CFS PHOENIX GLOSSARY

Definitions from Stedman’s Electronic Dictionary, 5^th ed.

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acetylcholine (ACH, Ach) - The acetic ester of choline, the neurotransmitter substance at cholinergic synapses, which causes cardiac inhibition, vasodilation, gastrointestinal peristalsis, and other parasympathetic effects. It is liberated from preganglionic and postganglionic endings of parasympathetic fibers and from preganglionic fibers of the sympathetic as a result of nerve injuries, whereupon it acts as a transmitter on the effector organ; it is hydrolyzed rapidly into choline and acetic acid by acetylcholinesterase in the tissues and by pseudocholinesterase in the blood.

acrocyanosis - A circulatory disorder in which the hands, and less commonly the feet, are persistently cold and blue; some forms are related to Raynaud phenomenon. Syn: Crocq disease, Raynaud sign.

adenylate cyclase - an enzyme acting on ATP to form 3c,5c-cyclic AMP plus pyrophosphate. A crucial step in the regulation and formation of second messengers. Syn: 3c,5c-cyclic AMP synthetase.

adenosine - . A condensation product of adenine and D-ribose; a nucleoside found among the hydrolysis products of all nucleic acids and of the various adenine nucleotides. Adenosine accumulates in severe combined immunodeficiency disease.
2. A potent coronary vasodilator used in place of exercise for radionuclide myocardial perfusion studies.

adrenal gland  - a flattened, roughly triangular body positioned in relation to the superior end of each kidney but attached primarily to the diaphragmatic crura; it is one of the endocrine (ductless) glands furnishing internal secretions (epinephrine and norepinephrine from the medulla and steroid hormones from the cortex). Syn: adrenal body, suprarenal body, adrenal capsule, atrabiliary capsule, suprarenal capsule, epinephros, adrenal gland, glandula atrabiliaris, glandula suprarenalis [TA], paranephros.

adrenergic - 1. Relating to nerve cells or fibers of the autonomic nervous system that employ norepinephrine as their neurotransmitter. Cf. cholinergic.
2. Relating to drugs that mimic the actions of the sympathetic nervous system. See: )-adrenergic receptors, *-adrenergic receptors.

adrenergic neurotransmitter - a neurotransmitter formed in sympathetic postganglionic synapses (e.g., norepinephrine).

adrenergic receptors - reactive components of effector tissues, most of which are innervated by adrenergic postganglionic fibers of the sympathetic nervous system. Such receptors can be activated by norepinephrine and/or epinephrine and by various adrenergic drugs; receptor activation results in a change in effector tissue function, such as contraction of arteriolar muscles or relaxation of bronchial muscles; adrenergic receptors are divided into )-receptors and *-receptors, on the basis of their response to various adrenergic activating and blocking agents. Syn: adrenoceptor, adrenoreceptors.

adrenocorticotropic hormone (ACTH) - the hormone of the anterior lobe of the hypophysis that governs the nutrition and growth of the adrenal cortex, stimulates it to functional activity, and also possesses extraadrenal adipokinetic activity; it is a polypeptide containing 39 amino acids, but exact structure varies from one species to another; sometimes prefixed by ) to distinguish it from *-corticotropin. The first 13 amino acids at the N-terminal region are identical to )-melanotropin. Syn: adrenocorticotropin, adrenotropin, corticotropin (1), adrenotropic hormone, corticotropic hormone.

albumin - A type of simple protein, varieties of which are widely distributed throughout the tissues and fluids of plants and animals; albumin is soluble in pure water, precipitable from solution by strong acids, and coagulable by heat in acid or neutral solution.

aldosterone - A mineralocorticoid hormone produced by the zona glomerulosa of the adrenal cortex; its major action is to facilitate potassium exchange for sodium in the distal renal tubule, causing sodium reabsorption and potassium and hydrogen loss; the principal mineralocorticoid. It exists in equilibrium with the aldehyde form. Syn: aldocortin.

alkaline phosphatase - a phosphatase with an optimum pH of above 7.0 (e.g., 8.6), present ubiquitously; localized cytochemically in membranes by modifications of Gomori nonspecific alkaline phosphatase stain; it hydrolyzes many orthophosphoric monoesters; low levels of this enzyme are seen in cases of hypophosphatasia.

allele - Any one of a series of two or more different genes that may occupy the same locus on a specific chromosome. As autosomal chromosomes are paired, each autosomal gene is represented twice in normal somatic cells. If the same allele occupies both units of the locus, the individual or cell is homozygous for this allele. If the alleles are different, the individual or cell is heterozygous for both alleles. See: DNA markers. See Also: dominance of traits. Syn: allelomorph.

amyloid - Any of a group of chemically diverse proteins that appears microscopically homogeneous, but is composed of linear nonbranching aggregated fibrils arranged in sheets when seen under the electron microscope; amyloid occurs characteristically as pathologic extracellular deposits (amyloidosis), especially in association with reticuloendothelial tissue; the chemical nature of the proteinaceous fibrils is dependent upon the underlying disease process.

amyloidosis - 1. A disease characterized by extracellular accumulation of amyloid in various organs and tissues of the body; may be local or generalized; may be primary or secondary. 2. The process of deposition of amyloid protein.

anemia - Any condition in which the number of red blood cells per mm3, the amount of hemoglobin in 100 ml of blood, and/or the volume of packed red blood cells per 100 ml of blood are less than normal; clinically, generally pertaining to the concentration of oxygen-transporting material in a designated volume of blood, in contrast to total quantities as in oligocythemia, oligochromemia, and oligemia. Anemia is frequently manifested by pallor of the skin and mucous membranes, shortness of breath, palpitations of the heart, soft systolic murmurs, lethargy, and fatigability.

angiotensin - A family of peptides of known and similar sequence, with vasoconstrictive activity, produced by enzymatic action of renin upon angiotensinogen. See: angiotensin I, angiotensin II, angiotensin III

angiotensin I -A decapeptide of slightly variable sequence, depending on the animal source, formed from the tetradecapeptide angiotensinogen by the removal of four amino acid residues, a reaction catalyzed by renin; a peptidase cleaves off a dipeptide (histidylleucine) to yield angiotensin II, the physiologically active form.

angiotensin II -A vasoactive octapeptide produced by the action of angiotensin-converting enzyme on angiotensin I; produces stimulation of vascular smooth muscle, promotes aldosterone production, and stimulates the sympathetic nervous system.

angiotensin III -A vasoactive heptapeptide less potent than angiotensin II on vascular smooth muscle but approximately equally active in promoting aldosterone secretion.

antibody (Ab )- an immunoglobulin molecule produced by B lymphoid cells with a specific amino acid sequence evoked in humans or other animals by an antigen (immunogen). These molecules are characterized by reacting specifically with the antigen in some demonstrable way, antibody and antigen each being defined in terms of the other. Antibodies may also exist naturally, without being present as a result of the stimulus provided by the introduction of an antigen; antibodies are found in the blood and body fluids, although the basic structure of the molecule consists of two light and two heavy chains, antibodies may also be found as dimers, trimers, or pentamers. See Also: immunoglobulin. Syn: immune protein, protective protein, sensitizer (2).

antigen (Ag) - Any substance that, as a result of coming in contact with appropriate cells, induces a state of sensitivity and/or immune responsiveness after a latent period (days to weeks) and that reacts in a demonstrable way with antibodies and/or immune cells of the sensitized subject in vivo or in vitro. Modern usage tends to retain the broad meaning of antigen, employing the terms “antigenic determinant” or “determinant group” for the particular chemical group of a molecule that confers antigenic specificity. See Also: hapten. Syn: immunogen.

antigen-presenting cells (APC)  - cells that process protein antigens into peptides and present them on their surface in a form that can be recognized by lymphocytes. APCs include Langerhans cells, dendritic cells, macrophages, B cells, and in humans, activated T cells. Syn: accessory cells

antinuclear antibody (ANA) - an antibody showing an affinity for nuclear antigens including DNA and found in the serum of a high proportion of patients with systemic lupus erythematosus, rheumatoid arthritis, and certain collagen diseases, in some of their healthy relatives; also in about 1% of normal individuals.

antisense DNA - strand of DNA complementary to the one bearing the genetic message and from which it may be reconstructed. A DNA sequence complementary to a portion of mRNA.  Used as potential therapeutic to stop transcription or translation of pathogens or inappropriately expressed host gene.

aorta - A large artery of the elastic type that is the main trunk of the systemic arterial system, arising from the base of the left ventricle and ending at the left side of the body of the fourth lumbar vertebra by dividing to form the right and left common iliac arteries. The aorta is subdivided into: ascending aorta; aortic arch; and descending aorta, which is in turn, divided into the thoracic aorta and the abdominal aorta. Syn: arteria aorta.

apoptosis - Programmed cell death; deletion of individual cells by fragmentation into membrane-bound particles, which are phagocytized by other cells. Syn: programmed cell death.

Whereas some cells (e.g., cardiac and skeletal muscle fibers, CNS neurons) last a lifetime, others (e.g., epithelial and glandular cells, erythrocytes) have limited life-spans, at the end of which they are genetically programmed to self-destruct, usually to be replaced by others formed by mitosis from surviving cells. Cells in tissue cultures spontaneously undergo apoptosis after about 50 cell divisions. In contrast to cell death caused by injury, infection, or circulatory impairment, apoptosis elicits no inflammatory response in adjacent cells and tissues. Features of apoptosis detectable by histologic and histochemical methods include cell shrinkage, due chiefly to dehydration; increased membrane permeability, with a rise in intracellular calcium and a fall in pH; endonucleolysis (fragmentation of nuclear DNA); and ultimately formation of apoptotic bodies, which are absorbed and removed by macrophages. Besides being due to genetic programming, apoptosis can be induced by injury to cellular DNA, as by irradiation and some cytotoxic agents used to treat cancer. It can be suppressed by naturally occurring factors (e.g., cytokines) and by some drugs (e.g., protease inhibitors). Apoptosis typically does not occur in malignant cells. Such cells therefore escape the destiny of their nonmalignant precursor cells and are said to be immortal. Immortalization can occur in various ways. The bcl-2 gene, present in many cancers, directs the production of an enzyme that blocks apoptosis and immortalizes affected cells. Injury to DNA normally triggers apoptosis by activating the p53 tumor suppressor gene, which is missing or mutated in about one-half of all human cancers. Cells that lack this gene can survive chemotherapy and irradiation intended to destroy cancer cells. Failure of apoptosis to occur is also involved in some degenerative diseases, including lupus erythematosus, and may be responsible for cellular damage caused by certain viruses, including HIV. [G. a falling or dropping off, fr. apo, off, + ptosis, a falling]

arachidonic acid - an unsaturated fatty acid, usually essential in nutrition; the biological precursor of the prostaglandins, the thromboxanes, and the leukotrienes (collectively known as eicosanoids).

arteriosclerosis - Hardening of the arteries; types generally recognized are: atherosclerosis, Mönckeberg arteriosclerosis, and arteriolosclerosis. See atherosclerosis.

artery - A relatively thick-walled, muscular, pulsating blood vessel conveying blood away from the heart. With the exception of the pulmonary and umbilical arteries, the arteries contain red or oxygenated blood. At the major arteries, the arterial branches are listed separately following the designation branches. Syn: arteria [TA].

atherosclerosis - Arteriosclerosis characterized by irregularly distributed lipid deposits in the intima of large and medium-sized arteries, causing narrowing of arterial lumens and proceeding eventually to fibrosis and calcification; lesions are usually focal and progress slowly and intermittently. Limitation of blood flow accounts for most clinical manifestations, which vary with the distribution and severity of lesions. In lower animals, atherosclerosis of swine and fowl closely resemble human atherosclerosis. Syn: nodular sclerosis.

Atherosclerosis, the most common form of arteriosclerosis, is a complex process that begins with the appearance of cholesterol-laden macrophages (foam cells) in the intima of an artery. Smooth muscle cells respond to the presence of lipid by proliferating, under the influence of platelet factors. A plaque forms at the site, consisting of smooth muscle cells, leukocytes, and further deposition of lipid; in time the plaque becomes fibrotic and may calcify. Expansion of an atherosclerotic plaque leads to gradually increasing obstruction of the artery and ischemia of tissues supplied by it. Ulceration, thrombosis, or embolization of a plaque, or intimal hemorrhage and dissection, can cause more acute and severe impairment of blood flow, with the risk of infarction. These are the principal mechanisms of coronary artery disease (arteriosclerotic heart disease with or without heart failure, angina pectoris, myocardial infarction), peripheral vascular disease (particularly occlusive disease of the lower extremity causing intermittent claudication or gangrene), and stroke (cerebral infarction due to occlusion of carotid or intracranial arteries). Independent risk factors for atherosclerosis are male sex, advancing age, the postmenopausal state, a family history of atherosclerosis, cigarette smoking, hypertension, diabetes mellitus, elevated plasma LDL cholesterol, elevated plasma homocysteine, overweight, and a sedentary life-style. Mounting evidence suggests that elevation of plasma levels of triglycerides, fasting insulin, fibrinogen, apolipoproteins A and B, and lipoprotein (a) are also independent risk factors. The diagnosis of atherosclerosis is usually based on history and physical examination and confirmed by angiography, Doppler ultrasonography, and other imaging techniques. Treatment is largely mechanical: balloon stretching, laser ablation, or surgical removal of plaques, and various bypass and grafting procedures. The prevention of atherosclerosis is a major objective of modern medicine. Preventive measures include regular vigorous exercise, a diet low in fat and cholesterol, maintenance of a healthful weight, avoidance of tobacco, and use of pharmacologic agents as indicated (e.g., rigorous control of hypertension and diabetes mellitus, reduction of elevated cholesterol, estrogen replacement therapy after menopause). See free radical; low-fat diet.

astrocyte - One of the large neuroglia cells of nervous tissue. See Also: neuroglia. Syn: astroglia, astroglia cell, Cajal cell (2), Deiters cells (2), macroglia cell, spider cell (1), macroglia.
 

atrium of heart - the upper chamber of each half of the heart.

autocrine - denoting self-stimulation through cellular production of a factor and a specific receptor for it.

autoimmune disease - any disorder in which loss of function or destruction of normal tissue arises from humoral or cellular immune responses to the body's own tissue constituents; may be systemic, as systemic lupus erythematosus, or organ specific, as thyroiditis

autonomic nervous system (ANS) - that part of the nervous system which represents the motor innervation of smooth muscle, cardiac muscle, and gland cells. It consists of two physiologically and anatomically distinct, mutually antagonistic components: the sympathetic and parasympathetic parts. In both of these parts the pathway of innervation consists of a synaptic sequence of two motor neurons, one of which lies in the spinal cord or brainstem as the presynaptic (preganglionic) neuron, the thin but myelinated axon of which (presynaptic (preganglionic) or B fiber) emerges with an outgoing spinal or cranial nerve and synapses with one or more of the postsynaptic (postganglionic or, more strictly, ganglionic) neurons composing the autonomic ganglia; the unmyelinated postsynaptic fibers in turn innervate the smooth muscle, cardiac muscle, or gland cells. Impulse transmission from presynaptic to postsynaptic neuron is mediated by acetylcholine in both the sympathetic and parasympathetic parts; transmission from the postsynaptic fiber to the visceral effector tissues is classically said to be by acetylcholine in the parasympathetic part and by noradrenalin in the sympathetic part; recent evidence suggests the existence of further noncholinergic, nonadrenergic classes of postsynaptic fibers. Sy

axon - The single process of a nerve cell that under normal conditions conducts nervous impulses away from the cell body and its remaining processes (dendrites. It is a relatively even filamentous process varying in thickness from about 0.25 to more than 10 4m. In contrast to dendrites, which rarely exceed 1.5 mm in length, Axons can extend great distances from the parent cell body (some axons of the pyramidal tract are 40–50 cm long). Axons 0.5 4m thick or over are generally enveloped by a segmented myelin sheath provided by oligodendroglia cells (in brain and spinal cord) or Schwann cells (in peripheral nerves). Like dendrites and nerve cell bodies, Axons contain a large number of neurofibrils. With some exceptions, nerve cells synaptically transmit impulses to other nerve cells or to effector cells (muscle cells, gland cells) exclusively by way of the synaptic terminals of their axon.

axon reflex - a response elicited by peripheral nerve stimulation; attributed to impulses traveling proximally from the stimulation site along motor axons, encountering a branch point, and then passing distally down the other branch to activate local arterioles (to cause vasodilation) or muscle (to cause contractions). Latency of the response decreases with more proximal stimulation; axon reflex is eliminated by axon degeneration or strong stimuli but not by proximal anesthetic blocks of the nerve.

B19 virus - a human parvovirus associated with arthritis and arthralgia and a number of specific clinical entities, including erythema infectiosum and aplastic crisis in the presence of hemolytic anemia.

bacterium - A unicellular prokaryotic microorganism that usually multiplies by cell division and has a cell wall that provides a constancy of form; they may be aerobic or anaerobic, motile or nonmotile, and free-living, saprophytic, commensal, parasitic, or pathogenic. See Also: Cyanobacteria.

baroreceptor - 1. In general, any sensor of pressure changes. 2. Sensory nerve ending in the wall of the auricles of the heart, vena cava, aortic arch, and carotid sinus, sensitive to stretching of the wall resulting from increased pressure from within, and functioning as the receptor of central reflex mechanisms that tend to reduce that pressure.

blood -  The “circulating tissue” of the body; the fluid and its suspended formed elements that are circulated through the heart, arteries, capillaries, and veins; blood is the means by which 1) oxygen and nutritive materials are transported to the tissues, and 2) carbon dioxide and various metabolic products are removed for excretion. The blood consists of a pale yellow or gray-yellow fluid, plasma, in which are suspended red blood cells (erythrocytes), white blood cells (leukocytes), and platelets.

brainstem, brain stem - Originally, the entire unpaired subdivision of the brain, composed of (in anterior sequence) the rhombencephalon, mesencephalon, and diecephalon as distinguished from the brain's only paired subdivision, the telencephalon. More recently, the term's connotation has undergone several arbitrary modifications.

calcium (Ca) - A metallic bivalent element; atomic no. 20, atomic wt. 40.078, density 1.55, melting point 842°C. The oxide of calcium is an alkaline earth, CaO, quicklime, which on the addition of water becomes calcium hydrate, Ca(OH)2, slaked lime. For some organic calcium salts not listed below, see the name of the organic acid portion. Many calcium salts have crucial uses in metabolism and in medicine. Calcium salts are responsible for the radiopacity of bone, calcified cartilage, and arteriosclerotic plaques in arteries.

cAMP - adenosine 3c,5c-cyclic monophosphate (cAMP) - An activator of phosphorylase kinase and an effector of other enzymes, formed in muscle from ATP by adenylate cyclase and broken down to 5c-AMP by a phosphodiesterase; the first compound referred to as a “second messenger.” It is a metabolic regulator. A related compound (2c,3c) is also known. Syn: cyclic adenylic acid, cyclic AMP, cyclic phosphate.

capillary (blood ) - a vessel whose wall consists of endothelium and its basement membrane; its diameter, when the capillary is open, is about 8 4m; with the electron microscope, fenestrated capillaries and continuous capillaries are distinguished.
 

cardiomyopathy - Disease of the myocardium. As a disease classification, the term is used in several different senses, but is limited by the World Health Organization to: “Primary disease process of heart muscle in absence of a known underlying etiology” when referring to idiopathic cardiomyopathy. Syn: myocardiopathy.

catabolism - 1. The breaking down in the body of complex chemical compounds into simpler ones (e.g., glycogen to CO2 and H2O), often accompanied by the liberation of energy.

catecholamines - Pyrocatechols with an alkylamine side chain; examples of biochemical interest are epinephrine, norepinephrine, and L-dopa. Catecholamines are major elements in responses to stress.

CD - Abbreviation for cluster of differentiation. cluster of differentiation (CD) antigen - an antigen (marker) on the surface of a cell, usually a lymphocyte. Cell membrane molecules that are used to classify leukocytes into subsets. CD molecules are classified by monoclonal antibodies. There are four general types: type I transmembrane proteins have their COOH-termini in the cytoplasm and their NH2-termini outside the cell; type II transmembrane proteins have their NH2-termini in the cytoplasm and their COOH-termini outside the cell; type III transmembrane proteins cross the plasma membrane more than once and hence may form transmembrane channels; and glycosylphosphatidylinositol-anchored proteins (type IV), which are tethered to the lipid bilayer via a glycosylphosphatidylinositol anchor. (see CD Markers for a list).  The below CD markers have received particular interest in CFS.

CD4 - a type I transmembrane protein found on helper/inducer T cells, monocytes, macrophages, and dendritic cells that is involved in T-cell recognition of antigens; expressed in mycosis fungoides, Sézary syndrome, and T-cell lymphomas.

CD5 - a type I transmembrane protein found on T cells, thymocytes, and some B cells that is a ligand for CD72 and is involved in cellular activation or adhesion; expressed in B-cell chronic lymphocytic leukemia and T-cell lymphoma.

CD8 - a type I transmembrane protein found on suppressor (cytotoxic) T cells, some natural killer cells, and most thymocytes that is involved in T-cell antigen recognition; expressed in some T-cell lymphomas and large granular lymphocyte leukemias.

CD11a - a type I transmembrane protein found on lymphocytes, neutrophils, monocytes, and macrophages that facilitates cell adhesion and cell activation; expressed in lymphomas.

CD25 - a type I transmembrane protein present on activated T cells, activated B cells, some thymocytes, myeloid precursors, and oligodendrocytes that associates with CD122 to form a heterodimer that can act as a high-affinity receptor for IL-2; expressed in most B-cell neoplasms, some acute nonlymphocytic leukemias, and neuroblastomas.
 

CD32 - a type I transmembrane protein present on monocytes, B cells, neutrophils, placental trophoblasts, and endothelium; acts as a signal transducer for IgG-mediated phagocytosis and neutrophil and monocyte oxidative burst; transduces an inhibitory signal on B cells and may play a role in placental IgG transport.

CD38 - a transmembrane protein present on macrophages, dendritic cells, and activated cells of the natural killer, B- and T-cell lines that can facilitate B-cell adhesion.

CD45 - a type I transmembrane protein present on all hemopoietic cells except erythrocytes that assists in cell activation; expressed in lymphomas, B-cell chronic lymphocytic leukemia, hairy cell leukemia, and acute nonlymphocytic leukemia.

cell-mediated immunity, cellular immunity (CMI)  - immune responses that are initiated by an antigen-presenting cell interacting with and mediated by T lymphocytes (e.g., graft rejection, delayed-type hypersensitivity). Syn: delayed hypersensitivity (1).

cerebral cortex - the gray cellular mantle (1–4 mm thick) covering the entire surface of the cerebral hemisphere of mammals; characterized by a laminar organization of cellular and fibrous components such that its nerve cells are stacked in defined layers varying in number from one, as in the archicortex of the hippocampus, to five or six in the larger neocortex; the outermost (molecular or plexiform) layer contains very few cell bodies and is composed largely of the distal ramifications of the long apical dendrites issued perpendicularly to the surface by pyramidal and fusiform cells in deeper layers. From the surface inward, the layers as classified in K. Brodmann's parcellation are: 1) molecular layer [TA]; 2) external granular layer [TA]; 3) external pyramidal layer [TA]; 4) internal granular layer [TA]; 5) internal pyramidal layer [TA]; and 6) multiform layer [TA], many of which are fusiform. This multilaminate organization is typical of the neocortex (homotypic cortex; isocortex [TA] in O. Vogt terminology), which in humans covers the largest part by far of the cerebral hemisphere. The more primordial heterotypic cortex or allocortex (Vogt) has fewer cell layers. A form of cortex intermediate between isocortex and allocortex, called juxtallocortex (Vogt) covers the ventral part of the cingulate gyrus and the entorhinal area of the parahippocampal gyrus. On the basis of local differences in the arrangement of nerve cells (cytoarchitecture), Brodmann outlined 47 areas in the cerebral cortex which, in functional terms, can be classified into three categories: motor cortex (areas 4 and 6), characterized by a poorly developed internal granular layer (agranular cortex) and prominent pyramidal cell layers; sensory cortex, characterized by a prominent internal granular layer (granular cortex or koniocortex) and comprising the somatic sensory cortex (areas 1 to 3), the auditory cortex (areas 41 and 42), and the visual cortex (areas 17 to 19); and association cortex, the vast remaining expanses of the cerebral cortex. Syn: cortex cerebri [TA], mantle (2), brain mantle, pallium [TA].

channelopathy - a number of diseases, mostly inherited and episodic in nature, caused by dysfunction of the calcium, chloride, potassium, or sodium channels of nerve or muscle; the inherited myotonias and periodic paralyses are included in this category; there is usually dominant inheritance, with the primary defect due to mutations of gene encoding on locus 7q32, 17q, or 1q31-32.

chemoreceptor - Any cell that is activated by a change in its chemical milieu and results in a nerve impulse. Such cells can be either 1) “transducer” cells innervated by sensory nerve fibers (e.g., the gustatory receptor cells of the taste buds; cells in the carotid body sensitive to changes in the oxygen and carbon dioxide content of the blood); or 2) nerve cells proper, such as the olfactory receptor cells of the olfactory mucosa, and certain cells in the brainstem that are sensitive to changes in the composition of the blood or cerebrospinal fluid. Syn: chemoceptor.

chemotaxis - 1. Movement of cells or organisms in response to chemicals, whereby the cells are attracted (positive chemotaxis) or repelled (negative chemotaxis) by substances exhibiting chemical properties.
2. The migration of polymorphonuclear leukocytes and macrophages toward higher concentrations of certain fragments of complement.

cholesterol (lipoprotein) - Any complex or compound containing both lipid and protein. Lipoproteins are important constituents of biological membranes and of myelin. Conjugation with protein facilitates transport of lipids, which are hydrophobic, in the aqueous medium of the plasma.  The principal classes by density are chylomicrons, which transport dietary cholesterol and triglycerides from the intestine to the liver and other tissues; very low density lipoproteins (VLDL), which transport triglycerides from intestine and liver to muscle and adipose tissue; low density lipoproteins (LDL), which transport cholesterol to tissues other than the liver; and high density lipoproteins (HDL), which transport cholesterol to the liver for excretion in bile. A plasma lipoprotein particle is typically spherical, with a hydrophobic core of triacylglycerol, cholesteryl esters, and apolar amino acid residues surrounded by hydrophilic protein structures and phospholipids.

The concentrations of certain serum lipoproteins correlate closely with the risk of atherosclerosis. An HDL cholesterol level below 35 mg/dL (0.90 mmol/L), an LDL cholesterol level above 160 mg/dL (4.15 mmol/L), and a fasting triglyceride level above 250 mg/dL are all independent risk factors for coronary artery disease. Although dietary factors are important in some persons, basal levels of lipoprotein, cholesterol, and triglycerides depend chiefly on heredity. Several phenotypes of familial hyperlipoproteinemia associated with risk of premature cardiovascular disease and death have been identified. SEE hyperlipoproteinemia. Medical management of patients with coronary artery disease (myocardial infarction, angina pectoris, history of coronary artery bypass graft or coronary angioplasty) and other atherosclerotic disorders (peripheral arterial disease, abdominal aortic aneurysm, carotid artery disease) includes detection and correction of hypercholesterolemia and hyperlipoproteinemia. Reducing elevated LDL cholesterol diminishes the risk of coronary artery disease; besides halting the progression of atherosclerosis, it may even shrink established atherosclerotic lesions. Of persons with elevated LDL cholesterol, 75% can achieve normal levels with diet, weight reduction, and exercise; the remainder need drug treatment. Factors besides familial hyperlipoproteinemias that can elevate LDL cholesterol include diabetes mellitus, hypothyroidism, nephrotic syndrome, obstructive liver disease, and drugs (progestogens, anabolic steroids, corticosteroids, thiazide diuretics). Dietary saturated fat raises LDL cholesterol more than any other dietary component, cholesterol itself not excepted.

choline - found in most animal tissues either free or in combination as lecithin (phosphatidylcholine), acetate (acetylcholine), or cytidine diphosphate (cytidine diphosphocholine). It is included in the vitamin B complex; as acetylcholine (choline esterified with acetic acid), it is essential for synaptic transmission. Several salts of choline are used in medicine. Syn: lipotropic factor, transmethylation factor.

cholinergic - Relating to nerve cells or fibers that employ acetylcholine as their neurotransmitter. Cf. adrenergic.

chlamydia - The only genus of the family Chlamydiaceae, including all the agents of the psittacosis-lymphogranuloma-trachoma disease groups; chlamydia are obligatory intracellular spherical or ovoid bacteria with a complex intracellular life cycle; the infective form is the elementary body, which penetrates the host cell, replicating as the rediculate body by binary fission; replication occurs in a vacuole called the inclusion body; chlamydia lack peptidoglycan in their cell walls.

Chlamydia pneumoniae -a bacterial species first isolated in 1986 and currently recognized as a common cause of pneumonia, bronchitis, rhinosinusitis, and pharyngitis in both adults and children. Syn: TWAR.

Chlamydia pneumoniae is responsible for about 25% of cases of acute bronchitis and 10% of community-acquired pneumonia. Recent studies have suggested that it may also play a role in the genesis of cardiovascular disease and late-onset Alzheimer dementia. Like C. trachomatis and C. psittaci, this organism is an occasional cause of myocarditis and endocarditis. Elevated levels of antibody to C. pneumoniae are found in persons with acute myocardial infarction (MI), and in persons showing significant atheroma formation at autopsy, significantly more often than in control groups. The organism has been detected by immunocytochemistry, polymerase chain reaction, and electron microscopy in macrophages and smooth muscle cells of atheromatous plaques of the aorta, coronary arteries, and carotid arteries (surgical and autopsy specimens), but not in normal arteries. The incidence of acute infection in MI patients, as detected by throat culture, is higher than in the general public. A retrospective review of medical records of persons with acute MI showed that they were less likely than matched controls to have been treated during the preceding 3 years with tetracycline or quinolone antibiotics, which are active against C. pneumoniae. To date, however, prospective studies have not shown an association between the presence of IgG antibody to C. pneumoniae and an increased risk of atherothrombotic disease. Researchers have speculated that infection with C. pneumoniae may be one of several factors capable of initiating changes that culminate in atherosclerosis, or that reinfection may trigger coronary atherothrombosis. Antibody to C. pneumoniae is also found in persons with severe hypertension at about twice the incidence rate for the general public. In addition, the organism has been detected in microglia and astroglia of the hippocampus and temporal cortex in persons with late-onset Alzheimer disease with much greater frequency than in normal brains.

ciguatera - An acute toxic syndrome with predominantly gastrointestinal and neuromuscular features induced by ingestion of the flesh or viscera of various marine fish of the Caribbean and tropical Pacific reefs that contain ciguatoxin.

Sporadic cases of ciguatera occur along the east coast of the United States from Vermont to southern Florida and in the U.S. Virgin Islands, Puerto Rico, and Hawaii. Occasional outbreaks result from group consumption of large catches of contaminated fish. The condition is probably underreported, many cases being dismissed as viral syndromes or seasickness. The lipid-soluble, heat-stable toxin is produced by the dinoflagellate Gambierdiscus toxicus, which is epiphytic on red and brown algae. Herbivorous fish foraging on reef algae consume the flagellates and are in turn consumed by carnivorous fish; the toxin becomes increasingly concentrated as it passes up the food chain. The heads and viscera of affected fish contain higher concentrations than other parts. Some 400 species of fish have been associated with human intoxication, including particularly predators such as amberjack, barracuda, grouper, moray eels, red snapper, sea bass, Spanish mackerel, and surgeon fish. Contaminated fish look, smell, and taste normal, and ciguatoxin is not destroyed by cooking, drying, salting, or freezing. Symptoms come on 3–12 hours after exposure (occasionally within minutes) and include vomiting and diarrhea, myalgia, dysesthesia and paresthesia of the extremities and perioral region, pruritus, headache, weakness, and diaphoresis. Bradycardia and hypotension may occur. A few deaths due to respiratory paralysis have been reported. Toxic effects usually resolve spontaneously in about 1 week but residual symptoms may persist for months. Repeated exposure can increase the sensitivity of an individual to the toxin. Diagnosis is confirmed by identification of toxin in uneaten portions of seafood or in the patient's serum. Treatment is purely supportive. [Sp. fr. cigua, sea snail]

citric acid cycle - Syn: tricarboxylic acid cycle.

codon - A set of three consecutive nucleotides in a strand of DNA or RNA that provides the genetic information to code for a specific amino acid which will be incorporated into a protein chain or serve as a termination signal. Syn: triplet (3).

complement - Ehrlich term for the thermolabile substance, normally present in serum, that is destructive to certain bacteria and other cells sensitized by a specific complement-fixing antibody. Complement is a group of at least 20 distinct serum proteins, the activity of which is affected by a series of interactions resulting in enzymatic cleavages and which can follow one or the other of at least two pathways. In the case of immune hemolysis (classical pathway), the complex comprises nine components (designated C1 through C9) that react in a definite sequence and the activation of which is usually effected by the antigen-antibody complex; only the first seven components are involved in chemotaxis, and only the first four are involved in immune adherence or phagocytosis or are fixed by conglutinins. An alternative pathway (see properdin system) may be activated by factors other than antigen-antibody complexes and involves components other than C1, C4, and C2 in the activation of C3. See Also: component of complement.     Properdin - A globulin in normal serum involved in resistance to infection that participates, in conjunction with other factors, in an alternative pathway to the activation of the terminal components of complement; a deficiency of properdin results in the lack of stabilization of the alternative C3-convertase enzyme (an X-linked recessive disorder). See Also: component of complement, factor P, .Orig [pro- + L. perdo, to destroy] Properdin system - an immunologic system that is the alternative pathway for complement, composed of several distinct proteins that react in a serial manner and activate C3 (third component of complement), seemingly without utilizing components C1, C4, and C2; in addition to properdin, the system includes Factors B, D, H, and I. The system can be activated, in the absence of specific antibody, by bacterial endotoxins, by a variety of polysaccharides and lipopolysaccharides, and by a component of cobra venom.

corticotropin-releasing factor (CRF) - a factor secreted by the hypothalamus that stimulates the pituitary to release adrenocorticotropic hormone. Syn

corticosteroid - A steroid produced by the adrenal cortex (i.e., adrenal corticoid); a corticoid containing a steroid. Syn: adrenocorticoid, corticoid (3),

cortisone - A glucocorticoid not normally secreted in significant quantities by the human adrenal cortex. Endogenously, it is probably a metabolite of hydrocortisone but exhibits no biological activity until converted to hydrocortisone (cortisol); it acts upon carbohydrate metabolism and influences the nutrition and growth of connective (collagenous) tissues. It was the first glucocorticoid available for therapy. Syn: Wintersteiner compound F.

cortisol - (hydrocortisone) A reduction product (at C-11) of cortisone; a steroid hormone secreted by the adrenal cortex (the active hormone secreted in the greatest quantity by the adrenals) and the most potent of the naturally occurring glucocorticoids in humans; an antiinflammatory agent.

Coxiella - A genus of filterable bacteria (order Rickettsiales) containing small, pleomorphic, rod-shaped or coccoid, Gram-negative cells that occur intracellularly in the cytoplasm of infected cells and possibly extracellularly in infected ticks. These organisms have not been cultivated in cell-free media; they are parasitic on humans and other animals; type species is Coxiella burnetii. Coxiella burnetii is a bacterial species that causes Q fever in humans; it is more resistant than other rickettsiae and may be passed via aerosols as well as living vectors. Acute pneumonia and chronic endocarditis are also associated with this species. The type species of the genus Coxiella.

cyclooxygenase - a protein complex that catalyzes two steps in prostaglandin biosynthesis; the cyclooxygenase activity (which is inhibited by aspirin and indomethacin) converts arachidonate and 2O2 to prostaglandin G2; the hydroperoxidase activity uses glutathione to convert prostaglandin G2 to prostaglandin H2.

cytochrome c oxidase - A cytochrome of the a type, containing copper, that catalyzes the oxidation of 4ferrocytochrome c by molecular oxygen to 4ferricytochrome c and 2H2O. A part of Complex IV of the respiratory chain. A deficiency of one or more of the polypeptides of this complex results in neuronal loss in brain leading to psychomotor retardation and neurodegenerative disease. Syn: cytochrome aa3, indophenolase, indophenol oxidase.

cytokine - Any of numerous hormonelike, low-molecular-weight proteins, secreted by various cell types, that regulate the intensity and duration of immune response and mediate cell-cell communication. See: chemokines, interferon, interleukin, lymphokine. See Also: interferon, interleukin, lymphokine.

Cytokines are produced by macrophages, B and T lymphocytes, mast cells, endothelial cells, fibroblasts, and stromal cells of the spleen, thymus, and bone marrow. They are involved in mediating immunity and allergy and in regulating the maturation, growth, and responsiveness of particular cell populations, sometimes including the cells that produce them (autocrine activity). A given cytokine may be produced by more than one type of cell. Some cytokines enhance or inhibit the action of other cytokines. The first cytokines to be identified were named according to their functions (e.g., T cell growth factor), but this nomenclature became awkward because several cytokines can have the same function, and the function of a cytokine can vary with the circumstances of its elaboration. Later, as the chemical structure of each cytokine was determined, it was designated an interleukin and assigned a number (e.g., interleukin-2 [IL-2], formerly T cell growth factor). Cytokines have been implicated in the generation and recall of long-term memory and the focusing of attention. Some of the degenerative effects of aging may be due to a progressive loss of regulatory capacity by cytokines. Because cytokines derived from the immune system (immunokines) are cytotoxic, they have been used against certain types of cancer.

dexamethasone - A potent synthetic analogue of cortisol, with similar biological action; used as an anti-inflammatory agent and as a test material for adrenal cortical function.

diastole - Normal postsystolic dilation of the heart cavities, during which they fill with blood; diastole of the atria precedes that of the ventricles; diastole of either chamber alternates rhythmically with systole or contraction of that chamber.

dopamine (DM) - An intermediate in tyrosine metabolism and precursor of norepinephrine and epinephrine; it accounts for 90% of the catecholamines; its presence in the central nervous system and localization in the basal ganglia (caudate and lentiform nuclei) suggest that dopamine may have other functions. Depletion of dopamine produces Parkinson disease. Syn: decarboxylated dopa, 3-hydroxytyramine.

echocardiography - The use of ultrasound in the investigation of the heart and great vessels and diagnosis of cardiovascular lesions.

edema - An accumulation of an excessive amount of watery fluid in cells or intercellular tissues.

eicosanoids - The physiologically active substances derived from arachidonic acid, i.e., the prostaglandins, leukotrienes, and thromboxanes; synthesized via a cascade pathway.

elastase -A serine proteinase hydrolyzing elastin; other elastase-like enzymes have been identified (e.g., pancreatic elastase [pancreatopeptidase E] and leukocyte elastase [lysosomal or neutrophil elastase]) with different sequences and kinetic parameters; all have fairly broad specificities.

elastin - A yellow elastic fibrous mucoprotein that is the major connective tissue protein of elastic structures (e.g., large blood vessels, tendons, ligaments, etc.); elastins precursor is proelastin. Syn: elasticin.

endoplasmic reticulum (ER) - the network of cytoplasmic tubules or flattened sacs (cisternae) with (rough ER) or without (smooth ER) ribosomes on the surface of their membranes in eukaryotes. Syn: endomembrane system

endothelium, pl. endothelia - A layer of flat cells lining especially blood and lymphatic vessels and the heart.

endotoxemia - Presence in the blood of endotoxins, which, if derived from Gram-negative rod-shaped bacteria, may cause a generalized Shwartzman phenomenon with shock.

endotoxin - 1. A bacterial toxin not freely liberated into the surrounding medium, in contrast to exotoxin. 2. The complex phospholipid-polysaccharide macromolecules that form an integral part of the cell wall of a variety of relatively avirulent as well as virulent strains of Gram-negative bacteria. The toxins are relatively heat-stable, are less potent than most exotoxins, are less specific, and do not form toxoids; on injection, they may cause a state of shock and, in smaller doses, fever and leukopenia followed by leukocytosis; they have the capacity of eliciting the Shwartzman and the Sanarelli-Shwartzman phenomena. Syn: intracellular toxin.

enzyme - A protein that acts as a catalyst to induce chemical changes in other substances, itself remaining apparently unchanged by the process. Enzymes, with the exception of those discovered long ago (e.g., pepsin, emulsin), are generally named by adding -ase to the name of the substrate on which the enzyme acts (e.g., glucosidase), the substance activated (e.g., hydrogenase), and/or the type of reaction (e.g., oxidoreductase, transferase, hydrolase, lyase, isomerase, ligase or synthetase—these being the six main groups in the Enzyme Nomenclature Recommendations of the International Union of Biochemistry). For individual enzymes not listed below, see the specific name. Syn: organic catalyst (1).

eosinophil - a polymorphonuclear leukocyte characterized by many large or prominent, refractile, cytoplasmic granules that are fairly uniform in size; the nuclei are usually larger than those of neutrophils; these leukocytes are motile phagocytes with distinctive antiparasitic functions. Syn: eosinocyte, eosinophil, acidophilic leukocyte, oxyphilic leukocyte, oxyphil

epinephrine - A catecholamine that is the chief neurohormone of the adrenal medulla of most species; also secreted by neurons. The L-isomer is the most potent stimulant (sympathomimetic) of adrenergic )- and *-receptors, resulting in increased heart rate and force of contraction, vasoconstriction or vasodilation, relaxation of bronchiolar and intestinal smooth muscle, glycogenolysis, lipolysis, and other metabolic effects; used in the treatment of bronchial asthma, acute allergic disorders, open-angle glaucoma, cardiac arrest, and heart block, and as a topical and local vasoconstrictor. Generally used salts are epinephrine hydrochloride and epinephrine bitartrate, the latter most frequently used in topical preparations. Syn: adrenaline.

epitope - The simplest form of an antigenic determinant, on a complex antigenic molecule, which can combine with antibody or T cell receptor.

Epstein-Barr virus (EBV) - a herpesvirus in the genus Lymphocryptovirus that causes infectious mononucleosis and is also found in cell cultures of Burkitt lymphoma; associated with nasopharyngeal carcinoma. Syn: human herpesvirus 4, EB virus.

erythema infectiosum  - a mild infectious exanthema of childhood characterized by an erythematous maculopapular eruption, resulting in a lacelike facial rash or “slapped cheek” appearance. Fever and arthritis may also accompany infection; caused by Parvovirus B 19. Syn: fifth disease.

erythrocyte sedimentation rate (ESR) - the rate of settling of red blood cells in anticoagulated blood; increased rates are often associated with anemia or inflammatory states.

extravasate - To exude from or pass out of a vessel into the tissues, said of blood, lymph, or urine.

fatty acid - Any acid derived from fats by hydrolysis (e.g., oleic, palmitic, or stearic acids); any long-chain monobasic organic acid; they accumulate in disorders associated with the peroxisomes.

fatty acid oxidation cycle - a series of reactions involving acyl-coenzyme A compounds, whereby these undergo beta oxidation and thioclastic cleavage, with the formation of acetyl-coenzyme A; the major pathway of fatty acid catabolism in living tissue.

fibrin - An elastic filamentous protein derived from fibrinogen by the action of thrombin, which releases fibrinopeptides A and B from fibrinogen in the coagulation of blood; a component of thrombi, vegetations, and acute inflammatory exudates such as in diphtheria and lobar pneumonia.

fibrinogen - A globulin of the blood plasma that is converted into fibrin by the action of thrombin in the presence of ionized calcium to produce coagulation of the blood; the only coagulable protein in the blood plasma of vertebrates; it is absent in afibrinogenemia and is defective in dysfibrinogenemia

fibroblast - A stellate or spindle-shaped cell with cytoplasmic processes present in connective tissue, capable of forming collagen fibers; an inactive fibroblast is sometimes called a fibrocyte.

fibromyalgia - A syndrome of chronic pain of musculoskeletal origin but uncertain cause. The American College of Rheumatology has established diagnostic criteria that include pain on both sides of the body, both above and below the waist, as well as in an axial distribution (cervical, thoracic, or lumbar spine or anterior chest); additionally there must be point tenderness in at least 11 of 18 specified sites. Syn: fibromyalgia syndrome.

frameshift -  As used in genetics: a mutation that causes a sequence such that the reading frame groups of three bases in mRNA become out of register; the insertion or deletion of one or two bases, for example, would lead to an altered grouping of three bases causing incorrect amino acid residues to be incorporated into growing polypeptide chains, or would signal premature chain termination.

free radical -a radical in its (usually transient) uncombined state; an atom or atom group carrying an unpaired electron and no charge; e.g., hydroxyl  and methyl Free radicals may be involved as short-lived, highly active intermediates in various reactions in living tissue, notably in photosynthesis. The free radical nitric oxide, NO, plays an important role in vasodilation. Syn: radical (4).

Free radicals occur naturally within the body as a result of metabolic processes and can also be introduced from without (through smoking, inhaling environmental pollutants, or exposure to UV radiation). They interact readily with nearby molecules and may cause cellular damage, including genetic alterations. It has been theorized that they are involved in plaque formation in atherosclerosis, in cancer, and in degenerative disorders such as Alzheimer dementia and parkinsonism. Natural enzymes such as superoxide dismutase and peroxidase are thought to counteract free radicals, and there is evidence that many nutrients, including vitamins C and E and *-carotene, also exert an antioxidant effect. SEE ALSO antioxidant.

gene - A functional unit of heredity that occupies a specific place (locus) on a chromosome, is capable of reproducing itself exactly at each cell division and directs the formation of an enzyme or other protein. The gene as a functional unit consists of a discrete segment of a giant DNA molecule containing the purine (adenine and guanine) and pyrimidine (cytosine and thymine) bases in the correct sequence to code the sequence of amino acids of a specific peptide. Protein synthesis is mediated by molecules of messenger-RNA formed on the chromosome with the gene acting as a template. The RNA then passes into the cytoplasm and becomes oriented on the ribosomes where it in turn acts as a template to organize a chain of amino acids to form a peptide. In organisms reproducing sexually, normally occur in pairs in all cells except gametes, as a consequence of the fact that all chromosomes are paired except the sex chromosomes (X and Y) of the male. Syn: facto

genetic polymorphism - the occurrence in the same population of multiple discrete alletic states of which at least two have high frequency (conventionally of 1% or more).

glial cells - Non-neuronal cellular elements of the central and peripheral nervous system; formerly believed to be merely supporting cells but now thought to have important metabolic functions, since they are invariably interposed between neurons and the blood vessels supplying the nervous system. In central nervous tissue they include oligodendroglia cells, astrocytes, ependymal cells, and microglia cells. The satellite cells of ganglia and the neurolemmal or Schwann cells around peripheral nerve fibers can be interpreted as the oligodendroglia cells of the peripheral nervous system. Syn: glia, reticulum (2) [TA], Kölliker reticulum.

globulins - Name for a family of proteins precipitated from plasma (or serum) by half-saturation with ammonium sulfate (i.e., addition of an equal volume of saturated ammonium sulfate). Globulins may be further fractionated by solubility, electrophoresis, ultracentrifugation, and other separation methods into many subgroups. The main groups are )-, *-, and +-globulin, which contains most antibodies.

glucocorticoid - Any steroid-like compound capable of significantly influencing intermediary metabolism such as promotion of hepatic glycogen deposition, and of exerting a clinically useful anti-inflammatory effect. Cortisol (hydrocortisone) is the most potent of the naturally occurring glucocorticoids; most semisynthetic glucocorticoids are cortisol derivatives

gluconeogenesis - The formation of glucose from noncarbohydrates, such as protein or fat. Syn: glyconeogenesis (2).

glutathione (GSH) -A tripeptide of glycine, L-cysteine, and L-glutamate, with L-glutamate having an isopeptide bond with the amino moiety of L-cysteine. Glutathione has a wide variety of roles in a cell; it is the most prevalent non-protein thiol. Glutathione disulfide (GSSG) consists of two glutathiones linked via a disulfide bridge; the term oxidized glutathione for GSSG should be avoided since it includes the sulfones and sulfoxides. The term reduced glutathione is not necessary since glutathione is the thiol form. A deficiency of glutathione can cause hemolysis with oxidative stress. It is also used in the course of intermediary metabolism as a donor of thiol (SH) groups and is essential for detoxification of acetaminophen. See Also: oxidized glutathione, reduced glutathione, glutathione reductase.

glutathione peroxidase -an enzyme that catalyzes the reaction of two glutathiones with H2O2 forming GSSG and two water molecules; a crucial enzyme in hydrogen peroxide detoxification.

glutathione reductase - an enzyme that catalyzes the reaction of GSSG with NADH (or NADPH) forming two glutathiones and NAD+ (or NADP+); involved in many redox reactions; a deficiency can cause hemolysis with oxidative stress.

glutathione S-transferase - a class of enzymes that catalyze the reaction of glutathione with an acceptor molecule (e.g., an arene oxide) to form an S-substituted glutathione; a key step in detoxification of many substances; start of the mercapturic acid pathway. Syn: ligandin.

glutathione synthetase - an enzyme that catalyzes the formation of glutathione, ADP, and orthophosphate from +-glutamylcysteine, ATP, and glycine; a deficiency will lead to metabolic acidosis and progressive brain dysfunction.

glutathione synthetase deficiency - an inborn error of metabolism associated with massive urinary excretion of 5-oxyproline, elevated levels of 5-oxyproline in the blood and cerebrospinal fluid, severe metabolic acidosis, tendency toward hemolysis, and defective central nervous systems function. Glutathione synthetase deficiency has been reported as a generalized condition or with a deficiency restricted to erythrocytes.

glycolysis -The energy-yielding conversion of D-glucose to lactic acid (instead of pyruvate oxidation products) in various tissues, notably muscle, when sufficient oxygen is not available (as in an emergency situation); since molecular oxygen is not consumed in the process, this is frequently referred to as “anaerobic glycolysis”

G proteins - intracellular membrane-associated proteins activated by several (e.g., *-adrenergic) receptors; they serve as second messengers or transducers of the receptor-initiated response to intracellular elements such as enzymes to initiate an effect. These proteins have a high affinity for guanine nucleotides and hence are named G proteins. Syn: G-protein, GTP binding proteins.

growth factors - natural substances produced by the body (hormones) or obtained from food (vitamins, minerals) that promote growth and development by directing cell maturation and differentiation and by mediating maintenance and repair of tissues; abnormalities in growth factors may be involved in benign and malignant neoplasia.

growth hormone (somatotropin) - A protein hormone of the anterior lobe of the pituitary, produced by the acidophil cells, that promotes body growth, fat mobilization, and inhibition of glucose utilization; diabetogenic when present in excess; a deficiency of somatotropin is associated with a number of types of dwarfism (type III is an X-linked disorder). Syn: growth hormone, pituitary growth hormone, somatotropic hormone.

hemopoiesis - The process of formation and development of the various types of blood cells and other formed elements. Syn: hematogenesis, hematopoiesis, hematosis (1), hemogenesis, sanguification.

hemoglobin (Hb) - The red respiratory protein of erythrocytes, consisting of approximately 3.8% heme and 96.2% globin, with a molecular weight of 64,450, which as oxyhemoglobin (HbO2) transports oxygen from the lungs to the tissues where the oxygen is readily released and HbO2 becomes Hb. When Hb is exposed to certain chemicals, its normal respiratory function is blocked; e.g., the oxygen in HbO2 is easily displaced by carbon monoxide, thereby resulting in the formation of fairly stable carboxyhemoglobin (HbCO), as in asphyxiation resulting from inhalation of exhaust fumes from gasoline engines. When the iron in Hb is oxidized from the ferrous to ferric state, as in poisoning with nitrates and certain other chemicals, a nonrespiratory compound, methemoglobin (MetHb).

hemopoiesis -  The process of formation and development of the various types of blood cells and other formed elements. Syn: hematogenesis, hematopoiesis, hematosis (1), hemogenesis, sanguification.

heparin - An anticoagulant principle that is a component of various tissues (especially liver and lung) and mast cells in humans and several mammalian species; its principal and active constituent is a glycosaminoglycan composed of D-glucuronic acid and D-glucosamine, both sulfated.  In conjunction with a serum protein cofactor (the so-called heparin cofactor), heparin acts as an antithrombin and an antiprothrombin. Synthetic preparations are commonly used in therapeutic anticoagulation. It also enhances activity of “clearing factors” (lipoprotein lipases). Syn: heparinic acid.

viral hepatitis type C - principal cause of non-A, non-B posttransfusion hepatitis caused by an RNA virus that is classified with the Flaviviridae family. The incubation period is 6–8 weeks with about 75% of infections subclinical and giving rise to chronic persistent infection. A high percentage of these develop chronic liver disease leading to cirrhosis and possible hepatocellular carcinoma. Syn: hepatitis C, virus C hepatitis.

Herpesvirus (herpesviridae) - A heterogeneous family of morphologically similar viruses, all of which contain double-stranded DNA and which infect man and a wide variety of other vertebrates. Infections produce type A inclusion bodies; in many instances, infection may remain latent for many years, even in the presence of specific circulating antibodies. Virions are enveloped, ether-sensitive, and vary up to 200 nm in diameter; the nucleocapsids are 100 nm in diameter and of icosahedral symmetry, with 162 capsomeres. The family is subdivided into 3 subfamilies Alphaherpesvirinae, Betaherpesvirinae, and Gammaherpesvirinae, and includes herpes simplex virus, varicella-zoster virus, cytomegalovirus, and EB virus (all of which infect humans). Human herpesvirus 6 - a human herpesvirus that was found in certain lymphoproliferative disorders, replicates in a number of different types of leukocytes, and is associated with the childhood disease roseola (exanthema subitum).

Herxheimer reaction - an inflammatory reaction in syphilitic tissues (skin, mucous membrane, nervous system, or viscera) induced in certain cases by specific treatment with Salvarsan, mercury, or antibiotics; believed to be due to a rapid release of treponemal antigen with an associated allergic reaction in the patient. Syn: Jarisch-Herxheimer reaction.

histamine (H) -  A vasodepressor amine derived from histidine by histidine decarboxylase and present in ergot and in animal tissues. It is a powerful stimulant of gastric secretion, a constrictor of bronchial smooth muscle, and a vasodilator (capillaries and arterioles) that causes a fall in blood pressure. Histamine, or a substance indistinguishable in action from it, is liberated in the skin as a result of injury. When injected intradermally in high dilution, it causes the triple response.

humoral immunity - immunity associated with circulating antibodies, in contradistinction to cellular immunity.

hydrolysis -A chemical process whereby a compound is cleaved into two or more simpler compounds with the uptake of the H and OH parts of a water molecule on either side of the chemical bond cleaved; hydrolysis is effected by the action of acids, alkalies, or enzymes. Cf. hydration. Syn: hydrolytic cleavage.

hydroperoxide/hydrogen peroxide - an unstable compound readily broken down to water and oxygen, a reaction catalyzed by various powdered metals and by the enzyme, catalase; a 3% solution is used as a mild antiseptic for skin and mucous membranes.

hypertension - High blood pressure; transitory or sustained elevation of systemic arterial blood pressure to a level likely to induce cardiovascular damage or other adverse consequences. Hypertension has been arbitrarily defined as a systolic blood pressure above 140 mm Hg or a diastolic blood pressure above 90 mm Hg. Consequences of uncontrolled hypertension include retinal vascular damage (Keith-Wagener-Barker changes), cerebrovascular disease and stroke, left ventricular hypertrophy and failure, myocardial infarction, dissecting aneurysm, and renovascular disease. An underlying disorder (e.g., renal disease, Cushing syndrome, pheochromocytoma) is identified in fewer than 10% of all cases of hypertension. The remainder, traditionally labeled “essential” hypertension, probably arise from a variety of disturbances in normal pressure-regulating mechanisms (which involve baroreceptors, autonomic influences on the rate and force of cardiac contraction and vascular tone, renal retention of salt and water, formation of angiotensin II under the influence of renin and angiotensin-converting enzyme, and other factors known and unknown), and most are probably genetically conditioned. Syn: hyperpiesis.

Because of its wide prevalence and its impact on cardiovascular health, hypertension is a major cause of disease and death in industrialized societies. It is estimated that 50–70 million Americans, including about 50% of all people over age 60, have hypertension, but that only about one-third of these are aware of their condition and are under appropriate treatment. Hypertension causes 35,000 deaths annually in the U.S., and is a contributing factor in a further 180,000 deaths. It is associated with a 3-fold increase in the risk of heart attack and a 7- to 10-fold increase in the risk of stroke. The prevalence of hypertension and the incidence of nonfatal and fatal consequences are substantially higher in African-Americans. Although people with extremely high diastolic pressure may experience headache, dizziness, and even encephalopathy, uncomplicated hypertension seldom causes symptoms. Hence the diagnosis of hypertension is usually made by screening apparently healthy persons or those under treatment for another condition. Risk factors for hypertension include a family history of hypertension, African-American race, advancing age, the postmenopausal state, excessive dietary sodium, obesity, excessive use of alcohol, sedentary lifestyle, and chronic emotional stress. Treatment options include lifestyle changes (maintenance of healthful weight; at least 30 minutes of aerobic exercise several days a week; limitation of sodium intake to 2.4 g daily and of ethanol to 1 oz daily; consumption of adequate potassium, calcium, and magnesium; and avoidance of excessive emotional stress) and a broad range of drugs, including diuretics, beta-blockers, calcium channel blockers, angiotensin-converting enzyme inhibitors, angiotensin II receptor antagonists, )1-adrenergic antagonists, centrally acting alpha-agonists, and others. In recent decades, early detection and aggressive treatment of hypertension have reduced associated morbidity and mortality. Current practice standards call for still more diligent management, including prevention through avoidance of known risk factors, particularly in persons with a family history of hypertension, and control of cofactors known to increase the risk of cardiovascular damage in persons with hypertension (smoking, hypercholesterolemia, diabetes mellitus). Some studies suggest that the goal of treatment should be a diastolic blood pressure of 80 or lower.

hypothalamus - The hypothalamus consists of the anterior hypothalamic area [TA], dorsal hypothalamic area [TA], intermediate hypothalamic area [TA], lateral hypothalamic area [TA], and posterior hypothalamic area [TA], each of these containing specific nuclei. It has afferent fiber connections with the mesencephalon, limbic system, cerebellum, and efferent fiber connections with the same structures and with the posterior lobe of the hypophysis. The hypothalamus is prominently involved in the functions of the autonomic (visceral motor) nervous system and, through its vascular link with the anterior lobe of the hypophysis, in endocrine mechanisms; it also appears to play a role in neural mechanisms underlying moods and motivational states. See Also: pituitary gland.

hypoxia  - Decrease below normal levels of oxygen in inspired gases, arterial blood, or tissue, short of anoxia.

ischemia - Local anemia due to mechanical obstruction (mainly arterial narrowing or disruption) of the blood supply.

inflammation - A fundamental pathologic process consisting of a dynamic complex of cytologic and chemical reactions that occur in the affected blood vessels and adjacent tissues in response to an injury or abnormal stimulation caused by a physical, chemical, or biologic agent, including: 1) the local reactions and resulting morphologic changes, 2) the destruction or removal of the injurious material, 3) the responses that lead to repair and healing. The so-called “cardinal signs” of inflammation are: rubor, redness; calor, heat (or warmth); tumor, swelling; and dolor, pain; a fifth sign, functio laesa, inhibited or lost function, is sometimes added. All of the signs may be observed in certain instances, but no one of them is necessarily always present.

immunoglobulin (Ig) - On the basis of the structural and antigenic properties of the H chains, Ig's are classified (in order of relative amounts present in normal human serum) as IgG (7S in size, 80%), IgA (10–15%), IgM (19S, a pentamer of the basic unit, 5–10%), IgD (less than 0.1%), and IgE (less than 0.01%).  Antibodies are Ig's, and all Ig's probably function as antibodies. However, Ig refers not only to the usual antibodies, but also to a great number of pathological proteins classified as myeloma proteins, which appear in multiple myeloma along with Bence Jones proteins, myeloma globulins, and Ig fragments.  The large number of possible combinations of L and H chains make up the “libraries” of antibodies of each individual.

ionophore - A compound or substance that forms a complex with an ion and transports it across a membrane.

integrins - A family of cell membrane glycoproteins that are heterodimers composed of )- and *-chain subunits. They serve as extracellular matrix glycoprotein receptors involved in cell adhesion, e.g., the mediation of adhesion of neutrophils to endothelial cells.

integrins - A family of cell membrane glycoproteins that serve as extracellular matrix glycoprotein receptors involved in cell adhesion, e.g., the mediation of adhesion of neutrophils to endothelial cells.

interferon (IFN) - A class of small protein and glycoprotein cytokines (15–28 kD) produced by T cells, fibroblasts, and other cells in response to viral infection and other biological and synthetic stimuli. Interferons bind to specific receptors on cell membranes; their effects include inducing enzymes, suppressing cell proliferation, inhibiting viral proliferation, enhancing the phagocytic activity of macrophages, and augmenting the cytotoxic activity of T lymphocytes. Interferons are divided into five major classes (alpha, beta, gamma, tau, and omega) and several subclasses (indicated by Arabic numerals and letters) on the basis of physicochemical properties, cells of origin, mode of induction, and antibody reactions.

The discovery in 1957 that viral infection of human cells induces the formation of natural antiviral agents raised the hope that these substances might have therapeutic potential. Early studies showed that, unlike antibodies, interferons are active against a broad range of viruses, but progress in applying this knowledge to human medicine was retarded by the difficulty of producing interferons in sufficient quantity. In the 1980s the development of recombinant DNA technology overcame this obstacle, and interferons now play an important role in the treatment not only of viral infections but also of certain malignancies. Commercially available interferons are produced by genetically altered colonies of Escherichia coli or Chinese hamster ovary cells, or are induced by controlled viral infection in pooled human leukocytes. Alpha interferons have found the widest application in medicine. (The spelling alpha is used with respect to naturally occurring interferons; in compliance with international conventions for generic drug names, the spelling alfa appears in names of pharmaceutical formulations.) Alpha interferons are used in the treatment of chronic hepatitis B and hepatitis C, hairy cell leukemia, chronic myelogenous leukemia, AIDS-related Kaposi sarcoma, malignant melanoma, condylomata acuminata and recurrent respiratory papillomatosis due to human papillomavirus, and infantile hemangiomatosis. About 50% of patients treated for chronic hepatitis B with interferon-alfa show disappearance of hepatitis Be antigen (HBeAg) and reversion of alanine aminotransferase to normal. The response rate in chronic hepatitis C is lower (15–25%), but better results are achieved by using more aggressive therapy (daily rather than thrice weekly administration) and continuing it longer (a minimum of 12 months). Modified formulations of interferon-alfa conjugated with polyethylene glycol (PEG), which have yielded promising results in hepatitis C with once-a-week dosing, are in phase III trials. Beta interferons reduce clinical recurrences and progression of myelin damage in multiple sclerosis. Gamma interferon is effective in retarding tissue changes in osteopetrosis and systemic scleroderma and in reducing the frequency and severity of infections in chronic granulomatous disease. Administration of interferons is parenteral (intravenous, intramuscular, subcutaneous, intranasal, intrathecal, or intralesional) and several weeks of treatment may be required before clinical response is noted. More than 50% of patients experience a flulike syndrome of fatigue, myalgia, and arthralgia. Gastrointestinal and CNS side effects are also common, and marrow suppression may occur with prolonged treatment.

interferon alpha (IFN-) - the major interferon made by virus-induced leukocytes; a number of different subtypes exist that are elaborated by leukocytes in response to viral infection or to stimulation with double-stranded RNA. There are 14 genes on the short arm of chromosome 9 that code for these substances in humans. IFN-)-2A and -2B are protein products made by recombinant DNA techniques and are used as antineoplastic agents. Syn: leukocyte interferon.

interferon beta (IFN-*) - interferon elaborated by fibroblasts and microphages in response to the same stimuli as interferon alpha; only one gene codes for this interferon. Syn: fibroblast interferon.

interferon gamma (IFN-+) - interferon elaborated by T lymphocytes in response to either specific antigen or mitogenic stimulation; only one gene codes for + interferon. interferon gamma behaves like a biological response modifies and is highly immunoregulatory. Syn: antigen interferon, immune interferon.

interleukin - The name given to a group of multifunctional cytokines once their amino acid structure is known. They are synthesized by lymphocytes, monocytes, macrophages, and certain other cells. See: cytokine, lymphokin

interleukin-1 (IL-1) - A cytokine, derived primarily from mononuclear phagocytes, which enhances the proliferation of T helper cells and growth and differentiation of B cells. When secreted in larger quantities it is a mediator of inflammation, entering the bloodstream and causing fever, inducing synthesis of acute phase proteins, and initiating metabolic wasting. There are two distinct forms of IL-1: ) and *, both of which perform the same functions, but represent different proteins.

interleukin-2 (IL-2) - A cytokine derived from T helper lymphocytes that causes proliferation of T lymphocytes and activated B lymphocytes.

interleukin-4 (IL-4) - A cytokine derived from T4 lymphocytes that causes differentiation of B lymphocytes. Promotes Ig class switch. It stimulates DNA biosynthesis. Syn: B cell differentiating factor.

interleukin-6 (IL-6) - A cytokine derived from macrophages and endothelial cells that increases synthesis and secretion of immunoglobulins by B lymphocytes; also induces acute phase proteins. In hepatocytes, it induces acute-phase reactants. Syn: B cell stimulatory factor 2, interferon-*2.

interleukin-10 (IL-10) - A cytokine derived from helper T-cell lymphocytes (TH2) that inhibits +-interferon (IFN+) and IL-2 secretion by T cell lymphocytes (TH1) and inhibits mononuclear cell inflammation.

interleukin-12 (IL-12) - A cytokine derived from B lymphocytes and macrophages that induces +-interferon (IFN+) gene expression and IL-2 in T lymphocytes and NK cells and down regulates TH2 cytokines.

interleukin-18 (IL-18) - A cytokine made by macrophages; a potent inducer of interferon-+ by T cells and NK cells.

intron - A portion of DNA that lies between two exons, is transcribed into RNA, but does not appear in that mRNA after maturation because the intron is removed and the exons spliced together, and so is not expressed (as protein) in protein synthesis. By customary usage, the term is extended to the corresponding regions in the primary transcript of mRNA prior to maturation.

ion channel - ion channel a specific macromolecular protein pathway, with an aqueous “pore,” that traverses the lipid bilayer of a cell's plasma membrane and maintains or modulates the electrical potential across this barrier by allowing controlled influx or exit of small inorganic ions such as Na+, K+, Cl-, and Ca2+. It plays an important role in propagation of the action potential in neurons, but also may control transduction of extracellular signals and contraction in muscle cells. In general, ion channels are characterized by their selectivity for certain ions, their specific regulation or gating of these ions, and their specific sensitivity to toxins.

ion channel disorders - a number of diseases, mostly inherited and episodic in nature, caused by dysfunction of the calcium, chloride, potassium, or sodium channels of nerve or muscle; the inherited myotonias and periodic paralyses are included in this category; there is usually dominant inheritance, with the primary defect due to mutations of gene encoding on locus 7q32, 17q, or 1q31-32. Syn: channelopathies.

ischemia - Local anemia due to mechanical obstruction (mainly arterial narrowing or disruption) of the blood supply.

lecithin - Traditional term for 1,2-diacyl-sn-glycero-3-phosphocholines or 3-sn-phosphatidylcholines, phospholipids that on hydrolysis yield two fatty acid molecules and a molecule each of glycerophosphoric acid and choline. In some varieties of lecithin, both fatty acids are saturated, others contain only unsaturated acids (e.g., oleic, linoleic, or arachidonic acid); in others again, one fatty acid is saturated, the other unsaturated. Lecithins are yellowish or brown waxy substances, readily miscible in water, in which they appear under the microscope as irregular elongated particles known as “myelin forms,” and are found in nervous tissue, especially in the myelin sheaths, in egg yolk, and as essential constituents of animal and vegetable cells.

left ventricle - the lower chamber on the left side of the heart that receives the arterial blood from the left atrium and drives it by the contraction of its walls into the aorta. Syn: ventriculus sinister [TA].

leukocyte  - A type of cell formed in the myelopoietic, lymphoid, and reticular portions of the reticuloendothelial system in various parts of the body, and normally present in those sites and in the circulating blood (rarely in other tissues). Under various abnormal conditions, the total numbers or proportions, or both, may be characteristically increased, decreased, or not altered, and they may be present in other tissues and organs. Leukocytes represent three lines of development from primitive elements: myeloid, lymphoid, and monocytic series. On the basis of features observed with various methods of staining with polychromatic dyes (e.g., Wright stain). cells of the myeloid series are frequently termed granular leukocytes, or granulocytes; cells of the lymphoid and monocytic series also have granules in the cytoplasm but, owing to their tiny, inconspicuous size and different properties (frequently not clearly visualized with routine methods), lymphocytes and monocytes are sometimes termed nongranular or agranular leukocytes. Granulocytes are commonly known as polymorphonuclear leukocytes (also polynuclear or multinuclear leukocytes), inasmuch as the mature nucleus is divided into two to five rounded or ovoid lobes that are connected with thin strands or small bands of chromatin; they consist of three distinct types: neutrophils, eosinophils, and basophils, named on the basis of the staining reactions of the cytoplasmic granules. Cells of the lymphocytic series occur as two, somewhat arbitrary, normal varieties: small and large lymphocytes; the former represent the ordinary forms and are conspicuously more numerous in the circulating blood and normal lymphoid tissue; the latter may be found in normal circulating blood, but are more easily observed in lymphoid tissue. The small lymphocytes have nuclei that are deeply or densely stained (the chromatin is coarse and bulky) and almost fill the cells, with only a slight rim of cytoplasm around the nuclei; the large lymphocytes have nuclei that are approximately the same size as, or only slightly larger than, those of the small forms, but there is a broader, easily visualized band of cytoplasm around the nuclei. Cells of the monocytic series are usually larger than the other leukocytes, and are characterized by a relatively abundant, slightly opaque, pale blue or blue-gray cytoplasm that contains myriad extremely fine reddish-blue granules. Monocytes are usually indented, reniform, or shaped similarly to a horseshoe, but are sometimes rounded or ovoid; their nuclei are usually large and centrally placed and, even when eccentrically located, are completely surrounded by at least a small band of cytoplasm. Syn: white blood cell.

limbic system - a collective term denoting a heterogeneous array of brain structures at or near the edge (limbus) of the medial wall of the cerebral hemisphere, in particular the hippocampus, amygdala, and fornicate gyrus; the term is often used so as to include also the interconnections of these structures, as well as their connections with the septal area, the hypothalamus, and a medial zone of mesencephalic tegmentum. By way of the latter connections, the limbic system exerts an important influence upon the endocrine and autonomic motor systems; its functions also appear to affect motivational and mood states.

lipoxygenase - A class of enzymes that catalyzes the oxidation of unsaturated fatty acids with O2 to yield hydroperoxides of the fatty acids; 5-lipoxygenase catalyzes the first step in leukotriene biosynthesis, acting on arachidonate. Syn: carotene oxidase, lipoxidase.

lipopolysaccharide (LPS) - 1. A compound or complex of lipid and carbohydrate. 2. The lipopolysaccharide (endotoxin) released from the cell walls of Gram-negative organisms that produces septic shock.

Lyme disease - a subacute inflammatory disorder caused by infection with Borrelia burgdorferi, a nonpyogenic spirochete transmitted by Ixodes scapularis, the deer tick, in the eastern U.S. and I. pacificus, the western black-legged tick, in the western U.S.; the characteristic skin lesion, erythema chronicum migrans, is usually preceded or accompanied by fever, malaise, fatigue, headache, and stiff neck; neurologic, cardiac, or articular manifestations may occur weeks to months later. Tick nymphs are thought to be responsible for about 90% of transmission to human beings. Nymphs and larvae feed especially on the white-footed mouse, Peromyscus leucopus, while the preferred host of adults is the deer. Infected reservoir animals and ticks do not become ill. Residual articular or neurologic symptoms, which may persist for months or years after the initial infection, probably represent an immune response to the organism. Variations in clinical features or severity from one patient to another may be due to inborn variations in immune response, perhaps linked to the human lymphocytic antigen system. Syn: Lyme borreliosis.

Because of media coverage, Lyme disease has a higher profile than its occurrence warrants. Fewer than 18,000 cases are confirmed annually in the U.S. It is generally a benign, self-limited disease, even when untreated. Antibody studies in endemic areas suggest that as many as 50% of persons who contract the infection never show symptoms. The case fatality rate is virtually zero. The diagnosis is essentially clinical. Serologic tests for antibody to B. burgdorferi are notoriously poor in both sensitivity and specificity. In nonendemic areas, false-positive test results statistically outnumber true positives. IgM antibody appears and peaks relatively late, so that one-half of patients are seronegative during the first month following appearance of the rash. Antibiotic treatment administered early can alter or prevent the expected acute immune response. IgG antibody persists for months or years after infection and hence affords no help in diagnosing acute disease. Given the nonspecific and variable clinical picture and the unreliability of laboratory diagnostic measures, it is inevitable that many cases of Lyme disease are missed, and that, conversely, the diagnosis is often wrongly made. A study assessing the costs of misdiagnosis of Lyme disease found that 60% of patients referred to a Lyme disease clinic had never had the disease and another 19% had a history of infection but no current disease. The drug of choice is doxycycline administered orally for several weeks. Amoxicillin is the standard alternative for children and pregnant patients. Recovery does not confer immunity to future attacks; in fact, in highly endemic areas, the reinfection rate may be as high as 20%. Infectious disease authorities do not recommend antibiotic prophylaxis after a tick bite, even in highly endemic areas, nor do they countenance treatment of asymptomatic persons who have serologic evidence of past infection. A vaccine consisting of outer surface protein A (OspA) of B. burgdorferi synthesized by a nonvirulent strain of recombinant Escherichia coli was released in 1998. Antibody induced by the vaccine enters a feeding tick and binds any spirochetes present, preventing their mobilization. Three doses of the vaccine administered over a 12-month period confer about 80% protection against Lyme disease. The vaccine is not approved for persons under age 15 and is recommended only for those living or working in highly endemic areas.

Origin
[Lyme, CT, where first observed]

lymph - A clear, transparent, sometimes faintly yellow and slightly opalescent fluid that is collected from the tissues throughout the body, flows in the lymphatic vessels (through the lymph nodes), and is eventually added to the venous blood circulation. Lymph consists of a clear liquid portion, varying numbers of white blood cells (chiefly lymphocytes), and a few red blood cells. Syn: lympha [TA].

lymph node  - 1. One of numerous round, oval, or bean-shaped bodies located along the course of lymphatic vessels, varying greatly in size (1–25 mm in diameter) and usually presenting a depressed area, the hilum, on one side through which blood vessels enter and efferent lymphatic vessels emerge. The structure consists of a fibrous capsule and internal trabeculae supporting lymphoid tissue and lymph sinuses; lymphoid tissue is arranged in nodules in the cortex and cords in the medulla of a node, with afferent vessels entering at many points of the periphery.
2.
Syn: lymph gland, lymphaden, lymphoglandula, lymphonodus, nodus lymphaticus, nodus lymphoideus [TA].

lymphocyte - A white blood cell formed in lymphatic tissue throughout the body (e.g., lymph nodes, spleen, thymus, tonsils, Peyer patches, and sometimes in bone marrow) and in normal adults making up approximately 22–28% of the total number of leukocytes in the circulating blood. Lymphocytes are generally small (7–8 4m), but larger forms are frequent (10–20 4m); with Wright (or a similar) stain, the nucleus is deeply colored (purple-blue), and is composed of dense aggregates of chromatin within a sharply defined nuclear membrane; the nucleus is usually round, but may be slightly indented, and is eccentrically situated within a relatively small amount of light blue cytoplasm that ordinarily contains no granules; especially in larger forms, the cytoplasm may be fairly abundant and include several bright red-violet fine granules; in contrast to granules of the myeloid series of cells, those in lymphocytes do not yield a positive oxidase or peroxidase reaction. Lymphocytes are divided into 2 principal groups, termed T and B cells, based on their surface molecules as well as function. Natural killer cells, which are large granular lymphocytes, represent a small percentage of the lymphocyte population. Syn: lymph cell, lympholeukocyte.

macrophage - Any mononuclear, actively phagocytic cell arising from monocytic stem cells in the bone marrow; these cells are widely distributed in the body and vary in morphology and motility, though most are large, long-lived cells with a nearly round nucleus and have abundant endocytic vacuoles, lysosomes, and phagolysosomes. Phagocytic activity is typically mediated by serum recognition factors, including certain immunoglobulins and components of the complement system, but also may be nonspecific for some inert materials and bacteria, as in the case of alveolar macrophages; macrophages also are involved in both the production of antibodies and in cell-mediated immune responses, participate in presenting antigens to lymphocytes, and secrete a variety of immunoregulatory molecules. Syn: rhagiocrine cell, macrophagocyte. activated macrophage -A mature macrophage, in an active metabolic state, that is cytotoxic to tumor/target cells, usually following exposure to certain cytokines. Syn: armed macrophage.alveolar macrophage - a vigorously phagocytic macrophage on the epithelial surface of lung alveoli where it ingests inhaled particulate matter. Syn: dust

macrophage-activating factor (MAF) - a primarily CD4+ T cell–derived lymphokine that induces macrophage activation. The major macrophage–activating factor is interferon gamma. In the mouse, interleukin-4 is also an MAF.

major histocompatibility complex (MHC) - a group of linked loci, collectively termed H-2 complex in the mouse and HLA complex in humans, that codes for cell-surface histocompatibility antigens and is the principal determinant of tissue type and transplant compatibility. See Also: human leukocyte antigens.

 malondialdehyde-modified low-density lipoprotein -lDL molecule with aldehyde-substituted lysine residue(s) in the apoprotein moiety, resulting from oxidative reaction accompanying prostaglandin synthesis and platelet aggregation.

mannose-binding protein - a protein involved in innate immunity that can bind mannosylated microorganisms and activate the complement pathway.

mast cell - a polymorphonuclear leukocyte characterized by many large, coarse, metachromatic granules (dark purple or blue-black when treated with Wright or similar stains) that usually fill the cytoplasm and may almost mask the nucleus; these leukocytes are unique in that they usually do not occur in increased numbers as the result of acute infectious disease, and their phagocytic qualities are probably not significant; the granules, which contain heparin and histamine, may degranulate in response to hypersensitivity reactions and can be of significance in general inflammation. Syn: basocyte, basophilocyte, mast leukocyte.

mediate - 1. (mTcdT-it). Situated between; intermediate.
2. (mTcdT-Qt). To effect something by means of an intermediary substance, as in complement-mediated phagocytosis.

medulla oblongata - the most caudal subdivision of the brainstem, immediately continuous with the spinal cord, extending from the lower border of the decussation of the pyramid to the pons. Motor nuclei of the medulla oblongata include the hypoglossal nucleus, the dorsal motor nucleus, inferior salivatory nucleus, and the nucleus ambiguus; sensory nuclei include the nuclei of the posterior column (gracile and cuneate), the cochlear and vestibular nuclei, the mid and caudal portions of the spinal trigeminal nucleus, and the nucleus of the solitary tract. See Also: medulla. Syn: myelencephalon [TA], oblo

messenger RNA (mRNA)- the RNA reflecting the exact nucleoside sequence of the genetically active DNA and carrying the “message” of the latter, coded in its sequence, to the cytoplasmic areas where protein is made in amino acid sequences specified by the mRNA, and hence primarily by the DNA; viral RNAs are considered to be natural messenger RNAs. Syn: informational RNA, template RNA.

metabolism The sum of the chemical and physical changes occurring in tissue, consisting of anabolism, those reactions that convert small molecules into large, and catabolism, those reactions that convert large molecules into small, including both endogenous large molecules as well as biodegradation of xenobiotics.

methemoglobin (metHb) - A transformation product of oxyhemoglobin because of the oxidation of the normal Fe2+ to Fe3+, thus converting ferroprotoporphyrin to ferriprotoporphyrin; it contains water in firm union with ferric iron, thus being chemically different from oxyhemoglobin and useless for respiration; found in sanguineous effusions and in the circulating blood after poisoning with acetanilid, potassium chlorate, and other substances. Syn: ferrihemoglobin

methemoglobinemia -  The presence of methemoglobin in the circulating blood; when severe, there is inadequate oxygenation of the tissues. Methemoglobin causes the blood to have a brownish color, which may be mistaken for cyanosis.

micturition -  1. Syn: urination..2. The desire to urinate. 3. Frequency of urination.

mitogen - A substance frequently derived from plants that stimulates mitosis and lymphocyte transformation; includes not only lectins such as phytohemagglutinins and concanavalin A, but also substances from streptococci (associated with streptolysin S) and from strains of)-toxin-producing staphylococci. Syn: transforming agent

mitral valve - the valve closing the orifice between the left atrium and left ventricle of the heart; its two cusps are called anterior and posterior.

monamine oxidase (flavin-containing) - an oxidoreductase containing flavin and oxidizing amines with the aid of O2 and water to aldehydes or ketones with the release of NH3 and H2O2. Acted upon by antidepressants. Syn: adrenaline oxidase, diamine oxidase, monoamine oxidase, tyraminase, tyramine oxidase.  Monoamine hypothesis - the classical theory of the neurochemical basis of depression linking it to a deficiency of at least one of three monoamine neurotransmitters, norepinephrine, serotonin, or dopamine. Monoamine oxidase inhibitor (MAOI) - a class of chemical compounds that exert antidepressant effect by the reversible or irreversible inhibition of monoamine oxidase A

monoclonal antibody (MAB, MoAb) - an antibody produced by a clone or genetically homogeneous population of fused hybrid cells, i.e., hybridoma; hybrid cells are cloned to establish cell lines producing a specific antibody that is chemically and immunologically homogeneous.

The technique for producing monoclonal antibodies, invented in 1975 by molecular biologists Cesar Milstein and Georges Kohler, has become a mainstay of immunologic research and medical diagnosis. MoAbs serve as experimental probes in cell biology, biochemistry, and parasitology, and are used in purification of biologic substances and certain drugs (e.g., interferons). Because of their high specificity in binding to target antigens, they provide far more accurate assays than conventional antiserum. Tagged with radionuclides, they have been employed to deliver radiation doses directly to cancerous tissues.

monocyte - A relatively large mononuclear leukocyte (16–22 4m in diameter), that normally constitutes 3–7% of the leukocytes of the circulating blood, and is normally found in lymph nodes, spleen, bone marrow, and loose connective tissue. When treated with the usual dyes, monocytes manifest an abundant pale blue or blue-gray cytoplasm that contains numerous, fine, dustlike, red-blue granules; vacuoles are frequently present; the nucleus is usually indented, or slightly folded, and has a stringy chromatin structure that seems more condensed where the delicate strands are in contact. See Also: monocytoid cell, endothelial leukocyte.

muscarinic receptors - membrane-bound proteins whose extracellular domain contains a recognition site for acetylcholine (ACh); combination of Ach with the receptor initiates a physiologic change (slowing of heart rate, increased glandular secretory activity, and stimulation of smooth muscle contractions); changes are observed after treatment with the mushroom alkaloid muscarine. Muscarinic receptors are to be distinguished from nicotinic receptors.

Muscarinic -1. Having a muscarinelike action, i.e., producing effects that resemble postganglionic parasympathetic stimulation.
2. An agent that stimulates the postganglionic parasympathetic receptor. See Also: muscarine, nicotinic.

muscle - A primary tissue, consisting predominantly of highly specialized contractile cells, which may be classified as skeletal muscle, cardiac muscle, or smooth muscle; microscopically, the latter is lacking in transverse striations characteristic of the other two types; one of the contractile organs of the body by which movements of the various organs and parts are effected; typical musculus is a mass of musculus fibers (venter or belly), attached at each extremity, by means of a tendon, to a bone or other structure; the more proximal or more fixed attachment is called the origin, the more distal or more movable attachment is the insertion; the narrowing part of the belly that is attached to the tendon of origin is called the caput or head. Syn: musculus [TA].

myocardial infarction (MI) - infarction of an segment of the heart muscle, usually as a result of occlusion of a coronary artery. Syn: heart attack, cardiac infarction.

Myocardial infarction is the most common cause of death in the U.S. About 800,000 people annually sustain first heart attacks, with a mortality rate of 30%, and 450,000 people sustain recurrent heart attacks, with a mortality rate of 50%. The most common cause of MI is thrombosis of an atherosclerotic coronary artery. Less common causes are coronary artery anomalies, vasculitis, or spasm induced by cocaine, ergot derivatives, or other agents. Risk factors for MI include male gender, family history of MI, obesity, hypertension, cigarette smoking, and elevation of total cholesterol, LDL cholesterol, homocysteine, lipoprotein (a), or C-reactive protein. At least 80% of MIs occur in people without a prior history of angina pectoris, and 20% are not recognized, either because they cause no symptoms (silent infarction) or because symptoms are attributed to other causes. Some 20% of people sustaining MI die before reaching a hospital. The classical symptom of MI is crushing anterior chest pain radiating into the neck, shoulder, or arm, lasting more than 30 minutes, and not relieved by nitroglycerin; typically pain is accompanied by dyspnea, diaphoresis, weakness, and nausea. Significant physical findings, often absent, include an atrial gallop rhythm (4th heart sound) and a pericardial friction rub. The electrocardiogram shows ST segment elevation (later changing to depression) and T wave inversion in leads reflecting the area of infarction. Q waves indicate transmural damage and a poorer prognosis. Diagnosis is supported by acute elevation in serum levels of myoglobin, lactic dehydrogenase, the MB isoenzyme of creatine kinase, and troponins. Unequivocal evidence of MI may be lacking during the first 6 hours in as many as 50% of patients. Death from acute MI is usually due to arrhythmia (ventricular fibrillation or asystole), shock (forward failure), congestive heart failure, or papillary muscle rupture. Other grave complications, which may occur during convalescence, include cardiorrhexis, ventricular aneurysm, and mural thrombus. Acute MI is treated (ideally under continuous ECG monitoring in the intensive care or coronary care unit of a hospital) with narcotic analgesics, oxygen by inhalation, intravenous administration of a thrombolytic agent, antiarrhythmic agents when indicated, and usually anticoagulants (aspirin, heparin), beta-blockers, and ACE inhibitors. Patients with evidence of persistent ischemia require angiography and may be candidates for balloon angioplasty. Data from the Framingham Heart Study show that a higher percentage of acute MIs are silent or unrecognized in women and the elderly. Several studies have shown that women and the elderly tend to wait longer before seeking medical care after the onset of acute coronary symptoms than men and younger persons. In addition, women seeking emergency treatment for symptoms suggestive of acute coronary disease are less likely than men with similar symptoms to be admitted for evaluation, and women are less frequently referred than are men for diagnostic tests such as coronary angiography. Other studies have shown important gender differences in the presenting symptoms and medical recognition of MI. Chest pain is the most common symptom reported by both men and women, but men are more likely to complain of diaphoresis, while women are more likely to experience neck, jaw, or back pain, nausea, vomiting, dyspnea, or cardiac failure, in addition to chest pain. The incidence rates of acute pulmonary edema and cardiogenic shock in MI are higher in women, and mortality rates at 28 days and 6 months are also higher.

myasthenia gravis - a disorder of neuromuscular transmission marked by fluctuating weakness and fatigue of certain voluntary muscles, including those innervated by brainstem motor nuclei; caused by a marked reduction in the number of acetylcholine receptors in the postsynaptic membrane of the neuromuscular junction, resulting from an autoimmune mechanism. Syn: Goldflam disease.

mycoplasma - A genus of aerobic to facultatively anaerobic bacteria (family Mycoplasmataceae) containing Gram-negative cells that do not possess a true cell wall but are bounded by a three-layered membrane; they do not revert to bacteria containing cell walls or cell wall fragments. The minimal reproductive units of these organisms are 0.2–0.3 4m in diameter. The cells are pleomorphic, and in liquid media appear as coccoid bodies, rings, or filaments. Colonies of most species consist of a central core, growing down into the medium, surrounded by superficial peripheral growth. They require sterol for growth. They also require enrichment with serum or ascitic fluid. These organisms are found in humans and other animals and can be pathogenic. The type species is Mycoplasma mycoides. Syn: Asterococcus.

myelin sheath - the lipoproteinaceous envelope in vertebrates surrounding most axons of more than 0.5-4m diameter; it consists of a double plasma membrane wound tightly around the axon in a variable number of turns, and supplied by oligodendroglia cells (in the brain and spinal cord) or Schwann cells (in peripheral nerves); unwound, the double membrane would appear as a sheetlike cell expansion that is empty of cytoplasm but for a few narrow cytoplasmic strands corresponding to apparent interruptions of the regular myelin structure, the incisures of Schmidt-Lanterman; the myelin sheath of each axon is composed of a fairly regular longitudinal sequence of segments, each corresponding to the length of sheath supplied by a single oligodendroglia or Schwann cell; in the short interval between each two neighboring segments, the nodes of Ranvier, the axon is unmyelinated even though enclosed by complex finger-like plasmatic expansions of the neighboring oligodendroglia or Schwann cells. Syn: medullary sheath.

myofascial syndrome - irritation of the muscles and fascia of the back and neck causing acute and chronic pain not associated with any neurologic or bony evidence of disease; presumed to arise primarily from poorly understood changes in the muscle and fascia themselves.

myofascial pain-dysfunction syndrome - dysfunction of the masticatory apparatus related to spasm of the muscles of mastication precipitated by occlusal dysharmony or alteration in vertical dimension of the jaws, and exacerbated by emotional stress; characterized by pain in the preauricular region, muscle tenderness, popping noise in the temporomandibular joint, and limitation of jaw motion. Syn: temporomandibular joint pain-dysfunction syndrome.

nicotinamide adenine dinucleotide (NAD, NAD+, NADH) - Ribosylnicotinamide 5c-phosphate (NMN) and adenosine 5c-phosphate (AMP) linked by phosphoanhydride linkage between the two phosphoric groups; binds as a coenzyme to proteins, serves in respiratory metabolism (hydrogen acceptor and donor) through alternate oxidation and reduction (NAD+ B NADH).

nicotinamide adenine dinucleotide phosphate (NADP, NADP+, NADPH) - A coenzyme of many oxidases (dehydrogenases), in which the reaction NADP+ + 2H B NADPH + H+ takes place; the third phosphoric group esterifies the 2c-hydroxyl of the adenosine moiety of NA

natural killer cells- large granular lymphocytes which do not express markers of either T or B cell lineage. These cells do possess Fc receptors for IgG and can kill target cells using antibody-dependent cell-mediated cytotoxicity. NK cells can also use perforin to kill cells in the absence of antibody. Killing occurs without previous sensitization. Syn: NK cells.

neurasthenia - An ill-defined condition, commonly accompanying or following depression, characterized by vague fatigue believed to be brought on by psychological factors. Actually this is the old name for CFS.  The term neurasthenia was real big at one time but hasn't really been in wide use for many decades. It has disappeared from many medical texts but is still alive and well in this one.  Neurasthenia was finally given a psychological basis after no one could figure out what caused it.  Notice the 'vague' fatigue - I guess thats what you can expect from a standard reference text.  This dictionary lists 7 different kinds of neurasthenia including gastric, pulsating and my favorite, sexual neurasthenia - an obsolete term for a form in which sexual erethism (?), weakness, or perversion is a marked symptom.  And we thought we had it bad. Chronic fatigue syndrome is not found in the dictionary.  Fibromyalgia is.

neurasthenic personality - an obsolete term for a condition characterized by some of the following features: poor appetite or overeating, insomnia or hypersomnia, low energy or fatigue, low self esteem, poor concentration or difficulty making decisions, and feelings of hopelessness. In its most severe form it may become a chronic disturbance of mood called dysthymia (depressive neurosis) in which a depressive mood accompanies the features listed above.  IAt least they say its obsolete. Given the wide variety of features listed they obviously didn't even have a good symptom profile. 

neuroglia - Non-neuronal cellular elements of the central and peripheral nervous system; formerly believed to be merely supporting cells but now thought to have important metabolic functions, since they are invariably interposed between neurons and the blood vessels supplying the nervous system. In central nervous tissue they include oligodendroglia cells, astrocytes, ependymal cells, and microglia cells. The satellite cells of ganglia and the neurolemmal or Schwann cells around peripheral nerve fibers can be interpreted as the oligodendroglia cells of the peripheral nervous system. Syn: glia, reticulum (2) [TA], Kölliker reticulum.

neuropathy -1. A classical term for any disorder affecting any segment of the nervous system.2. In contemporary usage, a disease involving the cranial nerves or the peripheral or autonomic nervous system. Syn: neuritis (2), neuropathia.

nerve growth factor (NGF) - a protein (MW about 26,000) that controls the development of sympathetic postganglionic neurons and possibly also sensory (dorsal root) ganglion cells in mammals; similar, but not identical, factors have been isolated from the venoms of several species of snakes; it has been isolated from the submaxillary glands of male mice, and when injected into newborn animals, sympathetic ganglia become hyperplastic and hypertrophic; stimulates synthesis of nucleic acids and protein

nicotinic receptors - a class of cholinergic receptors on skeletal muscle cells that are linked to ion channels in the cell membrane.

Nicotinic - Relating to the stimulating action of acetylcholine and other nicotine-like agents on autonomic ganglia, adrenal medulla, and the motor end-plate of striated muscle.

nitric oxide (NO·)- A colorless, radical-free gas that reacts rapidly with O2 to form other nitrogen oxides (e.g., NO2, N2O3, and N2O4) and ultimately is converted to nitrite (NO2-) and nitrate (NO3-); a gaseous mediator of cell-to-cell communication and potent vasodilator, formed from L-arginine in bone, brain, endothelium, granulocytes, pancreatic beta cells, and peripheral nerves by a constitutive nitric oxide synthase, and in hepatocytes, Kupffer cells, macrophages, and smooth muscle by an inducible nitric oxide synthase (e.g., induced by endotoxin). NO· activates soluble guanylate cyclase, mediates penile erection, and may be the first known retrograde neurotransmitter.

The short-lived NO· molecule is a product of various tissues and plays a role in various processes. NO· elaborated by endothelium, which is identical to endothelium-derived relaxing factor, dilates vessels by relaxing vascular smooth muscle; nitrites used in coronary and peripheral vascular disease induce or mimic this action. The 1998 Nobel Prize in Medicine or Physiology was awarded to 3 U.S. pharmacologists, Robert F. Furchgott, Ferid Murad, and Louis J. Ignarro, for their independent discoveries of the role of nitric oxide in cardiovascular physiology. In the immune system, macrophages use NO· as a cytotoxic agent. Deficiency or inactivation of NO· may contribute to the pathogenesis of both hypertension and atherosclerosis. An excess of NO·, which is a free radical, is toxic to brain cells, and NO· is also responsible for the precipitate, often fatal, drop in blood pressure accompanying septic shock. Free NO· in the bloodstream is rapidly reduced by the iron of hemoglobin.

nitroprusside - The anion [Fe(CN)5NO]=; as in sodium nitroprusside; used as a vasodilator by the intravenous route.

norepinephrine - a catecholamine hormone of which the natural form is D, although the L form has some activity; the base is considered to be the postganglionic adrenergic mediator, acting on ) and * receptors; it is stored in chromaffin granules in the adrenal medulla, in much smaller amounts than epinephrine, and secreted in response to hypotension and physical stress; in contrast to epinephrine it has little effect on bronchial smooth muscle, metabolic processes, and cardiac output, but has strong vasoconstrictive effects and is used pharmacologically as a vasopressor, primarily as the bitartrate salt. Syn: levarterenol, noradrenaline.

nuclear factor-kB -an transcription factor associated with cytokine production.

occipital - Relating to the occiput; referring to the occipital bone or to the back of the head. Syn: occipitalis.

organophosphates - A series of phosphorus-containing organic compounds usually also containing a halide ion that reacts with cholinesterase. Organophosphates phosphorylate cholinesterase and thus irreversibly inhibit it. Used as insecticides; have also been used as war gases.

open reading frame - a gene presumed to code for a protein but for which no gene product has been identified; also known as unidentified reading frame. Syn: unidentified reading frame.

osteoblast - A bone-forming cell that is derived from mesenchymal osteoprognitor cells and forms an osseous matrix in which it becomes enclosed as an osteocyte. Syn: osteoplast.

osteopenia - 1. Decreased calcification or density of bone; a descriptive term applicable to all skeletal systems in which such a condition is noted; carries no implication about causality.
2. Reduced bone mass due to inadequate osteoid synthesis.

oxidation - 1. Combination with oxygen. 2. Increasing the valence of an atom or ion by the loss from it of hydrogen or of one or more electrons thus rendering it more electropositive, as when iron is changed from the ferrous (2+) to the ferric (3+) state. 3. In bacteriology, the aerobic dissimilation of substrates with the production of energy and water; in contrast to fermentation, the transfer of electrons in the oxidation process is accomplished via the respiratory chain, which utilizes oxygen as the final electron acceptor.

oxidize - To combine or cause an element or radical to combine with oxygen or to lose electrons.

oxidative phosphorylation - formation of high-energy phosphoric bonds (e.g., in pyrophosphates) from the energy released by the flow of electrons to O2 and the dehydrogenation (i.e., oxidation) of various substrates, most notably isocitric acid, )-ketoglutaric acid, succinic acid, and malic acid in the tricarboxylic acid cycle.

paracrine - Relating to a kind of hormone function in which the effects of the hormone are restricted to the local environment. Cf. endocrine.

Parvovirus - A genus of viruses (family Parvoviridae) that replicate autonomously in suitable cells. Strain B19 infects humans, causing erythema infectiosum and aplastic crisis in hemolytic anemia.

peptidergic - Referring to nerve cells or fibers that are believed to employ small peptide molecules as their neurotransmitter.

pH - Symbol for the negative decadic logarithm of the H+ ion concentration (measured in moles per liter); a solution with pH 7.00 (1 × 10-7 g molecular weight of hydrogen per liter) is neutral at 22°C (i.e., [H+] = [OH-]), one with a pH value of more than 7.00 is alkaline, one with a pH lower than 7.00 is acid. At a temperature of 37°C, neutrality is at a pH value of 6.80. Cf. dissociation constant of water.   pH of arterial blood; normal is 7.4 (normal range 7.36–7.44). Origin -[p (power or potency) of [H+ ],

p53 - A tumor suppressor gene located on the short arm of chromosome 17 that encodes a nucleophosphoprotein that binds DNA and negatively regulates cell division; frequently measured as a marker of malignant diseases.

phagocyte - A cell possessing the property of ingesting bacteria, foreign particles, and other cells. Phagocytes are divided into two general classes: 1) microphages, polymorphonuclear leukocytes that ingest chiefly bacteria; 2) macrophages, mononucleated cells (histiocytes and monocytes) that are largely scavengers, ingesting dead tissue and degenerated cells. Syn: carrier cell, scavenger cell.

phagocytosis  - The process of ingestion and digestion by cells of solid substances, e.g., other cells, bacteria, bits of necrosed tissue, foreign particles. See Also: endocytosis.

phosphocreatine - A phosphagen; a compound of creatine (through its NH2 group) with phosphoric acid; a source of energy in the contraction of vertebrate muscle, its breakdown furnishing phosphate for the resynthesis of ATP from ADP by creatine kinase. Cf. phosphoarginine. Syn: creatine phosphate, N?-phosphonocreatine.

phospholipase C - an enzyme that catalyzes the hydrolysis of phosphatidylcholine (and perhaps other phospholipids) to produce choline phosphate and 1,2-diacylglycerol; also acts on sphingomyelin; a key enzyme in the formation of inositol 1,4,5-trisphosphate. Syn: lecithinase C, lipophosphodiesterase I.

phosphorylation - Addition of phosphate to an organic compound, such as glucose to produce glucose monophosphate, through the action of a phosphotransferase (phosphorylase) or kinase.

phytohemagglutinin (PHA) -A phytomitogen from plants that agglutinates red blood cells. The term is commonly used specifically to refer to the lectin obtained from the red kidney bean (Phaseolus vulgaris), which is also a mitogen that stimulates T lymphocytes more vigorously than B lymphocytes. Syn: phytolectin.

polymerase chain reaction (PCR) - an enzymatic method for the repeated copying of the two strands of DNA of a particular gene sequence. It is widely used to amplify minute quantities of biological material so as to provide adequate specimens for laboratory study.

The replication of DNA in the living cell is facilitated by polymerases. The two DNA chains of the double helix first unzip from one another, and DNA polymerase then generates a copy of each strand by adding free nucleotides to form a sequence of base pairs complementary with the sequence in the strand. The laboratory technique known as polymerase chain reaction, for which the American biochemist Kary Mullis won a Nobel Prize in Chemistry in 1993, exploits the capacity of DNA polymerase to assemble new DNA. Taq polymerase, named for its source, Thermus aquaticus, a thermophilic bacterium, is added to a mixture of free nucleotides and primers. (Primers are specially prepared units containing both RNA and DNA with a free terminus where the polymerase will react.) The short sequence of DNA to be amplified is flanked by two primers. Once the reaction begins, the polymerase generates numerous copies of the target sequence. The sequential phases of the reaction are initiated simply by making a series of strategic changes in the temperature of the system. Millions of copies of the target sequence can be generated by cyclically repeating these temperature changes as many as 30 times, each DNA strand produced by one cycle giving rise to many more in the next. The technique is used to amplify specimens for diagnosis of both infectious and genetic diseases, to carry out DNA fingerprinting, and in genomic research.

pressor - Exciting to vasomotor activity; producing increased blood pressure; denoting afferent nerve fibers that, when stimulated, excite vasoconstrictors, which increase peripheral resistance. Syn: hypertensor.

prolactin (PRL) - A protein hormone of the anterior lobe of the hypophysis that stimulates the secretion of milk and possibly, during pregnancy, breast growth. Syn: mammotropic factor, galactopoietic hormone, lactation hormone, lactogenic hormone, mammotropic hormone, lactotropin.

promoter - In molecular biology, a DNA sequence at which RNA polymerase binds and initiates transcription.

prostacyclin - A potent natural inhibitor of platelet aggregation and a powerful vasodilator. It is the principal vasodilating prostanoid released by the endothelium.

prostaglandin (PG) - Any of a class of physiologically active substances present in many tissues, with effects such as vasodilation, vasoconstriction, stimulation of intestinal or bronchial smooth muscle, uterine stimulation, and antagonism to hormones influencing lipid metabolism. Prostaglandins are prostanoic acids with side chains of varying degrees of unsaturation and varying degrees of oxidation. Often abbreviated PGA, PGB, PGC, PGD, etc. with numeric subscripts, according to structure.

prostanoids - are derivatives of prostanoic acid; they include prostaglandins, thromboxanes, etc. Prostanoic acid is a 20-carbon acid that is the skeleton of the prostaglandins.

protein (p) - Macromolecules consisting of long sequences of )-amino acids [H2N–CHR–COOH] in peptide (amide) linkage (elimination of H2O between the )-NH2 and )-COOH of successive residues). Protein is three-fourths of the dry weight of most cell matter and is involved in structures, hormones, enzymes, muscle contraction, immunologic response, and essential life functions. The amino acids involved are generally the 20 )-amino acids (glycine, L-alanine, etc.) recognized by the genetic code. Cross-links yielding globular forms of protein are often effected through the –SH groups of two L-cysteinyl residues, as well as by noncovalent forces (hydrogen bonds, lipophilic attractions, etc.).

protein kinases - a class of enzymes that phosphorylates other proteins; many of these kinases are responsive to other effectors (e.g., cAMP, cGMP, insulin, epidermal growth factor, calcium and calmodulin, calcium and phospholipids).

protease - Descriptive term for proteolytic enzymes, both endopeptidases and exopeptidases; enzymes that hydrolize (break) polypeptide chains.

proteolysis - The decomposition of protein; primarily via the hydrolysis of peptide bonds, both enzymatically and nonenzymatically.

Q fever - a disease caused by the rickettsia Coxiella burnetii, which is propagated in sheep and cattle, where it produces no symptoms; human infections occur as a result of contact not only with such animals but also with other infected humans, air and dust, wild reservoir hosts, and other sources. Syn: nine mile fever.

rate constants (k )- proportionality constants equal to the initial rate of a reaction divided by the concentration of the reactant(s); e.g., in the reaction A B B + C, the rate of the reaction equals -d[A]/dt = k1[A]. The rate constant k1 is a unimolecular rate constant since there is only one molecular species reacting and has units of reciprocal time (e.g., s-1). For the reverse reaction, B + C B A, the rate equals -d[B]/dt = d[A]/dt = k2[B][C]. The rate constant k2 is a bimolecular rate constant and has units of reciprocal concentration-time (e.g., M-1 s-1). Syn: velocity constants.

reduction -  In chemistry, a reaction involving a gain of one or more electrons by a substance, such as when iron passes from the ferric (3+) to the ferrous (2+) state, or when hydrogen is added to the double bond of an organic compound, or when an aldehyde is converted to an alcohol.

renin - A term originally used for a pressor substance obtained from rabbits' kidneys, now an enzyme that converts angiotensinogen to angiotenson I.

respiration - 1. A fundamental process of life, characteristic of both plants and animals, in which oxygen is used to oxidize organic fuel molecules, providing a source of energy as well as carbon dioxide and water. In green plants, photosynthesis is not considered respiration

retrovirus - Any virus of the family Retroviridae. Retroviruses are potent disease agents, but they have also served as invaluable research tools in molecular biology. In 1979, the molecular biologist Richard Mulligan used a genetically altered retrovirus to trigger the production of hemoglobin in vitro by monkey kidney cells. His technique for using retroviruses to import alien genes into cells has been widely adopted. Medical researchers have also explored retroviral transport as a means of gene therapy. However, evidence suggesting that retroviruses may play a role in carcinogenesis raises questions as to the safety of their use in gene therapy. See oncogen

ribosome - A granule of ribonucleoprotein, 120–150 Å in diameter, that is the site of protein synthesis from aminoacyl-tRNAs as directed by mRNAs. Syn: Palade granule.

ribonuclease (RNase) - A transferase or phosphodiesterase that catalyzes the hydrolysis of ribonucleic acid. See Also: ribonuclease (Bacillus subtilis), ribonuclease (pancreatic). Syn: ribonucleinase.

Rickettsia - A genus of bacteria (order Rickettsiales) containing small (nonfilterable), often pleomorphic, coccoid to rod-shaped, Gram-negative organisms that usually occur intracytoplasmically in lice, fleas, ticks, and mites but do not grow in cell-free media; pathogenic species infect humans and other animals, causing epidemic typhus, murine, or endemic typhus, Rocky Mountain spotted fever, tsutsugamushi disease, rickettsialpox, and other diseases; type species is Rickettsia prowazekii.

sarcoidosis - A systemic granulomatous disease of unknown cause, especially involving the lungs with resulting interstitial fibrosis, but also involving lymph nodes, skin, liver, spleen, eyes, phalangeal bones, and parotid glands; granulomas are composed of epithelioid and multinucleated giant cells with little or no necrosis. Syn: Besnier-Boeck-Schaumann disease, Boeck disease, sarcoid, Boeck sarcoid, Besnier-Boeck-Schaumann syndrome, Schaumann syndrome.

sepsis - the presence of various pathogenic organisms, or their toxins, in the blood or tissues; septicemia is a common type of sepsis. Sepsis syndrome - clinical evidence of acute infection with hyperthermia or hypothermia, tachycardia, tachypnea and evidence of inadequate organ function or perfusion manifested by at least one of the following: altered mental status, hypoxemia, acidosis, oliguria, or disseminated intravascular coagulation

serotonin - A vasoconstrictor, liberated by blood platelets, that inhibits gastric secretion and stimulates smooth muscle; present in relatively high concentrations in some areas of the central nervous system (hypothalamus, basal ganglia), and occurring in many peripheral tissues and cells and in carcinoid tumors. Syn: enteramine, 5-hydroxytryptamine, thrombocytin, thrombotonin.
Origin (sero- + G. tonos, tone, tension, + -in]

smooth muscle  - one of the muscle fibers of the internal organs, blood vessels, hair follicles, etc.;  See Also: involuntary muscles. Syn: unstriated muscle, visceral muscle. involuntary muscles - muscles not ordinarily under control of the will; except in the case of the heart, they are composed of smooth (nonstriated) muscle fibers, innervated by the autonomic nervous system.

spleen -  A large vascular lymphatic organ lying in the upper part of the abdominal cavity on the left side, between the stomach and diaphragm, composed of white and red pulp; the white consists of lymphatic nodules and diffuse lymphatic tissue; the red consists of venous sinusoids between which are splenic cords; the stroma of both red and white pulp is reticular fibers and cells. A framework of fibroelastic trabeculae extending from the capsule subdivides the structure into poorly defined lobules. It is a blood-forming organ in early life and later a storage organ for red corpuscles and platelets; because of the large number of macrophages, it also acts as a blood filter, both identifying and destroying effete erythrocytes. Syn: lien, splen [TA]

steroids - A large family of chemical substances, comprising many hormones, body constituents, and drugs, each containing the tetracyclic cyclopenta[a]phenanthrene skeleton. Stereoisomerism among steroids is not only common but of critical biologic significance. The natural and synthetic derivatives are named by adding conventional chemical prefixes and suffixes for substituents; e.g., -ol for a hydroxyl group, -on(e) for a keto group, -al for an aldehyde group. “Nor” indicates loss of a –CH2— group; “homo,” the addition of a –CH2— group; each is preceded by the letter indicating which ring is contracted or expanded, respectively, or, in the case where the –CH2— is lost from a methyl group, the number of the carbon atom lost. “Seco” indicates fission of a ring with the addition of hydrogen atoms at the positions indicated by numerals preceding the term. Unsaturation is denoted, as usual, by substituting appropriate terms, e.g., -en(e), -yn(e), -adien(e), for the -ane or -an parts of the hydrocarbon or parent class names, with numerals indicating locations of the unsaturated bonds.

steroid hormones - those hormones possessing the steroid ring system; e.g., androgens, estrogens, adrenocortical hormones.

St. John's wort - a shrubby perennial (Hypericum perforatum) with numerous orange-yellow flowers whose petals may be speckled black along their margins; a herbal antidepressant that compares favorably with standard synthetic psychopharmaceutical agents in the treatment of mild to moderate depression.

In medieval folk-medicine this herb, traditionally gathered on the eve of the feast of St. John the Baptist (June 24), was used against various illnesses, including hysteria and epilepsy, as well as witches' spells and diabolical possession. In Europe, St. John's wort is widely prescribed for the treatment of depression. The herb has been shown in placebo-controlled trials to lessen depression, anxiety, apathy, sleep disturbances, insomnia, anorexia, and feelings of worthlessness. EEG studies have shown that it improves sleep intensity without increasing total sleep duration or interfering with REM sleep. In clinical comparisons it was only slightly inferior to the tricyclic agents imipramine, amitriptyline, and desipramine in abolishing depressive symptoms. In addition, memory and other mental functions may be improved instead of being blunted as with prescription antidepressants. No controlled studies comparing the efficacy of St. John's wort with that of selective serotonin reuptake inhibitors have been published. Fewer than 3% of subjects in clinical trials noted any side effects. Those most frequently experienced were gastrointestinal irritation, allergic reactions, fatigue, restlessness, and photodermatitis. The principal active ingredient of St. John's wort is believed to be hypericin, which has been shown in vitro to inhibit the uptake or biodegradation of several neurotransmitters, including serotonin, norepinephrine, and dopamine. It also binds to +-aminobutyric acid receptors on CNS neurons and improves the signal produced by serotonin after it binds to its receptors. Ongoing studies seek to define the psychopharmaceutical potential of this agent more precisely and to confirm the safety of its use. Because it inhibits monoamine oxidase, at least in vitro, its use with other antidepressants is not recommended. It is not considered appropriate during pregnancy or in the treatment of severe depression with serious risk of suicide or of depression accompanied by psychosis.

substance P - a peptide neurotransmitter composed of 11 amino acid residues (with the carboxyl group amidated), normally present in minute quantities in the nervous system and intestines of humans and various animals and found in inflamed tissue, that is primarily involved in pain transmission and is one of the most potent compounds affecting smooth muscle (dilation of blood vessels and contraction of intestine) and thus presumed to play a role in inflammation.

superantigen - An antigen that interacts with the T-cell receptor in a domain outside the antigen recognition site. This interaction induces the activation of larger numbers of T cells than are induced by antigens that are presented in the antigen recognition site leading to the release of numerous cytokines.

synapse - The functional membrane-to-membrane contact of the nerve cell with another nerve cell, an effector (muscle, gland) cell, or a sensory receptor cell. The synapse subserves the transmission of nerve impulses, commonly from a variably large (1–12 4m), generally knob-shaped or club-shaped axon terminal (the presynaptic element) to the circumscript patch of the receiving cell's plasma membrane (the postsynaptic element) on which the synapse occurs. In most cases the impulse is transmitted by means of a chemical transmitter substance (such as acetylcholine, +-aminobutyric acid, dopamine, norepinephrine) released into a synaptic cleft (15–50 nm wide) that separates the presynaptic from the postsynaptic membrane; the transmitter is stored in quantal form in synaptic vesicles: round or ellipsoid, membrane-bound vacuoles (10–50 nm in diameter) in the presynaptic element. In other synapses transmission takes place by direct propagation of the bioelectrical potential from the presynaptic to the postsynaptic membrane; in such electrotonic synapses (“gap junctions”), the synaptic cleft is no more than about 2 nm wide. In most cases, synaptic transmission takes place in only one direction (“dynamic polarity” of the synapse), but in some synapses synaptic vesicles occur on both sides of the synaptic cleft, suggesting the possibility of reciprocal chemical transmission.

systole - Contraction of the heart, especially of the ventricles, by which the blood is driven through the aorta and pulmonary artery to traverse the systemic and pulmonary circulations, respectively; its occurrence is indicated physically by the first sound of the heart heard on auscultation, by the palpable apex beat, and by the arterial pulse.

tachycardia - Rapid beating of the heart, conventionally applied to rates over 90 beats/min. Syn: polycardia, tachyrhythmia, tachysystole

TATA box - a highly conserved bacterial DNA sequence found about 25 bp upstream from the transcription start site of genes, usually flanked by GC rich sequences; binding site of transcription factors but not RNA polymerase.

T cytotoxic cells (Tc) -  a subset of CD8 T lymphocytes that bind to other cells via class I MHC and are involved in their destruction. Syn: T cytotoxic cells

T helper cells (Th) - a subset of lymphocytes that secrete various cytokines that regulate the immune response: subset 1, which synthesize gamma interferon and interleukin 2 and are involved in cell-mediated immunity; subset 2, which synthesize interleukins 4, 5, 10, and are involved in immunoglobulin synthesis. Syn: helper cells.

thiol - monovalent radical –SH when attached to carbon; a hydrosulfide; a mercaptan.

thrombin - An enzyme (proteinase), formed in shed blood, that converts fibrinogen into fibrin by hydrolyzing peptides (and amides and esters) of L-arginine; formed from prothrombin by the action of prothrombinase (factor Xa, another proteinase).

thymus -  A primary lymphoid organ, located in the superior mediastinum and lower part of the neck, that is necessary in early life for the normal development of immunologic function. It reaches its greatest relative weight shortly after birth and its greatest absolute weight at puberty; it then begins to involute, and much of the lymphoid tissue is replaced by fat. It is supplied by the inferior thyroid and internal thoracic arteries, and its nerves are derived from the vagus and sympathetic nerves. Syn: thymus gland.

thyroid gland -  an endocrine (ductless) gland, consisting of irregularly spheroidal follicles, lying in front and to the sides of the upper part of the trachea, and of horseshoe shape. It is supplied by branches from the external carotid and subclavian arteries, and its nerves are derived from the middle cervical and cervicothoracic ganglia of the sympathetic system. It secretes thyroid hormone and calcitonin. Syn: thyroid body, glandula thyroidea [TA], thyroidea.

thyrotropin - A glycoprotein hormone produced by the anterior lobe of the hypophysis that stimulates the growth and function of the thyroid gland; it also is used as a diagnostic test to differentiate primary and secondary hypothyroidism. Syn: thyroid-stimulating hormone, thyrotropic hormone, thyrotrophin.

transcription - Transfer of genetic code information from one kind of nucleic acid to another, especially with reference to the process by which a base sequence of messenger RNA is synthesized (by an RNA polymerase) on a template of complementary DNA.

translation -The rather complex process by which messenger RNA, transfer RNA, and ribosomes effect the production of protein from amino acids, the specificity of synthesis being controlled by the base sequences of the messenger RNA.

transposable element - a DNA sequence that can move from one location in the genome to another; the transposition event can involve both recombination and replication, producing two copies of the moving piece of DNA; the insertion of these DNA fragments can disrupt the integrity of the target gene, possibly causing activation of dormant genes, deletions, inversions, and a variety of chromosomal aberrations. See Also: transposon.

transposon - A segment of DNA (e.g., an R-factor gene) which has a repeat of an insertion sequence element at each end that can migrate from one plasmid to another within the same bacterium, to a bacterial chromosome, or to a bacteriophage; the mechanism of transposition seems to be independent of the host's usual recombination mechanism. See: transposable element, jumping gene.

tricarboxylic acid -  Together with oxidative phosphorylation, the main source of energy in the mammalian body and the end toward which carbohydrate, fat, and protein metabolism are directed; a series of reactions, beginning and ending with oxaloacetic acid, during the course of which a two-carbon fragment is completely oxidized to carbon dioxide and water with the production of 12 high-energy phosphate bonds. So called because the first four substances involved (citric acid, cis-aconitic acid, isocitric acid, and oxalosuccinic acid) are all tricarboxylic acids; from oxalosuccinate, the others are, in order, )-ketoglutarate, succinate, fumarate, L-malate, and oxaloacetate, which condenses with acetyl-CoA (from fatty acid degradation) to form citrate (citric acid) again. Syn: citric acid cycle, Krebs cycle.

tumor necrosis factor (TNF) - A polypeptide cytokine, produced by endotoxin-activated macrophages, which has the ability to modulate adipocyte metabolism, lyse tumor cells in vitro, and induce hemorrhagic necrosis of certain transplantable tumors in vivo. Syn: cachetin.

ubiquitin - A small (76 amino acyl residues) protein found in all cells of higher organisms and one whose structure has changed minimally during evolutionary history; involved in at least two processes; histone modification and intracellular protein breakdown.

vagus nerve -  a mixed nerve that arises by numerous small roots from the side of the medulla oblongata, between the glossopharyngeal above and the accessory below; it leaves the cranial cavity by the jugular foramen and passes down to supply the pharynx, larynx, trachea, lungs, heart, and the gastrointestinal tract as far as the left colic (splenic) flexure; the only cranial nerve that does not arise from the brain, but is classified as such because it exits from the cranium. Syn: pneumogastric nerve, tenth cranial nerve [CN X], nervus vagus [CN X] [TA], vagus.

Valsalva maneuver - any forced expiratory effort (“strain”) against a closed airway, whether at the nose and mouth or at the glottis, the reverse of Müller maneuver; because high intrathoracic pressure impedes venous return to the right atrium, this maneuver is used to study cardiovascular effects of raised peripheral venous pressure and decreased cardiac filling and cardiac output, as well as post-strain responses.

Valsalva test - the heart is monitored by ECG, pressure recording, or other methods while the patient performs the Valsalva maneuver; the heart becomes smaller in normal persons but may dilate in the patient with impaired myocardial reserve; there is a characteristic complex sequence of cardiocirculatory events, departure from which indicates disease or malfunction.

vascular - Relating to or containing blood vessel

vasculitis - Inflammation of a blood vessel (arteritis, phlebitis) or lymphatic vessel (lymphangitis). Syn: angitis

vasoconstriction - Narrowing of the blood vessels. 

vasodilation - Widening of the lumen of blood vessels. Syn: vasodilatation.

vasopressin (VP) - A nonapeptide neurohypophysial hormone related to oxytocin and vasotocin; synthetically prepared or obtained from the posterior lobe of the pituitary of healthy domestic animals. In pharmacological doses vasopressin causes contraction of smooth muscle, notably that of all blood vessels; large doses may produce cerebral or coronary arterial spasm. Syn: antidiuretic hormone, Pitressin.

vasopressor -1. Producing vasoconstriction and a rise in blood pressure, usually understood to be systemic arterial pressure unless otherwise specified.
2. An agent that has this effect.

vein -  A blood vessel carrying blood toward the heart; postnatally, all veins except the pulmonary carry dark unoxygenated blood. Syn: vena  (see below).

virion - The complete virus particle that is structurally intact and infectious.

virus, pl. viruses  - Specifically, a term for a group of infectious agents, which with few exceptions are capable of passing through fine filters that retain most bacteria, are usually not visible through the light microscope, lack independent metabolism, and are incapable of growth or reproduction apart from living cells. They have a prokaryotic genetic apparatus but differ sharply from bacteria in other respects. The complete particle usually contains either DNA or RNA, not both, and is usually covered by a protein shell or capsid that protects the nucleic acid. They range in size from 15 nanometers up to several hundred nanometers. Classification of viruses depends upon physiochemical characteristics of virions as well as upon mode of transmission, host range, symptomatology, and other factors. For viruses not listed below, see the specific name.

venous blood - blood which has passed through the capillaries of various tissues, except the lungs, and is found in the veins, the right chambers of the heart, and the pulmonary arteries; it is usually dark red as a result of a lower content of oxygen.

xanthine (Xan) - oxidation product of guanine and hypoxanthine, precursor of uric acid; occurs in many organs and in the urine, occasionally forming urinary calculi; elevated in molybdenum cofactor deficiency and in xanthinuria.

xanthine oxidase - a flavoprotein containing molybdenum; an oxidoreductase catalyzing the reaction of xanthine, O2, and H2O to produce urate and superoxide; also oxidizes hypoxanthine, some other purines and pterins, and aldehydes. A lower activity is observed in molybdenum cofactor deficiency. Syn: Schardinger enzyme, hypoxanthine oxidase.

yohimbine - An alkaloid, the active principle of yohimbé, the bark of Corynanthe yohimbi (family Rubiaceae); it produces a competitive blockade, of limited duration, of adrenergic )-receptors; has also been used for its alleged aphrodisiac properties