatment of disorders of the endocrine system.

Endocytosis: Cell uptake of substances when part of the plasma membrane forms a vesicle around them; major routes are pinocytosis, phagocytosis, and receptor-mediated endocytosis.

Endoderm: Embryonic germ layer; gives rise to the gastrointestinal tract, urinary bladder, urethra, and respiratory tract.

Endogenous: Originating or produced within the organism or one of its parts.

Endolymph: The fluid within the membranous labyrinth of the internal ear.

Endometrium: Mucous membrane lining of the uterus.

Endomysium: Fine areolar connective tissue that surrounds each individual muscle fiber.

Endoneurium: Connective tissue wrapping around individual nerve axons.

Endoplasmic reticulum (ER): Organelle continuous with the nuclear membrane; rough ER has ribosomes attached and functions in protein synthesis; smooth ER is a site of steroid synthesis and lipid metabolism.

Endosteum: The thin membrane that lines the medullary cavity of long bones and covers the trabeculae of spongy bone.

Endothelium: Single layer of simple squamous cells that line the walls of the heart, blood vessels, and lymphatic vessels.

Energy: The capacity to do work and to move matter; energy may be stored (potential energy), or energy in action (kinetic energy).

Energy intake: Energy liberated during food oxidation.

Energy output: Sum of energy lost as heat, as work, and as fat or glycogen storage.

Enteric nervous system: The part of the nervous system that is embedded in the submucosa and muscularis of the gastrointestinal (GI) tract; governs motility and secretions of the GI tract.

Enteroendocrine cell: A cell of the mucosa of the gastrointestinal tract that secretes a hormone that governs function of the GI tract.

Enteroendocrine cell of intestine: A cell of the mucosa of the small intestine that secretes the hormones cholecystokinin (CCK) and secretin.

Enteroendocrine cell of stomach: A cell in the gastric glands that secretes the hormone gastrin.

Enzyme: A biological catalyst that increases the rate of a chemical reaction, but is not consumed.

Eosinophil: Granular white blood cell that kills parasitic worms and destroys antigen-antibody complexes; its granules take up an acid stain called eosin and stain reddish.

Ependymal cell: A type of CNS supporting cell that covers the choroid plexuses and produces cerebrospinal fluid (CSF); it also lines the ventricles of the brain and assist in the circulation of CSF.

Epicardium: The visceral layer of the serous pericardium that covers the external surface of the heart; composed of serous tissue and mesothelium. Also called the visceral pericardium.

Epicondyle: Raised area on or above a condyle on a bone.

Epidemiology: Study of the occurrence and transmission of diseases and disorders in human populations.

Epidermis: The superficial layer of skin, composed of keratinized stratified squamous epithelium.

Epidermal dendritic cell: Phagocytic immune cell (macrophage) of the epidermis that functions as an antigen presenting cell (APC) during an immune response. Also called a Langerhans cell.

Epididymis: The portion of the male duct system in which sperm mature. Empties into the ductus deferens.

Epidural space: A space between the spinal dura mater and the vertebral canal, containing areolar connective tissue and a plexus of veins.

Epigenesis: Development of offspring from a zygote.

Epiglottis: Elastic cartilage at the back of the throat; covers the opening of the larynx during swallowing.

Epileptic seizures: Abnormal electrical discharges of groups of brain neurons, during which no other messages can get through.

Epimysium: Sheath of dense irregular connective tissue that surrounds an entire muscle organ and attaches it either directly by fusing to the periosteum of bone or perichondrium of cartilage, or indirectly by extending beyond the muscle as a ropelike tendon or sheetlike aponeurosis.

Epinephrine: Hormone secreted by the adrenal medulla that produces actions similar to those that result from sympathetic stimulation. Also called adrenaline.

Epineurium: The superficial connective tissue covering around an entire nerve.

Epiphyseal line: The remnant of the epiphyseal plate in a long bone.

Epiphyseal plate: Plate of hyaline cartilage at the junction of the diaphysis and epiphysis of a long bone, which provides for growth in length.

Epiphyses: The ends of a long bone, which are attached to the diaphysis.

Epistaxis: Loss of blood from the nose due to trauma, infection, allergy, neoplasm, and bleeding disorders. Also called a nosebleed.

Epithalamus: Most dorsal portion of the diencephalon; forms the roof of the third ventricle with the pineal gland extending from its posterior border; involved in olfactory stimulation; contains the pineal gland which sets the body’s biological clock.

Epithelial tissue: A basic tissue type that covers the body surface, lines internal cavities and hollow organs, and forms glands; it has the special characteristics of polarity, specialized contacts, supported by connective tissue, avascular, innervated, and regeneration. Also called epithelium.

Epitope: The simplest form of an antigenic determinant which can bind to an antibody or T cell receptor.

Eponychium: Narrow band of stratum corneum at the proximal border of a nail that extends from the margin of the nail wall. Also called the cuticle.

Erectile dysfunction: Failure to maintain an erection long enough for sexual intercourse. Also known as impotence.

Erection: The enlarged and stiff state of the penis or clitoris resulting from the engorgement of the spongy erectile tissue with blood.

Erector spinae (Iliocostalis, Longissimus, and Spinalis muscles): Major muscle group of the vertebral column; laterally flex spine and extend vertebral column. O: Iliac crest, vertebrae and ribs. I: Vertebrae and ribs.

Eructation: The forceful expulsion of gas from the stomach. Also called belching.

Erythema: Skin redness usually caused by dilation of the capillaries.

Erythrocytes: Red blood cells that transport oxygen to the body cells, and transport some carbon dioxide away from the body cells.

Erythropoiesis: Process of erythrocyte formation.

Erythropoietin (EPO): A protein hormone that enhances erythropoiesis (red blood cell production), and is released by the kidney and liver.

Esophageal achalasia: Failure of the lower esophageal sphincter to open, resulting in obstruction and difficulty swallowing.

Esophagus: The hollow muscular tube that connects the pharynx and the stomach.

Estrogens: Female sex hormones produced by the ovaries; govern development of oocytes, maintenance of female reproductive structures, and appearance of secondary sex characteristics.

Ethmoid bone: Deep, irregularly shaped cranial bone, between the sphenoid and nasal bones that forms the superior and middle conchae, and parts of the nasal cavity, nasal septum, and orbits, and contains ethmoidal sinuses. Markings: Crista galli is attachment point for the falx cerebri, a dural membrane. Cribriform plate allows passage of nerve filaments of the olfactory nerves (cranial nerve I). Perpendicular plate forms superior nasal septum. Superior and middle nasal conchae form part of lateral walls of nasal cavity that increase turbulence of airflow.

Eukaryotic cell: Cell having a nucleus and other membrane-bound organelles.

Eupnea: Normal quiet breathing.

Eustachian tube: Tube that connects the middle ear and the pharynx. Also called auditory tube, pharyngotympanic tube.

Eversion: (1) Eversion: The movement of the sole of the foot at the ankle joint so that it faces laterally. (2) The movement of an atrioventricular valve into an atrium during ventricular contraction.

Evaporation: The conversion of a substance from a liquid state to a gaseous state.

Exchange reaction: Chemical reaction in which bonds are both made and broken; atoms become combined with different atoms. Also called a displacement reaction

Excitability: The ability of muscle fibers to receive and respond to stimuli; the ability of neurons to respond to stimuli and generate nerve impulses.

Excitation-contraction coupling: Sequence of events by which transmission of an action potential along the sarcolemma leads to the sliding of myofilaments.

Excretion: Elimination of waste products from the body.

Exergonic reaction: Chemical reaction that releases energy, such as a catabolic reaction or oxidation reaction.

Exhalation: Breathing out; expelling air from the lungs into the atmosphere. Also called expiration.

Exocrine glands: Glands that have ducts through which their secretions are carried to a particular site.

Exocytosis: Movement of substances outside a cell as a secretory vesicle fuses with the plasma membrane.

Exogenous: Developing or originating outside an organ or part.

Exons: Amino acid specifying informational sequences (separated by introns) in the genes of higher organisms.

Expectoration: Matter, such as mucus, that is ejected through the mouth from the lungs, bronchi, and trachea. Also called sputum.

Extensibility: The ability of muscle tissue to stretch when it is pulled.

Extension: Movement at a joint which increases the angle between the articulating bones.

Extensor carpi radialis longus: Posterior, lateral forearm; extend wrist and abduct hand. O: Distal humerus. I: Metacarpal 2.

Extensor carpi ulnaris: Posterior, medial forearm; extend wrist and adduct hand. O: Distal humerus and proximal ulna. I: Metacarpal 5.

Extensor digitorum longus: Anterior, lateral leg muscle; dorsiflex foot and extend toes. O: Proximal tibia and fibula. I: Phalanges of toes 2-5.

Extensor digitorum: Posterior, center of forearm; extend wrist and extend fingers. O: Distal humerus. I: Phalanges of fingers 2-5.

External: Located on or near the surface.

External acoustic meatus: The S-shaped tube that leads to the eardrum. Also called auditory canal.

External auditory meatus: A curved tube in the temporal bone that leads to the middle ear.

External ear: The outer ear, consisting of the pinna, external auditory canal, and tympanic membrane (eardrum).

External intercostals: Superficial muscles between ribs; elevate rib cage, expand thorax and aid in inspiration. O: Ribs. I: Ribs.

External nares: Anterior openings to the nasal cavity. Also called the nostrils.

External oblique: Superficial, lateral trunk muscle; strongest of the trunk muscles; one laterally flex and rotate vertebral column; both flex vertebral column and compress abdomen. O: Ribs 5-12. I: Iliac crest and linea alba.

External respiration: The exchange of respiratory gases between the lungs and blood. Also called pulmonary respiration.

Exteroceptor: Sensory end organ that responds to stimuli from the external world.

Extracellular fluid (ECF): Internal fluid located outside cells; includes plasma and interstitial fluid.

ExtracelIular materials: Substances found outside the cell; include interstitial fluid, blood plasma, and cerebrospinal fluid.

Extracellular matrix: Nonliving material in connective tissue consisting of ground substance and fibers that separates the living cells.

Extrasystole: Premature heart contraction.

Extrinsic: Of external origin.

Extrinsic eye muscles: The six skeletal muscles which attach to and move each eye.

Exudate: Material including fluid, pus, or cells that has escaped from blood vessels and been deposited in tissues.

Exon: Portion of a pre-mRNA transcript that is expressed and will become translated.

Eyebrow: The hairy ridge superior to the eye.


F

Facet: Smooth, nearly flat articular surface on a bone.

Facilitated diffusion: Passive transport process used by certain molecules that are too large to pass through plasma membrane pores. Involves movement through channels or movement facilitated by a membrane carrier.

Falciform ligament: A sheet of parietal peritoneum between the two principal lobes of the liver. The ligamentum teres, or remnant of the umbilical vein, lies within its fold.

Fallopian tube: Tube through which the ovum is transported to the uterus. Also called the uterine tube, or oviduct.

False ribs: Ribs 8-12; includes the vertebrochondral ribs 8-10 that connect indirectly with the sternum through the costal cartilage of rib 7, and the vertebral ribs 11-12 (floating ribs) that are not attached anteriorly.

Falx cerebelli: A small triangular process of the dura mater attached to the occipital bone in the posterior cranial fossa and projecting inward between the two cerebellar hemispheres.

Falx cerebri: A fold of the dura mater extending deep into the longitudinal fissure between the two cerebral hemispheres.

Fascia: A fibrous membrane covering, supporting, and separating muscles.

Fascicle: Bundle of nerve or muscle fibers bound together by connective tissues.

Fat: Lipid with glycerol bound to three fatty acids; the body’s most concentrated source of energy fuel. Also called a triglyceride or triacylglycerol.

Fatty acid: Molecule with a backbone of up to 36 carbon atoms, a carboxylic acid group (-COOH) at one end, and hydrogen atoms at the other bonding sites.

Fauces: The opening from the mouth into the pharynx.

Feces: Material discharged from the bowel; composed of food residue, secretions, bacteria.

Female reproductive cycle: General term for the ovarian and uterine cycles, the hormonal changes that accompany them, and cyclic changes in the breasts and cervix; includes changes in the endometrium of a nonpregnant female that prepares the lining of the uterus to receive a fertilized ovum. Also termed the menstrual cycle.

Femur: Thigh bone; largest bone of the body. Markings: Head is proximal hemispheric extremity; articulates with acetabulum to form the ball-and-socket hip joint. Neck is constricted region distal to the head. Trochanters (Greater and Lesser) are attachment sites of thigh and buttock muscles. Gluteal tuberosity is attachment site of gluteus maximus muscle. Condyles (Lateral and Medial) articulate with corresponding condyles of the tibia. Epicondyles (Lateral and Medial) are attachment sites of muscles. Linea aspera is posterior ridge; attachment site of thigh muscles. Patellar surface is anterior groove; accommodates the patella.

Fenestrated: Pierced with one or more small openings.

Fertilization: Penetration of a secondary oocyte by a sperm cell, meiotic division of secondary oocyte to form an ovum, and subsequent union of the nuclei of the gametes.

Fetal circulation: The cardiovascular system of the fetus, including the placenta and special blood vessels involved in the exchange of materials between fetus and mother.

Fetus: In humans, the developmental stage extending from the ninth week to birth.

Fever: An elevation in body temperature above the normal temperature of 37.0 °C (98.6 °F) due to a resetting of the hypothalamic thermostat.

Fiber: A slender thread-like structure or filament.

Fibrillation: Condition of rapid and irregular or out-of-phase heart contractions, in which the heart is uncoordinated and useless as a pump, like a “squirming bag of worms”.

Fibrin: Fibrous insoluble protein formed during blood clotting; the enzyme thrombin converts fibrinogen (soluble) into fibrin (insoluble), which forms the threads of the blood clot.

Fibrinogen: A blood protein that is converted to fibrin during blood clotting.

Fibrinolysis: Process that removes unneeded blood clots when healing has occurred.

Fibroblast: A large, flat, actively mitotic cell that secretes most of the extracellular matrix of areolar and dense connective tissues.

Fibrocartilage: Tissue with many chondrocytes that lie in lacunae, amorphous but firm matrix, and many thick collagen fibers. Functions in providing great tensile strength with the ability to absorb compressive shock. Located in the intervertebral discs, pubic symphysis, and menisci of the knee.

Fibrocyte: Mature fibroblast; maintains the matrix of fibrous types of connective tissue.

Fibroid: Resembling or composed of fibers or fibrous tissue.

Fibrosis: Proliferation of fibrous connective tissue called scar tissue.

Fibrous joint: An articulation in which the bones are joined together by dense fibrous connective tissue, lack a joint cavity, and almost no motion is possible; types are sutures, syndesmoses, and gomphoses.

Fibrous pericardium: Superficial layer of the heart that protects, anchors, and prevents overfilling

Fibrous skeleton of heart: A complex framework of fibrous tissue that anchors cardiac muscle fibers, supports the heart valves and openings to the great vessels, and acts as an electrical insulator to limit the spread of action potentials to specific paths.

Fibrous tunic: The superficial coat of the eyeball, made up of the posterior sclera and the anterior cornea.

Fibula: Lateral leg bone; stick-like bone that does not bear weight. Markings: Head is proximal end; articulates with undersurface of the lateral condyle of the tibia. Lateral malleolus forms the lateral ankle bulge; articulates with the talus.

Fibularis longus and brevis: Superficial, lateral leg muscle; plantar flex and evert foot. O: Proximal fibula. I: Tarsals & metatarsals. Also called Peroneus longus and brevis

Fight-or-flight response: The effects produced upon stimulation of the sympathetic division of the autonomic nervous system.

Filiform papilla: One of the conical projections that are distributed in parallel rows over the anterior two-thirds of the tongue and lack taste buds.

Filtrate: A plasma derived fluid that is processed by the renal tubules to form urine.

Filtration: The flow of a liquid through a filter (or membrane that acts like a filter) due to a hydrostatic pressure; occurs in capillaries due to blood pressure.

Filum terminale: Non-nervous fibrous tissue of the spinal cord that extends inferiorly from the conus medullaris to the coccyx.

Fimbriae: Fingerlike structures, especially the lateral ends of the uterine (Fallopian) tubes.

First-degree burn: Superficial burn that damages only the epidermis.

Fissure: (1) A groove or cleft. (2) Narrow, slit-like opening in a bone. (3) The deepest depressions or inward folds on the brain.

Fixator: A muscle that stabilizes the origin of the prime mover so that the prime mover can act more efficiently.

Fixed macrophage: Stationary phagocytic cell found in the liver, lungs, brain, spleen, lymph nodes, subcutaneous tissue, and red bone marrow. Also called a histiocyte.

Flaccid: Relaxed, flabby, or soft; lacking muscle tone.

Flagellum: A long whip-like projection, composed of microtubules; propels the sperm cell.

Flatulence: Presence of an excessive amount of gas in the gastrointestinal tract.

Flatus: Gas in the gastrointestinal tract that may be expelled through the anus.

Flexion: Movement at a joint which decreases the angle between the articulating bones.

Flexor carpi radialis: Anterior, center of forearm; flex wrist and abduct hand. O: Distal humerus. I: Metacarpals 2-3.

Flexor carpi ulnaris: Anterior, medial forearm; flex wrist and adduct hand. O: Distal humerus and proximal ulna. I: Carpals and metacarpal 5.

Flexor (withdrawal) reflex: Reflex initiated by a painful stimulus (actual or perceived); causes automatic withdrawal of the threatened body part from the stimulus. Also called the withdrawal reflex

Fluid phase endocytosis: The cellular process of actively engulfing liquid by forming invaginations in the surface of the cell membrane then closing to form fluid-filled vesicles. Also called pinocytosis.

Fluid mosaic model: A depiction of the structure of the plasma membranes of a cell, which contains a fluid bilayer of phospholipid molecules in which protein molecules are floating in a “in a sea of lipid”.

Follicle: (1) Ovarian structure consisting of a developing egg surrounded by one or more layers of follicle cells. (2) colloid containing structure of the thyroid gland.

Follicle stimulating hormone (FSH): Hormone produced by the anterior pituitary; in females it stimulates the maturation of ovarian follicles and secretion of estradiol; in males it stimulates sperm production in the testes. Also called follitropin.

Fontanels: One of several membranous intervals between the angles and margins of the cranial bones in the infant; they include the midline anterior and posterior fontanels, and the paired sphenoidal and mastoid fontanels; they allow the fetal skull to be compressed slightly during birth, and accommodate brain growth in the fetus and infant.

Foramen: (1) Round or oval opening through a bone. (2) Hole or opening between body cavities.

Foramen ovale: Fetal heart structure; an opening in the interatrial septum that allows blood entering the right atrium to flow directly into the left atrium; closes after birth and remnants are seen as an oval depression on the lower part of the septum of the right atrium, which is called the fossa ovalis.

Forebrain (prosencephalon): Anterior portion of the brain consisting of the telencephalon and the diencephalon.

Formed elements: Cellular portion of blood.

Fornix: (1) An arch or fold. (2) A tract in the brain made up of association fibers, connecting the hippocampus with the mammillary bodies. (3) A recess around the cervix of the uterus where it protrudes into the vagina.

Fossa: (1) A depression. (2) Shallow, basin-like depression in a bone, often serving as an articular surface.

Fossa ovalis: The oval depression on the lower part of the septum of the right atrium seen after birth; it is a remnant of the fetal foramen ovale, which had connected the right atrium to the left atrium.

Fourth ventricle: A cavity filled with cerebrospinal fluid within the brain lying between the cerebellum and the medulla oblongata and pons.

Fovea: A pit.

Fovea centralis: Depression in the center of the macula lutea that contains the greatest density of cones, and is the area of greatest visual acuity.

Fracture: A break in a bone.

Frank-Starling law of the heart: The greater the volume of blood in the heart during diastole, the greater the force of contraction during systole.

Free nerve endings: Sensory nerve fibers in the dermal papillae that detect pain, heat and cold.

Free radicals: Highly reactive chemicals with unpaired electrons that can scramble the structure of proteins, lipids, and nucleic acids.

Frontal bone: Forehead bone that forms anterior cranium & roof of orbits and contains frontal sinuses. Markings: Supraorbital foramen allows passage of supraorbital arteries and nerves. Supraorbital margins are superior margins of orbits that form the eyebrow ridges.

Frontal plane: Longitudinal (vertical) plane that divide the body into anterior and posterior parts. Also called a coronal plane.

Frontalis: Forehead muscle; raises eyebrows, wrinkles forehead skin. O: Galea aponeurotica. I: Skin of eyebrows. Also called frontal belly of occipitofrontalis (epicranius).

Fulcrum: The fixed point on which a lever moves when a force applied.

Functional classification of joints: Based on the amount of movement allowed; all joints are either synarthroses, amphiarthroses, or diarthroses.

Functional group: An atom, or group of atoms, that is covalently bonded to the carbon backbone of an organic compound and influences its chemical behavior.

Fundus: Base of an organ; part farthest from the opening of the organ.

Fungiform papilla: A mushroom-like elevation on the upper surface of the tongue appearing as a red dot; most contain taste buds.

Furuncle: A boil; painful nodule caused by bacterial infection and inflammation of a hair follicle or sebaceous (oil) gland.

Gallbladder: A small pouch, located inferior to the liver, that stores bile and empties by means of the cystic duct.

Gallstone: Crystallized cholesterol that obstructs the flow of bile from the gallbladder. Also called a biliary calculus.

Gamete: A male or female reproductive cell; a sperm cell or secondary oocyte.

Gametogenesis: Formation of gametes.

Gamma fibers: Nerve fibers that have a conduction rate of 15–40 m/sec.

Ganglion: A collection of neuron cell bodies in the PNS.

Ganglionic neuron: Autonomic motor neuron that has its cell body in a peripheral ganglion and projects its postganglionic axon to an effector.

Gap junction: A passageway between two adjacent cells; formed by transmembrane proteins called connexons.

Gastric glands: Glands in the mucosa of the stomach composed of cells that empty their secretions into narrow channels called gastric pits.

Gastrin: Hormone secreted by enteroendocrine cells in the stomach that stimulates parietal cells to increase HCl secretion.

Gastrocnemius: Superficial calf muscle; flex leg and plantar flex foot. O: Distal femur. I: Calcaneus.

Gastroenteritis: Inflammation of the gastrointestinal tract.

Gastroenterology: The medical specialty that deals with the structure, function, diagnosis, and treatment of diseases of the stomach and intestines.

Gastroesophageal: Relating to both stomach and esophagus.

Gastrointestinal tract: The stomach, small intestine, and large intestine. Also called GI tract or digestive tract.

Gastrulation: Developmental process that produces the three primary germ layers (ectoderm, mesoderm, and endoderm)

Gene: Unit of information on DNA for a heritable trait, passed from parents to offspring.

Genetic code: The basic language of protein synthesis in cells; correspondence between nucleotide triplets in DNA, then mRNA, and specific sequences of amino acids in a polypeptide chain.

Genetics: The study of genes and heredity.

Genitalia: The internal and external reproductive organs.

Genital tubercle: An elevated midline swelling in an embryo that is the primordium of the penis of the male or the clitoris of the female. Also called phallic tubercle.

Genome: The complete set of genes of an organism.

Genotype: The genetic makeup of an individual

Genu varum: A deformity marked by medial angulation of the leg in relation to the thigh; an outward bowing of the legs.

Geriatrics: The branch of medicine devoted to the medical problems and care of elderly persons.

Germ layers: Three cellular layers (ectoderm, mesoderm, and endoderm) that represent the initial specialization of cells in the embryonic body and from which all body tissues arise.

Germ cell: A gamete (sperm or oocyte), or a precursor cell destined to become a gamete.

Germinal: Pertaining to a gamete (germ cell), or the primordial stage of development.

Gestation period: The period of development from fertilization to birth, about 280 days for humans.

Gingivae: Gums; they cover the alveolar processes of the mandible and maxilla and extend slightly into each socket.

Gland: Organ specialized to secrete or excrete substances for further use in the body or for elimination.

Glandular epithelium: Endocrine glands: Secrete hormones that diffuse into the blood. Functions in production of hormones that regulate body activities and maintain homeostasis. Located in the pituitary gland at base of brain, pineal gland in brain, thyroid and parathyroid glands near larynx (voice box), adrenal glands superior to kidneys, pancreas near stomach, ovaries in pelvic cavity, testes in scrotum, and thymus in thoracic cavity.

Glandular epithelium: Exocrine glands: Secretory products released into ducts. Functions in production of substances such as sweat, oil, earwax, saliva, or digestive enzymes. Located in sweat, oil, and earwax glands of the skin; digestive glands such as salivary glands, which secrete into mouth cavity, and pancreas, which secretes into the small intestine.

Glans penis: The slightly enlarged region at the distal end of the penis.

Glaucoma: An eye disorder in which there is increased intraocular pressure due to an excess of aqueous humor.

Glial cells: The supporting cells in the central nervous system.

Gliding: Movement of a synovial joint in a slight, gliding motion, in which one flat bone surface glides or slips over another similar surface.

Gliding joint: A nonaxial synovial joint in which the articulating surfaces are flat, which permits only side-to-side and back-and-forth movements, as between carpal bones, tarsal bones, and the scapula and clavicle. Also called an arthrodial joint.

Glomerular capsule: Double-walled cup at a renal tubule that encloses a glomerulus; its inner (visceral) membrane forms part of the filtration membrane. Also called Bowman’s capsule

Glomerular filtrate: The fluid produced when blood is filtered by the filtration membrane in the glomeruli of the kidneys.

Glomerular filtration The first step in urine formation in which substances in blood pass through the filtration membrane, then the filtrate enters the proximal convoluted tubule of a nephron.

Glomerular filtration rate (GFR): Rate of filtrate formation by kidneys.

Glomerulonephritis: Autoimmune disease that produces a severe impairment of renal function.

Glomerulus: Cluster of capillaries forming part the nephron that is the site of filtrate formation.

Glottis: The vocal folds (true vocal cords) in the larynx plus the space between them (rima glottidis).

Glucagon: Hormone formed by alpha cells of pancreatic islets; raises the glucose level of blood.

Glucocorticoids: Adrenal cortex hormone that increase blood glucose levels and aid the body in resisting long term stressors.

Glucogenesis: Formation of glucose.

Gluconeogenesis: Formation of new glucose from noncarbohydrates, such as protein or fat.

Glucose: Principal blood sugar with the formula C6H12O; the chief source of energy for living organisms; produced by plants during photosynthesis; degraded to produce ATP during cellular respiration.

Glucosuria: The presence of glucose in the urine; may be temporary or pathological. Also called glycosuria.

Gluteus maximus: Large, superficial buttock muscle; extend and laterally rotate thigh. O: Sacrum and iliac crest. I: Gluteal tuberosity of femur.

Gluteus medius: Deep buttock muscle; abduct and medially rotate thigh. O: Ilium. I: Greater trochanter of femur.

Glyceride: Molecule having 1, 2, or 3 fatty acid tails attached to glycerol; one of the fats or oils.

Glycerol: A modified simple sugar (a sugar alcohol).

Glycocalyx: A layer of externally facing glycoproteins on a cell’s plasma membrane (sugar coating); determines blood type, involved in the cellular interactions of fertilization, embryonic development, and immunity, and acts as an adhesive between cells.

Glycogen: A highly branched polysaccharide of glucose monomers; main carbohydrate stored in animals; abundant in liver and muscles.

Glycogenesis: Formation of glycogen from glucose.

Glycogenolysis: Breakdown of glycogen into glucose.

Glycolipid: A lipid with one or more covalently attached sugars.

Glycolysis: Breakdown of glucose to pyruvic acid to make ATP and NADH.

Glycoprotein: Protein that contains covalently linked carbohydrates, such as surface proteins of animal cells and many blood proteins.

Glycosidic bond: A covalent bond (-C-O-C-) that links two monosaccharides together.

Goblet cells: A goblet-shaped unicellular exocrine gland that secretes mucus; present in epithelium of the airways and intestines.

Goiter: An enlarged thyroid gland.

Golgi apparatus: Flattened membranous sacs; packages proteins into vesicles for secretion, modifies proteins that become part of cell membranes, and packages enzymes into lysosomes. Also called Golgi complex or Golgi body.

Golgi tendon organs: Proprioceptors located in tendons, close to the point of skeletal muscle insertion; important to smooth onset and termination of muscle contraction.

Gomphosis: A fibrous joint in which a tooth articulates with its bony alveolar socket.

Gonad: Primary reproductive organ that produces gametes and hormones; the testis of the male and the ovary of the female.

Gonadocorticoids: Sex hormones, primarily androgens, secreted by the adrenal cortex.

Gonadotropins: Gonad-stimulating hormones produced by the anterior pituitary. Also called gonadotropic hormones.

Gout: Hereditary condition associated with excessive uric acid in the blood; the acid crystallizes and deposits in joints, kidneys, and soft tissue.

Graafian follicle: See Vesicular follicle.

Gracilis: Superficial muscle on medial thigh; adduct thigh, flex leg. O: Pubis. I: Tibia.

Graded muscle responses: Variations in the degree of muscle contraction by changing either the frequency or strength of the stimulus.

Graded potential: A local change in membrane potential that varies directly with the strength of the stimulus, declines with distance.

Granzymes: Digestive enzymes secreted by cytotoxic T lymphocytes and natural killer cells.

Graves’ disease: Autoimmune disorder which prompts the thyroid gland to produce excessive amounts of thyroxine.

Gray commissure: A narrow strip of gray matter connecting the two lateral gray masses within the spinal cord.

Gray matter: Gray areas in the CNS that contain neuron cell bodies, dendrites and unmyelinated axons.

Great cardiac vein: Drains blood from the coronary circulation and merges with the the coronary sinus.

Greater omentum: A large fold of the peritoneum that descends from the greater curvature of the stomach and hangs down like an apron, anterior to the intestines.

Greater vestibular glands: A pair of glands on either side of the vaginal orifice that open by a duct into the space between the hymen and the labia minora. Also called Bartholin’s glands.

Greenstick fracture: Bone breaks incompletely; common in children.

Groin: The depression between the thigh and the trunk; the inguinal region.

Groove: Furrow in a bone.

Gross anatomy: The branch of anatomy that deals with structures that can be studied without using a microscope. Also called macroscopic anatomy.

Growth: An increase in size due to an increase in (1) the number of cells, (2) the size of existing cells as internal components increase in size, or (3) the size of intercellular substances.

Growth hormone (GH): Hormone secreted by the anterior pituitary that stimulates metabolism and growth of body tissues, especially skeletal and muscular tissues. Also called somatotropin, or somatotropic hormone.

Guanine (G): One of two major purines occurring in all nucleic acids.

Gullet: (1) The esophagus. (2) The pharynx.

Gustation: Taste.

Gut-brain peptides: Neuropeptides produced by nonneural tissue that are widespread in the gastrointestinal tract.

Gynecology: The branch of medicine dealing with the study and treatment of disorders of the female reproductive system.

Gyrus: An outward fold of the surface of the cerebral cortex. Plural is gyri. Also called a convolution.

Hair: A threadlike structure produced by hair follicles that develops in the dermis. Also called a pilus.

Hair follicle: Tubelike invagination of the epidermis with outer and inner root sheaths, from which the hair grows.

Hair follicle receptor: Nerve receptors that detect hair movement. Also called hair root plexus.

Hair root: The part of a hair that is embedded in the hair follicle

Hair root plexus: Nerve receptors that detect hair movement. Also called hair follicle receptor.

Hair shaft: The nongrowing portion of a hair, which protrudes from the skin.

Halitosis: A foul odor from the mouth. Also called bad breath.

Hallux: Great toe

Hamstring Group (Biceps femoris, Semimembranosus, Semitendinosus): Posterior thigh muscle; antagonist to quadriceps; flex leg at knee, extend thigh at hip. O: Ischial tuberosity. I: Proximal tibia and fibula.

Haploid: Having half the number of chromosomes characteristically found in the somatic cells of an organism; characteristic of mature gametes (sperm and oocyte). Symbolized n.

Hapten: A small molecule that is not antigenic by itself, but when bound to a carrier protein, it can stimulate antibody production and it can activate T cells. Also called an incomplete antigen.

Hard palate: The anterior portion of the roof of the mouth, formed by the maxillae and palatine bones and lined by mucous membrane.

Haustra: A series of pouches that characterize the colon; caused by tonic contractions of the teniae coli. Singular is haustrum.

Haversian canal: (1) A tube running the length of the spinal cord in the gray commissure. (2) A circular channel running longitudinally in the center of an osteon (haversian system) of mature compact bone, containing blood and lymphatic vessels and nerves. Also called a central canal.

Haversian system: The basic unit of structure in adult compact bone, consisting of a central (haversian) canal with its concentrically arranged lamellae, lacunae, osteocytes, and canaliculi. Also called an osteon.

Head of bone: Bony expansion carried on a narrow neck.

Heart: A hollow muscular organ lying slightly to the left of the midline of the chest that pumps the blood through the cardiovascular system.

Heart attack: Condition characterized by dead tissue areas in the myocardium; caused by interruption of blood supply to the area.

Heart block: Impaired transmission of electrical impulses from atria to ventricles, resulting in dysrhythmia. In first-degree heart block, there is prolongation of AV conduction time (PR interval). In second-degree heart block, some atrial impulses fail to reach the ventricles, thus some ventricular beats are missing. In third degree heart block, complete atrioventricular dissociation occurs, thus atria and ventricles beat independently.

Heart murmur: Abnormal heart sound; usually resulting from valve problems.

Heart rate (HR): The number of beats per minute (bpm) for the heart.

Heimlich maneuver: Procedure in which the air in a person’s own lungs is used to expel an obstructing piece of food.

Helper T cell: Type of T lymphocyte that helps cellular immunity by direct contact with other lymphocytes and by releasing cytokines.

Hemangioblast: A precursor mesodermal cell that develops into blood and blood vessels.

Hematocrit: The percentage of erythrocytes to total blood volume.

Hematology: The study of blood.

Hematoma: Mass of clotted blood that forms at an injured site.

Hematopoiesis: Blood cell production, which occurs in red bone marrow after birth. Also called hemopoiesis.

Hematopoietic: Pertaining to or related to the formation of blood cells. Also called hemopoietic.

Hematopoietic tissue: Tissue that produces all of the blood cells and other formed elements of blood. Also called hemopoietic tissue.

Heme: Iron containing pigment that is essential to oxygen transport by hemoglobin.

Hemiplegia: Paralysis of the upper limb, trunk, and lower limb on one side of the body.

Hemocytoblast: Bone marrow cell that gives rise to all the formed elements of blood.

Hemodynamics: The study of the dynamics of the blood circulation.

Hemoglobin: An iron containing respiratory protein that binds oxygen in red blood cells.

Hemolysis: Rupture of erythrocytes.

Hemophilia: A hereditary blood disorder where there is a deficient production of certain factors involved in blood clotting, resulting in excessive bleeding into deep tissues, joints, and elsewhere.

Hemopoiesis: Blood cell production, which occurs in red bone marrow after birth. Also called hematopoiesis.

Hemopoietic tissue: Tissue that produces all of the blood cells and other formed elements of blood. Also called hematopoietic tissue.

Hemorrhage: Bleeding; the escape of blood from blood vessels, especially when the loss is profuse.

Hemorrhoids: Dilated or varicosed blood vessels (usually veins) in the anal region. Also called piles.

Hemostasis: Stoppage of bleeding; blood clotting.

Henry’s law: States that the amount of gas dissolved in a liquid is directly proportional to the partial pressure of the gas that is in contact with the liquid.

Heparin: Natural anticoagulant that is secreted into the blood by basophils.

Hepatic: Refers to the liver.

Hepatic duct: A duct that receives bile from the bile capillaries.

Hepatic portal system: Circulation in which the hepatic portal vein carries dissolved nutrients to the liver tissues for processing.

Hepatitis: Inflammation of the liver.

Hepatocyte: A liver cell.

Hepatopancreatic ampulla: A small, raised area in the duodenum where the combined common bile duct and main pancreatic duct empty into the duodenum. Also called the ampulla of Vater.

Hernia: Abnormal protrusion of an organ or a body part through the containing wall of its cavity.

Heterozygous: Having different allelic genes at one locus or (by extension) many loci.

Hiatus: An opening; a foramen.

Hilton’s law: Any nerve serving a muscle producing movement at a joint; also innervates the joint itself and the skin over the joint.

Hilum: An area, depression, or pit where blood vessels and nerves enter or leave an organ. Also called a hilus.

Hilum of lung: A depression on the medial surface of each lung, where the primary (main) bronchus, blood vessels, nerves, and lymphatics enter or leave.

Hinge joint: A uniaxial synovial joint in which the convex end of one bone fits into the corresponding concave end of the other bone, allowing motion in one plane only.

Hippocampus: A long curved structure of gray matter in the temporal lobe of the brain that forms part of the limbic system, and plays a role in converting new information into long term memories.

Histamine: Substance that causes vasodilation, increased vascular permeability, and constriction of bronchioles; found in basophils, mast cells, and platelets, that release it when cells are injured.

Histology: Branch of anatomy dealing with the microscopic structure of tissues.

Histone: Protein with many positive charges that eukaryotic DNA will wrap around.

HIV (human immunodeficiency virus): Virus that destroys helper T cells, thus depressing cell-mediated immunity; symptomatic AIDS gradually appears when lymph nodes can no longer contain the virus.

Holocrine glands: An exocrine gland in which entire secretory cells, along with their accumulated secretions, make up the secretory product of the gland, as in the sebaceous (oil) glands.

Homeostasis: The condition in which the body’s internal environment remains relatively constant within physiological limits.

Homologous: Parts or organs corresponding in structure but not necessarily in function.

Homologous chromosomes: Pairs of chromosomes that are identical in size, shape, and type of genes they carry.

Homozygous: Having identical genes at one or more loci.

Hormones: A secretion of endocrine cells, which may be steroidal or amino acid based molecules, that are released to the blood and alter the physiological activity of target cells, in order to regulate cellular metabolism and energy balance, or regulate electrolyte, water, and nutrient balance, or regulate reproduction, growth, and development, or mobilize body defenses.

Human chorionic gonadotropin (hCG): A hormone produced by the developing placenta that maintains the corpus luteum.

Human chorionic somatomammotropin (hCS): Hormone produced by the chorion of the placenta that stimulates breast tissue for lactation, enhances body growth, and regulates metabolism. Also called human placental lactogen (hPL).

Human growth hormone (hGH): Hormone secreted by the anterior pituitary that stimulates metabolism and growth of body tissues, especially skeletal and muscular tissues. Also called somatotropin, or somatotropic hormone.

Humerus: Arm bone. Markings: Head is proximal hemispheric extremity; articulates with glenoid cavity of the scapula to form the ball-and-socket shoulder joint. Tubercles (Greater and Lesser) attachment sites for scapular muscles. Intertubercular sulcus guides a tendon of the biceps muscle of the arm to the rim of the glenoid cavity. Deltoid tuberosity is attachment site for deltoid muscle of the shoulder. Radial groove guides the radial nerve. Epicondyles (Lateral and Medial) are attachment sites for forearm muscles; the ulnar nerve passes behind the medial epicondyle and when hit, the “funny bone” sensation occurs. Radial fossa receives head of the radius when the forearm is flexed. Capitulum is the distal lateral ball-like condyle; articulates with head of the radius. Olecranon fossa is the posterior distal depression; receives olecranon processes of ulna when forearm is extended. Coronoid fossa is the anterior distal depression; receives coronoid processes of ulna when forearm is flexed. Trochlea is the distal medial pulley-like condyle; articulates with trochlear notch of the ulna.

Humoral immunity: Immunity conferred by antibodies present in blood plasma and other body fluids.

Huntington’s disease: Hereditary disorder leading to degeneration of the basal nuclei and the cerebral cortex.

Hyaline cartilage: Tissue with many chondrocytes that lie in lacunae, amorphous but firm matrix, and thin collagen fibers. Functions in providing support, flexibility, and smooth surfaces for joint movements. Located in cartilages of the trachea, larynx, and nose; costal cartilages of the ribs; articular cartilages of long bones; embryonic and fetal skeleton.

Hyaluronic acid: A viscous, amorphous extracellular material that binds cells together, lubricates joints, and maintains the shape of the eyeballs.

Hydrocarbon: Organic compound that contains only hydrogen and carbons atoms.

Hydrochloric acid: Acid that aids protein digestion in the stomach, and produced by parietal cells; has the chemical formula HCl.

Hydrogen bond: A weak bond between an oxygen or nitrogen atom, and a hydrogen atom that is bound to another oxygen or nitrogen atom.

Hydrogen ion (H+): A hydrogen atom minus its electron and therefore carrying a positive charge (i.e., a proton).

Hydrolysis: Breakdown of a large molecule into small molecules by adding water, H2O.

Hydrophilic: A polar molecule, or molecular region, that is very soluble in water (water loving).

Hydrophobic: A nonpolar molecule, or molecular region, that is insoluble in water (water fearing).

Hydrostatic pressure: Pressure exerted by fluid against a membrane.

Hydroxide ion: Negative ion containing one oxygen and one hydrogen atom (OH– ).

Hydroxyapatite: An inorganic mineral, Ca10(PO4)6(OH), that comprises about 65% of bone; also found in teeth and pathologic calcifications.

Hymen: A thin fold of vascularized mucous membrane at the vaginal orifice.

Hyoid Bone: U-shaped bone in the anterior neck, the only bone of the body that does not articulate directly with another bone; suspended by ligament and muscle from the skull; provides attachment for tongue, neck and pharyngeal muscles.

Hyperalgesia: Pain amplification.

Hypercapnia: Abnormally high carbon dioxide levels in arterial blood, which often causes acidosis.

Hyperemia: An increase in blood flow into a tissue or organ; congested with blood.

Hyperextension: Movement at a joint to produce excessive extension, which increases the angle between the articulating bones beyond the normal range of motion.

Hyperglycemic: Term used to describe hormones such as glucagon that elevate blood glucose level.

Hyperopia: A condition in which visual images are routinely focused behind the retina; commonly known as farsightedness.

Hyperoxia: An increased amount of oxygen in blood and tissues.

Hyperplasia: Accelerated growth; an abnormal increase in the number of normal cells in a tissue or organ, increasing its size.

Hyperpnea: Deeper and more vigorous breathing, but with unchanged respiratory rate, as during exercise.

Hypersecretion: Overactivity of glands resulting in excessive secretion.

Hypersensitivity: Overreaction to an allergen that results in pathological changes in tissues. Also called allergy.

Hypersplenism: A condition in which the cellular components of the blood are removed by the spleen, resulting in low circulating levels.

Hypertension: High blood pressure.

Hyperthermia: An elevated body temperature.

Hypertonia: Increased muscle tone that is expressed as spasticity or rigidity.

Hypertonic solution: A solution that has a a greater solute concentration relative to another fluid; cells placed in a hypertonic solution will shrink and crenate due to water leaving the cell.

Hypertrophy: Increase in size of a tissue or organ independent of the body’s general growth.

Hyperventilation: Increased depth and rate of breathing, resulting in hyperoxia, but also causes hypocapnia and alkalosis.

Hypocapnia: Abnormally low carbon dioxide levels in arterial blood, which often causes alkalosis.

Hypodermis: Subcutaneous tissue deep to the skin; consists of adipose and areolar connective tissue.

Hypoglycemic: Term used to describe hormones such as insulin that decrease blood glucose level.

Hyponatremia: Abnormally low concentrations of sodium ions in extracellular fluid.

Hyponychium: Free edge of the fingernail.

Hypophyseal fossa: A depression on the superior surface of the sphenoid bone that houses the pituitary gland.

Hypophysis: Pituitary gland.

Hypoproteinemia: A condition of unusually low levels of plasma proteins causing a reduction in colloid osmotic pressure; results in tissue edema.

Hyposecretion: Underactivity of glands resulting in diminished secretion.

Hypotension: Low blood pressure.

Hypothalamic-hypophyseal tract: Nerve bundles that run through the infundibulum and connect the neurohypophysis and the hypothalamus.

Hypothalamic releasing hormones: Hormones secreted by the hypothalamus that stimulate the anterior pituitary gland to secrete its hormones.

Hypothalamic inhibiting hormones: Hormones secreted by the hypothalamus that inhibit the anterior pituitary gland from secreting its hormones.

Hypothalamus: Region of the diencephalon, lying beneath the thalamus, and forming the floor of the third ventricle of the brain; main visceral control center and homeostasis regulator; controls ANS, body temperature; contains the mammillary bodies that are involved in olfactory reflexes, the supraoptic nucleus that produces antidiuretic hormone which is stored in the posterior pituitary, the paraventricular nucleus that produces oxytocin which is stored in the posterior pituitary, and the arcuate nucleus that secretes releasing and inhibiting hormones that regulate the anterior pituitary.

Hypothermia: Lowering of body temperature.

Hypotonia: Decreased or lost muscle tone in which muscles appear flaccid.

Hypotonic solution: A solution that has a lower concentration of solutes relative to another fluid; cells placed in hypotonic solutions will swell and possibly burst as water rushes into them.

Hypoventilation: Decreased depth and rate of breathing, which causes hypoxia, hypercapnia, and acidosis.

Hypovolemic shock: Most common form of shock; results from extreme blood loss.

Hypoxia: Abnormally low oxygen levels in blood and tissues.

Hysterectomy: The surgical removal of the uterus.

Ileocecal valve: Site where the ileum of the small intestine joins the large intestine. Also called the ileocecal sphincter.

Ileum: Terminal part of the small intestine; between the jejunum and the cecum of the large intestine.

Iliopsoas (Iliacus, Psoas major): Anterior hip muscles; flex thigh and trunk. O: Ilium, sacrum and lumbar vertebrae. I: Lesser trochanter of femur.

Immune system: A functional system whose components attack foreign substances or prevent their entry into the body.

Immunity: Resistance to disease; ability of the body to resist many agents that can cause disease, particularly by invading pathogens, foreign proteins, and poisons.

Immunocompetence: The ability to produce a normal immune response.

Immunodeficiency: Any congenital or acquired condition causing a deficiency in the production or function of immune cells or certain molecules (complement, antibodies, etc.) required for normal immunity.

Immunoglobulin (Ig): An protein molecule synthesized by plasma cells derived from B lymphocytes in response to the introduction of an antigen. Immunoglobulins are divided into five kinds (IgA, IgD, IgE, IgG, IgM). Also called an antibody.

Immunology: The study of the responses of the body when challenged by antigens.

Impacted fracture: Broken bone ends are forced into each other.

Imperforate: Abnormally closed.

Implantation: (1) The insertion of a tissue or a part into the body. (2) The attachment of the blastocyst to the stratum basalis of the endometrium about 6 days after fertilization.

In vitro: In a test tube, glass, or artificial environment.

In vivo: In the living body.

Incompetent valve: Valve which does not close properly.

Incontinence: Inability to retain urine, semen, or feces through loss of sphincter control.

Indolamines: Biogenic amine neurotransmitters; include serotonin and histamine.

Induction: The process by which one tissue (inducting tissue) stimulates the development of an adjacent unspecialized tissue (responding tissue) into a specialized one.

Infarction: A localized area of necrotic tissue, produced by inadequate oxygenation of the tissue.

Infection: Invasion and multiplication of microorganisms in body tissues, which may be inapparent or characterized by cellular injury.

Infectious mononucleosis: Highly contagious viral disease; marked by excessive agranulocytes.

Inferior: Nearer the soles of the feet or lower part of a structure; equivalent to caudal in bipeds.

Away from the head or toward the lower part of a structure. Also called caudad.

Inferior nasal conchae bones: Pair of bones that form part of the lateral walls of the nasal cavity, and separates the middle and inferior nasal meatus.

Inferior vena cava: Large vein that returns blood from body areas below the diaphragm.

Infertility: Inability to conceive or to cause conception. Also called sterility.

Inflammation: Protective response to tissue injury characterized by redness, swelling, pain, and heat.

Infraspinatus: Rotator cuff muscle of scapula; tendon reinforces the shoulder rotator cuff; stabilizes shoulder joint; rotates arm laterally. O: Infraspinous fossa of scapula. I: Greater tubercle of humerus.

Infundibulum: (1) A stalk of tissue that connects the pituitary gland to the hypothalamus. (2) the distal end of the fallopian (uterine) tube.

Ingestion: The taking in of food, liquids, or drugs, by mouth.

Inguinal: Pertaining to the groin region.

Inhalation: The act of drawing air into the lungs. Also termed inspiration.

Inheritance: The acquisition of body traits by transmission of genetic information from parents to offspring.

Inhibin: A hormone that inhibits release of follicle-stimulating hormone (FSH) by the anterior pituitary; in females, it is secreted by granulosa cells in the ovary; in males, it is secreted by sustentacular cells in the testis.

Inhibiting hormone: Hormone secreted by the hypothalamus that can suppress secretion of hormones by the anterior pituitary.

Inner cell mass: An aggregation of cells at the embryonic pole of the blastocyst that forms the embryo and some extraembryonic membranes. Also called an embryoblast.

Innervation: Supply of nerves to a body part.

Inorganic compound: Chemical substances that do not contain carbon, including water, salts, and many acids and bases.

Insertion: The attachment of a muscle tendon to a movable bone or the end opposite the origin.

Insula: A triangular area of the cerebral cortex that lies deep within the lateral cerebral fissue, under the parietal, frontal, and temporal lobes.

Insulin: A protein hormone produced by the beta cells of a pancreatic islet (islet of Langerhans) that decreases the blood glucose level.

Integration: The process by which the nervous system processes and interprets sensory input and makes decisions about what should be done at each moment.

Integrins: A family of transmembrane glycoproteins in plasma membranes that function in cell adhesion; they are present in hemidesmosomes, which anchor cells to a basement membrane, and they mediate adhesion of neutrophils to endothelial cells during emigration.

Integument: The skin, including the epidermis, dermis, hairs, nails, and glands.

Integumentary system: Skin and its derivatives; provides the external protective covering of the body.

Interatrial septum: The wall between the two atria of the heart.

Intercalated disc: An irregular transverse thickening of cardiac sarcolemma that contains desmosomes, which hold cardiac muscle cells together, and gap junctions, which aid in conduction of muscle action potentials from one fiber to the next.

Intercostal: Between the ribs.

Intercostal spaces: Interval between the ribs, occupied by intercostal muscles, veins, arteries, and nerves.

Interferon (IFN): Cytokines released by virus infected cells that helps protect body cells from viral replication.

Intermediate: Between two structures, one of which is medial and one of which is lateral.

Intermediate filaments: Cytoskeletal element composed of rope-like assemblies of fibrous proteins; provide support and strength to cells; act as internal “guy wires”; help form desmosomes.

Internal: Away from the surface of the body.

Internal capsule: A large tract of projection fibers that runs between the basal nuclei and the thalamus; it is the major connection between the cerebral cortex and the brain stem and spinal cord

Internal ear: The inner ear, or labyrinth, lying inside the temporal bone, containing the organs of hearing and balance.

Internal intercostals: Deep muscles between ribs; depress rib cage, compress thorax and aid in forced expiration. O: Ribs. I: Ribs.

Internal nares: The opening from the nasal cavity into the nasopharynx. Also called the choana.

Internal oblique: Deep, lateral trunk muscle; one laterally flex and rotate vertebral column; both flex vertebral column and compress abdomen. O: Iliac crest. I: Ribs 9-12 and linea alba.

Internal respiration: The exchange of respiratory gases between blood and body cells. Also called tissue respiration.

Interneuron: Nerve cell located between sensory and motor neurons that govern coordinated activity. Also called association neurons.

Interoceptor: Sensory receptor located in blood vessels and viscera that provides information about the body’s internal environment. Also called visceroceptor.

Interphase: The period of the cell cycle between cell divisions, consisting of the G1 (gap or growth) phase, when the cell is engaged in growth, metabolism, and production of substances required for division; S (synthesis) phase, during which chromosomes are replicated; and G2 phase.

Interstitial cell-stimulating hormone (ICSH): In males, it stimulates the development and functional activity of testicular Leydig cells that secrete testosterone.

Interstitial endocrinocyte: A cell that is located in the connective tissue between seminiferous tubules in a mature testis that secretes testosterone. Also called interstitial cell of Leydig.

Interstitial fluid (IF): Fluid between the cells. Also called intercellular or tissue fluid.

Interstitial growth: Tissue growth from a number of different centers within a nonrigid matrix, such as cartilage.

Interstitial lamella: Bony lamella that lie between intact osteons.

Interventricular foramen: A narrow, oval opening through which the lateral ventricles of the brain communicate with the third ventricle. Also called the foramen of Monro.

Interventricular septum: The wall between the two ventricles of the heart.

Interventricular sulcus: A groove on the surface of the heart, marking the location of the septum between the two ventricles. Also called interventricular groove, or IV groove.

Intervertebral discs: Discs of fibrocartilage between vertebrae.

Intestinal gland: A gland that opens onto the surface of the intestinal mucosa and secretes digestive enzymes. Also called a crypt of Lieberkiihn.

Intracapsular ligament: Ligament located within and separate from the articular capsule of a synovial joint.

Intracellular fluid (ICF): Fluid within a cell.

Intrafusal fibers: Three to ten specialized muscle fibers (cells), partially enclosed in a spindle-shaped connective tissue capsule, that make up a muscle spindle.

Intramembranous ossification: Formation of osseous tissue between mesenchymal membranes; process for the formation of many flat bones in the fetus.

Intraocular pressure (IOP): Pressure in the eyeball, produced mainly by aqueous humor.

Intrinsic factor: A glycoprotein that is secreted by the parietal cells of the gastric glands, which facilitates absorption of vitamin B12 in the small intestine; deficiency results in pernicious anemia.

Intron: A noncoding portion of a pre-mRNA transcript that is excised before translation.

Invagination: The pushing of the wall of a cavity into the cavity itself.

Inversion: Turning the sole of the foot so that it faces medially.

Involuntary muscle: Muscles that cannot ordinarily be controlled voluntarily.

Involuntary nervous system: The autonomic nervous system.

Ion: Atom with a positive or negative electric charge.

Ionic bond: Chemical bond formed when anions and cations are held together by the attraction of their opposite charges.

Ipsilateral: (1) Situated on the same side. (2) Affecting the same side of the body.

Iris: Pigmented smooth muscle structure that controls the amount of light entering the eye.

Irritability: Ability to respond to stimuli.

Irritable bowel syndrome (IBS): Disease of the entire gastrointestinal tract in which a person reacts to stress by developing symptoms (such as cramping and abdominal pain) associated with alternating patterns of diarrhea and constipation. Excessive amounts of mucus may appear in feces, and other symptoms include flatulence, nausea, and loss of appetite. Also known as irritable colon or spastic colitis.

Ischemia: A lack of sufficient blood to a body part due to obstruction or constriction of a blood vessel.

Islet of Langerhans: A cluster of endocrine gland cells in the pancreas that secretes insulin, glucagon, somatostatin, and pancreatic polypeptide. Also called a pancreatic islet.

Isograft: Tissue graft donated by an identical twin.

Isomer: Chemical compounds that have the same chemical formula, but different 3-D structures.

Isometric contraction: Contraction in which the muscle does not shorten (the load is too heavy) but its internal tension increases.

Isotonia: Having equal tension or tone.

Isotonic contraction: Contraction in which muscle tension remains constant at a given joint angle and load, and the muscle shortens.

Isotonic solution: A solution with the same solute concentration as another fluid to which it is being compared.

Isotopes: Different atomic forms of an element that have the same number of protons and are chemically identical, but contain different numbers of neutrons, and thus have different atomic mass numbers.

Isthmus: A narrow strip of tissue or narrow passage connecting two larger parts.

Jaundice: A condition characterized by yellowness of the skin, white of the eyes, mucous membranes, and body fluids because of a buildup of bilirubin.

Jejunum: The part of the small intestine between the duodenum and the ileum.

Joint (articulation): The junction of two or more bones.

Joint kinesthetic receptor: Receptor that provides information on joint position and motion.

Juxtaglomerular apparatus (JGA): Kidney structure that consists of the macula densa (cells of the distal convoluted tubule adjacent to the afferent and efferent arteriole) and juxtaglomerular cells (modified cells of the afferent and sometimes efferent arteriole); secretes renin when blood pressure starts to fall.

Karyotype: The diploid chromosomal complement, typically shown as homologous chromosome pairs arranged from longest to shortest (X and Y are arranged by size rather than paired).

Keratin: Fibrous protein found in the epidermis, hair, and nails that makes those structures hard and water-repellent; precursor is keratohyaline.

Keratinocytes: Epidermal cells that produce the protein keratin.

Ketoacidosis: Acidosis caused by the enhanced production of ketone bodies, such as in diabetes or starvation.

Ketone bodies: Fatty acid metabolites that are organic acids.

Ketosis: Abnormal condition during which an excess of ketone bodies are produced.

Kidneys: The paired reddish organs located in the lumbar region that produce urine and regulate the composition, volume, and pressure of blood..

Kidney stone: A solid mass, usually consisting of calcium oxalate, uric acid, or calcium phosphate crystals, that may form in any portion of the urinary tract. Also called a renal calculus.

Kilocalories (kcal): A measure of energy equal to 1,000 calories. Also called a food Calorie.

Kinesiology: The study of the movement of body parts.

Kinesthesia: The perception of the extent and direction of movement of body parts; this sense is possible due to nerve impulses generated by proprioceptors.

Kinetic energy: The energy of motion or movement, e.g., the constant movement of atoms, or the push given to a swinging door that sets it into motion.

Kinetochore: Protein complex attached to the outside of a centromere to which kinetochore microtubules attach.

Korotkoff sounds: The sounds heard over an artery when pressure is reduced below systolic arterial pressure, as when blood pressure is determined by the auscultatory method.

Krebs cycle: Aerobic metabolic pathway occurring within mitochondria, in which food metabolites are oxidized and CO2 is liberated, and coenzymes are reduced.

Kupffer’s cell: See Stellate reticuloendothelial cell.

Kyphosis: An exaggeration of the thoracic curve of the vertebral column, resulting in a “round-shouldered” appearance. Also called hunchback.

Labial frenulum: A medial fold of mucous membrane between the inner surface of the lip and the gums.

Labia majora: Two longitudinal folds of skin extending downward and backward from the mons pubis of the female.

Labia minora: Two small folds of mucous membrane lying medial to the labia majora of the female.

Labium: A lip, or liplike structure. Plural is labia.

Labor: The process of giving birth in which a fetus is expelled from the uterus through the vagina.

Labyrinth: Intricate communicating passageway, especially in the internal ear.

Lacrimal: Pertaining to tears.

Lacrimal apparatus: Structures that produces and provides drainage for lacrimal fluid (tears).

Lacrimal bones: Pair of bones that form part of the medial orbit wall and contains lacrimal fossa that houses the lacrimal sac.

Lacrimal canal: A duct, one on each eyelid, beginning at the punctum at the medial margin of an eyelid and conveying tears medially into the nasolacrimal sac.

Lacrimal gland: Secretory cells, located at the superior anterolateral portion of each orbit, that secrete tears into excretory ducts that open onto the surface of the conjunctiva.

Lacrimal sac: The superior expanded portion of the nasolacrimal duct that receives the tears from a lacrimal canal.

Lactation: Production and secretion of milk.

Lacteal: Special lymphatic vessels in villi of the small intestine that absorb lipids.

Lactic acid: Product of anaerobic metabolism, especially in muscle.

Lacuna: A small, hollow space, such as that found in bones in which the osteocytes lie. Plural is lacunae.

Lambdoid suture: Line of junction of the occipital with the two parietal bones.

Lamellae: Concentric rings of hard, calcified extracellular matrix found in compact bone.

Lamellated corpuscle: Oval-shaped pressure receptor located in the dermis or subcutaneous tissue and consisting of concentric layers of connective tissue wrapped around the dendrites of a sensory neuron. Also called a pacinian corpuscle.

Lamina: (1) A thin layer or flatplate. (2) the portion of a vertebra between the transverse process and the spinous process.

Lamina propria: The layer of areolar connective tissue under the basement membrane that is attached to the epithelium of mucous membranes.

Langerhans cells: Phagocytic immune cells of the epidermis. Also called epidermal dendritic cells.

Large intestine: Portion of the digestive tract extending from the ileocecal valve to the anus; includes the cecum, appendix, colon, rectum, and anal canal.

Laryngeal prominence: The projection on the anterior portion of the neck formed by the thyroid cartilage of the larynx. Also called the Adam’s apple.

Laryngopharynx: The inferior portion of the pharynx that branches into the esophagus and larynx; it is lined with stratified squamous epithelium.

Larynx: The voice box, the cartilaginous organ located between the trachea and the pharynx.

Latent period: Period of time between stimulation and the onset of muscle contraction.

Lateral: Nearer the left or right side of the body.

Lateral ventricle: A cavity within a cerebral hemisphere that communicates with the lateral ventricle in the other cerebral hemisphere and with the third ventricle by way of the interventricular foramen.

Latissimus dorsi: Swimmer’s muscle on lower back; extend, rotate and adduct arm. O: Lower spine and iliac crest. I: Proximal humerus.

Lens: Transparent structure posterior to the pupil that changes shape to focus on objects at various distances.

Leptin: hormone secreted by Adipose tissue; suppresses appetite; increases energy expenditure

Lesion: Any localized, abnormal change in a body tissue.

Lesser omentum: A fold of the peritoneum that extends from the liver to the lesser curvature of the stomach and the first part of the duodenum.

Lesser vestibular gland: One of the paired mucussecreting glands with ducts that open on either side of the urethral orifice in the vestibule of the female.

Leukemia: Progressive proliferation of abnormal leukocytes; cancer of white blood cells.

Leukocytes: White blood cells; formed elements of the blood involved in body protection; functions include phagocytosis, inflammation, and the immune responses.

Leukocytosis: An increase in the number of leukocytes (white blood cells); usually the result of a microbiological attack on the body.

Leukopenia: Abnormally low white blood cell count.

Leukopoiesis: Formation and development of the various types of leukocytes (white blood cells).

Lever system: Consists of a lever (bone), effort (muscle action), resistance (weight of object to be moved), and fulcrum (joint).

Leydig cell: A type of cell that secretes testosterone; located in the connective tissue between seminiferous tubules in a mature testis. Also known as interstitial cell of Leydig or interstitial endocrinocyte.

Ligament: Dense regular connective tissue that attaches bone to bone.

Ligamentum arteriosum: Fibrous remnant seen after birth of the fetal ductus arteriosus, which had connected the pulmonary trunk to the aortic arch.

Ligand: A chemical substance that binds to a specific receptor.

Limbic system: A part of the forebrain; called the emotional brain; contains hippocampus, amygdala, cingulate gyrus, and other cerebral nuclei; mediates response to emotion, mood, and smell; involved in memory processing.

Line on a bone: Narrow ridge of bone; less prominent than a crest.

Lingual frenulum: A fold of mucous membrane that connects the tongue to the floor of the mouth.

Lingual tonsil: A collection of lymphoid follicles at the base of the tongue.

Lipase: An enzyme that splits fatty acids from triglycerides and phospholipids.

Lipid: A major class of biological molecules that are hydrophobic or amphipathic; used as storage forms of energy, in cell membranes, as hormones, and as vitamins.

Lipid bilayer: Arrangement of phospholipid, glycolipid, and cholesterol molecules in two parallel sheets in which the hydrophilic “heads” face outward and the hydrophobic “tails” face inward; found in cellular membranes.

Lipogenesis: Formation of fat molecules.

Lipolysis: Breakdown of fat into glycerol and fatty acids.

Lipoprotein: One of several types of particles containing lipids and proteins that make it water soluble for transport in the blood; high levels of low-density lipoproteins (LDLs) are associated with increased risk of atherosclerosis, whereas high levels of high-density lipoproteins (HDLs) are associated with decreased risk of atherosclerosis.

Liver: Lobed accessory organ that overlies the stomach; produces bile to help digest fat, and serves other metabolic and regulatory functions.

Lordosis: An exaggeration of the lumbar curve of the vertebral column. Also called hollow back.

Lumbar: Region of the back and side between the ribs and pelvis; loin.

Lumbar plexus: A network formed by the anterior (ventral) branches of spinal nerves Ll through L4.

Lumbar vertebrae: The five vertebrae of the lumbar region of the vertebral column; called the small of the back.

Lumen: Cavity inside a tube, blood vessel, or hollow organ.

Lumpectomy: Removal of a benign or malignant lesion from the breast with preservation of essential anatomy of the breast.

Lungs: The organs of respiration in which blood is aerated; the right lung is larger than the left and is divided into three lobes (superior, middle and inferior); the left lung has two lobes (superior and inferior).

Lunula: The moon-shaped white area at the base of a nail.

Luteinizing hormone (LH): Anterior pituitary hormone. In females, it stimulates ovulation, formation of the corpus luteum, and secretion of progesterone. In males, it stimulates secretion of testosterone. Also called lutropin, or in males is called interstitial cell-stimulating hormone (ICSH).

Lymph: Fluid in lymphatic vessels that is returned to the blood.

Lymph node: Small bean-shaped lymphatic organ that filters lymph and contains macrophages and lymphocytes; large collections occur in the inguinal, axillary, and cervical regions.

Lymphatic capillary: Microscopic closed-ended vessel with flaplike minivalves that begins in spaces between cells and returns lymph to the blood.

Lymphatic system: System consisting of lymphatic vessels, lymph nodes, and other lymphoid organs and tissues; drains excess tissue fluid from the extracellular space and provides a site for immune surveillance.

Lymphatic tissue: A specialized form of reticular tissue that contains large numbers of lymphocytes.

Lymphatic vessel: A large vessel that collects lymph from lymphatic capillaries and converges with other lymphatic vessels to form the thoracic and right lymphatic ducts.

Lymphatics: General term used to designate the lymphatic vessels that collect and transport lymph.

Lymphocyte: Agranular white blood cell that helps carry out immune responses; found in blood and lymphatic tissues.

Lymphokines: Proteins involved in cell-mediated immune responses that enhance immune and inflammatory responses.

Lysosome: Vesicle containing strong digestive enzymes; originates from the Golgi apparatus.

Lysozyme: Enzyme that destroys the cell walls of certain bacteria; present in tears, saliva, mucus, milk, and other body fluids. Also called muramidase.

Macromolecules: Large, complex molecules containing from 100 to over 10,000 amino acids.

Macrophage: Actively phagocytic cells that are widely distributed in the body; participate in presenting antigens to lymphocytes; derived from monocytes.

Macula: (1) Sensory receptor organ for balance and static equilibrium in the saccule and utricle of the vestibule. (2) A colored area or spot.

Macula lutea: A yellow oval spot at the center of the retina which absorbs harmful ultraviolet light; it contains only cones and provides sharp, detailed central vision.

Major histocompatibility complex (MHC): Surface glycoproteins on nucleated cells that are involved in immune responsiveness to antigens and compatibility of transplanted tissues. Also called human 1eukocyte antigens (HLA).

Malignant: Referring to diseases that tend to become worse and cause death, especially the invasion and spreading of cancer.

Malignant melanoma: The most dangerous form of skin cancer, which can originate wherever there is pigment, but often arises from existing moles, metastasizing rapidly into surrounding circulatory vessels.

Malnutrition: Faulty nutrition resulting from malabsorption, poor diet, or overeating.

Mammary glands: The milk secreting glands lying within the female breast; the milk producing alveolar glands develop only during pregnancy and remain active until weaning.

Mammillary bodies: Two small, rounded bodies on the inferior aspect of the hypothalamus that are involved in reflexes related to the sense of smell.

Mandible: Lower jawbone. Markings: Coronoid processes are insertion points for the temporalis muscles. Mandibular condyle articulates with mandibular fossa of temporal bone. Mandibular symphysis is medial fusion point of the mandibular bones. Alveoli are sockets for the teeth. Mandibular foramina allows passage of inferior alveolar nerves. Mental foramina allows passage of blood vessels and nerves to the chin and lower lip.

Marrow: Soft, spongelike material in the cavities of bone; red bone marrow produces blood cells; yellow bone marrow contains adipose tissue that stores triglycerides.

Masseter: Inferior, superficial muscle of mastication; closes jaw. O: Maxilla and zygomatic arch of temporal bone. I: Mandible.

Mast cells: Immune cells found in connective tissue that release histamine during inflammation, and are involved in hypersensitivity (allergic) reactions.

Mastoid fontanels: Paired membranous intervals in the skull of a fetus and infant; located between the mastoid angle of the parietal bone, the petrous portion of the temporal bone, and the occipital bone. Also called the posterolateral fontanel.

Mastication: Chewing.

Matter: Anything that has mass and volume.

Mature follicle: A large, fluid-filled follicle containing a secondary oocyte and surrounding granulosa cells that secrete estrogens. Also called a Graafian follicle.

Maxilla: Pair of upper jawbones and keystone bones of the face that forms anterior hard palate, and part of orbits and nasal cavity and contains maxillary sinuses. Markings: Alveoli are sockets for the teeth. Palatine processes form the anterior hard palate. Frontal processes form part of lateral aspect of bridge of nose. Incisive fossa allows passage of blood vessels and nerves through the hard palate. Inferior orbital fissures allows passage of maxillary nerve, zygomatic nerve, and blood vessels. Infraorbital foramen allows passage of infraorbital nerve and artery to skin of face.

Mean arterial pressure (MAP): The average blood pressure in arteries; MAP = DBP + (SBP – DBP)/3

Meatus: (1) External opening of a canal. (2) Canal-like passageway in a bone.

Mechanical advantage (power lever): Condition that occurs when a load is close to a fulcrum and an effort is applied far from the fulcrum; allows a small effort exerted over a large distance to move a large load over a small distance.

Mechanical disadvantage (speed lever): Condition that occurs when the load is far from the fulcrum and the effort is applied near the fulcrum; the effort applied must be greater than the load to be moved.

Mechanical energy: The energy directly involved in moving matter.

Mechanoreceptor: Receptor sensitive to mechanical pressure such as touch, pressure, vibration,

proprioception, hearing, equilibrium, and blood pressure.

Medial: Nearer the midline of the body (midsagittal plane).

Medial lemniscus: The pathway to the cerebral cortex for the sensations of proprioception, fine touch, vibration, hearing, and equilibrium.

Median aperture: One of the three openings in the roof of the fourth ventricle through which cerebrospinal fluid enters the subarachnoid space of the brain and spinal cord. Also called the foramen of Magendie.

Median plane: A vertical plane that lies exactly on the midline and divides the body into right and left halves. Also called the midsagittal plane.

Mediastinum: A subdivision of the thoracic cavity containing the pericardial cavity.

Medulla: Central, or inner portion of certain organs.

Medulla oblongata: Inferior-most part of the brain stem; pathway for ascending sensory tracts and descending motor tracts; contains decussation of pyramids, respiratory and cardiovascular centers, and reflex centers for swallowing, coughing, sneezing, and vomiting. Also called the medulla.

Medullary cavity: The space within the diaphysis of a bone that contains yellow bone marrow. Also called the marrow cavity.

Meibomian gland: See Tarsal gland.

Meiosis: Nuclear division process that occurs during production of gametes, involving two successive nuclear divisions that result in cells with the haploid (n) number of chromosomes; occurs only in certain reproductive organs.

Meissner corpuscles: Oval receptors in the dermal papillae that are responsible for fine discriminative touch. Also called tactile corpuscles.

Melanin: A dark black, brown, or yellow pigment found in some parts of the body such as the skin, hair, and pigmented layer of the retina.

Melanocytes: Cells deep in the epidermis that produce melanin pigments; branching cell processes transfer melanin granules to keratinocytes, resulting in pigmentation of the epidermis.

Melanocyte-stimulating hormone (MSH): A hormone secreted by the pituitary gland that causes dispersion of melanin by melanocytes, resulting in darkening of the skin. Also called melanotropin.

Melanoma: Most dangerous type of skin cancer, where melanocytes grow rapidly and often metastasize.

Melatonin: A hormone secreted by the pineal gland that helps set the timing of the body’s biological clock.

Membrane: A thin, flexible sheet of tissue composed of an epithelial layer and an underlying connective tissue layer, as in an epithelial membrane, or of areolar connective tissue only, as in a synovial membrane.

Membrane potential: Voltage across the plasma membrane.

Membrane receptors: A large, diverse group of integral proteins and glycoproteins that serve as binding sites.

Membranous labyrinth: A complex of membranous tubes suspended within the bony labyrinth, filled with endolymph and surrounded by perilymph.

Memory: The ability to recall thoughts; commonly classifed as shortterm (activated) and long-term.

Memory cells: Clones of B or T lymphoctyes that provide enhanced immune reactions when reexposed to an antigen.

Menarche: The first menses (menstrual flow) and beginning of ovarian and uterine cycles.

Meninges: Three membranes covering the brain and spinal cord, called the dura mater, arachnoid mater, and pia mater. Singular is meninx.

Meningitis: Inflammation of the meninges.

Menopause: The termination of the menstrual cycles.

Menstrual cycle: A series of changes in the endometrium of a nonpregnant female that prepares the lining of the uterus to receive a fertilized ovum.

Menstruation: Periodic discharge of blood, tissue fluid, mucus, and epithelial cells that usually lasts for 5 days; caused by a sudden reduction in estrogens and progesterone. Also called the menstrual phase or menses.

Merkel cell: Epidermal cell that is associated with a tactile sensory nerve ending, which forms a complex known as a Merkel disc or tactile disc, and functions in the sense of touch.

Merkel disc: A complex of an epidermal Merkel cell associated with a tactile sensory nerve ending that is responsible for light touch.

Merocrine gland: An exocrine gland made up of secretory cells that remain intact throughout the process of formation and discharge of the secretory product by exocytosis, as in the salivary and pancreatic glands.

Mesencephalon: Region of the brain stem between the diencephalon and the pons. Also called the midbrain.

Mesenchyme: Primordial embryonic connective tissue derived from mesoderm; consists of star-shaped mesenchymal cells in a gel-like ground substance with many fibers. Function is to give rise to all other connective tissue types. Located primarily in the embryo and fetus.

Mesenteries: Double-layered extensions of the peritoneum that support most organs in the abdominal cavity.

Mesocolon: A fold of peritoneum attaching the colon to the posterior abdominal wall.

Mesoderm: The middle primary germ layer that gives rise to connective tissues, blood and blood vessels, and muscles.

Mesothelium: The layer of simple squamous epithelium that lines serous membranes.

Mesovarium: A short fold of peritoneum that attaches an ovary to the broad ligament of the uterus.

Messenger RNA (mRNA): Long nucleotide strands that reflect the exact nucleotide sequences of the genetically active DNA and carry the message of the latter.

Metabolic (fixed) acid: Acid generated by cellular metabolism that must be eliminated by the kidneys.

Metabolic rate: Amount of energy expended by the body per unit time.

Metabolic water (water of oxidation): Water produced from cellular metabolism (about 10% of our body’s water).

Metabolism: All of the chemical reactions that occur in the body.

Metacarpus: Palm bones; five bones between the wrist and fingers. Also called the metacarpal bones.

Metaphase: The second stage of mitosis, in which chromatid pairs line up on the metaphase plate of the cell.

Metaphysis: Region of a long bone between the dia- physis and epiphysis that contains the epiphyseal plate in a growing bone.

Metarteriole: A blood vessel that emerges from an I arteriole, traverses a capillary network, and empties into a venule.

Metastasis: The spread of cancer from one body part or organ into another not directly connected to it.

Metatarsus: Distal portion of the foot; five bones between the instep and toes. Also called the metatarsal bones.

Metencephalon: A secondary brain vesicle; anterior portion of the rhombencephalon of the developing brain; becomes the pons and the cerebellum. Also called the afterbrain.

Microcirculation: The flow of blood in the smallest vessels, such as arterioles, capillaries, or venules.

Microfilaments: Cytoskeletal element composed of thin strands of the contractile protein actin; helps move cell organelles, and helps produce and maintain cell shapes; core of microvilli.

Microglia: A type of CNS supporting cell that can transform into a phagocyte in areas of neural damage or inflammation.

Microtubules: Cytoskeletal element composed of hollow tubes made of the protein tubulin; determines cell shape and movement of organelles; component of cilia, flagella and spindle fibers.

Microvilli: Tiny hairlike extensions of cell membranes, organized around microfilaments; greatly increase the surface area of absorptive cells.

Micturition: Urination, or voiding; emptying the bladder.

Midbrain: Region of the brain stem between the diencephalon and the pons; contains the red nucleus, substantia nigra, cerebral peduncles which connects the cerebrum to the brainstem, and the corpora quadrigemina which has visual and auditory reflex centers. Also called the mesencephalon.

Middle ear: A small, epithelial-lined cavity hollowed out of the temporal bone, separated from the external ear by the eardrum and from the internal ear by a thin bony partition containing the oval and round windows; extending across the middle ear are the three auditory ossicles. Also called the tympanic cavity.

Midline: An imaginary vertical line that divides the body into equal left and right sides.

Midsagittal plane: A vertical plane through the midline of the body that divides the body or organs into equal right and left sides. Also called a median plane.

Milliequivalents per liter (mEq/L): The units used to measure electrolyte concentrations of body fluids; a measure of the number of electrical charges in I liter of solution.

Mineralocorticoid: Steroid hormone of the adrenal cortex that regulates mineral metabolism and fluid balance.

Minerals: Inorganic chemical compounds found in nature; salts.

Mitochondrion: Powerhouse of the cell; rod-shaped organelle bounded by two membranes; produces ATP by aerobic cellular respiration.

Mitosis: Type of nuclear division that maintains the parental chromosome number for daughter cells; the basis of growth in size, tissue repair, and often asexual reproduction for eukaryotes; consists of prophase, metaphase, anaphase, and telophase.

Mitotic spindle: Collective term for a football-shaped assembly of microtubules (nonkinetochore, kinetochore, and aster) that is responsible for the movement of chromosomes during cell division.

Mixed nerves: Nerves containing the processes of motor and sensory neurons; their impulses travel to and from the central nervous system.

Mixture: Two or more substances intermingled in proportions that can vary and be heterogeneous.

Modality: Any of the specific sensory entities, such as vision, smell, taste, or touch.

Modiolus: The central pillar or column of the cochlea.

Molar: A solution concentration determined by mass of solute; one liter of solution contains an amount of solute equal to its molecular weight in grams.

Molarity: A way to express the concentration of a solution; moles per liter of solution.

Mole (mol): A mole of any element or compound is equal to its atomic weight or its molecular weight (sum of atomic weights) measured in grams.

Molecule: Particle consisting of two or more atoms joined together by chemical bonds.

Monoclonal antibodies: Pure preparations of identical antibodies that exhibit specificity for a single antigen.

Monocyte: Agranular white blood cell; phagocyte that develops into a macrophage in tissues.

Monokines: Chemical mediators that enhance the immune response; secreted by macrophages.

Monomer: Small molecule used as the subunits of polymers, such as the sugar monomers of a polysaccharide.

Monosaccharide: Building block of carbohydrates; simple sugar such as glucose, galactose, and fructose.

Monounsaturated fat: A fat whose fatty acid tails contain one C=C double bond; plentiful in olive and peanut oils.

Mons pubis: The rounded, fatty prominence over the pubic symphysis, covered by coarse pubic hair.

Morula: A solid sphere of cells produced by successive cleavages of a fertilized ovum about four days after fertilization.

Motor area: The region of the cerebral cortex that governs muscular movement, particularly the precentral gyrus of the frontal lobe.

Motor end plate: Region of the sarcolemma of a muscle fiber (cell) that includes acetylcholine (ACh) receptors, which bind ACh released by synaptic end bulbs of somatic motor neurons.

Motor neurons: Neurons that conduct impulses from the brain toward the spinal cord or out of the brain and spinal cord into cranial or spinal nerves to effectors that may be either muscles or glands. Also called efferent neurons.

Motor unit: A motor neuron together with all of the muscle fibers (cells) that it stimulates.

Mucosa-associated lymphatic tissue (MALT): Lymphatic nodules scattered throughout the lamina propria (connective tissue) of mucous membranes lining the gastrointestinal tract, respiratory airways, urinary tract, and reproductive tract.

Mucous cell: A unicellular gland that secretes mucus. Two types are mucous neck cells and surface mucous cells in the stomach.

Mucous membrane: A membrane that lines a body cavity that opens to the exterior. Also called the mucosa.

Mucus: The thick fluid secretion of goblet cells, mucous cells, mucous glands, and mucous membranes.

Multinucleate cell : Cell with more than one nucleus, e.g., skeletal muscle cells, liver cells.

Multiple sclerosis (MS): Autoimmune demyelinating disorder of the CNS; destroys the white matter of the brain and spinal cord, causing patches of sclerosis.

Multiple-wave summation: When a muscle fiber is stimulated repeatedly, complete relaxation cannot occur between stimuli, and the tension produced is greater than that from a single stimulus, which results from the greater concentration of Ca2+ in the sarcoplasm and the stretch of the elastic components of the muscle early in contraction.

Multipolar neuron: Nerve cell with many processes projecting from its cell body, many dendrites and one axon; most cell bodies reside in the CNS; the most abundant neuron type.

Muscarinic receptors: Acetylcholine-binding receptors of the autonomic nervous system’s target organs; named for activation by the mushroom poison muscarine.

Muscle: An organ composed of one of three types of muscle tissue (skeletal, cardiac, or smooth), specialized for contraction to produce voluntary or involuntary movement of parts of the body.

Muscle action potential: A stimulating impulse that propagates along the sarcolemma and transverse tubules; in skeletal muscle, it is generated by acetylcholine, which increases the permeability of the sarcolemma to cations, especially sodium ions (Na).

Muscle fatigue: Inability of a muscle to maintain its strength of contraction or tension; may be related to insufficient oxygen, depletion of glycogen, and/or lactic acid buildup.

Muscle fiber: A muscle cell.

Muscle spindle: Encapsulated receptor found in skeletal muscle that is sensitive to stretch. Also called a neuromuscular spindle.

Muscle tension: The force exerted by a contracting muscle on some object.

Muscle tone: Sustained partial contraction of a muscle in response to stretch receptor inputs; keeps the muscle healthy and ready to act, and maintains posture.

Muscle twitch: The response of a muscle to a single brief threshold stimulus.

Muscular artery: An artery with a tunica media composed principally of circularly arranged smooth muscle. Also called distributing artery.

Muscular dystrophy: A group of inherited muscle-destroying diseases.

Muscular system: The organ system consisting of the skeletal muscles of the body and their connective tissue attachments.

Muscular tissue: A basic tissue type that contracts upon stimulation to produce movement; its three varieties are skeletal, cardiac, and smooth muscle.

Muscularis: A muscular layer (coat or tunic) of an organ.

Muscularis mucosae: A thin layer of smooth muscle fibers that underlie the lamina propria of the mucosa of the gastrointestinal tract.

Mutation: Any change in the sequence of bases in a DNA molecule resulting in a permanent alteration in some inheritable trait.

Myasthenia gravis: Autoimmune disease, which impairs communication between nerves and skeletal muscles.

Myelencephalon: A secondary brain vesicle; lower part of the developing hindbrain, especially the medulla oblongata. Also called the spinal brain.

Myelin sheath: Multilayered lipid and protein covering around neuron axons; formed by Schwann cells in the PNS, and oligodendrocytes in the CNS.

Myelinated fiber: Neuron axon with a myelin sheath that conducts nerve impulses very rapidly.

Myenteric plexus: A network of autonomic axons and postganglionic cell bodies located in the muscularis of the gastrointestinal tract. Also called the plexus of Auerbach.

Mylohyoid: Flat, triangular throat muscle; elevate hyoid bone and elevate floor of mouth during swallowing. O: Mandible. I: Hyoid bone.

Myoblasts: Embryonic mesoderm cells from which all muscle fiber develops.

Myocardial infarction (MI): Prolonged blockage of coronary blood flow that causes necrosis of myocardial tissue. MI is the most common cause of death in the U.S.A. Also called a heart attack.

Myocardium: The middle layer of the heart wall, located between the epicardium and the endocardium; it constitutes the bulk of the heart, and is composed of cardiac muscle tissue

Myofibril: A bundle of myofilaments that form a threadlike structure with a banded appearance in muscle cells.

Myofilaments: Filaments of contractile proteins found in muscle cells, consisting mainly of thick filaments (myosin) and thin filaments (actin, troponin, and tropomyosin).

Myoglobin: The oxygen-binding, iron-containing protein present in the sarcoplasm of muscle fibers (cells); contributes the red color to muscle.

Myogram: A graphic recording of mechanical contractile activity produced by an apparatus that measures muscle contraction.

Myology: The study of muscles.

Myometrium: The smooth muscle layer of the uterus.

Myopathy: Any abnormal condition or disease of muscle tissue.

Myopia: A condition in which visual images are focused in front of rather than on the retina; nearsightedness.

Myosin: The contractile protein that makes up the thick filaments of muscle fibers.

Myotome: A group of muscles innervated by the motor neurons of a single spinal segment. In an embryo, the portion of a somite that develops into some skeletal muscles.

Myxedema: Condition resulting from underactive thyroid gland.

Nail: A hard plate, composed largely of keratin, that develops from the epidermis of the skin to form a protective covering on the dorsal surface of the distal phalanges of the fingers and toes.

Nail matrix: The part of the nail beneath the body and root from which the nail is produced.

Nasal bones: Pair of bones that form bridge of the nose.

Nasal cavity: The mucosa-lined cavity on either side of the nasal septum that extends from the external nares to the nasopharynx.

Nasal conchae: Bony ridges that protrude from the lateral walls of the nasal navity, which increase air turbulence.

Nasal septum: The mucosa-lined vertical partition of bone that separates the nasal cavity into left and right sides.

Nasolacrimal duct: A canal that transports the lacrimal secretion (tears) from the nasolacrimal sac into the nose.

Nasopharynx: The superior portion of the pharynx, lying posterior to the nose and extending inferiorly to the soft palate; it is lined with ciliated pseudostratified columnar epithelium with goblet cells.

Natriuresis: Urinary excretion of sodium.

Natural killer cell (NK cell): Lymphocyte capable of killing a cell without prior sensitization to it.

Necrosis: Death or disintegration of a cell or tissues caused by disease or injury, in which many adjacent cells burst and spill their contents into the interstitial fluid, triggering an inflammatory response.

Negative feedback mechanisms: The most common homeostatic control mechanism. The net effect is that the output of the system shuts off the original stimulus or reduces its intensity.

Neonatal: Pertaining to the first four weeks after birth.

Neonatal period: The four-week period immediately after birth.

Neoplasm: An abnormal mass of proliferating cells. Benign neoplasms remain localized; malignant neoplasms are cancers, which can spread to other organs.

Nephron: Structural and functional unit of the kidney; consists of the glomerulus and renal tubule.

Nerve: Cordlike bundle of nerve fibers with associated connective tissue in the PNS.

Nerve cell: A neuron.

Nerve fiber: Axon of a neuron.

Nerve growth factor (NGF): Protein that controls the development of sympathetic ganglionic neurons; secreted by the target cells of postganglionic axons.

Nerve impulse: A self-propagating wave of depolarization. Also called an action potential.

Nerve plexuses: Interlacing nerve networks that occur in the cervical, brachial, lumbar and sacral regions and primarily serve the limbs.

Nervous tissue: (1) A basic tissue type that contains neurons to initiate and conduct nerve impulses for internal communication and to coordinate homeostasis, and neuroglia that support, insulate, and protect the neurons. (2) Tissue containing neurons with cell processes extending from the nucleus-containing cell body, plus supporting cells called neuroglia. Functions in transmission of electrical signals from sensory receptors to effectors. Located in the brain, spinal cord, and nerves.

Nervous system: Fast acting control system that triggers muscle contraction or gland secretion.

Neural tube: Fetal tissue which gives rise to the brain, spinal cord, and associated neural structures; formed from ectoderm by day 23 of embryonic development.

Neuralgia: Attacks of pain along the entire course or branch of a peripheral sensory nerve.

Neural plate: A thickening of ectoderm, induced by the notochord, that forms early in the third week of development and represents the beginning of the development of the nervous system.

Neural tube defect (NTD): A developmental abnormality in which the neural tube does not close properly. Examples are spina bifida and anencephaly.

Neurilemma: The outer nucleated cytoplasmic layer of a Schwann cell. Also called neurolemma, or sheath of Schwann.

Neuritis: Inflammation of one or more nerves.

Neurocranium: The bones of the skull that enclose the brain.

Neurofibral node: A space in the myelin sheath of a nerve fiber, between two neighboring Schwann cells in the PNS, or oligodendrocytes in the CNS. Also called node of Ranvier.

Neurofibril: Cytoskeletal structure in a neuron, composed of microtubules and intermediate filaments.

Neuroglia: Nonneuronal cells of the nervous system that perform various supportive functions. The neuroglia of the central nervous system are the astrocytes, oligodendrocytes, microglia, and ependymal cells; neuroglia of the peripheral nervous system include Schwann cells and satellite cells. Also called glial cells.

Neurohypophyseal bud: An outgrowth of ectoderm located on the floor of the hypothalamus that gives rise to the posterior pituitary.

Neurohypophysis: Posterior pituitary plus infundibulum; portion of the pituitary gland derived from the brain.

Neurolemma: The outer nucleated cytoplasmic layer of a Schwann cell. Also called neurilemma, or sheath of Schwann.

Neurology: The study of the normal functioning and disorders of the nervous system.

Neuromuscular junction (NMJ): A synapse between the axon terminals of a motor neuron and the sarcolemma of a muscle fiber (cell).

Neuron: A nerve cell, consisting of a cell body, dendrites, and axon.

Neuron cell body: The biosynthetic center of a neuron. Also called the perikaryon, or soma.

Neuronal pools: Functional groups of neurons that process and integrate information.

Neuropeptides: A class of neurotransmitters including beta endorphins and enkephalins (which act as euphorics and reduce perception of pain) and gut-brain peptides.

Neurosecretory cell: A neuron that secretes a hypothalamic releasing hormone or inhibiting hormone into blood capillaries of the hypothalmus; a neuron that secretes oxytocin or antidiuretic hormone into blood capillaries of the posterior pituitary.

Neurotransmitter: Chemical released by neurons that crosses the synapse and either stimulates or inhibits the postsynaptic cell (another neuron, muscle or gland cell).

Neurulation: The process by which the neural plate, neural folds, and neural tube develop.

Neutral fats: Consist of fatty acid chains and glycerol. Also called triglycerides or triacylglycerols. Commonly known as oils when liquid.

Neutralization reaction: Displacement reaction in which mixing an acid and a base forms water and a salt.

Neutron: Subatomic particle of matter with no electric charge that is located in the nucleus of the atom; often abbreviated n.

Neutrophil: Granular white blood cell; active phagocyte that increases rapidly during acute infection; the most abundant type of white blood cell; its granules take up a mixture of acidic and basic stains and turn pale lilac.

Nicotinic receptors: Acetylcholine-binding receptors of all autonomic ganglionic neurons and skeletal muscle neuromuscular junctions; named for activation by nicotine.

Nipple: A pigmented, wrinkled projection on the surface of the breast that is the location of the openings of the lactiferous ducts for milk release.

Nissl bodies: The rough endoplasmic reticulum in neurons.

Nociceptor: Receptor sensitive to potentially damaging stimuli that result in pain.

Node of Ranvier: A space in the myelin sheath of a nerve fiber, between two neighboring Schwann cells in the PNS, or oligodendrocytes in the CNS. Also called neurofibral node.

Nondisjunction: Failure of sister chromatids to separate during mitosis or failure of homologous pairs to separate during meiosis; results in abnormal numbers of chromosomes in the resulting daughter cells.

Nonpolar molecules: Electrically balanced molecules.

Norepinephrine (NE): A catecholamine (biogenic amine) neurotransmitter and adrenal medullary hormone, associated with sympathetic nervous system activation. Also called noradrenaline.

Notochord: A flexible rod of mesodermal tissue that lies where the future vertebral column will develop and plays a role in induction.

Nuclear envelope: Double membrane surrounding the cell nucleus; contains large nuclear pores.

Nuclear pore: Octagonal opening in the nuclear envelope where the two nuclear membranes are in contact; produced by proteins that regulate the transport of materials between the nucleus and the cytoplasm.

Nuclei: (1) Plural of nucleus. (2) Clusters of neuron cell bodies in the CNS.

Nucleic acid: A major class of biological molecules that contain sugars, phosphates, and nitrogenous bases, such as DNA, RNA, and ATP.

Nucleolus: Round dense body in the cell nucleus where the ribosomal subunits are synthesized.

Nucleoplasm: Contents of the cell nucleus other than the chromatin and nucleoli.

Nucleosome: Fundamental unit of chromatin; consists of a strand of DNA wound around a cluster of eight histone proteins.

Nucleotide: Building block of nucleic acids; contains a five-carbon sugar (ribose or deoxyribose), a phosphate group, and a nitrogenous base.

Nucleus: (1) Control center of a cell that contains genetic material; surrounded by a double membrane. (2) A cluster of neuron cell bodies in the CNS.

Nucleus pulposus: A soft, pulpy, highly elastic substance in the center of an intervertebral disc; a remnant of the notochord.

Nutrients: Chemical substances taken in via the diet that are used for energy and cell building.

Obesity: Body weight more than 20% above a desirable standard due to excessive accumulation of fat by hypertrophy and hyperplasia of adipose tissue cells. Also called adiposity or corpulency.

Oblique plane: A plane that passes through the body or an organ at an angle between the transverse plane and either the midsagittal, parasagittal, or frontal plane.

Oblique section: A cut made diagonally between the horizontal and vertical plane of the body or an organ.

Obstetrics: The specialized branch of medicine that deals with pregnancy, labor, and the period of time immediately after delivery (about 6 weeks).

Occipital bone: Posterior cranial bone. Markings: Foramen magnum allows the spinal cord to attach to the brain stem. Hypoglossal canal allows passage of the hypoglossal nerve (cranial nerve XII). Occipital condyles articulate with the atlas (first vertebra). External occipital protuberance and nuchal lines are attachment sites of muscles. External occipital crest is attachment site of ligamentum nuchae.

Occipitalis: Pulls scalp posteriorly. O: Occipital and temporal bones. I: Galea aponeurotica. Also called occipital belly of occipitofrontalis (epicranius).

Occlusion: Closure or obstruction.

Octet rule (rule of eights): The tendency of atoms to interact in such a way that they have eight electrons in their valence shell.

Olfaction: Smell.

Olfactory: Pertaining to smell.

Olfactory bulb: A mass of gray matter containing cell bodies of neurons that form synapses with neurons of the olfactory (I) nerve, lying inferior to the frontal lobe of the cerebrum on either side of the crista galli of the ethmoid bone.

Olfactory receptor: A bipolar neuron with its cell body lying between supporting cells located in the mucous membrane lining the superior portion of each nasal cavity; transduces odors into neural signals.

Olfactory tract: A bundle of axons that extends from the olfactory bulb posteriorly to olfactory regions of the cerebral cortex.

Oligodendrocyte: A type of CNS supporting cell that forms a myelin sheath around a neuron axon.

Oligosaccharide: Short-chain carbohydrate containing several monosaccharides that are linked by glycosidic bonds.

Oliguria: Daily urinary output usually less than 250 mL.

Olive: A prominent oval mass on each lateral surface of the superior part of the medulla oblongata.

Oncogenes: Cancer-causing genes; they derive from normal genes, termed proto-oncogenes, that encode proteins involved in cell growth or cell regulation but have the ability to transform a normal cell into a cancerous cell when they are mutated or inappropriately activated.

Oncology: The study of tumors.

Oocyte: Immature female gamete.

Oogenesis: Formation and development of oocytes (female gametes).

Oogonium: Diploid stem cell in the fetal ovary that undergoes oogenesis to form primary oocytes.

Oophorectomy: Surgical removal of the ovaries.

Ophthalmic: Pertaining to the eye.

Ophthalmologist: A physician who specializes in the diagnosis and treatment of eye disorders using drugs, surgery, and corrective lenses.

Ophthalmology: The study of the structure, function, and diseases of the eye.

Opposition: Movement of the thumb so that it touches the tips of the other fingers

Optic: Refers to the eye, vision, or properties of light.

Optic chiasm: A crossing point of the two branches of the optic (II) nerve, anterior to the pituitary gland. Also called optic chiasma.

Optic disc: The blind spot; area in the retina that lacks photoreceptors and the optic nerve exits the eye.

Optic tract: A bundle of axons that carry nerve impulses from the retina of the eye between the optic chiasm and the thalamus.

Oral cavity: The mouth.

Ora serrata: The irregular margin of the retina lying internal and slightly posterior to the junction of the choroid and ciliary body.

Orbicularis oculi: Blinking muscle; blinks, winks, and closes eye. O: Frontal bone and maxilla. I: Tissue around eyes.

Orbicularis oris: Kissing muscle; closes mouth, purses and protrudes lips. O: Mandible and maxilla. I: Skin and muscle around mouth.

Orbit: The bony, pyramidal-shaped cavitY of the skull that holds the eyeball.

Orchitis: Inflammation of the testis.

Organ: A part of the body formed of two or more tissues and adapted to carry out a specific function.

Organ system: A group of organs that work together to perform a vital body function; e.g., the nervous system.

Organelle: Any structure within a cell that performs specialized metabolic functions.

Organic compound: Any compound composed of atoms (some of which are carbon) held together by covalent (shared electron) bonds.

Organic: Pertaining to carbon-containing molecules, such as proteins, fats, and carbohydrates.

Organism: The living animal (or plant), which represents the sum total of all its organ systems working together to maintain life.

Organogenesis: The formation of body organs and systems. By the end of the eighth week of development, all major body systems have begun to develop.

Orifice: Any aperture or opening.

Origin: The attachment of a muscle tendon to a stationary bone or the end opposite the insertion.

Oropharynx: The intermediate portion of the pharynx, lying posterior to the mouth and extending from the soft palate to the hyoid bone; it is lined with stratified squamous epithelium.

Orthopedics: The branch of medicine that deals with the preservation and restoration of the skeletal system, articulations, and associated structures.

Osmolality: The number of solute particles dissolved in one liter (1000 g) of water; reflects the solution’s ability to cause osmosis.

Osmolarity: The total concentration of all solute particles in a solution.

Osmoreceptor: Structure sensitive to osmotic pressure or concentration of solution.

Osmosis: The diffusion of water through a semipermeable membrane, from a region of lower solute concentration into a region of higher solute concentration.

Osmotic pressure: The pressure that must be applied to a solution to prevent the passage of solvent into it; the tendency to resist further net water entry.

Osseous: Bony.

Ossicle: One of the small bones of the middle ear (malleus, incus, stapes).

Ossification: Formation of bone. Also called osteogenesis.

Ossification center: An area in the cartilage model of a future bone where the cartilage cells hypertrophy, secrete enzymes that calcify their extracellular matrix, and die, and the area they occupied is invaded by osteoblasts that then lay down bone.

Osteoarthritis: A common chronic, “wear and tear” arthritis, which is the result of erosion of articular cartilage and hypertrophy of bone at the margins, accompanied by pain and loss of function; mainly affects weight-bearing joints and is more common in older people.

Osteoblast: Bone-forming cell.

Osteoclast: A large, multinuclear cell that resorbs (destroys) bone matrix.

Osteocyte: Mature bone cell.

Osteogenesis: The process of bone formation. Also called ossification.

Osteogenic cell: Bone stem cell found in the inner layer of the periosteum that develops into osteoblasts.

Osteogenic layer: The inner layer of the periosteum that contains ceOs responsible for forming new bone during growth and repair.

Osteoid: Newly formed organic bone matrix before calcification.

Osteology: The study of bones.

Osteomalacia: Disorder in which bones are inadequately mineralized; soft bones.

Osteomyelitis: Inflammation of the bone marrow and adjacent bone.

Osteon: The basic structural unit of adult compact bone, consists of concentric osseous lamellae around a central canal that contains blood vessels.

Osteoporosis: Age-related disorder characterized by decreased bone mass and increased susceptibility to fractures, often as a result of decreased levels of estrogens.

Otic: Pertaining to the ear.

Otoliths: Ear stones; grains of calcium carbonate in the maculae.

Otolithic membrane: Thick, gelatinous, glycoprotein layer located directly over hair cells of the macula in the saccule and utricle of the internal ear.

Otorhinolaryngology: The branch of medicine that deals with the diagnosis and treatment of diseases of the ears, nose, and throat.

Oval window: A small, membrane-covered opening that transmits the vibratory motion of the stapes to the fluid in the scala vestibuli of the inner ear.

Ovarian cycle: Monthly cycle of follicle development, ovulation, and corpus luteum formation in an ovary.

Ovarian follicle: A general name for oocytes (immature ova) in any stage of development, along with their surrounding epithelial cells.

Ovarian ligament: A rounded cord of connective tissue that attaches the ovary to the uterus.

Ovary: Female gonad that produces oocytes and the estrogens, progesterone, inhibin, and relaxin hormones.

Ovulation: The rupture of a mature ovarian (Graafian) follicle with discharge of a secondary oocyte into the pelvic cavity.

Ovum: The female reproductive or germ cell; an egg cell; arises through completion of meiosis in a secondary oocyte after penetration by a sperm.

Oxidases: Enzymes that catalyze the transfer of oxygen in oxidation-reduction reactions.

Oxidation: Chemical reaction in which electrons and energy are lost by a molecule (often accompanied by the gain of oxygen atoms, or the loss of hydrogen atoms).

Oxidation-reduction (redox) reaction: A reaction that couples the oxidation (loss of electrons) of one substance with the reduction (gain of electrons) of another substance.

Oxidative deamination: Removal of the amino group, -NH, from glutamic acid, which produces ammonia, NH, α-keto glutaric acid, and NADH.

Oxidative phosphorylation: Process of ATP synthesis during which an inorganic phosphate group is attached to ADP; occurs via the electron transport chain within the mitochondria.

Oxygen debt: The volume of oxygen required after exercise to oxidize the lactic acid formed during exercise.

Oxyhemoglobin: (Hb-O2): Hemoglobin combined with oxygen.

Oxytocin (OT): A hormone secreted by neurosecretory cells in the hypothalamus and stored in the posterior pituitary gland; stimulates uterine muscle contraction during labor, and promotes milk release by mammary glands during lactation.

P wave: The deflection wave of an electrocardiogram that signifies atrial depolarization.

Pacinian corpuscles: Oval receptors deep in the dermis that are responsible for deep cutaneous pressure and vibration. Also called lamellated corpuscles.

Paget’s disease: Disorder characterized by excessive bone breakdown and abnormal bone formation.

Palate: Roof of the mouth.

Palatine bones: Pair of bones that form posterior hard palate, and part of nasal cavity and orbits.

Palatine tonsils: A pair of collections of lymphoid follicles embedded in the left and right lateral walls of the oropharynx.

Palpate: To examine by touch; to feel.

Palpitation: A rapid or irregular heart beat that is perceptible to the patient.

Pancreas: Gland located behind the stomach, between the spleen and the duodenum. It is both an exocrine gland (secreting pancreatic juice) and an endocrine gland (secreting insulin, glucagon, somatostatin, and pancreatic polypeptide).

Pancreatic duct: A single large tube that unites with the common bile duct from the liver and gallbladder and drains pancreatic juice into the duodenum at the hepatopancreatic ampulla (ampulla of Vater). Also called the duct of Wirsung.

Pancreatic islet: A cluster of endocrine gland cells in the pancreas that secretes insulin, glucagon, somatostatin, and pancreatic polypeptide. Also called an islet of Langerhans.

Pancreatic juice: Bicarbonate rich secretion of the pancreas containing enzymes for digestion of all food categories.

Papanicolaou test: A cytological staining test for the detection and diagnosis of premalignant and malignant conditions of the female genital tract. Cells scraped from the epithelium of the cervix of the uterus are examined microscopically. Also called a Pap test or Pap smear.

Papilla: Small, nipple-like projection.

Paracrine hormone: A local chemical messenger whose effects are restricted to the local environment, and that acts on cells neighboring the cell that secretes it.

Paralysis: Loss or impairment of motor function due to a lesion of nervous or muscular origin.

Paranasal sinuses: The paired air-filled cavities that lighten four skull bones and open into the nasal cavity; they are lined with ciliated pseudostratified columnar epithelium with goblet cells, and are located in the frontal, maxillary, ethmoid, and sphenoid bones.

Paraplegia: Paralysis of both lower limbs.

Parasagittal plane: A vertical plane that does not pass through the midline and that divides the body or organs into unequal left and right portions.

Parasympathetic division: The division of the autonomic nervous system that oversees digestion, elimination, and glandular function; the resting and digesting subdivision.

Parasympathetic tone: State of parasympathetic effects; e.g., unnecessary heart accelerations; normal activity levels of digestive and urinary tracts.

Parathyroid glands: Small endocrine glands located on the posterior aspect of the thyroid gland that secrete PTH.

Parathyroid hormone (PTH): Hormone released by the parathyroid glands that raises blood calcium level, increases intestinal absorption of calcium, and promotes kidney reabsorption of calcium and excretion of phosphate; acts as an antagonist to calcitonin (CT). Also called parathormone or parathyrin.

Parietal: Pertaining to the walls of a cavity.

Parietal bones: Pair of superolateral skull bones that form roof and sides of the cranium.

Parietal cell: A cell in the gastric glands that secretes hydrochloric acid and intrinsic factor. Also called an oxyntic cell.

Parietal pleura: The outer layer of the serous pleural membrane that encloses and protects the lungs; the layer that is attached to the wall of the pleural cavity.

Parietal serosa: The part of the double-layered membrane that lines the walls of the ventral body cavity.

Parkinson’s disease: Neurodegenerative disorder of the basal nuclei of the cerebrum involving abnormalities of the neurotransmitter dopamine; symptoms include persistent tremor, slowing of voluntary movements, and muscle weakness.

Parotid gland: Largest of the salivary glands; situated anterior to each ear.

Pars intermedia: A small avascular zone between the anterior and posterior pituitary glands.

Partial pressure: The pressure exerted by a single component of a mixture of gases.

Parturition: Culmination of pregnancy; giving birth.

Passive immunity: Short lived immunity resulting from the introduction of “borrowed antibodies” obtained from an immune animal or human donor; immunological memory is not established.

Passive transport processes: Membrane transport processes that do not require cellular energy (ATP), e.g., diffusion, which is driven by kinetic energy.

Patella: Kneecap; sesamoid bone lodged in the tendon of the quadriceps muscles; articulates with the patellar surface of the femur; ligaments attach to the tibial tuberosity.

Patent ductus arteriosus: A congenital heart defect in which the ductus arteriosus remains open. As a result, aortic blood flows into the lower-pressure pulmonary trunk, increasing pulmonary trunk pressure and overworking both ventricles.

Pathogen: Disease causing microorganism.

Pathological anatomy: The study of structural changes caused by disease.

Pectinate muscles: Projecting muscle bundles of the anterior atrial walls and the lining of the auricles.

Pectineus: Anterior muscle on middle of proximal thigh; flex and adduct thigh. O: Pubis. I: Femur.

Pectoral: Pertaining to the chest.

Pectoral girdle: Bones that attach the upper limbs to the axial skeleton; includes the clavicle and scapula. Also called shoulder girdle.

Pectoralis major: Large, fan-shaped, chest muscle; flex, rotate and adduct arm. O: Sternum, clavicle and ribs 1-6. I: Proximal humerus.

Pedicel: Footlike structure, as on podocytes of a glomerulus.

Pedigree: Traces a particular genetic trait through several generations and helps predict the genotype of future offspring.

Pelvic cavity: Inferior portion of the abdominopelvic cavity that contains the urinary bladder, sigmoid colon, rectum, and internal female and male reproductive structures.

Pelvic inlet (brim): Upper opening of true pelvis; wide oval-shape in females, and narrow heart-shape in males

Pelvic girdle: Consists of the paired coxal bones that attach the lower limbs to the axial skeleton. Also called hip girdle.

Pelvic splanchnic nerves: Consist of preganglionic parasympathetic axons from the levels of S2, S3, and S4 that supply the urinary bladder, reproductive organs, and the descending and sigmoid colon and rectum.

Pelvis: (1) Basin shaped, bony structure composed of the pelvic girdle, sacrum, and coccyx. (2) expanded proximal portion of the ureter within the kidney.

Penis: Male organ of copulation and urination.

Pepsin: A protein digesting enzyme of gastric juice, formed from pepsinogen that is secreted by the gastric glands; it digests proteins into smaller peptide chains at low pH values

Peptic ulcer: An ulcer that develops in areas of the gastrointestinal tract exposed to hydrochloric acid; classified as a gastric ulcer if in the lesser curvature of the stomach and as a duodenal ulcer if in the first part of the duodenum.

Peptide: A polymer of amino acids. Also called a polypeptide.

Peptide bond: A covalent bond (-CO-NH-) that joins two amino acids.

Percussion: The act of striking (percussing) an underlying part of the body with short, sharp taps as an aid in diagnosing the part by the quality of the sound produced.

Perforating canals: Canals that run at right angles to the long axis of the bone, connecting the vascular and nerve supplies of the periosteum to those of the central canals and medullary cavity. Also called Volkmann’s canals.

Perforin: Protein released by cytotoxic T lymphocytes and natural killer cells that causes lysis of the target cell.

Pericardial cavity: Small potential space between the visceral and parietal layers of the serous pericardium that contains pericardial fluid.

Pericardium: Double-layered serosa enclosing the heart and forming its superficial layer.

Perichondrium: Fibrous membrane covering the external surface around cartilage; consists mostly of dense irregular connective tissue.

Perilymph: The fluid contained between the bony and membranous labyrinths of the inner ear.

Perimetrium: The serosa of the uterus.

Perimysium: Fibrous connective tissue that surrounds each muscle fascicle.

Perineum: That region of the body spanning the region between the ischial tuberosities and extending from the anus to the scrotum in males and from the anus to the vulva in females.

Perineurium: Connective tissue wrapping around fascicles in a nerve.

Periodontal disease: A collective term for conditions characterized by degeneration of gingivae, alveolar bone, periodontalligament, and cementum.

Periodontal ligament: The periosteum lining the alveoli (sockets) for the teeth in the alveolar processes of the mandible and maxillae.

Periosteum: The thick membrane that covers the entire surface of a bone except its articular cartilage; it consists of two layers, an outer tough fibrous layer containing blood vessels that nourish the bone, and a deeper osteogenic layer that can form new bone tissue.

Peripheral: Located on the outer part or a surface of the body.

Peripheral congestion: Condition caused by failure of the right side of the heart; results in edema in the extremities.

Peripheral nervous system (PNS): Portion of the nervous system that consists of nerves and ganglia that lie outside of the CNS (brain and spinal cord).

Peripheral resistance: A measure of the amount of friction encountered by blood as it flows through the blood vessels.

Perirenal fat capsule: A fatty cushion that surrounds the kidneys, located between the renal fascia and renal capsule. Also called renal adipose capsule.

Peristalsis: Progressive, wave-like contractions that move foodstuffs through the alimentary tube organs, or that move other substances through other hollow body organs.

Peritoneum: Serous membrane lining the interior of the abdominal cavity and covering the surfaces of abdominal organs.

Peritonitis: Inflammation of the peritoneum.

Permeability: That property of membranes that permits passage of molecules and ions.

Peroxisome: Vesicle that detoxifies poisonous molecules and participates in metabolic oxidations involving hydrogen peroxide.

Perspiration: Sweat; produced by sudoriferous (sweat) glands and containing water, salts, urea, uric acid, amino acids, ammonia, sugar, lactic acid, and ascorbic acid. Helps maintain body temperature and eliminate wastes.

Petechiae: Small, purplish skin blotches caused by widespread hemorrhage due to thrombocytopenia.

Peyer patches: Collections of lymphoid follicles in the ileum of the small intestine. Also called aggregated lymphoid nodules of the small intestine.

pH scale: A measure of the concentration of free hydrogen ions in solution; pH 0 is the most acidic, pH 14 is the most basic (alkaline), and pH 7 is a neutral solution.

Phagocytosis: (1) Cell eating. (2) The cellular process of ingestion and digestion of solid substances. (3) The process by which phagocytes ingest and destroy microbes, cell debris, and other foreign matter.

Phagolysosome: Vesicle formed by the fusion of a phagosome with a lysosome, in which digestion of the phagocytized particles occur.

Phagosome: Endocytotic vesicle formed by phagocytosis.

Phalanges: (1) Finger bones; two in digit 1 (thumb); three in digits 2-5. (2) Toe bones; two in digit 1 (great toe); three in digits 2-5.

Phalanx: The bone of a finger or toe. Plural is phalanges.

Pharmacological dose: A drug dose that is dramatically higher than normal levels of that substance (e.g., hormone) in the body.

Pharmacology: The science of the effects and uses of drugs in the treatment of disease.

Pharyngeal tonsil: A collection of lymphoid follicles on the posterior wall of the nasopharynx. Also called adenoid.

Pharyngotympanic tube: Tube that connects the middle ear and the pharynx. Also called the eustachian tube, or auditory tube.

Pharynx: The throat; a muscular tube that starts at the internal nares and runs partway down the neck, where it opens into the esophagus posteriorly and the larynx anteriorly.

Phenotype: The observable expression of genotype; physical characteristics of an organism determined by genetic makeup and influenced by interaction between genes and internal and external environmental factors.

Phlebitis: Inflammation of a vein, usually in a lower limb.

Phospholipid: The main structural component of cell membranes; usually contains a glycerol backbone, two fatty acid tails, and a hydrophilic head with a phosphate group and a nitrogenous base.

Phosphorylation: The mechanism of ATP synthesis; includes substrate-level and oxidative phosphorylation.

Photopigment: A substance that can absorb light and undergo structural changes that can lead to the development of a receptor potential. An example is rhodopsin. In the eye, also called visual pigment.

Photoreceptors: Retinal cells responsible for vision; rod cells detect only black and white, while cone cells detect color.

Physiological acidosis: Arterial pH lower than 7.35 resulting from any cause.

Physiological dose: A drug dose that replicates normal levels of that substance (e.g., hormone) in the body.

Physiology: Study of the function of living organisms or its parts.

Pia mater: The innermost of the three meninges (coverings) of the brain and spinal cord.

Pineal gland: A cone-shaped gland located in the roof of the third ventricle and part of the diencephalon of the brain; it secretes melatonin, thought to be involved in setting the biological clock and influencing reproductive function. Also called the pineal body, or epiphysis cerebri.

Pinealocyte: Secretory cell of the pineal gland that releases melatonin.

Pinna: The flesh covered elastic cartilage of the ear located on the sides of the head. Also called auricle.

Pinocytosis: Cell drinking; the cellular process of actively engulfing liquid by forming invaginations in the surface of the cell membrane then closing to form fluid-filled vesicles. Also called fluid phase endocytosis.

Pituicyte: Supporting cell of the posterior pituitary.

Pituitary gland: Neuroendocrine gland occupying the hypophyseal fossa of the sphenoid bone and attached to the hypothalamus by the infundibulum; it serves a variety of functions including regulation of gonads, thyroid, adrenal cortex, lactation, and water balance. Also called the hypophysis. See anterior pituitary gland and posterior pituitary gland.

Pivot joint: An uniaxial synovial joint in which the cylindrical end of one bone fits into a corresponding cavity on the other bone, allowing rotational motion around the long axis.

Placenta: A fetomaternal organ that exchanges nutrients and wastes between the fetus and mother; the chorion is of embryonic origin that receives blood vessels from the yolk sac and the allantois in the chorionic villil; the decidua basalis is the maternal portion that develops blood-filled lacunae.

Placentation: Formation of the placenta by the proliferation of the trophoblast; the placenta is fully functional as a nutritive, respiratory, excretory, and endocrine organ by the end of the third month of gestation.

Plane joint: A nonaxial synovial joint in which the opposing surfaces are nearly planar, and there is only a slight, gliding motion.

Plantar flexion: Downward movement of the foot that decreases the angle between the sole of the foot (plantar surface) and the posterior side of the tibia.

Plaque: A layer of dense proteins on the inside of a plasma membrane in adherens junctions and desmosomes. A mass of bacterial cells, dextran (polysaccharide), and other debris that adheres to teeth (dental plaque). See also Atherosclerotic plaque.

Plasma: The noncellular fluid portion of the circulating blood.

Plasma cell: Cell that develops from a B cell (lymphocyte) and produces antibodies.

Plasma membrane: Outer cell membrane composed of phospholipid bilayer with embedded proteins, cholesterol, and surface polysaccharides; encloses cell contents and regulates entry and exit of materials. Also called cell membrane.

Platelet: Cell fragment lacking a nucleus that is found in blood and involved in clotting. Also called a thrombocyte.

Platelet plug: Aggregation of platelets (thrombocytes) at a site where a blood vessel is damaged that helps stop or slow blood loss.

Platysma: Anterior, flat neck muscle; depress jaw, lowers corner of mouth, tenses skin of neck. O: Fascia of the cervical region. I: Mandible and tissue around mouth.

Pleura: The double-layered serous membrane that protects the lung; the parietal pleura lines the wall of the pulmonary cavity, the pleural cavity is a slit-like space filled with lubricating fluid, and the visceral pleura covers the outer surface of the lungs.

Pleural cavity: Small slit-like space between the visceral and parietal pleurae that is filled with lubricating fluid.

Plexus: A network of nerves, veins, or lymphatic vessels.

Plexus of Auerbach: See Myenteric plexus.

Plexus of Meissner: See Submucosal plexus.

Pluripotent stem cell: Immature stem cell in red bone marrow that gives rise to precursors of all the different mature blood cells.

Pneumonia: The most common infectious cause of death in the United States, which causes alveoli to fill with thick fluid, making gas exchange difficult.

Pneumotaxic area: Part of the respiratory centers; nuclei in the pons that rhythmically inhibits inspiration and facilitates exhalation, which regulates the respiratory rate. Also called the pontine respiratory group (PRG).

Peripheral nervous system (PNS): Portion of the nervous system that consists of nerves and ganglia that lie outside of the CNS (brain and spinal cord).

Polar molecules: Nonsymmetrical molecules that contain electrically unbalanced atoms.

Polarized: State of a plasma membrane of an unstimulated neuron or muscle cell in which the inside of the cell is relatively negative in comparison to the outside; the resting state.

Polycythemia: Abnormal increase in the number of red blood cells (hematocrit above 55%).

Polymer: Large molecule formed by joining together many monomers.

Polypeptide: A polymer of amino acids. Also called a peptide.

Polyps: Benign mucosal tumors.

Polyribosome: String of ribosomes bound to a molecule of messenger RNA that are active in protein synthesis.

Polysaccharide: A polymer of monosaccharides, such as glycogen, starch, and cellulose.

Polyunsaturated fat: A fat whose fatty acid tails have many C=C double bonds; abundant in corn, safflower, sunflower, and cottonseed oils.

Polyuria: An excessive production of urine.

Pons: (1) Any bridge-like structure or part. (2) The part of the brain stem anterior to the cerebellum; forms a bridge between the cerebellum and cerebrum; contains the middle cerebellar peduncle and a respiratory center.

Pontine respiratory group (PRG): Part of the respiratory centers; nuclei in the pons that rhythmically inhibits inspiration and facilitates exhalation, which regulates the respiratory rate. Also called the pneumotaxic center.

Pore: The surface opening of the duct of a sweat gland.

Portal system: The circulation of blood from one capillary network into another through a vein.

Positive feedback mechanisms: Feedback that tends to cause the level of a variable to change in the same direction as an initial change.

Postcentral gyrus: Gyrus of cerebral cortex located immediately posterior to the central sulcus; contains the primary somatosensory area.

Posterior: Nearer the back of the body; equivalent to dorsal in bipeds.

Posterior column-medial lemniscus pathways: Sensory pathways that carry information related to proprioception, fine touch, two-point discrimination, pressure, and vibration.

Posterior fontanel: A triangular-shaped membranous interval in the skull of a fetus and infant; located at the union of the lambdoid and sagittal sutures, where occipital angles of the parietal bones meet the occipital bone.

Posterior pituitary gland: Posterior lobe of the pituitary gland that is derived from nervous tissue; secretes the hormones antidiuretic hormone (ADH) and oxytocin (OT). Also called the neurohypophysis.

Posterior root: The structure composed of sensory axons lying between a spinal nerve and the dorsolateral aspect of the spinal cord. Also called the dorsal (sensory) root.

Posterior root ganglion: A group of cell bodies of sensory neurons and their supporting cells located along the posterior root of a spinal nerve. Also called a dorsal (sensory) root ganglion.

Postganglionic axon (fiber): Axon of a ganglionic neuron, an autonomic motor neuron that has its cell body in a peripheral ganglion; the axon projects to an effector.

Postganglionic neuron: The second autonomic motor neuron in an autonomic pathway, having its cell body and dendrites located in an autonomic ganglion and its unmyelinated axon ending at cardiac muscle, smooth muscle, or a gland.

Postsynaptic neuron: The nerve cell that is activated by the release of a neurotransmitter from another neuron and carries nerve impulses away from the synapse.

Potential energy: Stored or inactive energy.

Pouch of Douglas: A pocket formed by the parietal peritoneum as it moves posteriorly from the surface of the uterus and is reflected onto the rectum; the most inferior point in the pelvic cavity. Also called the Rectouterine pouch.

Precapillary sphincter: A ring of smooth muscle fibers (cells) at the site of origin of true capillaries that regulate blood flow into true capillaries.

Precentral gyrus: Gyrus of cerebral cortex located immediately anterior to the central sulcus; contains the primary motor area.

Prefrontal cortex: Located in the anterior frontal lobe; controls intellect, complex reasoning, conscience, personality and mood. (Brodmann areas 9, 10, 11, 12)

Preganglionic neuron: The first autonomic motor neuron in an autonomic pathway, with its cell body and dendrites in the brain or spinal cord and its myelinated axon ending at an autonomic ganglion, where it synapses with a postganglionic neuron.

Pregnancy: Sequence of events that normally includes fertilization, implantation, embryonic growth, and fetal growth and terminates in birth.

Premenstrual syndrome (PMS): Severe physical and emotional stress ocurring late in the postovulatory phase of the menstrual cycle and sometimes overlapping with menstruation.

Prepuce: The loose-fitting skin covering the glans of the penis and clitoris. Also called the foreskin.

Presbyopia: A loss of elasticity of the lens of the eye due to advancing age with resulting inability to focus clearly on near objects; typical onset is around age 40.

Pressoreceptor: A nerve ending in the wall of the carotid sinus and aortic arch sensitive to vessel stretching.

Pressure gradient: Difference in hydrostatic pressure that drives filtration.

Presynaptic neuron: A neuron that propagates nerve impulses toward a synapse.

Prevertebral ganglion: A cluster of cell bodies of postganglionic sympathetic neurons anterior to the spinal column and close to large abdominal arteries. Also called a collateral ganglion.

Primary active transport: A type of active transport in which the energy needed to drive the transport process is provided directly by hydrolysis of ATP

Primary auditory area: Located in the temporal lobe; receives the sense of hearing from the ears. (Brodmann areas 41, 42)

Primary germ layer: One of three layers of embryonic tissue, called ectoderm, mesoderm, and endoderm, that give rise to all tissues and organs of the body.

Primary gustatory area: Located in the parietal lobe; receives the sense of taste from the tongue. (Brodmann area 43)

Primary motor area: Located in the precentral gyrus of the frontal lobe; innervates motor neurons controlling the skeletal muscles. (Brodmann area 4)

Primary olfactory area: Located deep within the temporal lobe; receives the sense of smell from the nose. (Brodmann area 28 )

Primary oocyte: An oocyte during its growth phase and before it completes the first meiotic division.

Primary somatosensory area: Located in the postcentral gyrus of the parietal lobe; receives the somatic sensory information from the body. (Brodmann areas 1, 2, 3)

Primary visual area: Located in the occipital lobe; receives the sense of sight from the eyes. Area (Brodmann area 17)

Prime mover muscle: Muscle that bears the major responsibility for effecting a particular movement. Also called an agonist muscle.

Primitive gut: Embryonic structure formed from the dorsal part of the yolk sac that gives rise to most of the gastrointestinal tract.

Primordial: Existing first; especially primordial egg cells in the ovary.

Primordium: An aggregation of cells in the embryo indicating the first trace of an organ or structure.

Principal cell: Cell type in the distal convoluted tubules and collecting ducts of the kidneys that is stimulated by aldosterone and antidiuretic hormone.

Process: (1) Prominence or projection. (2) series of actions for a specific purpose.

Proctology: The branch of medicine concerned with the rectum and its disorders.

Proenzyme: The inactive precursor of an enzyme, which can be converted into the active enzyme. Also called a zymogen.

Progeny: Offspring or descendants.

Progesterone: A female sex hormone produced by the ovaries that helps prepare the endometrium of the uterus for implantation of a fertilized ovum, and the mammary glands for milk secretion.

Prognosis: A forecast of the probable results of a disorder; the outlook for recovery.

Projection fibers: Neuron axons that connect the cerebral cortex to the brain stem and spinal cord.

Prokaryote: Bacteria; single celled organism with no nucleus and no organelles.

Prolactin (PRL): A hormone secreted by the anterior pituitary that initiates and maintains milk production (lactation) by the mammary glands.

Prolapse: A dropping or falling down of an organ, especially the uterus or rectum.

Proliferation: Rapid and repeated reproduction of new parts, especially cells.

Promoter: Short stretch of DNA, to which RNA polymerase can bind and start transcription.

Pronation: Rotating the arm medially so that the palm faces posteriorly or inferiorly, and the radius crosses diagonally over the ulna.

Prophase: The first stage of mitosis during which duplicated DNA condenses into chromosomes, the nuclear envelope disassembles, while centrosomes move to opposite poles and form spindle fibers that attach to centromeres on the chromosomes.

Proprioception: The perception of the position of body parts, especially the limbs, independent of vision; this sense is possible due to nerve impulses generated by proprioceptors.

Proprioceptor: A receptor located in muscles, tendons, joints, or the internal ear that provides information about body position and movements; concerned with locomotion, posture, and muscle tone.

Prostaglandin (PG): A membrane-associated lipid; released in small quantities and acts as a local hormone.

Prostate gland: A doughnut-shaped accessory reproductive gland in the male, lying inferior to the urinary bladder that surrounds the superior portion of the male urethra; it secretes a milky fluid that activates sperm and breaks down clots and mucus, and contains citric acid.

Proteasome: Tiny barrel-shaped protein complex (smaller than a ribosome) with proteases that degrade endogenous proteins that have been marked by binding to ubiquitin.

Protein: A major class of biological molecules; contains one or more peptides.

Prothrombin: An inactive blood-clotting factor synthesized by the liver, released into the blood, and converted to active thrombin in the process of blood clotting by the activated enzyme prothrombinase.

Prothrombin time: Diagnostic test to determine status of hemostasis system.

Proto-oncogene: Gene responsible for some aspect of normal growth and development; it may transform into an oncogene, a gene capable of causing cancer.

Proton: Positively charged subatomic particle of matter that is located in the in the nucleus of the atom;

often abbreviated p.

Proton acceptor: A substance that takes up hydrogen ions in detectable amounts. Commonly referred to as a base.

Proton donor: A substance that releases hydrogen ions in detectable amounts; an acid.

Protraction: Movement of the mandible into a position anterior to normal.

Proximal: Nearer the trunk or the point of origin.

Pseudopods: Temporary protrusions of the leading edge of a migrating cell; cellular projections that surround a particle undergoing phagocytosis.

Pseudostratified columnar epithelium: Tissue with a stratified appearance, but containing a single layer of cells of differing heights with nuclei at different levels; all cells are attached to the basement membrane, but some do not reach the free surface; some tissue types contain ciliated cells and mucus-secreting goblet cells (unicellular glands). Functions in secretion. Nonciliated type is located in the lining of the male sperm-carrying ducts, and ducts of some glands. Ciliated type is located in the lining of the larynx, trachea, and large bronchi of the lungs. Also called pseudostratified epithelium.

Pseudounipolar neuron: Another term for unipolar neuron.

Psychosomatic illnesses: Emotion induced illnesses.

Pterygoid (lateral and medial): Deep muscles of mastication; elevate, protrude and move mandible from side to side (as in grinding food). O: Sphenoid bone and maxilla. I: Mandible.

Pterygopalatine ganglion: A cluster of cell bodies of parasympathetic postganglionic neurons ending at the lacrimal and nasal glands.

Ptosis: Drooping, as of the eyelid or the kidney.

Puberty: The time of life during which the secondary sex characteristics begin to appear and the capability for sexual reproduction is possible; usually occurs between the ages of 10 and 17.

Pubic arch: Inverted V-shaped arch inferior to pubic symphysis, over 90̊ in females, and about 60̊ in males

Pubic symphysis: A slightly movable cartilaginous joint between the anterior surfaces of the hip bones.

Puerperium: The period immediately after childbirth, usually 4-6 weeks.

Pulmonary: Pertaining to the lungs.

Pulmonary arteries: Vessels that deliver blood to the lungs to be oxygenated.

Pulmonary circulation: The flow of deoxygenated blood from the right ventricle through the pulmonary artery to the lungs, and the return of oxygenated blood through the pulmonary veins to the left atrium.

Pulmonary edema: Leakage of fluid into the air sacs and tissue of the lungs.

Pulmonary embolism (PE): The presence of/a blood clot or a foreign substance in a pulmonary arterial blood vessel that obstructs circulation to lung tissue.

Pulmonary fibrosis: Fibrous connective tissue builds up in lungs, reducing their elasticity.

Pulmonary valve: The heart valve between the right ventricle and the pulmonary trunk; it consists of three fibrous semilunar cusps. Also called right semilunar valve, or right SL valve.

Pulmonary veins: Vessels that deliver freshly oxygenated blood from the respiratory zones of the lungs to the heart.

Pulmonary ventilation: Breathing; consists of inspiration and expiration.

Pulp cavity: A cavity within the crown and neck of a tooth, which is filled with pulp, a connective tissue containing blood vessels, nerves, and lymphatic vessels.

Pulse: The rhythmic expansion and elastic recoil of a systemic artery after each contraction of the left ventricle; can be felt from outside the body.

Pulse pressure (PP): The variation in blood pressure occurring in an artery during the cardiac cycle; PP = SBP – DBP.

Pupil: Opening in the center of the iris through which light enters the eye.

Purkinje fibers: Modified cardiac muscle fibers of the conduction system of the heart.

Pus: Fluid product of inflammation composed of white blood cells, the debris of dead cells and a thin fluid.

Pyloric sphincter: Valve of the distal end of the stomach that controls food entry into the duodenum. Also called the pyloric valve.

Pyorrhea: A discharge or flow of pus, especially in the alveoli (sockets) and the tissues of the gums.

Pyramid: (1) A pointed or cone-shaped structure. (2) One of two roughly triangular structures on the anterior aspect of the medulla oblongata composed of the largest motor tracts that run from the cerebral cortex to the spinal cord. (3) A triangular structure in the renal medulla.

Pyramidal (corticospinal) tracts: Major motor pathways concerned with voluntary movement; descend from the frontal lobes of each cerebral hemisphere.

Pyrogen: A fever-inducing agent.

Pyruvic acid: An intermediate compound in the metabolism of carbohydrates.

QRS wave: The deflection waves of an electrocardiogram that represent onset of ventricular depolarization.

Quadrant: One of four parts.

Quadratus lumborum: Flat muscle of posterior abdominal wall, from iliac crest to rib 12; one laterally flex spine, both extend vertebral column. O: Iliac crest. I: Vertebrae L1-L4 and rib 12.

Quadriceps Femoris Group (Rectus femoris, Vastus lateralis, Vastus medialis, Vastus intermedius): Football Kicker’s muscle on anterior thigh; extend leg at knee, flex thigh at hip. O: Femur and ileum. I: Tibial tuberosity.

Quadriplegia: Paralysis of four limbs: two upper and two lower.

Radioactivity: The process of spontaneous decay seen in some of the heavier isotopes, during which particles or energy is emitted from the atomic nucleus; results in the atom becoming more stable.

Radioisotope: A radioactive element that has an unstable atomic nucleus and spontaneously emits subatomic particles and energy, resulting in its decay into a different element.

Radiographic anatomy: Diagnostic branch of anatomy that includes the use of X-rays.

Radius: Lateral forearm bone (thumb side); carries the wrist. Markings: Head is the proximal disc-shaped extremity, the superior surface articulates with capitulum of the humerus, and the medial surface articulates with radial notch of the ulna. Radial tuberosity is attachment site for the biceps brachii muscle. Styloid process is distal lateral pointed projection; attachment site for wrist ligaments. Ulnar notch is distal medial concave surface; articulates with head of the ulna.

Rami communicantes: Branches of a spinal nerve. Singular is ramus communicans.

Ramus: Branch of a nerve, artery, vein, or bone.

Rathke’s pouch: See Hypophyseal pouch.

Rapid eye movement (REM) sleep: Stage of sleep in which rapid eye movements, an alert EEG pattern, and dreaming occur. Also called paradoxical sleep.

Reactant: A substance taking part in a chemical reaction.

Reaction, Decomposition: Chemical reaction that breaks down a large molecule into smaller molecules, usually with the net release of energy. Also called a hydrolysis reaction when water is added to the reactant.

Reaction, Oxidation: Chemical reaction were there is a loss of electrons, usually with the net release of energy, often by either adding the element oxygen, or removing the element hydrogen.

Reaction, Reduction: Chemical reaction were there is a gain of electrons, usually with the net absorption of energy, often by either adding the element hydrogen, or removing the element oxygen.

Reaction, Synthesis: Chemical reaction where small molecules are combined to form a large molecule, usually with the net absorption of energy. Also called a dehydration or condensation reaction when water is removed from the reactant.

Receptor: (1) A cell or nerve ending of a sensory neuron specialized to respond to particular types of stimuli. (2) molecule that binds specifically with other molecules, e.g., neurotransmitters, hormones, antigens.

Receptor-mediated endocytosis: A highly selective type of endocytosis, whereby cells take up specific ligands that attach to receptors, then envelop them within a sac of plasma membrane.

Receptor potential: A graded potential that occurs at a sensory receptor membrane.

Recessive traits: A trait due to a particular allele that does not manifest itself in the presence of other alleles that generate traits dominant to it; must be present in double dose in order to be expressed.

Recombinant DNA: Synthetic DNA, formed by joining a fragment of DNA from one source to a portion of DNA from another.

Rectouterine pouch: A pocket formed by the parietal peritoneum as it moves posteriorly from the surface of the uterus and is reflected onto the rectum; the most inferior point in the pelvic cavity. Also called the pouch or cui de sac of Douglas.

Rectum: The last 20 cm (8 in.) of the gastrointestinal tract, from the sigmoid colon to the anus.

Rectus abdominis: Sit-up muscle; medial trunk muscle from the pubis to rib cage; gives abdomen a washer-board appearance (8-pack); flex vertebral column; compress abdomen. O: Pubis. I: Sternum and ribs 5-7.

Recumbent: Lying down.

Red bone marrow: Hematopoietic tissue that produces all of the blood cells; located in spaces between trabeculae of spongy bone.

Red nucleus: A cluster of cell bodies in the midbrain, occupying a large part of the tectum from which axons extend into the rubroreticular and rubrospinal tracts.

Red pulp: That portion of the spleen that consists of venous sinuses filled with blood and thin plates of splenic tissue called splenic (Billroth’s) cords.

Reduction: Chemical reaction in which electrons and energy are gained by a molecule (often accompanied by the gain of hydrogen atoms, or the loss of oxygen atoms).

Referred pain: Pain that is felt at a site remote from the place of origin.

Reflex: Fast response to a change (stimulus) in the internal or external environment that attempts to restore homeostasis.

Reflex arc: The most basic conduction pathway through the nervous system, connecting a receptor to an effector, and consisting of a receptor, a sensory neuron, an integrating center in the central nervous system, a motor neuron, and an effector.

Refraction: The bending of a light ray when it meets a different surface at an oblique rather than right angle.

Regeneration: Replacement of destroyed tissue with the same kind of tissue.

Regional anatomy: The division of anatomy dealing with a specific region of the body, such as the head, neck, chest, or abdomen.

Regulatory protein: Component of mechanisms that control transcription, translation, and gene products by interacting with DNA, RNA, new polypeptide chains, or proteins (e.g., enzymes).

Regurgitation: (1) Return of solids or fluids to the mouth from the stomach. (2) Backward flow of blood through incompletely closed heart valves.

Relative refractory period: Follows the absolute refractory period; interval when a threshold stimulus is unable to trigger an action potential unless the stimulus is particularly strong.

Relaxin (RLX): A female hormone produced by the ovaries and placenta that increases flexibility of the pubic symphysis and helps dilate the uterine cervix to ease delivery of a baby.

Releasing hormones: Hormones secreted by the hypothalamus that can stimulate secretion of hormones of the anterior pituitary.

Remodeling: Replacement of old bone by new bone tissue.

Renal: Pertaining to the kidney.

Renal autoregulation: Process the kidney uses to maintain a nearly constant glomerular filtration rate despite fluctuations in systemic blood pressure.

Renal calyces: The funnel-shaped structures in the pelvis of the kidney; the minor calyces collect urine from the renal papillae, which flows into the major calyces, then empties into the renal pelvis.

Renal clearance: The volume flow rate (mL/min) at which the kidneys clear the plasma of a particular solute; provides information about renal function.

Renal capsule: Fibrous membrane that surrounds the kidney and is tightly adherent to the kidney surface.

Renal columns: Areas of cortical tissue running between the renal pyramids.

Renal cortex: The lighter, outer portion of the kidney that contains most of the nephron structures.

Renal fascia: Outermost sheath of dense fibrous connective tissue that surrounds the adipose capsule and anchors the kidneys.

Renal adipose capsule: A fatty cushion that surrounds the kidneys, located between the renal fascia and renal capsule. Also called perirenal fat capsule.

Renal hilum: Area of the kidney which allows entry and exit of ureters, renal blood vessels, lymphatics, and nerves

Renal papilla: Tip of the renal pyramid that releases urine into the minor calyx.

Renal pelvis: A funnel-shaped cavity in the center of the kidney that is continuous with the ureter, and that opens into the major calyces.

Renal pyramid: A conical structure in the renal medulla that contains the renal papillae and the bulk of the loops of Henle and collecting ducts.

Renin: An enzyme released by the kidneys that is involved with activating the hormone angiotensin II, which can increase blood pressure.

Rennin: Stomach-secreted enzyme that acts on milk protein; not produced in adults.

Repolarization: Movement of the membrane potential to the initial resting (polarized) state.

Reproduction: The formation of new cells for growth, repair, or replacement; the production of a new individual.

Reproductive cell division: Type of cell division in which gametes (sperm and oocytes) are produced; consists of meiosis and cytokinesis.

Reproductive system: Organ system that functions to produce offspring.

Resistance: (1) A force exerted in opposition to an active force. (2) The opposition to flow of a fluid through one or more passageways (e.g., blood flow, or respiratory gases in the tracheobronchial tree). (3) The natural or acquired ability of an organism to maintain its immunity to a pathogenic microorganism.

Resistance exercise: High intensity exercise in which the muscles are pitted against high resistance or immovable forces and, as a result, muscle cells increase in size.

Resistin: hormone secreted by Adipose tissue; antagonizes insulin’s action on fat, muscle, and liver cells.

Respiration: Overall exchange of gases between the atmosphere, blood, and body cells consisting of pulmonary ventilation, external respiration, and internal respiration.

Respiratory centers: Nuclei in the brain stem that coordinate respiratory movements; the pontine respiratory group (PRG) in the pons rhythmically inhibits inspiration and facilitates exhalation, which regulates the respiratory rate (also called the pneumotaxic center); the ventral respiratory group (VRG) in the medulla oblongata stimulates the muscles of forced exhalation; the dorsal respiratory group (DRG) in the medulla oblongata generates the basic rhythm of breathing.

Respiratory system: Organ system that carries out gas exchange; includes the nose, pharynx, larynx, trachea, bronchi, lungs.

Resting membrane potential: The voltage that exists across the plasma membrane during the resting state of an excitable cell; ranges from -50 to -200 millivolts, depending on cell type.

Retention: A failure to void urine due to obstruction, nervous contraction of the urethra, or absence of sensation of desire to urinate.

Rete testis: The network of ducts in the testes.

Reticular activating system (RAS): A portion of the reticular formation that has many ascending connections with the cerebral cortex; when this area of the brain stem is active, nerve impulses pass to the thalamus and widespread areas of the cerebral cortex, resulting in generalized alertness or arousal from sleep.

Reticular connective tissue: Tissue with many cell types on a network of reticular fibers in a typical loose ground substance. Functions as the internal skeleton (stroma) of organs, protection against disease, and removal of worn-out cells. Located in lymphoid organs, such as lymph nodes, spleen, and bone marrow.

Reticular fibers: Fine network of connective tissue fibers that form the internal supporting framework of lymphoid organs.

Reticular formation: Functional system that runs through the brain stem; controls consciousness, arousal, alertness, and sleep-wake cycles.

Reticular lamina: A layer of extracellular material containing a fine network of collagen protein fibers; together with the basal lamina it is a major component of the basement membrane.

Reticulocyte: Immature erythrocyte.

Reticulum: A network.

Retina: The deep tunic of the eye containing the photoreceptors.

Retinaculum: A thickening of deep fascia that holds structures in place, for example, the superior and inferior retinacula of the ankle.

Retraction: Movement of the mandible into a position posterior to normal

Retroperitoneal: External to the peritoneal lining of the abdominal cavity.

Rh factor: An inherited antigen on the surface of red blood cells in Rh+ individuals; not present in Rh- individuals.

Rheumatoid arthritis: A chronic and progressive inflammatory disorder of the joints that is an autoimmune disease which systematically destroys joints, leading to deformities and disability.

Rhinology: The study of the nose and its disorders.

Rhombencephalon (hindbrain): Caudal portion of the developing brain; constricts to form the metencephalon and myelencephalon; includes the pons, cerebellum, and medulla oblongata.

Ribonucleic acid: Single-stranded nucleic acid that contains ribose, phosphate, and the nitrogenous bases G, C, A, and U; carries out DNA instructions for protein synthesis; three types are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Also called RNA.

Ribosomal RNA (rRNA): A constituent of ribosome; exists within the ribosomes of cytoplasm and assists in protein synthesis.

Ribosome: Tiny organelle that is the site of protein synthesis; complex of rRNA and proteins that uses mRNA as a template during translation; exists as two subunits (40S and 60S) that join together (80S) when bound to mRNA.

Ribs: 12 pairs of elongated curved bones that form the main portion of the thoracic cage. Markings: Tubercle is a knob on posterior surface at junction of neck and shaft; articulates with the transverse process of the corresponding vertebra. Head is a rounded medial extremity; articulates by two facets with bodies of the corresponding and the superior vertebrae in ribs 2-9; articulates by one facet with body of the corresponding vertebra in ribs 1 and 10-12.

Right lymphatic duct: Large lymph vessel that drains lymph from the right arm and the right side of the head and thorax, and empties into the right brachiocephalic vein, at the junction between the internal jugular and subclavian veins.

Rigidity: Hypertonia characterized by increased muscle tone, but reflexes are not affected.

Rigor mortis: State of partial contraction of muscles after death due to lack of ATP; myosin heads (crossbridges) remain attached to actin, thus preventing relaxation.

RNA: Single-stranded nucleic acid that contains ribose, phosphate, and the nitrogenous bases G, C, A, and U; carries out DNA instructions for protein synthesis; three types are messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). Also called ribonucleic acid.

RNA polymerase: Enzyme that catalyzes addition of nucleotides to the 3′ end of a growing strand of RNA during transcription.

Rod: One of two types of photoreceptors in the retina of the eye; specialized for vision in dim light.

Root canal: A narrow extension of the pulp cavity lying within the root of a tooth.

Root of penis: Attached portion of penis that consists of the bulb and crura.

Rostral: Toward the head or nasal region, which may mean superior (for areas of the spinal cord) or anterior (for brain areas).

Rotation: Turning movement of a bone around its own long axis.

Rough endoplasmic reticulum (rER): Flattened membranous sacs that are continuous with the outer nuclear membrane; contains attached ribosomes, synthesizes proteins and transports them to other sites in the cell; attaches carbohydrates to glycoproteins; synthesizes phospholipids.

Round ligament: A band of fibrous connective tissue enclosed between the folds of the broad ligament of the uterus, emerging from the uterus just inferior to the uterine tube, extending laterally along the pelvic wall and through the deep inguinal ring to end in the labia majora.

Round window: A small, membrane-covered opening that acts as a pressure relief valve for the increased fluid pressure in the scala tympani as it bulges into the tympanic cavity.

Ruffini corpuscle: A sensory receptor embedded deeply in the dermis and deeper tissues that detects stretching of skin. Also called a type II cutaneous mechanoreceptor.

Rugae: Large folds in the mucosa of an empty hollow organ, such as the stomach and vagina.

Rule of ABCD for skin cancer: Carcinoma may become fatal if any of the following conditions exist; A: Asymmetry; the two sides of the pigmented area do not match; B: Border is irregular and exhibits indentations; C: Color (pigmented area) is black, brown, tan, and sometimes red or blue; D: Diameter is larger than 6 mm (size of a pencil eraser).

Rule of Nines for Burns: Method of computing the severity of burns by dividing the body into a number of areas, each accounting for 9 % of the total area. Burns are considered critical if over 25% of the body has second-degree burns, or over 10% of the body has third-degree burns, or there are third-degree burns on the face, hands, or feet.

S (synthetic) phase: The part of the interphase period of the cell life cycle in which DNA replicates itself, ensuring that the two future cells will receive identical copies of genetic material.

Saccule: The inferior and smaller of the two chambers in the membranous labyrinth inside the vestibule of the internal ear containing a receptor organ for static equilibrium.

Sacral plexus: A network formed by the ventral branches of spinal nerves L4 through S3.

Sacral promontory: The superior surface of the body of the first sacral vertebra that projects anteriorly into the pelvic cavity; a line from the sacral promontory to the superior border of the pubic symphysis divides the abdominal and pelvic cavities.

Saddle joint: A biaxial synovial joint in which double motion is allowed by the opposition of two surfaces, each of which is concave in one direction and convex in the other.

Sagittal plane: A plane that divides the body or organs into left and right portions. Such a plane may be midsagittal (median), in which the divisions are equal, or parasagittal, in which the divisions are unequal.

Sagittal suture: Line of junction of the two parietal bones.

Saliva: A clear, alkaline, somewhat viscous secretion produced mostly by the three pairs of salivary glands; contains various salts, mucin, lysozyme, salivary amylase, and lingual lipase (produced by glands in the tongue).

Salivary amylase: An enzyme in saliva that initiates the chemical breakdown of starch.

Salivary gland: One of three pairs of glands that lie external to the mouth and pour their secretory product (saliva) into ducts that empty into the oral cavity; the parotid, submandibular, and sublingual glands.

Salpingectomy: Removal of a uterine tube (fallopian tube).

Salt: A compound produced by the reaction of an acid with a base; when dissolved in water, it dissociates into ions and the resulting solution will conduct electricity.

Saltatory conduction: Transmission of an action potential along a myelinated fiber, in which the nerve impulse appears to leap from node to node of Ranvier.

Sarcolemma: The cell membrane of a muscle fiber (cell), especially of a skeletal muscle fiber.

Sarcomere: The functional contractile unit of myofibrils in a striated muscle fiber (cell), which extends from one Z disc to the next Z disc.

Sarcoplasm: The cytoplasm of a muscle fiber (cell).

Sarcoplasmic reticulum (SR): Elaborate system of smooth endoplasmic reticulum in a muscle cell; consists of a network of saccules and tubes surrounding myofibrils of a muscle fiber (cell), functions to reabsorb calcium ions during relaxation and to release them to cause contraction.

Sartorius: Tailor’s muscle; longest muscle in the body; runs obliquely across anterior thigh, from hip to knee; flex, abduct and rotate thigh. O: Ilium. I: Proximal tibia.

Satellite cell: A type of PNS supporting cell that surrounds a neuron cell body in a ganglion; provides structural support and regulates the exchange of material between the neuron cell body and interstitial fluid.

Saturated fat: A fat whose fatty acid tails are linear with only C-C single bonds, and is a solid at room temperature; prevalent in animal fat.

Scala tympani: The inferior membranous tube filled with perilymph that leads from the apex of the cochlea to the round window.

Scala vestibuli: The superior membranous tube filled with perilymph that leads from the oval window to the apex of the cochlea.

Scapula: Shoulder blade in posterior thorax; forms part of the shoulder joint; articulates with humerus and clavicle. Markings: Glenoid cavity articulates with head of the humerus to form the ball-and-socket shoulder joint. Acromion articulates with acromial end of the clavicle to form part of the shoulder joint. Coracoid process is an attachment site for the biceps brachii muscle of the arm. Spine is a prominant ridge; runs diagonally across the posterior surface of the body of the scapula. Suprascapular notch allows nerves to pass.

Schwann cell: A type of PNS supporting cell that forms a myelin sheath around a neuron axon, and is vital to regeneration of a damaged axon.

Sciatica: Inflammation and pain along the sciatic nerve; felt along the posterior aspect of the thigh extending down the inside of the leg.

Sclera: The white of the eye; superficial tunic composed of white fibrous connective tissue.

Scleral venous sinus: A sinus located at the junction of the sclera and cornea, where aqueous humor drains from the anterior chamber of the eyeball into the blood. Also called canal of Schlemm.

Sclerosis: A hardening with loss of elasticity of tissues.

Scoliosis: An abnormal lateral curvature from the normal vertical line of the backbone.

Scrotum: A skin-covered, external pouch that contains the testes and their accessory structures.

Sebaceous glands: Exocrine glands in the dermis that usually open into hair follicles, and secrete oily sebum by a holocrine mechanism.

Sebum: Oily secretion of sebaceous glands.

Secondary oocyte: An oocyte in which the first meiotic division is completed, but the second meiotic division usually stops short of completion unless fertilization occurs.

Secondary sex characteristic: A characteristic of the male or female body that develops at puberty under the influence of sex hormones but is not directly involved in sexual reproduction; examples are distribution of body hair, voice pitch, body shape, and muscle development.

Second-degree burn: Partial-thickness burn that damages the epidermis and upper region of the dermis, usually forming blisters.

Second messenger: Intracellular molecule generated by the binding of a chemical (hormone or neurotransmitter) to a plasma membrane receptor; mediates intracellular responses to the chemical messenger.

Secondary sex characteristics: Anatomic features of the male or female body that develops at puberty under the influence of sex hormones, but is not directly involved in sexual reproduction; examples are body hair distribution, voice pitch, pattern of bone growth, muscle development and body shape, etc.

Secretin: Hormone secreted by enteroendocrine cells in the duodenum that stimulates the secretion of pancreatic juice rich in bicarbonate ions, and stimulates the liver to increases bile output.

Secretion: (1) The passage of material formed by a cell to its exterior. (2) cell product that is transported to the exterior of a cell.

Secretory vesicles (granules): Vesicles containing proteins that migrate to the plasma membrane of a cell and discharge their contents from the cell by exocytosis.

Section: A cut through the body (or an organ) that is made along a particular plane; a thin slice of tissue prepared for microscopic study.

Segmentation: Localized, mixing contractions that occur in the intestine, which mix chyme with the digestive juices.

Segregation: During meiosis, the distribution of the members of the allele pair to different gametes.

Selective permeability: The property of a material that permits the passage of certain substances but restricts the passage of others.

Selectively permeable membrane: A membrane that allows certain substances to pass while restricting the movement of others. Also called semi-permeable membrane, or differentially permeable membrane.

Semen: A fluid discharged at ejaculation by a male that consists of a mixture of sperm and the secretions of the seminiferous tubules, seminal vesicles, prostate, and bulbourethral (Cowper’s) glands.

Semicircular canals: Three semicircular channels in the bony labyrinth of the inner ear for the

sense of dynamic equilibrium.

Semicircular ducts: The membranous semicircular canals filled with endolymph and floating in the perilymph of the bony semicircular canals; they contain cristae that are concerned with dynamic equilibrium.

Semilunar valves: The two valves that prevent blood return back to the ventricles after systole (contraction); they are rigid and remain closed most of the time, and consist of three fibrous semilunar cusps; they include the aortic valve between the left ventricle and the ascending aorta (also called left SL valve), and the pulmonary valve between the right ventricle and the pulmonary trunk (also called right SL valve).

Seminal vesicles: Paired accessory reproductive glands in the male, lying posterior and inferior to the urinary bladder and anterior to the rectum, that secrete a viscous alkaline fluid to neutralize acid, and contains vitamin C and fructose for ATP production by sperm, a coagulating enzyme to clot the semen after ejaculation, and prostaglandins for sperm motility and viability and to stimulate uterine contractions.

Seminiferous tubule: A tightly coiled duct, located in the testis, where sperm are produced.

Sensation: A state of awareness of external or internal conditions of the body.

Sense organs: Localized collections of many types of cells working together to accomplish a specific receptive process.

Sensory areas: Functional areas of the cerebral cortex that provide for conscious awareness of sensation.

Sensory neurons: Neurons that carry sensory information from cranial and spinal nerves into the brain and spinal cord, or from a lower to a higher level in the spinal cord and brain. Also called afferent neurons.

Sensory receptor: Dendritic end organs, or parts of other cell types, specialized to respond to a stimulus.

Sepsis: The presence of pathogenic microorganisms or their toxins in the tissues.

Septal defect: An opening in the atrial septum (atrial septal defect) because the foramen ovale fails to close, or the ventricular septum (ventricular septal defect) due to incomplete development of the ventricular septum.

Septicemia: Systemic disease associated with the presence and persistence of pathogenic microorganisms or their toxins in the blood. Also called septemia, or blood poisoning.

Septum: A wall dividing two cavities.

Septum pellucidum: A thin plate of tissue in the brain that is stretched like a flat, vertical sheet in the median plane, which forms a partition between the left and right frontal horns of the lateral ventricles.

Serous membrane: (1) A membrane that lines a body cavity that does not open to the exterior. (2) The external layer of an organ formed by a serous membrane. (3) The membrane that lines the pulmonary, pericardial, and peritoneal cavities. Also called a serosa.

Serous fluid: Clear; watery fluid secreted by cells of a serous membrane.

Serous pericardium: Deep layer of the heart that contains two layers separated by a pericardial cavity, which contains fluid that decreases friction; the parietal layer lines the internal surface of the fibrous pericardium, and the visceral layer ( epicardium ) covers the external surface of the heart.

Serratus anterior: Boxers muscle; superficial, lateral chest muscle; abduct and rotate scapula; aid horizontal arm movements (as in punching). O: Ribs 1-9. I: Scapula.

Sertoli cell: A supporting cell in the seminiferous tubules that secretes fluid for supplying nutrients to sperm and the hormone inhibin, removes excess cytoplasm from spermatogenic cells, and mediates the effects of FSH and testosterone on spermatogenesis. Also called sustentacular cell.

Serum: The clear fluid portion of blood obtained after coagulation and centrifugation, to remove the fibrin clot and blood cells.

Sesamoid bones: Small bones usually found in tendons; largest is the patella (kneecap).

Severe combined immunodeficiency syndromes (SCIDs): Congenital conditions resulting in little or no protection against disease causing organisms of any type.

Sex chromosomes: The chromosomes, X and Y, that determine genetic sex (XX = female; XY = male); the 23rd pair of chromosomes.

Sex-linked inheritance: Inherited traits determined by genes on the sex chromosomes, e.g., X-linked genes are passed from mother to son, Y-linked genes are passed from father to son.

Sexual intercourse: The insertion of the erect penis of a male into the vagina of a female. Also called coitus.

Sexually transmitted disease (STD): Infectious disease spread through sexual contact.

Sheath of Schwann: See Neurolemma.

Shock: Failure of the cardiovascular system to deliver adequate amounts of oxygen and nutrients to meet the metabolic needs of the body due to inadequate cardiac output. It is characterized by hypotension; clammy, cool, and pale skin; sweating; reduced urine formation; altered mental state; acidosis; tachycardia; weak, rapid pulse; and thirst. Types include hypovolemic, cardiogenic, vascular, and obstructive.

Shoulder joint: A synovial joint where the humerus articulates with the scapula.

Sigmoid colon: The S-shaped part of the large intestine that begins at the level of the left iliac crest, projects medially, and terminates at the rectum at about the level of the third sacral vertebra.

Sign: Any objective evidence of disease that can be observed or measured, such as a lesion, swelling, or fever.

Signal sequence: A short peptide segment present in a protein being synthesized that causes the associated ribosome to attach to the membrane of rough ER.

Simple columnar epithelium: Tissue with a single layer of tall cells that have round to oval nuclei; some tissue types contain ciliated cells; most tissue types contain mucus-secreting goblet cells (unicellular glands). Functions in secretion or absorption. Nonciliated type is located in the lining of the gastrointestinal tract (stomach to rectum), and ducts of some glands. Ciliated type is located in the lining of the small bronchi of the lungs, uterine tubes, and parts of the uterus.

Simple cuboidal epithelium: Tissue with a single layer of cubelike cells that have large spherical central nuclei. Functions in secretion or absorption. Located in kidney tubules, small ducts of some glands, and ovary surface.

Simple diffusion: The unassisted transport across a plasma membrane of substances that are lipid soluble or very small.

Simple squamous epithelium: Tissue with a single layer of flattened cells that have disc-shaped central nuclei and sparse cytoplasm. Functions in rapid diffusion or filtration; secretes serous fluid in serosa. Located in lung alveoli; kidney glomeruli; lining of the heart and blood vessels; serous membranes.

Sinoatrial node: Specialized myocardial cells in the wall of the right atrium that normally acts as the “pacemaker” of the cardiac conduction system. Also called the SA node.

Sinus: (1) Mucous membrane-lined, air-filled cavity in certain cranial bones. (2) Dilated channel for the passage of blood or lymph. (3) Any cavity having a narrow opening.

Sinusoid: A large, thin-walled, and leaky type of capillary, having large intercellular clefts that may allow proteins and blood cells to pass from a tissue into the bloodstream; present in the liver, spleen, anterior pituitary, parathyroid glands, and red bone marrow.

Skeletal cartilage: Composes most of the skeleton in early fetal life; articular cartilage, nasal cartilage in the adult skeleton.

Skeletal muscle tissue: Tissue with long cylindrical cells that are multinucleate and striated. Functions in voluntary movement, posture, protection, and heat production. Located in skeletal muscles.

Skeletal system: System of protection and support composed primarily of bone and cartilage.

Skene’s gland: See Paraurethral gland.

Skin: The external covering of the body that consists of a superficial, thinner epidermis (epithelial tissue) and a deep, thicker dermis (connective tissue) that is anchored to the subcutaneous layer.

Skull: The skeleton of the head consisting of the cranial and facial bones. Also called the cranium.

Sleep: A state of partial unconsciousness from which a person can be aroused; associated with a low level of activity in the reticular activating system.

Small intestine: A long tube of the gastrointestinal tract where digestion is completed and virtually all absorption occurs; it begins at the pyloric sphincter of the stomach, coils through the central and inferior part of the abdominal cavity, and ends at the ileocecal valve where it joins the large intestine; divided into three segments: duodenum, jejunum, and ileum.

Smooth endoplasmic reticulum (sER): Membranous tubules continuous with rough endoplasmic reticulum; metabolism of lipids, steroids, carbohydrates, and drugs.

Smooth muscle tissue: Tissue with sheets of spindle-shaped cells that are uninucleate with no striations. Functions in constriction, or propulsion of material through hollow organs under involuntary control. Located mostly in the walls of hollow organs.

Sodium-potassium (Na-K) pump: A primary active transport system located in the plasma membrane that simultaneously that transports sodium ions out of the cell and potassium ions into the cell at the expense of cellular ATP. Also called sodium-potassium ATPase.

Soft palate: The posterior portion of the roof of the mouth, extending from the palatine bones to the uvula; it is a muscular partition lined with mucous membrane; during swallowing, the soft palate and uvula move superiorly to close off the nasopharynx and prevent food from entering the nasal cavity.

Soleus: Deep calf muscle; plantar flex foot. O: Proximal tibia and fibula. I: Calcaneus.

Sol-gel transformation: Reversible change of a colloid from a fluid (sol) to a more solid (gel) state:

Solute: A substance that is dissolved in a solution.

Solute pump: Protein carrier that mediates active transport of solutes uphill against their concentration gradients.

Solution: A homogeneous mixture of one or more substances (solutes) dispersed molecularly in a dissolving medium (solvent).

Solvent: A dissolving medium that holds another substance in solution.

Somatic cell division: Type of cell division in which a single starting cell duplicates itself to produce two identical cells; consists of mitosis and cytokinesis.

Somatic nervous system (SNS): The portion of the peripheral nervous system consisting of somatic sensory (afferent) neurons and somatic motor (efferent) neurons; it provides the motor innervation of skeletal muscles. Also called the voluntary nervous system.

Somatic reflexes: Reflexes that activate skeletal muscle.

Somatosensory system: That part of the sensory system dealing with reception in the body wall and limbs; receives inputs from exteroceptors, proprioceptors, and interoceptors.

Somite: A mesodermal segment in a developing embryo that is distinguished into a myotome (which forms most of the skeletal muscles), dermatome (which forms connective tissues), and sclerotome (which forms the vertebrae).

Spasm: A sudden, involuntary contraction of large groups of muscles.

Spasticity: Hypertonia characterized by increased muscle tone, increased tendon reflexes, and pathological reflexes (Babinski sign).

Spatial discrimination: The ability of neurons to identify the site or pattern of stimulation.

Special senses: The senses of taste, smell, vision, hearing, and equilibrium.

Specialization: The diversification of unspecialized cells as they develop different characteristics and become specialized in structure and function. Also called differentiation.

Specific gravity: Term used to compare the weight of a substance to the weight of an equal volume of distilled water.

Specificity: (1) The quality or state of being specific, of having a fixed relation to a single cause or to a definite result; manifested in the relation of a disease to its pathogenic microorganism, of a reaction to a certain chemical union, or of an antibody to its antigen, or the reverse. (2) In clinical pathology and medical screening, the conditional probability that a person not having a disease will be correctly identified by a clinical test, i.e., true negative results as a proportion of the total of true-negative and false-positive results.

Sperm: Male gamete. Also called spermatozoa.

Spermatic cord: A supporting structure of the male reproductive system, extending from a testis to the deep inguinal ring, that includes the vas (ductus) deferens, arteries, veins, lymphatic vessels, nerves, cremaster muscle, and connective tissue.

Spermatogenesis: The formation and development of sperm in the seminiferous tubules of the testes.

Spermicide: An agent destructive to spermatozoa. Also called a spermatocide.

Spermiogenesis: The maturation of spermatids into sperm.

Sphenoid bone: Keystone bone of the cranium; deep, bat-shaped bone that forms part of the orbits, and contains sphenoidal sinuses, main parts are the body, greater wings, lesser wings, and pterygoid processes. Markings: Sella turcica contains hypophyseal fossa that houses the pituitary glandOptic canals allow passage of the optic nerve (cranial nerve II) and the ophthalmic arteries. Superior orbital fissures allow passage of cranial nerves III, IV, VI, part of V, and ophthalmic vein. Foramen rotundum allows passage of the maxillary division of cranial nerve V. Foraman ovale allows passage of the mandibular division of cranial nerve V. Foramen spinosum allows passage of the middle meningeal artery.

Sphenoidal fontanels: Paired irregularly shaped membranous intervals in the skull of a fetus and infant; located on the anterolateral aspect of the fetal cranium, bounded anteriorly by the frontal bone, superiorly by the parietal bone, posteriorly by the squamous portion of the temporal bone, and inferiorly by the greater wing of the sphenoid bone. Also called the anterolateral fontanel.

Sphincter: A circular muscle that constricts an opening.

Sphincter of Oddi: See Sphincter of the hepatopancreatic ampulla.

Sphincter of the hepatopancreatic ampulla: A circular muscle at the opening of the common bile and main pancreatic ducts in the duodenum. Also called the sphincter of Oddi.

Spina bifida: Embryologic failure of fusion of one or more vertebral arches.

Spinal cord: A mass of nerve tissue located in the vertebral canal from which 31 pairs of spinal nerves originate, and provides a conduction pathway to and from the brain.

Spinal nerves: The 31 nerve pairs that arise from the spinal cord.

Spinal shock: A period from several days to several weeks following transection of the spinal cord that is characterized by the abolition of all reflex activity.

Spindle apparatus: Dynamic array of microtubules that moves chromosomes during mitosis or meiosis.

Spine on a bone: Sharp, slender, often pointed projection on a bone.

Spinothalamic tracts: Sensory (ascending) tracts that convey information up the spinal cord to the thalamus for sensations of pain, temperature, crude touch, and deep pressure.

Spinous process: (1) A sharp ridge running diagonally across the posterior surface of the scapula. (2) A sharp or thornlike process or projection; also called a spine.

Spiral fracture: Ragged break occurs when excessive twisting forces are applied to a bone.

Spiral organ: The organ of hearing, consisting of supporting cells and hair cells that rest on the basilar membrane and extend into the endolymph of the cochlear duct. Also called the organ of Corti.

Splanchnic: Pertaining to the viscera.

Splanchnic circulation: The blood vessels serving the digestive system.

Spleen: Largest lymphoid organ; provides for blood cleansing, immune surveillance and response, and lymphocyte proliferation.

Splenius capitis and cervicus: Posterior neck muscles; one rotates head laterally, both extend head. O: Vertebrae C7-T6. I: Occipital bone and mastoid process of temporal bone.

Spongy bone: Lightweight bone tissue that makes up the interior of bones; consists of an irregular latticework of trabeculae containing many spaces filled with red bone marrow. Also called cancellous bone.

Sprain: Forcible wrenching or twisting of a joint with partial rupture or other injury to its attachments without dislocation.

Sputum: Matter, such as mucus, that is ejected through the mouth from the lungs, bronchi, and trachea. Also called expectoration.

Squamous: Flat or scalelike.

Squamous cell carcinoma: A type of skin cancer where keratinocytes of the stratum spinosum grow rapidly and may metastasize if not removed.

Squamous suture: Line of junction of the parietal with the temporal bone.

Starch: A polysaccharide of glucose monomers; the main storage carbohydrate in plants.

Starvation: The loss of energy stores in the form of glycogen, triglycerides, and proteins due to inadequate intake of nutrients or inability to digest, absorb, or metabolize ingested nutrients.

Static equilibrium: The maintenance of posture in response to changes in the orientation of the body, mainly the head, relative to the ground.

Stellate reticuloendothelial cell: Phagocytic cell bordering a sinusoid of the liver. Also called a Kupffer cell.

Stem cell: An unspecialized cell that has the ability to divide for indefinite periods and give rise to a specialized cell.

Stenosis: An abnormal narrowing of the lumen of a duct, canal, or hollow organ. Also called stricture, or coarctation.

Stereocilia: Groups of extremely long, slender, nonmotile microvilli projecting from epithelial cells lining the epididymis.

Sterile: (1) Free from any living microorganisms. (2) Unable to conceive or produce offspring.

Sterilization: (1) Elimination of all living microorganisms. (2) Any procedure that renders an individual incapable of reproduction (for example, castration, vasectomy, hysterectomy, or oophorectomy).

Sternocleidomastoid: Paired, anterior neck muscles; one rotates head laterally; both flex neck. O: Sternum and clavicle. I: Mastoid process of temporal bone.

Sternum: Breastbone; flat narrow bone formed by fusion of the manubrium, body, and xiphoid process; forms middle part of anterior wall of the thorax; articulates with the clavicle and cartilages of the first seven ribs. Parts and Markings: Manubrium is flat handle-like bone fused with the body; forms upper segment of the sternum. Body is the middle and largest portion of the sternum. Xiphoid process is a sword-shaped hyaline cartilage at lower end of the sternum; ossifies in adulthood. Clavicular notches are hollows on the sides of upper surfaces of the manubrium; articulates with the clavicles. Jugular notch is a central indentation in superior margin of the manubrium. Sternal angle is a junction of manubrium and body of the sternum; at the level of the second costal cartilage, aortic arch, bifurcation of trachea, and T4/T5 intervertebral disc. Xiphisternal joint is the cartilaginous union between the xiphoid process and the body of the sternum.

Steroid: Lipid with a rigid backbone of four fused carbon rings, such as cholesterol, testosterone, and estrogen.

Stimulus: (1) An excitant or irritant. (2) A change in the environment that evokes a response.

Stomach: The J-shaped enlargement of the gastrointestinal tract where chemical breakdown of proteins begins and food is converted into chyme.

Straight tubule: A duct in a testis leading from a convoluted seminiferous tubule to the rete testis.

Stratified columnar epithelium: Tissue with several layers of irregularly shaped cells; the apical layer has columnar cells. Functions in protection and secretion. Located in the lining of part of the urethra, and large ducts of some glands.

Stratified cuboidal epithelium: Tissue with two or more layers of cells; the apical layer has cube-shaped cells. Functions in protection, secretion or absorption. Located in ducts of adult sweat glands, and part of male urethra.

Stratified squamous epithelium: Tissue with several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous). Functions in protection from abrasion. Nonkeratinized type is located in the lining of the oral cavity, pharynx, esophagus, and vagina. Keratinized type is located in the skin epidermis.

Stratum: A layer.

Stratum basale: Deepest layer of epidermis, composed of dividing stem cells.

Stratum basalis: The uterine layer of the endometrium next to the myometrium that is maintained during menstruation and gestation and produces a new stratum functionalis following menstruation or parturition.

Stratum corneum: Outer layer of epidermis, consisting of several layers of dead, flat, keratinized cells.

Stratum functionalis: The layer of the endometrium next to the uterine cavity that is shed during menstruation and that forms the maternal portion of the placenta during gestation.

Stratum granulosum: A middle layer of epidermis, consisting of several layers of flattened cells with granules.

Stratum spinosum: A middle layer of epidermis, composed of keratinocytes.

Stressor: Any stimulus that directly or indirectly causes the hypothalamus to initiate stress reducing responses, such as the fight-or-flight response.

Stretch receptor: Receptor in the walls of blood vessels, airways, or organs that monitors the amount of stretching. Also termed baroreceptor.

Stricture: An abnormal narrowing of the lumen of a duct, canal, or hollow organ. Also called stenosis, or coarctation.

Stroke: See Cerebrovascular accident.

Stroke volume (SV): Amount of blood pumped out of a ventricle during one contraction; SV is equal to end diastolic volume (EDV) minus end systolic volume (ESV), according to the formula: SV = EDV ─ESV.

Stroma: The tissue that forms the ground substance, foundation, or framework of an organ, as opposed to its functional parts (parenchyma).

Structural classification of joints: Based on the material binding the bones together, and whether or not a joint cavity is present; all joints are either fibrous, cartilaginous, or synovial joints.

Structural proteins: Consist of extended, strandlike polypeptide chains forming a strong, ropelike structure that is linear, insoluble in water, and very stable; e.g., collagen. Also called fibrous proteins.

Subarachnoid space: A space between the arachnoid mater and the pia mater that surrounds the brain and spinal cord and through which cerebrospinal fluid circulates.

Subcutaneous: Beneath the skin. Also called hypodermic.

Subcutaneous layer: A continuous sheet of areolar connective tissue and adipose tissue between the dermis of the skin and the deep fascia of the muscles. Also called the superficial fascia.

Subdural space: A space between the dura mater and the arachnoid mater of the brain and spinal cord that contains a small amount of fluid.

Sublingual gland: One of a pair of salivary glands situated in the floor of the mouth deep to the mucous membrane and to the side of the lingual frenulum, with a duct (Rivinus) that opens into the floor of the mouth.

Submandibular gland: One of a pair of salivary glands found inferior to the base of the tongue deep to the mucous membrane in the posterior part of the floor of the mouth, posterior to the sublingual glands, with a duct (Wharton’s) situated to the side of the lingual frenulum. Also called the submaxillary gland.

Submucosa: A layer of connective tissue located deep to a mucous membrane, as in the gastrointestinal tract or the urinary bladder; the submucosa connects the mucosa to the muscularis layer.

Submucosal plexus: A network of autonomic nerve fibers located in the superficial part of the submucous layer of the small intestine. Also called the plexus of Meissner.

Subscapularis: Rotator cuff muscle of scapula; tendon reinforces the shoulder rotator cuff; stabilizes shoulder joint; rotates arm medially. O: Subscapular fossa of scapula. I: Lesser tubercle of humerus.

Substrate: A molecule upon which an enzyme acts.

Subthalamus: Part of the diencephalon inferior to the thalamus; the substantia nigra and red nucleus extend from the midbrain into the subthalamus.

Sucrose: A disaccharide composed of glucose and fructose joined by a glycosidic bond.

Sudoriferous glands: Exocrine sweat glands in the dermis that secrete sweat by a merocrine mechanism.

Sulcus: A groove or depression between parts, especially between the convolutions of the brain. Plural is sulci.

Summation: Accumulation of effects, especially those of muscular, sensory, or mental stimuli.

Superficial: Nearer the surface of the body or an organ.

Superficial fascia: A continuous sheet of fibrous connective tissue between the dermis of the skin and the deep fascia of the muscles. Also called subcutaneous layer or hypodermis.

Superficial inguinal ring: A triangular opening in the aponeurosis of the external oblique muscle that represents the termination of the inguinal canal.

Superior: Nearer the head or upper part of a structure; equivalent to cranial or cephalic in bipeds.

Superior vena cava (SVC): Large vein that collects blood from parts of the body superior to the heart and returns it to the right atrium.

Supination: Rotating movement of the forearm laterally so that the palm faces anteriorly or superiorly.

Suppressor T cells: Regulatory T lymphocytes that suppress the immune response.

Supraspinatus: Rotator cuff muscle of scapula; tendon reinforces the shoulder rotator cuff; stabilizes shoulder joint; abducts arm. O: Supraspinous fossa of scapula. I: Greater tubercle of humerus.

Surface anatomy: The study of the structures that can be identified from the outside of the body.

Surfactant: Secretion containing a mixture of phospholipids and lipoproteins, produced by type II alveolar (septal) cells in the lungs, that reduces the surface tension of water molecules, thus preventing the collapse of the alveoli after each expiration.

Suspension: Heterogeneous mixtures with large, often visible solutes that tend to settle out.

Suspensory ligament: (1) Ligament that attaches the lens to the ciliary body; allows the lens to change shape. (2) A fold of peritoneum extending laterally from the surface of the ovary to the pelvic wall.

Sutural bone: A small bone located within a suture between certain cranial bones. Also called Wormian bone.

Suture: A fibrous joint between two bones of the skull in which the bone edges interlock, and the junction is filled by very short fibers in a fibrous membrane that is continuous with the periosteum.

Sweat gland: Epidermal gland that produces sweat. Also called sudoriferous gland.

Sweat glands, Apocrine: Sudoriferous glands that open into hair follicles, and develop during puberty in the axilla and pubis; they secrete a viscous milky sweat that supports bacteria growth, leading to body odor.

Sweat glands, Eccrine: Sudoriferous glands that open into pores at the surface of the skin, and found on almost all parts of the body; they secrete a watery sweat that cools the body.

Sympathetic division: The division of the autonomic nervous system that activates the body to cope with some stressors (danger, excitement, etc.); the “fight or flight” response.

Sympathetic tone: State of partial vasoconstriction of the blood vessels maintained by sympathetic fibers. Also called vasomotor tone

Sympathetic trunk ganglion: A cluster of cell bodies of sympathetic postganglionic neurons lateral to the vertebral column, close to the body of a vertebra. Also called sympathetic chain or vertebral chain ganglia.

Symphysis: (1) A line of union. (2) A cartilaginous joint in which two bones are united by fibrocartilage.

Symptom: A subjective change in body function not apparent to an observer, such as pain or nausea, that indicates the presence of a disease or disorder of the body. .

Synapse: The functional junction between a neuron and a postsynaptic cell (another neuron, a muscle, gland, or sensory receptor cell).

Synapsis: The pairing of homologous chromosomes during prophase I of meiosis.

Synaptic cleft: The narrow gap at a synapse that separates the neuron axon terminal from a postsynaptic cell, across which a neurotransmitter diffuses to transmit the impulse.

Synaptic delay: Time required for an impulse to cross a synapse between two neurons.

Synaptic knob: Expanded distal end of an axon terminal that contains synaptic vesicles. Also called a synaptic bouton or synaptic end bulb.

Synaptic vesicle: Membrane-enclosed sac in a synaptic knob that stores neurotransmitters.

Synarthrosis: An immovable joint, such as a suture, gomphosis, or synchondrosis.

Synchondrosis: A cartilaginous joint in which two bones are united by hyaline cartilage.

Syndesmosis: A fibrous joint in which the opposing surfaces are relatively far apart and united by ligaments.

Synergism: A situation that occurs when two agents produce the same effects, and their combined effects are amplified.

Synergist muscle: A muscle that assists the prime mover by reducing undesired action or unnecessary movement.

Synergistic effect: A hormonal interaction in which the effects of two or more hormones acting together is greater or more extensive than the sum of each hormone acting alone.

Synostosis: A completely ossified joint; a joint in which the dense fibrous connective tissue that unites bones at a suture has been replaced by bone, resulting in a complete fusion across the suture line.

Synovial cavity: The space between the articulating bones of a synovial joint, filled with synovial fluid. Also called a joint cavity.

Synovial fluid: Fluid secreted by the synovial membrane; lubricates joint surfaces and nourishes articular cartilages.

Synovial joint: An articulation in which the opposing bony surfaces are covered with a layer of articular cartilage within a joint cavity that contains synovial fluid, is lined with synovial membrane, and is reinforced by a fibrous capsule and ligaments.

Synovial membrane: The deeper of the two layers of the articular capsule of a synovial joint, composed of areolar connective tissue that secretes synovial fluid into the synovial (joint) cavity.

Synthesis reaction: A chemical reaction in which larger; more complex molecules are formed from simpler ones. Also called a combination reaction.

System: An association of organs that have a common function.

Systemic: Affecting the whole body; generalized.

Systemic anatomy: The anatomic study of particular systems of the body, such as the skeletal, muscular, nervous, cardiovascular, or urinary systems.

Systemic circulation: The flow of oxygenated blood from the left ventricle to the aorta and through the other arteries to the capillaries of the body, and the return of deoxygenated blood through the veins to the right atrium.

Systemic lupus erythematosus (SLE): Autoimmune disease that particularly affects the kidneys, heart, lungs, and skin.

Systole: In the cardiac cycle, the phase of contraction of the heart muscle, especially of the ventricles.

Systolic blood pressure (SBP): The force exerted by blood on arterial walls during ventricular contraction; the highest blood pressure measured in the large arteries, normally about 120 torr (mm Hg) in a young adult.

T cell: Type of lymphocyte that becomes immunocompetent in the thymus; when properly stimulated by a specific antigen, it can develop into a clone of helper T cells, cytotoxic T cells, or other types of T cells, which function in cell-mediated immunity. Also called T lymphocyte.

T tubule (transverse tubule): Small, cylindrical invagination of the sarcolemma of striated muscle fibers (cells) that conduct muscle action potentials toward the center of the muscle fiber.

T wave: The deflection wave of an electrocardiogram that represents ventricular repolarization.

Tachycardia: An abnormally rapid, resting heartbeat or pulse rate, that is over 100 beats per minute.

Tactile: Pertaining to the sense of touch.

Tactile disc: A complex of an epidermal cell associated with a tactile sensory nerve ending, which functions in the sense of touch. Also called a Merkel disc.

Target cell: A cell whose activity is affected by a particular hormone.

Tarsal bones: The seven bones of the ankle. Also called the tarsus.

Tarsal gland: Sebaceous (oil) gland that opens on the edge of each eyelid. Also called a Meibomian gland.

Tarsal plate: A thin, elongated sheet of connective tissue, one in each eyelid, giving the eyelid form and support.

Tarsus: Ankle bones; seven bones of the instep; the talus articulates with the tibia and fibula to form the ankle joint; the calcaneus forms the heel. The remaining tarsals are the cuboid, navicular, lateral cuneiform, intermediate cuneiform, and medial cuneiform bones. The cuboid and cuneiform bones articulate with the metatarsal bones anteriorly.

Taste buds: Sensory receptor organs that house gustatory cells, which respond to dissolved food chemicals.

Tectorial membrane: Gel-like membrane overlying the hearing receptor cells of the organ of Corti.

Teeth: Accessory structures of digestion, composed of calcified connective tissue and embedded in bony sockets of the mandible and maxilla, that cut, shred, crush, and grind food. Also called dentes.

Telencephalon: Anterior subdivision of the primary forebrain that develops into olfactory lobes, cerebral cortex, and corporal striata. Also called the endbrain.

Telodendria: The terminal branches of an axon.

Telophase: The final stage of mitosis, where chromosomes unwind into chromatin and two nuclear envelopes form.

Temporal bones: Pair of inferolateral cranial bones that contain mastoid sinuses, and internal and middle ear cavities with ear ossicles (malleus, incus, and stapes), and has a squamous, mastoid, tympanic, and petrous regions. Markings: Zygomatic process is a bridgelike projection that forms the posterior zygomatic arch. Mastoid process is attachment site for neck muscles. Styloid process is a needlelike projection and attachment site for tongue and neck muscles and ligaments. External auditory (acoustic) meatus are canals leading to the eardrum and middle ear. Mandibular fossa articulates with mandibular condyle of mandible. Jugular foramen allows passage of the internal jugular vein and cranial nerves IX, X, and XI. Carotid canal allows passage of the internal carotid artery. Internal acoustic meatus allows passage of cranial nerves VII and VIII. Stylomastoid foramen allows passage of facial nerve.

Temporalis: Superior muscle of mastication; closes jaw. O: Temporal bone. I: Coronoid process of mandible.

Tendon: A white fibrous cord of dense regular connective tissue that attaches muscle to bone.

Tendonitis: Inflammation of tendon sheaths, typically caused by overuse.

Tendon organ: A proprioceptive receptor, sensitive to changes in muscle tension and force of contraction, found chiefly near the junctions of tendons and muscles. Also called a Golgi tendon organ.

Tendon reflex: A polysynaptic, ipsilateral reflex that protects tendons and their associated muscles from damage that might be brought about by excessive tension. The receptors involved are called tendon organs (Golgi tendon organs).

Tendon sheath: An elongated bursa that wraps completely around a tendon, and is often found where a tendon passes over a bone.

Teniae coli: The three flat bands of thickened, longitudinal smooth muscle running the length of the large intestine, except in the rectum. Singular is tenia coli.

Tensor fascia latae: Lateral hip muscle; flex and abduct thigh. O: Iliac crest. I: Tibia.

Tentorium cerebeli: A transverse shelf of dura mater that forms a partition between the occipital lobe of the cerebral hemispheres and the cerebellum and that covers the cerebellum.

Teratogen: Any agent or factor that causes physical defects in a developing embryo.

Teres major: Muscle of inferior scapula; extends arm at shoulder, adducts and medially rotates arm. O: Scapula. I: Intertubercular sulcus of humerus.

Teres minor: Rotator cuff muscle of scapula; tendon reinforces the shoulder rotator cuff; stabilizes shoulder joint; adducts and laterally rotates arm. O: Scapula. I: Greater tubercle of humerus.

Terminal ganglion: A cluster of cell bodies of parasympathetic postganglionic neurons either lying very close to the visceral effectors or located within the walls of the visceral effectors supplied by the postganglionic neurons.

Testes: The primary sex organs of the male; the gonad that produces sperm and the hormones testosterone and inhibin. Also called testicles.

Testosterone: A male sex hormone (androgen) secreted by interstitial cells (Leydig cells) of the mature testes; encourages development of male secondary sex characteristics, and stimulates the development of sperm and activity of the accessory male sex organs.

Tetanus: (1) A smooth, sustained muscle contraction resulting from high frequency stimulation. (2) An infectious disease caused by an anaerobic bacterium.

Tetralogy of Fallot: A combination of four congenital heart defects: (1) constricted pulmonary semilunar valve, (2) interventricular septal opening, (3) emergence of the aorta from both ventricles instead of from the left only, and (4) enlarged right ventricle.

Thalamus: A large, oval structure in the diencephalon of the brain; located bilaterally on either side of the third ventricle, consisting of two masses of gray matter organized into nuclei; gateway to the cerebral cortex; major sensory relay center; influences mood and movement

Thermogenesis: Heat production.

Thermoreceptor: Sensory receptor that detects changes in temperature.

Theta brain wave: A wave pattern in the encephalogram in the frequency band of 4–7 Hz; found in normal children, and in adults with mental disorders. Also called theta rhythm.

Thigh: The portion of the lower limb between the hip and the knee.

Third-degree burn: Full-thickness burn that destroys all of the epidermis and dermis, may damage deeper tissue, and usually requires skin grafting.

Third ventricle: A slitlike cavity between the right and left halves of the thalamus and between the lateral ventricles of the brain.

Thoracic cavity: Cavity superior to the diaphragm that contains two pleural cavities, the mediastinum, and the pericardial cavity.

Thoracic duct: The largest lymph vessel in the body that drains lymph from the left side of the body, the abdomen, and both lower limbs; it begins at the cisterna chyli and empties into the left brachiocephalic vein, at the junction between the internal jugular and subclavian veins. Also called the left lymphatic duct.

Thoracolumbar outflow: The axons of sympathetic preganglionic neurons, which have their cell bodies in the lateral gray columns of the thoracic segments and first two or three lumbar segments of the spinal cord.

Thorax: The chest; the portion of the body trunk above the diaphragm and below the neck.

Threshold stimulus: Weakest stimulus capable of producing a response in an irritable tissue.

Thrombectomy: Excision of a thrombus from a blood vessel.

Thrombin: Enzyme that induces clotting by converting fibrinogen to fibrin.

Thrombocyte: Platelets; cell fragments that participate in blood coagulation.

Thrombocytopenia: A reduction in the number of platelets circulating in the blood.

Thrombosis: The formation of a thrombus.

Thrombus: A stationary clot formed in an unbroken blood vessel that does not obstruct the vessel.

Thymine (T): Single-ring base (a pyrimidine) in DNA.

Thymus: An endocrine gland and primary lymphoid organ in which T cells develop immunocompetence.

Thyrocalcitonin: Hormone released by the thyroid gland that lowers blood calcium level and inhibits bone resorption; acts as an antagonist to parathyroid hormone (PTH). Also called calcitonin (CT).

Thyroid cartilage: The largest single cartilage of the larynx, consisting of two fused plates that form the anterior wall of the larynx.

Thyroid follicle: Spherical sac that forms the parenchyma of the thyroid gland and consists of follicular cells that produce thyroxine (T4) and triiodothyronine (T3).

Thyroid gland: An endocrine gland with right and left lateral lobes on either side of the trachea connected by an isthmus; located anterior to the trachea just inferior to the cricoid cartilage; secretes thyroid hormones (TH), and calcitonin (CT).

Thyroid hormones (TH): The hormones secreted by the thyroid gland follicular cells, contains thyroxine (T4) and triiodothyronine (T3); regulates the metabolic rate.

Thyroid-stimulating hormone (TSH): Adenohypophyseal hormone that stimulates the growth of the thyroid gland and secretion of the thyroid hormones. Also called thyrotropin.

Thyroxine (T4): Iodine containing hormone secreted by the thyroid gland that regulates metabolism, growth and development, and the activity of the nervous system.

Tibia: Shinbone; medial leg bone; large weight-bearing bone. Markings: Condyles (Lateral and Medial) articulate with corresponding condyles of the femur. Tibial tuberosity is anterior oval elevation; attachment site of patellar ligament. Anterior border is the shin; sharp anterior ridge; also called anterior crest, or tibial crest. Medial malleolus forms the medial bulge of the ankle.

Tibialis anterior: Large, anterior leg muscle; dorsiflex and invert foot. O: Proximal tibia. I: Tarsal & metatarsal 1.

Tic: Spasmodic, involuntary twitching of muscles that are normally under voluntary control.

Tight junction: Structure that fuses adjacent cells and produces a water tight junction between cells.

Tissue: A group of similar cells and their intercellular substance joined together to perform a specific function; the four primary tissue types of the body are epithelial, connective, muscle, and nervous tissue.

Tissue perfusion: Blood flow through body tissues or organs.

Tissue rejection: Phenomenon by which the body recognizes the protein (HLA antigens) in transplanted tissues or organs as foreign and produces antibodies against them.

Tongue: A large skeletal muscle covered by a mucous membrane located on the floor of the oral cavity.

Tonicity: A measure of the ability of a solution to cause a change in cell shape (or tone) by promoting osmotic flows of water.

Tonsils: Aggregations of large lymphatic nodules embedded in the mucous membrane of the throat.

Topical: Applied to the surface rather than ingested or injected.

Torn cartilage: A tearing of an articular disc (meniscus) in the knee.

Toxin: Normal metabolic product of a species that can hurt or kill a different species.

Trabecula: (1) Fibrous cord of connective tissue extending from the capsule into the interior of an organ. (2) Irregular latticework of thin plates of spongy bone tissue. Plural is trabeculae.

Trabeculae carneae: Ridges and folds of the myocardium in the ventricles.

Trachea: Windpipe; cartilage reinforced tube extending from larynx to bronchi.

Tracts: Bundles of myelinated nerve fibers in the CNS.

Transamination: The transfer of the amino group from an amino acid to α-keto glutaric acid, which forms a new keto acid and glutamic acid.

Transcription: First stage of protein synthesis, where a complementary strand of mRNA is assembled on exposed bases of an unwound strand of a DNA double helix.

Transduction: The conversion of the energy of a stimulus into an electrical event.

Transepithelial transport: Movement of substances through, rather than between, adjacent epithelial cells connected by tight junctions, such as absorption of nutrients in the small intestine.

Transfer RNA (tRNA): Short chain RNA molecules that transfer amino acids to the ribosome.

Transfusion reaction: Occurs when the donor’s red blood cells are attacked by the recipient’s plasma agglutinins.

Transitional epithelium: Tissue with several cell layers that change shape when stretched basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Functions in stretching and distension of urinary organs. Located in the lining of the urinary bladder, ureters, and part of the urethra.

Translation: Second stage of protein synthesis in which the information carried by mRNA is decoded and used to assemble polypeptides.

Transplantation: The transfer of living cells, tissues, or organs from a donor to a recipient or from one part of the body to another in order to restore a lost function.

Transport protein: Membrane-bound protein used in transport of substances across the plasma membrane.

Transverse colon: The portion of the large intestine extending across the abdomen from the right colic (hepatic) flexure to the left colic (splenic) flexure.

Transverse fissure: The deep cleft that separates the cerebrum from the cerebellum.

Transverse plane: A plane that divides the body or organs into superior and inferior portions. Also called a cross-sectional or horizontal plane.

Transverse tubule (T tubule): Small, cylindrical invagination of the sarcolemma of striated muscle fibers (cells) that conduct muscle action potentials toward the center of the muscle fiber.

Transversus abdominis: Deepest of the lateral trunk muscles; compress abdomen. O: Iliac crest and ribs 7-12. I: Pubis and linea alba.

Trapezius: Large, superficial, kite-shaped, upper back muscle ; adduct and elevate scapula (as in shrugging shoulders), hyperextend head. O: Occipital bone and thoracic vertebrae. I: Clavicle and scapula.

Tremor: Rhythmic, involuntary, purposeless contraction of opposing muscle groups.

Triacylglycerol: Lipid with glycerol bound to three fatty acids; the body’s most concentrated source of energy fuel. Also called a triglyceride or neutral fat.

Triad: A complex of three units in a muscle fiber composed of a transverse tubule and the sarcoplasmic reticulum terminal cisterns on both sides of it.

Triceps brachii: Posterior arm muscle; extend forearm. O: Scapula and proximal humerus. I: Olecranon process of ulna.

Tricuspid valve: The heart closing the orifice between the right atrium and right ventricle of the heart; it consists of three fibrous cusps. Also called right atrioventricular valve, or right AV valve

Triglyceride: Lipid with glycerol bound to three fatty acids; the body’s most concentrated source of energy fuel. Also called a triacylglycerol or neutral fat.

Trigone: A triangular region at the base of the urinary bladder, where the two ureters enter and the urethra exits the bladder.

Triiodothyronine (T3): Iodine containing hormone secreted by the thyroid gland that regulates metabolism, growth and development, and the activity of the nervous system. It has several times the biological activity of thyroxine (T4) and is the “tissue-active” form of thyroid hormones (TH).

Tripeptide: A combination of three amino acids united by means of peptide bonds.

Trochanter: Very large, blunt, irregularly shaped process on the femur bone.

Trophoblast: A layer of extraembryonic ectodermal tissue covering the blastocyst that attaches the blastocyst to the endometrium of the uterus and supplies nutrition to the embryo; it forms the chorion and amnion, and it contributes to the formation of the placenta.

Tropic hormone: A hormone that regulates the function of another endocrine organ.

True ribs: Vertebrosternal ribs 1-7 that articulate directly with the sternum.

Trunk: The part of the body to which the upper and lower limbs are attached.

Trypsin: A protein digesting enzyme found in the small intestine, formed from trypsinogen that is secreted by the pancreas.

Tubal ligation: A sterilization procedure in which the uterine (fallopian) tubes are tied and cut.

Tubercle: Small, rounded projection or process on a bone.

Tuberculosis: A lung disease where infection spread by airborne bacteria; tubercles encapsulate bacteria, elasticity of lungs is reduced, and infected tissues and lymph nodes may eventually calcify.

Tuberosity: Large, rounded projection in a bone; may be roughened.

Tubular reabsorption: The movement of filtrate from renal tubules back into blood in response to the body’s specific needs.

Tubular secretion: The movement of undesirable substances (such as drugs, urea, excess ions) from blood into renal tubular fluid in response to the body’s specific needs.

Tumor: An abnormal growth of cells; a swelling; cancerous at times.

Tumor angiogenic factor (TAF): A substance released by solid tumors that induces formation of new blood vessels to supply the tumor.

Tumor suppressor gene: A gene coding for a protein that normally inhibits cell division; loss or alteration of a tumor suppressor gene called p53 is the most common genetic change in a wide variety of cancer cells.

Tunica: A covering or tissue coat; membrane layer.

Tunica albuginea: A dense white fibrous capsule covering a testis or deep to the surface of an ovary.

Tunica externa: Outer blood vessel wall that contains collagen and elastic fibers; it protects, reinforces and anchors the vessel to surrounding structures; larger vessels contain a vasa vasorum ( vessels of the vessels ) to nourish the tissue in the outer and middle blood vessel walls.

Tunica intima: Inner blood vessel wall that contains an endothelial lining, a subendothelial connective tissue basement membrane, and an internal elastic lamina in vessels larger than 1 mm. Also called the tunica interna.

Tunica media: Middle blood vessel wall that contains smooth muscle and an external elastic lamina; sympathetic vasomotor nerve fibers control the vascular tone that produces vasoconstriction or vasodilation of the vessels.

Tympanic antrum: An air space in the middle ear that leads into the mastoid air cells or sinus.

Tympanic membrane: Thin partition of fibrous connective tissue between the external auditory meatus and the middle ear. Also called eardrum.

Type II cutaneous mechanoreceptor: A sensory receptor embedded deeply in the dermis and deeper tissues that detects stretching of skin. Also called a Ruffini corpuscle.

Ulcer: Lesion or erosion of the mucous membrane, such as gastric ulcer of stomach.

Ulna: Medial forearm bone; forms elbow joint. Markings: Coronoid process is anterior elbow projection; receives trochlea of the humerus when the forearm is flexed. Olecranon process is posterior elbow projection; grips trochlea of the humerus, forming the elbow joint. Radial notch is a concavity on lateral coronoid process; articulates with head of the radius. Trochlear notch is a large semicircular notch between the olecranon and coronoid process, that articulates with the trochlea of humerus to form part of the elbow joint. Styloid process is a distal medial pointed projection, and an attachment site for wrist ligament. Head is the distal knob-like extremity, that articulates with ulnar notch of the radius and the articular disk.

Umbilical cord: The long, ropelike structure containing the umbilical arteries and vein that connect the fetus to the placenta.

Umbilicus: A small scar on the abdomen that marks the former attachment of the umbilical cord to the fetus. Also called the navel.

Unipolar neuron: Nerve cell with only one process projecting from its cell body; the process divides into a sensory nerve fiber and an axon which synapses with neurons in the CNS; its cell body resides in a ganglion in the PNS.

Unmyelinated fiber: Neuron axon lacking a myelin sheath that conducts nerve impulses very slowly.

Unsaturated fat: A fat whose fatty acid tails have one or more C=C double bonds that produce bends in the tail, and is a liquid at room temperature; abundant in plant oils.

Up-regulation: Increased target cell formation of receptors in response to increasingly higher levels of the hormones to which they respond.

Upper limb: The appendage attached at the shoulder girdle, consisting of the arm, forearm, wrist, hand, and fingers. Also called upper extremity.

Uracil (U): A smaller, single-ring base (a pyrimidine) found in RNA.

Urea: Main nitrogen containing waste excreted in urine.

Urea cycle: The sequence of chemical reactions that occur primarily in the liver, which convert ammonia, NH, into urea, CO(NH).

Uremia: Accumulation of toxic levels of urea and other nitrogenous waste products in the blood, usually resulting from severe kidney malfunction.

Ureters: The two tubes that transport urine from the kidneys to the urinary bladder.

Urethra: The duct from the urinary bladder to the exterior of the body that conveys urine in females, and urine or semen in males.

Urethral groove: The groove on the ventral surface of the embryonic penis that ultimately is closed to form the spongy portion of the urethra.

Uric acid: The nitrogenous waste product of nucleic acid metabolism; component of urine.

Urinalysis: An analysis of the volume and physical, chemical, and microscopic properties of urine.

Urinary bladder: A collapsible sac that stores urine temporarily until it is excreted; its lining is transitional epithelium; its wall it smooth muscle called the detrusor that contracts to expel urine; its trigone is a triangular region at the base where the two ureters enter and the urethra exits; it is located in the pelvic cavity posterior to the pubic symphysis.

Urinary system: System primarily responsible for water, electrolyte, and acid-base balance and removal of nitrogenous wastes.

Urine: The fluid produced by the kidneys that contains wastes and excess materials; excreted from the body through the urethra.

Urogenital triangle: The region of the pelvic floor inferior to the pubic symphysis, bounded by the pubic symphysis and the ischial tuberosities, and containing the external genitalia.

Urology: The specialized branch of medicine that deals with the structure, function, and diseases of the male and female urinary systems and the male reproductive system.

Uterine tube: Duct that transports ova from the ovary to the uterus. Also called the fallopian tube or oviduct.

Uterosacral ligament: A fibrous band of tissue extending from the cervix of the uterus laterally to the sacrum.

Uterovesical pouch: A shallow pouch formed by the reflection of the peritoneum from the anterior surlace of the uterus, at the junction of the cervix and the body, to the posterior surface of the urinary bladder.

Uterus: The hollow, muscular organ in females that is the site of menstruation, implantation, development of the fetus, and labor. Also called the womb.

Utricle: The larger of the two divisions of the membranous labyrinth located inside the vestibule of the inner ear, containing a receptor organ for static equilibrium.

Uvea: The three structures that together make up the vascular tunic of the eye.

Uvula: (1) A soft, fleshy mass. (2) The conical projection from the posterior edge of the middle of the soft palate; during swallowing, the soft palate and uvula move superiorly to close off the nasopharynx and prevent food from entering the nasal cavity.


V (2)

Vaccine: Preparation that provides artificially acquired active immunity.

Vagina: A muscular, tubular organ that leads from the uterus to the vestibule, situated between the urinary bladder and the rectum of the female. Also called the birth canal.

Valence electrons: Electrons in the outermost shell of an atom that take part in the chemical reactions of that atom.

Vallate papilla: One of the circular projections that is arranged in an inverted V-shaped row at the back of the tongue; the largest of the elevations on the upper surface of the tongue containing taste buds. Also called circumvallate papilla.

Varicocele: A twisted vein; especially, the accumulation of blood in the veins of the spermatic cord.

Varicose: Unnaturally and permanently distended or swollen.

Varicose veins: Permanent dilation of veins, most commonly seen in the legs.

Vas: A vessel or duct.

Vasa recta: Extensions of the efferent arteriole of a juxtamedullary nephron that run alongside the loop of Henle in the medullary region of the kidney.

Vasa Vasorum: Blood vessels that supply nutrients to the larger arteries and veins (vessels of the vessels).

Vascular: Pertaining to or containing many blood vessels.

Vascular sinus: A vein with a thin endothelial wall that lacks a tunica media and externa and is supported by surrounding tissue. Also called venous sinus.

Vascular spasm: Contraction of the smooth muscle in the wall of a damaged blood vessel to prevent blood loss.

Vascular tunic: The middle layer of the eyeball, composed of the choroid, ciliary body, and iris. Also called the uvea.

Vasectomy: A means of sterilization of males in which a portion of each vas (ductus) deferens is removed.

Vasoconstriction: A decrease in the size of the lumen of a blood vessel caused by contraction of the smooth muscle in the wall of the vessel.

Vasodilation: An increase in the size of the lumen of a blood vessel caused by relaxation of the smooth muscle in the wall of the vessel.

Vasomotion: Intermittent contraction or relaxation of the precapillary sphincter beds resulting in a staggered blood flow when tissue needs are not extreme.

Vasomotor center: Brain area concerned with regulation of blood vessel resistance.

Vasomotor fibers: Sympathetic nerve fibers that cause the contraction of smooth muscle in the walls of blood vessels, thereby regulating blood vessel diameter.

Vein: A blood vessel that conveys blood from tissues back to the heart.

Vena cava: One of two large veins that open into the right atrium, returning to the heart all of the deoxygenated blood from the systemic circulation except from the coronary circulation.

Venous sinus: A vein with a thin endothelial wall that lacks a tunica media and externa and is supported by surrounding tissue. Also called vascular sinus.

Ventral: Pertaining to the anterior or front side of the body; opposite of dorsal.

Ventral ramus: The anterior branch of a spinal nerve, containing sensory and motor fibers to the muscles and skin of the anterior surface of the head, neck, trunk, and the limbs.

Ventral respiratory group (VRG): Part of the respiratory centers; nuclei in the medulla oblongata that stimulates the muscles of forced exhalation;

Ventricle: A cavity in the brain filled with cerebrospinal fluid.

Ventricles of Heart: The two inferior discharging chambers of the heart that are separated internally by the interventricular septum; their walls are ridged by trabeculae carneae, and papillary muscles project into the ventricular cavities; they function as the major blood pumps; the right ventricle pumps blood into the pulmonary trunk; the left ventricle pumps blood into the aorta.

Ventricle, Fourth: A cavity filled with cerebrospinal fluid within the brain lying between the cerebellum and the medulla oblongata and pons.

Ventricle, Lateral: A cavity within a cerebral hemisphere that communicates with the lateral ventricle in the other cerebral hemisphere and with the third ventricle by way of the interventricular foramen.

Ventricle, Third: A slitlike cavity between the right and left halves of the thalamus and between the lateral ventricles of the brain.

Ventricular afterload: The back pressure exerted by the aorta and pulmonary trunk that the ventricles must overcome to eject blood.

Ventricular fibrillation: Rapid irregular twitchings of ventricular muscle; causes heart failure and death, unless reversed by defibrillation.

Ventricular preload: The degree of stretch of muscles in the ventricles prior to contraction.

Venule: A small vein that collects blood from capillaries and delivers it to a vein.

Vermiform appendix: A wormlike tube attached to the cecum that contains masses of lymphoid tissue. Also called the appendix.

Vermis: The central constricted area of the cerebellum that separates the two cerebellar hemispheres.

Vertebral canal: A cavity within the vertebral columri formed by the vertebral foramina of all the vertebrae and containing the spinal cord. Also called the spinal canal.

Vertebral column: The 26 vertebrae of an adult and 33 vertebrae of an infant; provides support, forms a flexible bony case for the spinal cord, and serves as a point of attachment for the ribs and back muscles. Also called the backbone, spine, or spinal column. Markings: Vertebral body is anterior thick disc-shaped, weight-bearing portion of vertebra; not present in the atlas (C1). Vertebral arch is posterior projection from the body of a vertebra that encloses the vertebral foramen; consists of paired pedicles and laminae; the spinous, transverse, and articular processes arise from the arch. Pedicles are paired, short, thick processes that project posteriorly from the body to the lamina to form the lateral vertebral arch. Laminae are paired, broad, flattened plates that extend from the pedicles and fuse at the midline to form the posterior vertebral arch. Vertebral notches are two cavities above (superior) and below (inferior) the pedicle of a vertebra; the notches of two adjacent vertebrae form the intervertebral foramen. Intervertebral foramen is an opening formed by the inferior and superior notches on the pedicles of adjacent vertebrae; allows passage of spinal nerves and vessels. Vertebral foramen is a large aperture in vertebra formed by body and arch; allows passage of the spinal cord. Vertebral canal is a cavity within the articulated vertebral column; formed by the vertebral foramina of successive vertebrae; contains the spinal cord. Also called the spinal canal. Spinous process is a posterior projection from junction of the two laminae; attachment site for muscles; not present in the atlas (C1). Transverse processes are lateral projections from the junction of lamina and pedicle; attachment site for muscles. Articular processes are paired protrusions above (superior) and below (inferior) the junction of the pedicles and laminae; form the synovial joints between vertebrae. Costal facets are articular surfaces above (superior) and below (inferior) the body of a thoracic vertebra for articulation with heads of the ribs. Transverse costal facets are articular surfaces on the transverse process of a thoracic vertebra for articulation with the tubercle of a rib.

Vesicle: (1) Membranous sacs in cytoplasm that function in the transport, storage, digestion, or chemical modification of substances. (2) Any small, liquid filled sac or bladder.

Vesicouterine pouch: A shallow pouch formed by the reflection of the peritoneum from the anterior surface of the uterus, at the junction of the cervix and the body, to the posterior surface of the urinary bladder.

Vesicular follicle: Mature ovarian follicle.

Vestibular apparatus: Collective term for the organs of equilibrium, which includes the saccule, utricle, and semicircular ducts.

Vestibular glands: A pair of glands on either side of the vaginal orifice that open by a duct into the space between the hymen and the labia minora. Also called greater vestibular glands, or Bartholin’s glands.

Vestibular membrane: The membrane that separates the cochlear duct from the scala vestibuli.

Vestibule: (1) Cavity in the middle of the bony labyrinth for the sense of balance and static equilibrium. (2) A small space or cavity at the beginning of a canal.

Villi: Finger-like projections of the small intestinal mucosa that tremendously increase its surface area for absorption. Singular is villus.

Viscera: The organs inside the ventral body cavity.

Visceral: Pertaining to an internal organ of the body, or the inner part of a structure.

Visceral effectors: Organs of the ventral body cavity that respond to neural stimulation, including cardiac muscle, smooth muscle, and glands.

Visceral muscle: Type of smooth muscle; its cells contract as a unit and rhythmically, are electrically coupled by gap junctions, and often exhibit spontaneous action potentials.

Visceral organs: The organs inside the ventral body cavity.

Visceral serosa: The part of the double-layered membrane that lines the outer surfaces of organs within the ventral body cavity.

Viscosity: State of being sticky or thick.

Viscous: Sticky; marked by high viscosity.

Visual field: The field of view seen when the head is still.

Vital capacity (VC): The volume of air that can be expelled from the lungs by forcible expiration after the deepest inspiration; total exchangeable air.

Vital signs: Includes pulse, blood pressure, respiratory rate, and body temperature measurements.

Vitamin: An organic molecule necessary in trace amounts that acts as a catalyst in normal metabolic processes in the body.

Vitreous body: A transparent jellylike substance that fills the posterior segment of the eyeball, composed of a mesh of protein fibers and vitreous humor.

Vitreous humor: Transparent fluid component of the vitreous body.

Vocal folds: Mucosal folds that function in voice production (speech). Also called the true vocal cords.

Volatile acid: An acid that can be eliminated by the lungs; carbonic acid is converted to CO, which diffuses into the alveoli.

Volkmann’s canals: Canals that run at right angles to the long axis of the bone, connecting the vascular and nerve supplies of the periosteum to those of the central canals and medullary cavity. Also called perforating canals.

Voluntary muscle: Muscle under strict nervous control; skeletal muscle.

Voluntary nervous system: The somatic nervous system.

Vomer bone: Forms floor of nasal cavity, and inferior nasal septum.

Vulva: Female external genitalia. Also called the pudendum.


W (2)

Wallerian degeneration: Degeneration of the portion of the axon and myelin sheath of a neuron distal to the site of injury.

Wandering macrophage: Phagocytic cell that develops from a monocyte, leaves the blood, and migrates to infected tissues.

Wax: Sticky solid that repels water, and consists of a long-chain fatty acid bound to a long-chain alcohol.

Wernicke’s area: Located in the parietal and temporal lobes; essential for understanding and formulating coherent speech. (Brodmann areas 22, 39, 40)

Wheeze: (1) To breathe noisily and with difficulty. (2) A whistling, squeaking, musical, or puffing sound made on exhalation through a partially obstructed airway.

White matter: White area of the CNS; contains mostly myelinated nerve fibers.

White pulp: The regions of the spleen composed of lymphatic tissue, mostly B lymphocytes..

White ramus communicans: The portion of apreg@glionic sympathetic axon that branches from the anterior ramus of a spinal nerve to enter the nearest sympathetic trunk ganglion.

Withdrawal reflex: Reflex initiated by a painful stimulus (actual or perceived); causes automatic withdrawal of the threatened body part from the stimulus. Also called the flexor reflex


x

Xenograft: Tissue graft taken from another animal species.

Xiphoid: Sword-shaped. The inferior portion of tlle sternum is the xiphoid process.

Yolk sac: An extraembryonic membrane composed of the exocoelomic membrane and hypoblast. It transfers nutrients to the embryo, is a source of blood cells, contains primordial germ cells that migrate into the gonads to form primitive germ cells, forms part of the gut, and helps prevent desiccation of the embryo.

Zona fasciculata: The middle zone of the adrenal cortex consisting of cells arranged in long, straight cords that secrete glucocorticoid hormones, mainly cortisol.

Zona glomerulosa: The outer zone of the adrenal cortex, directly under the connective tissue covering, consisting of cells arranged in arched loops or round balls that secrete mineralocorticoid hormones, mainly aldosterone.

Zona pellucida: Clear glycoprotein layer between a secondary oocyte and the surrouriding granulosa cells of the corona radiata.

Zona reticu1aris: The inner zone of the adrenal cortex, consisting of cords of branching cells that secrete sex hormones, chiefly androgens.

Zygomatic bones: Pair of cheek bones that form the cheek and part of the orbits. Markings: Temporal process of zygomatic bone are bridgelike projections that form the anterior zygomatic arch.

Zygomaticus: Smiling muscle; raises corner of mouth. O: Zygomatic bone. I: Skin and muscle at corner of lips

Zygote: The single cell resulting from the union of male and female gametes. Also called a fertilized egg or fertilized ovum.

Zymogen: The inactive precursor of an enzyme, which can be converted into the active enzyme. Also called a proenzyme.

References:

(1) Marieb, Elaine and Hoehn, K., 2013, Human Anatomy and Physiology, 9th Edition, Pearson.

(2) Tortora, Gerard and Derrickson, B., 2012, Principles of Anatomy and Physiology, 13th Edition, Wiley.

(3) Saladin, Kenneth, 2012, Anatomy & Physiology: The Unity of Form and Function, 6th Edition, McGraw-Hill.

(4) Seeley, Rod, VanPutte, C., Regan, J. and Russo, A., 2011, Anatomy & Physiology, 9th Edition, McGraw-Hill.

(5) Stedman’s Medical Dictionary, 28th Edition, 2007, Lippincott, Williams & Wilkins.

(6) Dorland’s Illustrated Medical Dictionary, 31st Edition, 2009, Elsevier Inc.