Glossary Click here to go to Prefixes and Suffixes.
Most of the words in this glossary are followed by a phonetic spelling that serves as a guide to pronunciation. The phonetic spellings reflect standard scientific usage and can be easily interpreted following a few basic rules.
abduction (ab-dukshun) The movement of a body part away from the axis or midline of the body; movement of a digit away from the axis of the limb.
ABO system The most common system of classification for red blood cell antigens. On the basis of antigens on the red blood cell surface, individuals can be type A, type B, type AB, or type O.
absorption (ab-sorpshun) The transport of molecules across epithelial membranes into the body fluids.
accessory organs (ak-sesuo-re) Organs that assist with the functioning of other organs within a system.
accommodation (ua-komuo-dashun) A process whereby the focal length of the eye is changed by automatic adjustment of the curvature of the lens to bring images of objects from various distances into focus on the retina.
acetabulum (asue-tabyuu-lum) A socket in the lateral surface of the hipbone (os coxa) with which the head of the femur articulates.
acetone (asue-t=on) A ketone body produced as a result of the oxidation of fats.
acetyl coenzyme A (acetyl CoA) (asue-tl, ua-setl) A coenzyme derivative in the metabolism of glucose and fatty acids that contributes substrates to the Krebs cycle.
acetylcholine (ACh) (ua-setl-kol=en) An acetic acid ester of choline-a substance that functions as a neurotransmitter in somatic motor nerve and parasympathetic nerve fibers.
acetylcholinesterase (ua-setl-kolu1-nestue-r=as) An enzyme in the membrane of postsynaptic cells that catalyzes the conversion of ACh into choline and acetic acid. This enzymatic reaction inactivates the neurotransmitter.
Achilles tendon (ua-kil=ez) See tendo calcaneous.
acid (asid) A substance that releases hydrogen ions when ionized in water.
acidosis (asu1-dosis) An abnormal increase in the H+ concentration of the blood that lowers the arterial pH to below 7.35.
acromegaly (akro-megua-le) A condition caused by the hypersecretion of growth hormone from the pituitary gland after maturity and characterized by enlargement of the extremities, such as the nose, jaws, fingers, and toes.
actin (aktin) A protein in muscle fibers that together with myosin is responsible for contraction.
action potential An all-or-none electrical event in an axon or muscle fiber in which the polarity of the membrane potential is rapidly reversed and reestablished.
active immunity (u1-myoonu1-te) Immunity involving sensitization, in which antibody production is stimulated by prior exposure to an antigen.
active transport The movement of molecules or ions across the cell membranes of epithelial cells by membrane carriers. An expenditure of cellular energy (ATP) is required.
adduction (au-dukshun) The movement of a body part toward the axis or midline of the body; movement of a digit toward the axis of the limb.
adenohypophysis (adn-o-hi-pofu1-sis) The anterior, glandular lobe of the pituitary gland that secretes FSH (follicle-stimulating hormone), LH (luteinizing hormone), ACTH (adrenocorticotropic hormone), TSH (thyroid-stimulating hormone), GH (growth hormone), and prolactin. Secretions of the adenohypophysis are controlled by hormones produced by the hypothalamus.
adenoids (adue-noidz) The tonsils located in the nasopharynx; pharyngeal tonsils.
adenylate cyclase (ua-denl-it sikl=as) An enzyme found in cell membranes that catalyzes the conversion of ATP to cyclic AMP and pyrophosphate (PP1). This enzyme is activated by an interaction between a specific hormone and its membrane receptor protein.
ADH Antidiuretic hormone; a hormone produced by the hypothalamus and released by the posterior pituitary that acts on the kidneys to promote water reabsorption; also known as vasopressin.
ADP Adenosine diphosphate; a molecule that together with inorganic phosphate is used to make ATP (adenosine triphosphate).
adrenal cortex (ua-drenal korteks) The outer part of the adrenal gland. Derived from embryonic mesoderm, the adrenal cortex secretes corticosteroid hormones (such as aldosterone and hydrocortisone).
adrenal medulla (mue-dulua) The inner part of the adrenal gland. Derived from embryonic postganglionic sympathetic neurons, the adrenal medulla secretes catecholamine hormones-epinephrine and (to a lesser degree) norepinephrine.
adrenergic (adreu-nerjik) A term used to describe the actions of epinephrine, norepinephrine, or other molecules with similar activity (as in adrenergic receptor and adrenergic stimulation).
adventitia (adven-tishua) The outermost epithelial layer of a visceral organ; also called serosa.
afferent (afer-ent) Conveying or transmitting to.
afferent arteriole (ar-tire-=ol) A blood vessel within the kidney that supplies blood to the glomerulus.
afferent neuron (nooron) See sensory neuron.
agglutinate (ua-glootn-=at) A clump of cells (usually erythrocytes) formed as a result of specific chemical interaction between surface antigens and antibodies.
agranular leukocytes (ua-granyuu-lar loo kuo-s1=tz) White blood cells (leukocytes) that do not contain cytoplasmic granules; specifically, lymphocytes and monocytes.
albumin (al-byoomin) A water-soluble protein produced in the liver; the major component of the plasma proteins.
aldosterone (al-doster-=on) The principal corticosteroid hormone involved in the regulation of electrolyte balance (mineralocorticoid).
alimentary canal The tubular portion of the digestive tract. See also gastrointestinal tract (GI tract).
allantois (ua-lanto-is) An extraembryonic membranous sac involved in the formation of blood cells. It gives rise to the fetal umbilical arteries and vein and also contributes to the formation of the urinary bladder.
allergens (aler-jenz) Antigens that evoke an allergic response rather than a normal immune response.
allergy (aler-je) A state of hypersensitivity caused by exposure to allergens. It results in the liberation of histamine and other molecules with histaminelike effects.
all-or-none principle The statement of the fact that muscle fibers of a motor unit contract to their maximum extent when exposed to a stimulus of threshold strength.
allosteric (aluo-sterik) A term used with reference to the alteration of an enzyme's activity as a result of its combination with a regulator molecule. Allosteric inhibition by an end product represents negative feedback control of an enzyme's activity.
alveolar sacs (al-veuo-lar) A cluster of alveoli that share a common chamber or central atrium.
alveolus (al-veuo-lus) 1.An individual air capsule within the lung. The alveoli are the basic functional units of respiration. 2.The socket that secures a tooth(tooth socket).
amniocentesis (amne-o-sen-tesis) A procedure in which a sample of amniotic fluid is aspirated to examine suspended cells for various genetic diseases.
amnion (amne-on) A developmental membrane surrounding the fetus that contains amniotic fluid.
amphiarthrosis (amfe-ar-throsis) A slightly movable articulation in a functional classification of joints.
amphoteric (am-fo-terik) Having both acidic and basic characteristics; used to denote a molecule that can be positively or negatively charged, depending on the pH of its environment.
ampulla (am-poolua) A saclike enlargement of a duct or tube.
ampulla of Vater (Fuater) See hepatopancreatic ampulla.
anabolic steroids (anua-bolik steroidz) Steroids with androgenlike stimulatory effects on protein synthesis.
anabolism (ua-nabuo-lizem) A phase of metabolism involving chemical reactions within cells that result in the production of larger molecules from smaller ones; specifically, the synthesis of protein, glycogen, and fat.
anaerobic respiration (an-ua-robik respu1-rashun) A form of cell respiration involving the conversion of glucose to lactic acid in which energy is obtained without the use of molecular oxygen.
anal canal (anal) The terminal tubular portion of the large intestine that opens through the anus of the GI tract.
anaphylaxis (anua-fu1-laksis) An unusually severe allergic reaction that can result in cardiovascular shock and death.
anastomosis (ua-nastuo-mosis) An interconnecting aggregation of blood vessels or nerves that form a network plexus.
anatomical position (anua-tomu1-kal) An erect body stance with the eyes directed interior, the arms at the sides, the palms of the hands facing interior, and the fingers pointing straight down.
anatomy (ua-natuo-me) The branch of science concerned with the structure of the body and the relationship of its organs.
androgens (andruo-jenz) Steroids containing 18 carbons that have masculinizing effects; primarily those hormones(such as testosterone) secreted by the testes, although weaker androgens are also secreted by the adrenal cortex.
anemia (ua-neme-ua) An abnormal reduction in the red blood cell count, hemoglobin concentration, or hematocrit, or any combination of these measurements. This condition is associated with a decreased ability of the blood to carry oxygen.
angina pectoris (an-jinua pektuo-ris) A thoracic pain, often referred to the left pectoral and arm area, caused by myocardial ischemia.
angiotensin II (anje-o-tensin) An 8-amino-acid polypeptide formed from angiotensin I(a 10-amino-acid precursor), which in turn is formed from cleavage of a protein(angiotensinogen) by the action of renin(an enzyme secreted by the kidneys). Angiotensin II is a powerful vasoconstrictor and a stimulator of aldosterone secretion from the adrenal cortex.
anions (ani-onz) Ions that are negatively charged, such as chloride, bicarbonate, and phosphate.
antagonist (an-taguo-nist) A muscle that acts in opposition to another muscle.
antebrachium (ante-brake-em) The forearm.
anterior (ventral) Toward the front; the opposite of posterior, or dorsal.
anterior pituitary (pu1-toou1-ter-e) See adenohypophysis.
anterior root The anterior projection of the spinal cord, composed of axons of motor neurons.
antibodies (antu1-bod=ez) Immunoglobin proteins secreted by B lymphocytes that have transformed into plasma cells. Antibodies are responsible for humoral immunity. Their synthesis is induced by specific antigens, and they combine with these specific antigens but not with unrelated antigens.
anticodon (antu1-kodon) A base triplet provided by three nucleotides within a loop of transfer RNA that is complementary in its base-pairing properties to a triplet(the codon) in mRNA. The matching of codon to anticodon provides the mechanism for translating the genetic code into a specific sequence of amino acids.
antigen (antu1-jen) A molecule that can induce the production of antibodies and react in a specific manner with antibodies.
antigenic determinant site (an-tu1-jenik) The region of an antigen molecule that specifically reacts with particular antibodies. A large antigen molecule may have a number of such sites.
antiserum (antu1-sirum) A serum that contains specific antibodies.
anus (anus) The terminal opening of the GI tract.
aorta (a-ortua) The major systemic vessel of the arterial system of the body, emerging from the left ventricle.
aortic arch The superior left bend of the aorta between the ascending and descending portions.
apex (apeks) The tip or pointed end of a conical structure.
aphasia (ua-fazhua) Defects in speech, writing, or in the comprehension of spoken or written language caused by brain damage or disease.
apneustic center (ap-noostik) A collection of nuclei(nerve cell bodies) in the brain stem that participates in the rhythmic control of breathing.
apocrine gland (apuo-krin) A type of sweat gland that functions in evaporative cooling. It may respond during periods of emotional stress.
aponeurosis (apuo-noo-rosis) A fibrous or membranous sheetlike tendon.
appendix A short pouch that attaches to the cecum.
aqueous humor (akwe-us) The watery fluid that fills the anterior and posterior chambers of the eye.
arachnoid mater (ua-raknoid) The weblike middle covering(meninx) of the central nervous system.
arbor vitae (arbor vite) The branching arrangement of white matter within the cerebellum.
arm (brachium) The portion of the upper extremity from the shoulder to the elbow.
arrector pili muscle (ah-rektor pihle) The smooth muscle attached to a hair follicle that, upon contraction, pulls the hair into a more vertical position, resulting in "goose bumps."
arteriole (ar-tire-=ol) A minute arterial branch.
arteriosclerosis (ar-tire-o-sklue-rosis) Any one of a group of diseases characterized by thickening and hardening of the artery wall and in the narrowing of its lumen.
arteriovenous anastomoses (ar-tire-o-venus ua-nastuo-mos=ez) Direct connections between arteries and veins that bypass capillary beds.
artery (artue-re) A blood vessel that carries blood away from the heart.
arthrology (ar-throluo-je) The scientific study of the structure and function of joints.
articular cartilage (ar-tikyuu-lar kartu1-lij) A hyaline cartilaginous covering over the articulating surface of the bones of synovial joints.
articulation (ar-tikyuu-lashun) A joint.
arytenoid cartilages (arue-tenoid) A pair of small cartilages located on the superior aspect of the larynx.
ascending colon (kolon) The portion of the large intestine between the cecum and the hepatic flexure.
association neuron (nooron) A nerve cell located completely within the central nervous system. It conveys impulses in an arc from sensory to motor neurons; also called interneuron or internuncial neuron.
astigmatism (ua-stigmua-tizem) Unequal curvature of the refractive surfaces of the eye (cornea and/or lens), so that light entering the eye along certain meridians does not focus on the retina.
atherosclerosis (athue-ro-sklue-rosis) A common type of arteriosclerosis found in medium and larger arteries in which raised areas within the tunica intima are formed from smooth muscle cells, cholesterol, and other lipids. These plaques occlude arteries and serve as sites for the formation of thrombi.
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Anatomy and Physiology - McGraw Hill Education