- 1. One of the contributing causes in any action. 2. One of the components that by multiplication makes up a number or expression. 3. SYN: gene. 4. A vitamin or other essential element. 5. An event, characteristic, or other definable entity that brings about a change in a health condition. 6. A categoric independent variable, used to identify, by means of numeric codes, membership in a qualitatively identifiable group; for example, overcrowding is a f. in disease transmission. [L. maker, causer, fr. facio, to make]- f. I in the clotting of blood a f. that is converted to fibrin through the action of thrombin. SEE ALSO: fibrinogen.- f. II a glycoprotein converted in the clotting of blood to thrombin by f. Xa, platelets, calcium ions, and f. V. SEE ALSO: prothrombin.- f. IIa SYN: thrombin.- f. III in the clotting of blood, tissue f. or thromboplastin; it initiates the extrinsic pathway by reacting with f. VII and calcium to form f. VIIa. See thromboplastin.- f. V in the clotting of blood, also known as: proaccelerin (Owren), labile or plasma labile f. (Quick), plasma accelerator globulin (Ware and Seegars), thrombogene (Nolf), prothrombokinase (Milstone), plasmin prothrombins conversion f. (Stefanini), component A of prothrombin (Quick), prothrombin accelerator (Fantl and Nance), cofactor of thromboplastin (Honorato), and accelerator f.. F. V does not have enzymatic action itself but participates in the common pathway of coagulation by binding f. Xa to platelet surfaces. Deficiency of this f. leads to a rare hemorrhagic tendency known as parahemophilia or hypoproaccelerinemia, with autosomal recessive inheritance; heterozygous individuals are recognized by reduced levels of f. V but have no bleeding tendency. SYN: accelerator f., labile f., plasma accelerator globulin, plasma labile f., plasmin prothrombins conversion f., proaccelerin, prothrombokinase, thrombogene.- f. V1a SYN: cobyric acid.- f. VII in the clotting of blood, also known as: proconvertin (Owren), convertin, serum prothrombin conversion accelerator (de Vries, Alexander), stable f. (Stefanini), cofactor V (Owren), prothrombinogen (Quick), cothromboplastin (Mann and Hurn), serum accelerator (Jacox). F. VII forms a complex with tissue thromboplastin and calcium to activate f. X. F. VII is known to be involved in: 1) the congenital deficiency of f. VII, with purpura and bleeding from mucous membranes, autosomal recessive inheritance; 2) the acquired deficiency of f. VII in association with a deficiency of vitamin K, the neonatal period, and the administration of prothrombinopenic drugs; 3) the acquired excess of f. VII in some patients with thromboembolism. It accelerates the conversion of prothrombin to thrombin, in the presence of tissue thromboplastin, calcium, and f. V. SYN: proconvertin, prothrombinogen, stable f..- f. VIII in the clotting of blood, also known as: antihemophilic f. A (Brinkhous), antihemophilic globulin (1) (Patek and Taylor), antihemophilic globulin A (Cramer), plasma thromboplastin f. (Ratnoff), plasma thromboplastin f. A (Aggeler), thromboplastic plasma component (Shinowara), thromboplastinogen (Quick), prothrombokinase (Feissly), platelet cofactor (Johnson), plasmokinin (Laki), thrombokatilysin (Leggenhager), and proserum prothrombin conversion accelerator. F. VIII participates in the clotting of the blood by forming a complex with f. IXa, platelets, and calcium and enzymatically catalyzing the activation of f. X. Deficiency of f. VIII is associated with classic hemophilia A. F. VIII:C is the coagulant component of f. VIII which, in normal persons, circulates in the plasma complexed with f. VIIIR (von Willebrand f.), the plasma f. VIII–related protein, a large glycoprotein component that is synthesized by endothelial cells and megakaryocytes, and circulates in the plasma where it binds to arteries that have lost their endothelial cell linings, creating a surface to which platelets adhere. Disorders involving f. VIIIR form a heterogenous group of abnormalities called von Willebrand disease. A deficiency of f. VIII can lead to impaired blood coagulation. SYN: antihemophilic f. A, antihemophilic globulin A, antihemophilic globulin (1), plasma thromboplastin f., platelet cofactor I, prothrombokinase.- f. IX in the clotting of blood, also known as: Christmas f. (Biggs and Macfarlane), plasma thromboplastin component (Aggeler), antihemophilic globulin B (Cramer), plasma thromboplastin f. B (Aggeler), plasma f. X (Shulman), antihemophilic f. B, and platelet cofactor II. F. IX is required for the formation of intrinsic blood thromboplastin and affects the amount formed (rather than the rate). Its active form, f. IXa (EC 184.108.40.206) is a serine proteinase converting f. X to f. Xa by cleaving an arginine-isoleucine bond. Deficiency of f. IX causes hemophilia B. SYN: antihemophilic f. B, antihemophilic globulin B, Christmas f., plasma f. X, plasma thromboplastin component, plasma thromboplastin f. B, platelet cofactor II.- f. X in the clotting of blood, also known as: Stuart f., Stuart-Prower f., prothrombase, and prothrombinase. Its active form, f. Xa (EC 220.127.116.11), is formed from f. X by limited proteolysis and assists in the conversion of prothrombin to thrombin. A deficiency of f. X will lead to impaired blood coagulation. SYN: prothrombinase, Stuart f., Stuart-Prower f..- f. XI in the clotting of blood, also known as plasma thromboplastin antecedent, a component of the contact system which is absorbed from plasma and serum by glass and similar surfaces. Its active form, f. XIa (EC 18.104.22.168), is a serine proteinase converting f. IX to f. IXa. Deficiency of f. XI results in a hemorrhagic tendency and is caused by an autosomal recessive gene. SYN: plasma thromboplastin antecedent.- f. XII in the clotting of blood, also known as glass f. and Hageman f. When activated by glass or otherwise to its active form, f. XIIa (EC 22.214.171.124), a serine proteinase, it activates factors VII and XI and converts f. XI to its active form, f. XIa. Deficiency of f. XII results in great prolongation of the clotting time of venous blood, but only rarely in a hemorrhagic tendency; deficiency is caused by an autosomal recessive gene. SYN: glass f., Hageman f..- f. XIII in the clotting of blood, also known as: fibrin-stabilizing f., Laki-Lorand f., and L-L f. It is catalyzed by thrombin into its active form, f. XIIIa, which cross-links subunits of the fibrin clot to form insoluble fibrin. SYN: fibrin-stabilizing f., L-L f., Laki-Lorand f..- f. 3 1. operational name given to an incompletely characterized selenium-containing natural product which, in minute amounts, prevents liver damage in rats due to deficiency of vitamin E; 2. f. III in the vitamin B12 series, 5-hydroxybenzimidazole, analogue of the usual B12 nucleotide components.- adrenal weight f. a postulated substance of adenohypophysial origin responsible for maintenance of the weight of the adrenal cortex.- adrenocorticotropic releasing f. hormone produced by hypothalamus that causes pituitary to secrete adrenocorticotropic hormone.- angiogenesis f. a substance of 2000–20,000 MW which is secreted by macrophages and stimulates neovascularization in healing wounds or in the stroma of tumors.- antialopecia f. SYN: inositol.- antiangiogenesis f. one of several molecules capable of inhibiting angiogenesis.- antiberiberi f. SYN: thiamin.- antidermatitis f. SYN: pantothenic acid.- antihemophilic f. B SYN: f. IX.- antineuritic f. SYN: thiamin.- antinuclear f. (ANF) a f., usually antibodies, present in serum with strong affinity for certain nuclear proteins and detected by fluorescent antibody technique; present in lupus erythematosus, rheumatoid arthritis, and certain other autoimmune conditions; may also be present at lower levels in normal individuals.- antipellagra f. SYN: nicotinic acid.- antisterility f. SYN: vitamin E (2).- atrial natriuretic f. (ANF) an early name given to a natriuretic f. derived from cardiac atria. Because the f. is now known to be a peptide, the term is no longer used.- f. B complement pathways.- BT f. SYN: carnitine.- bacteriocin factors SYN: bacteriocinogenic plasmids, under plasmid.- B cell differentiation/growth factors various substances, usually obtained from the supernatant of T cell cultures, such as interleukin 4, 5, and 6. These substances are necessary for B cell growth, maturation, and differentiation into plasma cells or B memory cells.- bifidus f. an unidentified substance associated with Lactobacillus bifidus pennsylvanicus, present in mammalian milk.- biotic factors environmental factors or influences resulting from the activities of living organisms, as contrasted to those resulting from climatic, geological, or other factors.- C factors SYN: coupling factors.- CAMP f. CAMP test.- clearing factors lipoprotein lipase s that appear in plasma during lipemia and catalyze hydrolysis of triglycerides only when the latter are bound to protein and when an acceptor ( e.g., serum albumin) is present, thus “clearing” the plasma.- clotting f. any of the various plasma components involved in the clotting process. SYN: coagulation f..- coagulation f. SYN: clotting f..- cobra venom f. a component of cobra venom that can activate the alternative pathway of complement.- colony-stimulating factors (CSF) a group of glycoprotein growth factors regulating differentiation of myeloid cells. These substances act in either paracrine or autocrine fashion on marrow cells, appear to act synergistically in complex and poorly understood ways; each appears to have the ability to exert action on several lines of progenitor cells, and to influence end cell function.- complement chemotactic f. the activated complex of the fifth, sixth, and seventh components of complement C 5a, C 3a, C 5b, 6, 7 which induces chemotaxis in the case of polymorphonuclear leukocytes.- complement f. I a heterodimeric glycoprotein; a deficiency results in uncontrolled activation of C3.- coupling factors proteins that restore phosphorylating ability to mitochondria that have lost it, i.e., have become “uncoupled” so that oxidation and electron transport no longer produce ATP. Usually termed coupling f. F1, F2, etc. SYN: C factors.- f. D complement pathways.- debranching factors SYN: debranching enzymes, under enzyme.- decapacitation f. a f., postulated to be present in epididymal fluid and seminal plasma, that prevents the capacitation of spermatozoa.- diabetogenic f. rarely used term for a f. in crude extracts of the anterior lobe of the hypophysis that produces degenerative changes in the islet cells of the pancreas and causes permanent diabetes.- diffusing f. SYN: hyaluronidase (1).- elongation f. proteins that catalyze the elongation of peptide chains during protein biosynthesis. SYN: transfer f. (3).- endothelial relaxing f. (en′do-the′li-al) nitric oxide, which functions as a neurotransmitter and is produced by activated macrophages. It is capable of killing tumor cells, parasites, and intracellular bacteria.- endothelium-derived relaxing f. (EDRF) a diffusible substance produced by endothelial cells that cause vascular smooth muscle relaxation; nitric oxide (NO).- eosinophil chemotactic f. of anaphylaxis (ECF-A) a peptide (MW 500 to 600) that is chemotactic for eosinophilic leukocytes and is released from disrupted mast cells.- epidermal growth f. (EGF) a heat-stable antigenic protein isolated from the submaxillary glands of male mice; when injected into newborn animals, it accelerates eyelid opening and tooth eruption, stimulates epidermal growth and keratinization, and, in larger doses, inhibits body growth and hair development and produces fatty livers.- essential food factors those substances required in the diet : certain amino acid s and unsaturated fatty acid s, vitamins, essential minerals, etc.- fertility f. SYN: F plasmid.- fibrin-stabilizing f. SYN: f. XIII.- Fletcher f. SYN: prekallikrein.- G f. 1. the single common variance or f. that is common to ( i.e., empirically intercorrelates with) different intelligence tests (general); 2. a substance required for the growth of a specific organism.- glucose tolerance f. a water-soluble complex containing chromium and nicotinate needed for normal glucose tolerance.- f. Gm a f. that determines certain of the allotypes of human immunoglobulins; found only on the γ chains of IgG (γ-globulin).- gonadotropin-releasing f. SYN: gonadoliberin (1).- granulocyte colony-stimulating f. (G-CSF) (gran′oo-lo-sit) glycoproteins that are synthesized by a variety of cells that stimulate the production of neutrophils from hematopoietic stem cells. SEE ALSO: colony-stimulating factors.- granulocyte-macrophage colony-stimulating f. (GM-CSF) (gran′oo-lo-sit-mak′ro-faj) a glycoprotein secreted by macrophages or bone stromal cells that functions as a growth f. for myeloid progenitor cells such as granulocytes, macrophages, and eosinophils. SEE ALSO: colony-stimulating factors.- 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.- f. H 1. former designation for biotin; 2. vitamin B12 analogue or precursor; 3. a glycoprotein that regulates the activity of complement f. C3b; a deficiency results in the lack of inhibition of the alternative hemolytic pathway leading to continuous activation and consumption of f. C3 (hemolytic uremic syndrome).- HG f. SYN: glucagon.- histamine-releasing f. a lymphokine produced from antigen-stimulated lymphocytes that induces the release of histamine from basophils.- human antihemophilic f. a lyophilized concentrate of f. VIII, obtained from fresh normal human plasma; used as a hemostatic agent in hemophilia. SYN: antihemophilic globulin (2), human antihemophilic fraction.- impact f. mathematical expression of frequency with which a particular medical journal's original articles are cited in other medical journals.- initiation f. (IF) one of several soluble proteins involved in the initiation of protein or RNA synthesis.- insulinlike growth f. (IGF) (formerly termed somatomedin C), is the most important somatomedin for postnatal growth; it is produced in the liver, kidney, muscle, pituitary, the gastrointestinal tract, and chondrocytes. IGF-I is a basic protein (7600 MW) that circulates bound to six distinct IGF binding proteins (IGF-BPs), which increase the half-life of circulating IGF-I to 3–18 h, as compared with the half-life of 20–30 min for unbound hormone. Local tissue generation of IGF-I/SM-C, particularly in bone, may play an important role in growth mediation through its paracrine effects. SYN: somatomedins.- intrinsic f. (IF) a relatively small mucoprotein (MW about 50,000) secreted by the neck cell of the gastric glands and required for adequate absorption of vitamin B12 and othe rcobalamins; deficiency results in pernicious anemia. SYN: Castle intrinsic f..- f. Inv obsolete term for Km allotypes on a f. of human immunoglobulins; found on the κ chains.- ischemia-modifying factors various factors that play a role in determining the extent of necrosis with cerebral stroke; these include blood viscosity and osmolality, the blood pressure, and the anatomy of the neck and intracranial arteries.- Lactobacillus casei f. SYN: folic acid (2).- Laki-Lorand f. SYN: f. XIII.- LE factors antinuclear immunoglobulins in plasma of persons with disseminated lupus erythematosus, associated with positive LE tests.- leukocytosis-promoting f. a substance obtained by Menkin from inflammatory exudates; it stimulates leukocytosis.- leukopenic f. a principle obtained by Menkin from inflammatory exudates; it causes leukopenia when injected into normal animals.- L-L f. SYN: f. XIII.- luteinizing hormone-releasing f. (LH-RF, LRF) former name for luteinizing hormone-releasing hormone.- lymph node permeability f. (LNPF) a substance, released by lymphocytes when stimulated or damaged, that increases capillary permeability and the accumulation of mononuclear cells.- macrophage-activating f. (MAF) (mak′ro-faj) a primarily CD4+ T cell–derived lymphokine that induces macrophage activation. The major macrophage–activating f. is interferon gamma. In the mouse, interleukin-4 is also an MAF.- macrophage colony-stimulating f. (M-CSF) a glycoprotein growth f. that causes the committed cell line to proliferate and mature into macrophages. SEE ALSO: colony-stimulating factors.- maize f. SYN: zeatin.- mammotropic f. SYN: prolactin.- migration-inhibitory f. (MIF) a soluble, nondialyzable substance that is produced by sensitized lymphocytes ( i.e., lymphocytes from a sensitized animal) when exposed to the specific antigen, and that causes adherence and inhibition of migration of macrophages. SYN: inhibition f..- müllerian inhibiting f. SYN: müllerian inhibiting substance.- müllerian regression f., müllerian duct inhibitory f. a nonsteroidal substance of fetal testicular origin that acts unilaterally to inhibit development of the paramesonephric (müllerian) ducts and acts with testosterone to promote development of the vas deferens and related structures.- myocardial depressant f. (MDF) a toxic f. in shock that impairs cardiac contractility; probably a peptide released with underperfusion of the splanchnic area at the release of proteolytic enzymes from the pancreas.- nephritic f. a serum protein (possibly an IgG autoantibody), found in some patients with membranoproliferative glomerulonephritis and hypocomplementemia, which, together with the cofactors of the alternate pathway of complement activation, cleaves the third component of complement (C3).- nerve growth f. (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 acid s and protein.- neutrophil-activating f. SYN: interleukin-8.- osteoclast activating f. a lymphokine that stimulates bone resorption and inhibits bone-collagen synthesis.- ψ f. SYN: psi f..- f. P a chemical (postulated by T. Lewis), formed in ischemic skeletal or cardiac muscle, held to be responsible for the pain of intermittent claudication and angina pectoris. SYN: P substance of Lewis.- pellagra-preventing f. (p-p f.) SYN: nicotinic acid.- platelet f. 3 a blood coagulation f. derived from platelets; chemically, a phospholipid lipoprotein that acts with certain plasma thromboplastin factors to convert prothrombin to thrombin.- platelet-activating f. (PAF) SYN: platelet-aggregating f..- platelet-aggregating f. (PAF) phospholipid mediator of platelet aggregation, inflammation, and anaphylaxis. Produced in response to specific stimuli by a variety of cell types, including neutrophils, basophils, platelets, and endothelial cells. Several molecular species of PAF have been identified which vary in the length of the O-alkyl side chain. It is an important mediator of bronchoconstriction. SYN: platelet-activating f..- platelet-derived growth f. (PDGF) a f. in platelets that is mitogenic for cells at the site of a wound, e.g., causing endothelial proliferation; cationic glycoprotein mitogen for fibroblasts, smooth muscle cells, and glial cells. Principal f. in serum required for the growth and proliferation of mesenchymal-derived cells in tissue culture.- p-p f. abbreviation for pellagra-preventing f.- predisposing factors attitudinal, personality, and related factors that motivate and guide an individual to take certain health actions.- prolactin-inhibiting f. dopamine, a substance that inhibits secretion of prolactin by the anterior pituitary gland.- properdin f. B a normal serum protein (MW 95,000) and a component of the properdin system, which combines with C3b to form the C3 convertase of the alternative pathway.- properdin f. D a normal serum α-globulin (MW about 25,000) required in the properdin system to cleave f. B into Bb and Ba. Bb combines with C3b to form the C3 convertase of the alternative complement pathway.- protein f. the f. (6.25) by which the nitrogen content of a protein is multiplied to give the amount of protein.- psi f. a protein responsible for the specific initiation of the RNA polymerase-catalyzed reaction at the promoter sites of genes. SYN: ψ f..- quality f. (QF) a f. by which absorbed radiation doses are multiplied to obtain, for radiation protection purposes, a quantity that expresses the approximate biologic effectiveness of the absorbed dose. Cf.:RBE, relative biologic effectiveness.- ρ f. SYN: rho f..- R factors SYN: resistance plasmids, under plasmid.- radiation weighting f. in radiation protection, a f. weighting the absorbed dose of radiation of a specific type and energy for its effect on tissue. See equivalent dose, relative biologic effectiveness, quality f..- releasing factors (RF) 1. substances, usually of hypothalamic origin, capable of accelerating the rate of secretion of a given hormone by the anterior pituitary gland; 2. factors required in the termination phase of either RNA biosynthesis or protein biosynthesis. SYN: termination f.. SYN: liberins, releasing hormone, statins.- resistance-inducing f. (RIF) an agent from normal chick embryos that interferes with multiplication of the avian sarcoma virus, and is a leukosis virus antigenically related to the avian sarcoma virus.- resistance-transfer f. the portion of the plasmid that contain genes that confer resistance to e.g., antibiotics.- rheumatoid factors (RF) antibodies in the serum of individuals with rheumatoid arthritis. These factors are autoantibodies of the classes IgM, IgG, and IgA. The most common f. is IgM and is the one usually measured. Rheumatoid factors also occur in other autoimmune and certain infectious diseases.- rho f. a termination f. that releases RNA from the DNA template; a bacterial protein that is an ATP-dependent helicase. SYN: ρ f..- risk f. a characteristic statistically associated with, although not necessarily causally related to, an increased risk of morbidity or mortality e.g., smoking as a risk f. for heart disease.- σ f. SYN: sigma f..- S f. the individual variables, or empirically most minute subclusters of intercorrelations or common variance, found in different intelligence tests (specific).- secretor f. the capacity to secrete antigens of the ABO blood group in saliva and other body fluids, controlled by a pair of allelic genes designated Se and se (or S and s), with the Se phenotype dominant to se; the saliva of genotypes SeSe and Sese contains the blood group substances A, B, or H found in their erythrocytes; the saliva of nonsecretors (genotype sese) contains no blood group substance; tests for ABH secretion are useful in genetic linkage and population studies; the secretor phenomenon is also closely associated with the Lewis blood group.- sex f. SYN: F plasmid.- sigma f. a f. that inhibits the nonspecific DNA binding of RNA polymerase, as well as helping to identify the starting point of transcription; it promotes attachment of the RNA polymerase to specific initiation sites. SYN: σ f..- SLR f., Streptococcus lactis R f. SYN: rhizopterin.- spreading f. SYN: hyaluronidase (1).- stem cell f. a cytokine that promotes growth and differentiation of hematopoietic stem cells into a variety of cell lineages.- stringent f. the gene product (an enzyme) that is crucial to the cellular response of decreased ribosome production as a result of amino acid starvation. SEE ALSO: stringent response.- sun protection f. (SPF) the ratio of the minimal ultraviolet dose required to produce erythema with and without a sunscreen; highly effective sunscreens have an SPF of 15 or more.- termination f. SYN: releasing factors (2).- testis-determining f. (TDF) the product of a gene on the short arm of the Y chromosome that is responsible for production of testes.- thymic lymphopoietic f. a glycoprotein (MW about 12,000) that has been extracted from thymus; this thymus-produced hormone(s) confers immunological competence on thymus-dependent cells and induces lymphopoiesis.- thyrotropin-releasing f. (TRF) former name for thyrotropin-releasing hormone.- tissue weighting f. in radiation protection, a f. weighting the equivalent dose in a particular tissue or organ in terms of its relative contribution to the total deleterious effects resulting from uniform irradiation of the whole body. See effective dose.- transfer f. 1. the transfer gene of a conjugative plasmid, especially of the resistance plasmid; 2. a dialyzable extract that is obtained from the leukocytes of a person with a delayed-type sensitivity and that, following injection into the skin of a nonsensitive person, transfers the specific sensitivity to the recipient; 3. SYN: elongation f..- transforming growth factors (TGF) two polypeptide growth factors; TGF-α stimulates growth of many epidermal and epithelial cells and is obtained from conditioned media of transformed or tumor cells; TGF-β is obtained from kidney and platelets and controls proliferation and differentiation in many cell types.- transforming growth f. α (TGFα) a cytokine made by tumor and transformed cells that is associated with growth and differentiation. It is also made in normal tissues during embryogenesis and in certain adult tissues.- transforming growth f. β (TGFβ) a regulatory cytokine that has multifunctional properties that can enhance or inhibit many cellular functions, including interfering with the production of other cytokines and enhancing collagen deposition. It exists in multiple subtypes and is produced by platelets and macrophages but can be made by many other cell types.- tumor angiogenic f. (TAF) a substance released by solid tumors which induces formation of new blood vessel s to supply the tumor.- tumor necrosis f.-α a pleiotropic cytokine synthesized widely throughout the female reproductive tract.- tumor necrosis f.-β a cytokine that is produced by CD4 and CD8 T cells after exposure to an antigen.- uncoupling factors SYN: uncouplers.- W f. SYN: biotin.
* * *fac·tor 'fak-tər n1 a) something that actively contributes to the production of a resultb) a substance that functions in or promotes the function of a particular physiological process or bodily system2) GENEfac·to·ri·al fak-'tōr-ē-əl, -'tȯr- adj
* * *n.(in biochemistry) a substance that is essential to a physiological process, often a substance the nature of which is unknown. See also coagulation factors, growth factor.
* * *fac·tor (fakґtər) [L. â€œmakerâ€] 1. any of several substances or activities that are necessary to produce a result, e.g., a coagulation factor. Often, use of the term â€œfactorâ€ indicates that the chemical nature of the substance or its mechanism of action is unknown, as in endocrinology, where â€œfactorsâ€ are renamed as â€œhormonesâ€ when their chemical nature is determined. 2. one of two or more quantities that multiplied together form a product. 3. a coefficient or conversion factor, a number by which a quantity is multiplied to produce a change of units of measurement.
Medical dictionary. 2011.