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 interpreted easily following a few basic rules.
1. Any unmarked vowel that ends a syllable or that stands alone as a syllable has the long sound. For example, ba, ma, and na rhyme with fay; be, de, and we rhyme with fee; bi, di, and pi rhyme with sigh; bo, do, and mo rhyme with go. Any unmarked vowel that is followed by a consonant has the short sound (for example, the vowel sounds in hat, met, pit, not, and but).
2. If a long vowel appears in the middle of a syllable (followed by a consonant), it is marked with a macron (-). Similarly, if a vowel stands alone or ends a syllable but should have short sound, it is marked with a breve (").
3. Syllables that are emphasized are indicated by stress marks. A single stress mark ( ) indicates the primary emphasis; a secondary emphasis is indicated by a double stress mark (").
a-, an- (Gk.) Not, without, lacking. ab- (L.) Off, away from.
abdomen (ab' do-men, ab-do men) The region of the trunk between the diaphragm and pelvis. abductor (ab-duk'tor) A muscle that moves the skeleton away from the midline of the body or away from the axial line of a 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-sorp shun) The transport of molecules across epithelial membranes into the body fluids. accommodation (a-kom"o-da'shun) Adjustment; specifically, the 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. acetyl (as'l-tl, a-set l) CoA Acetyl coenzyme A. An intermediate molecule in aerobic cell respiration that, together with oxaloacetic acid, begins the Krebs cycle. Acetyl CoA is also an intermediate in the synthesis of fatty acids.
acetylcholine (a-set'l-ko'len) (ACh) An acetic acid ester of choline—a substance that functions as a neurotransmitter chemical in somatic motor nerve and parasympathetic nerve fibers. acetylcholinesterase (ft-sefl-ko"ll-nes' te-ras) 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. acidosis (as"i-do'sis) An abnormal increase in the H+ concentration of the blood that lowers arterial pH below 7.35. acromegaly (ak"ro-meg ai-le) A condition caused by hypersecretion of growth hormone from the pituitary after maturity and characterized by enlargement of the extremities, such as the nose, jaws, fingers, and toes. ACTH Adrenocorticotropic (ai-dre"no-kor"ai-ko-
trop ik) hormone A hormone secreted by the anterior pituitary that stimulates the adrenal cortex.
actin (ak tin) A structural protein of muscle that, along with myosin, is responsible for muscle 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 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. ad- (L.) Toward, next to. adductor (ai-duk tor) A muscle that moves the skeleton toward the midline of the body or toward the axial plane of a limb. adenohypophysis (ad"n-o-hi-pof l-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 anterior pituitary are controlled by hormones secreted by the hypothalamus.
adenylate cyclase (a-den'l-it si'klase) An enzyme found in cell membranes that catalyzes the conversion of ATP to cyclic AMP and pyrophosphate (PPi). This enzyme is activated by an interaction between a specific hormone and its membrane receptor protein. ADH Antidiuretic (an"te-di"yui-ret ik) hormone, also known as vasopressin. A hormone produced by the hypothalamus and released from the posterior pituitary. It acts on the kidneys to promote water reabsorption, thus decreasing the urine volume. adipose (ad'i-pos) tissue Fatty tissue. A type of connective tissue consisting of fat cells in a loose connective tissue matrix. ADP Adenosine diphosphate (a-den'o-sen di-fo/fat). A molecule that, together with inorganic phosphate, is used to make ATP (adenosine triphosphate). adrenal cortex (ai-dre nal kor teks) The outer part of the adrenal gland. Derived from embryonic mesoderm, the adrenal cortex secretes corticosteroid hormones, including aldosterone and hydrocortisone. adrenal medulla (medul'a) 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 (ad" re-ne/jik) Denoting the actions of epinephrine, norepinephrine, or other molecules with similar activity (as in adrenergic receptor and adrenergic stimulation).
aerobic (ai-ro bik) capacity The ability of an organ to utilize oxygen and respire aerobically to meet its energy needs. afferent (af er-ent) Conveying or transmitting inward, toward a center. Afferent neurons, for example, conduct impulses toward the central nervous system; afferent arterioles carry blood toward the glomerulus. agglutinate (a-gloot n-at) A clumping of cells
(usually erythrocytes) as a result of specific chemical interaction between surface antigens and antibodies. agranular leukocytes (a-gran'yu-lar loo'ko-sits)
While blood cells (leukocytes) with cytoplasmic granules that are too small to be clearly visible; specifically, lymphocytes and monocytes. albumin (al-byoo'min) A water-soluble protein produced in the liver; the major component of the plasma proteins. aldosterone (al-dos ter-oin) The principal corticosteroid hormone involved in the regulation of electrolyte balance (mineralocorticoid). alkalosis (al"ka-lo' sis) An abnormally high alkalinity of the blood and body fuids (blood pH > 7.45). allergen (al -er-jen) An antigen that evokes an allergic response rather than a normal immune response.
allergy (al'er-je) A state of hypersensitivity caused by exposure to allergens. It results in the liberation of histamine and other molecules with histamine-like effects. all-or-none law The statement that a given response will be produced to its maximum extent in response to any stimulus equal to or greater than a threshold value. Action potentials obey an all-or-none law. allosteric (af'o-ste/ik) Denoting the alteration of an enzyme's activity by its combination with a regulator molecule. Allosteric inhibition by an end product represents negative feedback control of an enzyme's activity. alpha motoneuron (al fa mo"to-noor' on) The type of somatic motor neuron that stimulates extrafusal skeletal muscle fibers. alveoli (al-ve'o-li); sing., alveolus. Small, saclike dilations (as in lung alveoli). amniocentesis (am"ne-o-sen-te' sis) A procedure for obtaining amniotic fluid and fetal cells in this fluid through transabdominal perforation of the uterus.
amnion (am ne-on) A developmental membrane surrounding the fetus that contains amniotic fluid; commonly called the "bag of waters." amphoteric (am-fo-ter'ik) 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. amylase (am'il-ds) A digestive enzyme that hydrolyzes the bonds between glucose subunits in starch and glycogen. Salivary amylase is found in saliva and pancreatic amylase is found in pancreatic juice. an- (Gk.) Without, not.
anabolic steroids (an"a-bol'ik steZoidz) Steroids with androgen-like stimulatory effects on protein synthesis.
anabolism (a-nab' o-Uz"em) 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-a-ro'bik res"pi-ra'shun) A form of cell respiration involving the conversion of glucose to lactic acid in which energy is obtained without the use of molecular oxygen. anaerobic threshold The maximum rate of oxygen consumption that can be attained before a significant amount of lactic acid is produced by the exercising skeletal muscles through anaerobic respiration. This generally occurs when about 60% of the person's total maximal oxygen uptake has been reached. anaphylaxis (an"a-fi-lak'sis) An unusually severe allergic reaction that can result in cardiovascular shock and death. androgen (an' dro-jen) A steroid hormone that controls the development and maintenance of masculine characteristics; primarily testosterone secreted by the testes, although weaker androgens are secreted by the adrenal cortex.
anemia (a-ne'me-a) 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-jina pekkto-ris) A thoracic pain, often referred to the left pectoral and arm area, caused by myocardial ischemia.
angiogenesis (an"je-o-jen'e-sis) The growth of new blood vessels. angiotensin II (an"je-o-ten'sin) An eight-amino-acid polypeptide formed from angiotensin I (a ten-amino-acid precursor), which in turn is formed from the 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. anion (an i-on) An ion that is negatively charged, such as chloride, bicarbonate, or phosphate. antagonistic effects Actions of regulators such as hormones or nerves that counteract the effects of other regulators. The actions of sympathetic and parasympathetic neurons on the heart, for example, are antagonistic. anterior (an-teZe-or) At or toward the front of an organism, organ, or part; the ventral surface. anterior pituitary (pi-too' i-ter-e) See adenohypophysis. antibodies (an' ti-bod"ez) Immunoglobulin proteins secreted by B lymphocytes that have been 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. anticoagulant (an"te-ko-ag'yu-lant) A substance that inhibits blood clotting. anticodon (an"te-ko'don) 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 translation of the genetic code into a specific sequence of amino acids. antigen (an'ti-jen) A molecule able to induce the production of antibodies and to react in a specific manner with antibodies. antigenic (an-ti-jen' ik) determinant site The region of an antigen molecule that specifically reacts with particular antibodies. A large antigen molecule may have a number of such sites. antioxidants Molecules that scavenge free radicals, thereby relieving the oxidative stress on the body.
antiport (an'-ti-port) A form of secondary active transport (coupled transport) in which a molecule or ion is moved together with, but in the opposite direction to, Na+ ions; that is, out of the cell; also called countertransport. antiserum (an' ti-se"rum) A serum containing antibodies that are specific for one or more antigens.
aphasia (a-fa' ze-a) Absent or defective speech, writing, or comprehension of written or spoken language caused by brain damage or disease. Broca's area, Wernicke's area, the arcuate fasciculus, or the angular gyrus may be involved. apnea (ap' ne-a) The temporary cessation of breathing.
apneustic (ap-noo stik) center A collection of neurons in the brain stem that participates in the rhythmic control of breathing. apoptosis (ap"o-to'sis) Cellular death in which the cells show characteristic histological changes. It occurs as part of programmed cell death and other events in which cell death is a physiological response. aquaporins (d-kwd-por'inz) The protein channels in a cell (plasma) membrane that permit osmosis to occur across the membrane. In certain tissues, particularly the collecting ducts of the kidney, aquaporins are inserted into the cell membrane in response to stimulation by antidiuretic hormone. aqueous humor (a kwe-us) A fluid produced by the ciliary body that fills the anterior and posterior chambers of the eye. arteriosclerosis (dr-tir'e-o-skle-ro'sis) Any of a group of diseases characterized by thickening and hardening of the artery wall and narrowing of its lumen. arteriovenous anastomosis (dr-ti/'e-o-ve' nus a-nds to-mo'sis) A direct connection between an artery and a vein that bypasses the capillary bed. artery (aZte-re) A vessel that carries blood away from the heart. astigmatism (a-stig'ma-tizZ' em) Unequal curvature of the refractive surfaces of the eye (cornea and/or lens), so that light that enters the eye along certain meridians does not focus on the retina. atherosclerosis (dth"e-ro-skle-ro'sis) A common type of arteriosclerosis in which raised areas, or plaques, within the tunica interna of medium and large arteries are formed from smooth muscle cells, cholesterol, and other lipids. These plaques occlude the arteries and serve as sites for the formation of thrombi. atomic number A whole number representing the number of positively charged protons in the nucleus of an atom. atopic dermatitis (a-top' ik deZ'ma-ti'tis) An allergic skin reaction to agents such as poison ivy and poison oak; a type of delayed hypersensitivity. ATP Adenosine triphosphate (dden' o-sen tri-fos'fdt).
The universal energy carrier of the cell. atretic (d-tret'ik) Without an opening. Atretic ovarian follicles are those that fail to rupture and release an oocyte. atrial natriuretic (a'tre-dl na"tri-yoo-ref ik) factor A chemical secreted by the atria that acts as a natriuretic hormone (a hormone that promotes the urinary excretion of sodium). atrioventricular node (d'tre-o-ven-trikyu-ldr nod) A specialized mass of conducting tissue located in the right atrium near the junction of the interventricular septum. It transmits the impulse into the bundle of His; also called the AV node. atrioventricular valves One-way valves located between the atria and ventricles. The AV valve on the right side of the heart is the tricuspid, and the AV valve on the left side is the bicuspid, or mitral, valve. atrophy (at'rofe) A gradual wasting away, or decrease in mass and size of an organ; the opposite of hypertrophy. atropine (atro-pen) An alkaloid drug, obtained from a plant of the species Belladonna, that acts as an anticholinergic agent. It is used medically to inhibit parasympathetic nerve effects, dilate the pupil of the eye, increase the heart rate, and inhibit intestinal movements. auto- (Gk.) Self, same.
autoantibody (aw"to-dn'ti-bod"e) An antibody that is formed in response to, and that reacts with, molecules that are part of one's own body. autocrine (aw'to-krin) regulation A type of regulation in which one part of an organ releases chemicals that help to regulate another part of the same organ. Prostaglandins, for example, are autocrine regulators. autonomic (dw"to-nom'ik) nervous system The part of the nervous system that involves control of smooth muscle, cardiac muscle, and glands. The autonomic nervous system is subdivided into the sympathetic and parasympathetic divisions.
690 Glossary autoregulation (aw"to-reg'yu la 'shun) The ability of an organ to intrinsically modify the degree of constriction or dilation of its small arteries and arterioles, and thus to regulate the rate of its own blood flow. Autoregulation may occur through myogenic or metabolic mechanisms. autosomal chromosomes (aw"to-so'mal kro' mo-s omz) The paired chromosomes; those other than the sex chromosomes. axon (ak'son) The process of a nerve cell that conducts impulses away from the cell body. axonal (akso-nal, ak-son'al) transport The transport of materials through the axon of a neuron. This usually occurs from the cell body to the end of the axon, but retrograde (backward) transport can also occur.
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