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left iliac fossa; leukocyte inhibitory factor.


abbreviation for leukemia inhibitory factor.


symbol for lithium fluoride.


(fak'tor) [L. factor, maker]
1. A contributing cause in an action.
2. In genetics, a gene.
3. An essential chemical such as a vitamin or immunoglobulin.

angiogenic growth factor

Any of a group of polypeptides that stimulate the formation of new blood vessels. They include agents like vascular endothelial growth factor (VEGF) and blood vessel fibroblastic growth factor (bFGF). These factors are active in healing wounds, chronic inflammatory conditions, retrolental fibroplasia, and malignant tumors, which require new blood vessels for continued growth.

antihemophilic factor

Abbreviation: AHF.
Coagulation factor VIII, a glycoprotein clotting factor essential for the formation of blood thromboplastin. A deficiency results in hemophilia A.
See: blood coagulation; coagulation factor

atrial natriuretic factor

A peptide secreted by the atrial tissue of the heart in response to an increase in blood pressure. It influences blood pressure, blood volume, and cardiac output. It increases the excretion of sodium and water in urine, thereby lowering blood volume and blood pressure and influencing cardiac output. Its secretion rate depends on glomerular filtration rate and inhibits sodium reabsorption in distal tubules. These actions reduce the workload of the heart. Synonym: atrial natriuretic hormone; atrial natriuretic peptide; atriopeptin

autocrine factor

A growth factor produced by the cell that stimulates the same cell to grow.

autocrine motility factor

A chemical released by cancer cells that induces motility, enabling the cells to metastasize.

B cell growth factor


B cell stimulatory factor II


Bucky factor

See: Bucky, Gustav P.

cervical factor

In infertile women, any disease of the uterine cervix that prevents conception, e.g., cervical stenosis.

Christmas factor

See: Christmas, Stephen

citrovorum factor


clotting factor

Coagulation factor.

coagulation factor

Any of the factors involved in blood clotting. The generally accepted terms for the factors and their Roman numeral designations are as follows:

factor I, fibrinogen; factor II, prothrombin; factor III, thromboplastin; factor IV, calcium (ions); factor V, proaccelerin; factor VII, serum prothrombin conversion accelerator; factor VIII, antihemophilic factor; factor IX, plasma thromboplastin component; factor X, Stuart-Prower factor; factor XI, plasma thromboplastin antecedent; factor XII, Hageman factor; factor XIII, fibrin-stabilizing factor; prekallikrein; and high-molecular-weight kininogen, also called Fitzgerald, Flaujeac, or Williams factor, or contact activation cofactor. Factor VI, once called accelerin, is no longer used.

Synonym: clotting factor See: blood coagulation

colony-stimulating factor–1

Abbreviation: CSF-1
A protein in human serum that promotes monocyte differentiation.
See: granulocyte-macrophage colony-stimulating factor

contact factor

Hageman factor.

correction factor

A number by which a measured value is multiplied to correct for systematic measurement error.

corticotropin-releasing factor

Corticotropin-releasing hormone.

drop factor

The number of drops of an infusion that add to a volume equal to 1 milliliter.

edema factor

An enzyme made by Bacillus anthracis. It causes the cellular and tissue swelling characteristic of anthrax infection.

endothelium-derived hyperpolarizing factor

Abbreviation: EDHF
A vasodilating substance released by the vascular endothelium.
See: endothelium

endothelium-derived relaxing factor

Abbreviation: EDRF
An active vasodilator released by the vascular endothelium. It facilitates relaxation of vascular smooth muscle and inhibition of adhesion and aggregation of platelets. When the normal function of the endothelium is disrupted by mechanical trauma, hypertension, hypercholesterolemia, or atherosclerosis, less EDRF is released, and the inhibition of platelet aggregation is decreased. In addition, the damaged vessels constrict, which favors the formation of thrombi.
See: endothelium

eosinophil chemotactic factor

A mediator released in response to inflammation when mast cells are injured.

eosinophil colony-stimulating factor


eosinophil differentiation factor


epidermal growth factor

Abbreviation: EGF
A polypeptide that stimulates growth of several different cells, including keratinocytes. A receptor for EGF is located on the surface of many cancer cells. It has been used experimentally to promote wound healing.

extrinsic factor

1. Serum prothrombin conversion accelerator.
2. An obsolete term for vitamin B12.
See: pernicious anemia.

fibrin-stabilizing factor

Abbreviation: FSF
Coagulation factor XIII, a clotting factor that is active in the intrinsic, extrinsic, and common pathways of coagulation and, when activated by thrombin, transforms monomeric fibrin to stable fibrin polymers.
Synonym: plasma transglutaminase See: blood coagulation ; coagulation factor

fibroblast growth factor

Any of a group of polypeptides that stimulate the growth of tissues rich in fibroblasts, including blood vessels, connective tissues, and skin. Overactivity of these factors has been associated with neoplasia.

general intelligence factor

Abbreviation: g
The hypothetical common feature identified by all intelligence (IQ) tests. The concept of general intelligence was developed by Charles Spearman, a British psychologist and statistician, who noticed that students who do well in one subject tend to do well in all school subjects and that students who do poorly in one field of study also lag behind in others. He proposed that the general ability to master academic material was due to superior general intelligence and that specific cognitive talents correlated with overall intellectual superiority. This concept, like many others in the field of psychometrics and intelligence testing, is controversial.

granulocyte colony-stimulating factor

Abbreviation: G-CSF
A naturally occurring cytokine glycoprotein that stimulates the proliferation and functional activity of neutrophils. It is effective in treating bone marrow deficiency after cancer chemotherapy or bone marrow transplantation. The generic name is filgrastim.
See: colony-stimulating factor–1

granulocyte-macrophage colony-stimulating factor

Abbreviation: GM-CSF
A naturally occurring cytokine glycoprotein that stimulates the production of neutrophils, monocytes, and macrophages. It is effective in treating bone marrow deficiency following cancer chemotherapy or bone marrow transplantation. The generic name is sargramostim; trade names are Leukine and Prokine.
See: colony-stimulating factor–1

growth factor

Abbreviation: GF
A substance (generally a protein, polypeptide, or peptide) that stimulates the differentiation, division, development, and maintenance of cells and the tissues they make up. Growth factors are signaling molecules released by certain groups of cells, e.g., lymphocytes, to influence the activities of other cells. Growth factors can be divided into families, e.g., platelet-derived GFs, transforming GFs, and angiogenic GFs. They are released normally during fetal and embryonic development, wound healing, and tissue maturation. Massive releases of GFs are characteristic of some types of cancer cells. Artificial GFs, e.g., granulocyte colony-stimulating factor, are used in health care to restore depressed levels of cells to normal values, e.g., in patients who have received chemotherapy. See: cytokine

Hageman factor

Coagulation factor XII, a serine protease, not vitamin-K–dependent, involved in the intrinsic pathway of coagulation.
Synonym: contact factor See: blood coagulation; coagulation factor

hematopoietic growth factor

Any of a group of at least seventeen substances involved in the production of blood cells, including several interleukins and erythropoietin.

heparin-binding epidermal growth factor

Abbreviation: HB-EGF
A cytokine monokine involved in immune and inflammatory responses. It is produced by macrophages and stimulates production of smooth muscle cells and fibroblasts.

hepatocyte growth factor

A cytokine monokine involved in immune and inflammatory responses. It is produced by platelets, fibroblasts, macrophages, endothelial cells, and smooth muscle cells. It stimulates growth of hepatocytes and increases migration and motility of various epithelial and endothelial cells.

hepatocyte stimulatory factor


human factor

A general term for several areas of research that include human performance, technology, design, and human-computer interaction. It focuses on human abilities, limitations, and characteristics as they relate to their environment.

hypoxia-inducible factor

A factor within aerobic cells that helps them adapt to abnormally low oxygen concentrations.

insulin sensitivity factor

The decrease in blood sugar produced by each unit of injected insulin.

insulin-like growth factor

Abbreviation: IGF
Any of a group of related peptides, synthesized by the liver as a result of human growth hormone secretion. The IGF family of polypeptides is structurally similar to insulin in that it is composed of two subunits that are short polypeptides. IGF-1 and IGF-2, for example, each contain about 70 amino acids. They have a wide variety of functions, including the stimulation of cell growth and proliferation (as in the developing embryo and neonate), DNA synthesis, bone growth, and the replication of cancer cells. Drugs that block IGF have been tested for use in cancer chemotherapy.

intrinsic factor

A glycoprotein secreted by the parietal cells of the gastric mucosa. It is necessary for the absorption of ingested vitamin B12. The absence of this factor leads to vitamin B12 deficiency and pernicious anemia.
Synonym: Castle intrinsic factor

labile factor


lethal factor

1. A gene or an abnormality in genetic composition that causes death of a zygote or of an individual before reproductive age.
2. A protein made by Bacillus anthracis. It splits signal transduction proteins within infected cells, resulting in cellular dysfunction and death.

leukemia inhibitory factor

Abbreviation: LIF
A cytokine that regulates the growth and differentiation of many cells throughout the body, including endothelial cells, fat cells, embryonic stem cells, germ cells, osteoblasts, and peripheral nerve cells.

leukocyte inhibitory factor

Leukocyte migration inhibition factor.

leukocyte migration inhibition factor

Abbreviation: LMIF
A lymphokine that inhibits movement of neutrophils.
Synonym: leukocyte inhibitory factor

lymphocyte mitogenic factor

Abbreviation: LMF
A lymphokine that stimulates production of lymphocytes and other lymphokines.

lipotropic factor

Any of the compounds that promote the transportation and use of fats and help to prevent accumulation of fat in the liver.

macrophage activating factor

Abbreviation: MAF
A lymphokine that stimulates macrophages to become more effective killers of certain microbial cells. Macrophages stimulated by MAF can kill tumor cells.

macrophage chemotactic factor

Abbreviation: MCF
A lymphokine released by T and B cell lymphocytes in response to an antigen. It attracts macrophages to the site of the invading antigen.

macrophage colony stimulating factor

Abbreviation: M-CSF
A hematopoietic growth factor that stimulates monocytes to form colonies.

magnification factor

Abbreviation: MF
A quantitative expression of the degree of enlargement of an image in which the image size is divided by object size. In radiography, it is the ratio of the source-to-image-receptor distance to the source-to-object distance.

male factor

Any cause for a couple's difficulty in conceiving a child that results from diseases of the male reproductive organs, e.g., a low sperm count or inadequate sperm motility.

mast cell growth factor


mast cell growth factor II


maturation-promoting factor

Abbreviation: MPF
A complex cellular protein that stimulates cell division in eukaryotic cells. Part of MPF is the protein cyclin, which accumulates during interphase and triggers mitosis or meiosis. Synonym: M-phase promoting factor

milk factor

A substance present in certain strains of mammary cancer-prone mice that is transferred to offspring through milk from the mammary glands. It can induce the development of mammary cancer in suckling mice exposed to the factor.

M-phase promoting factor

Maturation-promoting factor.

multi-colony stimulating factor


natural killer cell stimulating factor


neutrophil chemotactic factor

A lymphokine that attracts neutrophils, but not other white blood cells, and causes proteolytic damage in sepsis and trauma.

nerve growth factor

Abbreviation: NGF
A protein necessary for the growth and maintenance of sympathetic and certain sensory neurons.

osteoclast-activating factor

Abbreviation: OAF
A lymphokine produced in certain conditions associated with resorption of bone, including periodontal disease and lymphoid malignancies such as multiple myeloma and malignant lymphoma. Interleukin-1 and other substances produced by T lymphocytes and prostaglandins are OAFs.

osteoclastogenesis inhibitory factor

Abbreviation: OCIF
A protein produced by activated T cells that inhibits the proliferation of osteoclasts.
Synonym: osteoprotegerin

ovarian factor

Any cause of female infertility that results from failure of egg production by the ovaries

ovulatory factor

1. In women who are infertile, any disease or condition that interferes with the monthly release of an unfertilized egg from the ovaries.
2. In ovarian cancer, the carcinogenic effect of ovulation on the surface epithelium of an ovary.

plasmacytoma simulating factor


platelet-activating factor

Abbreviation: PAF
A phospholipid that affects the signaling between cells in important body processes such as inflammation, sepsis, and thrombosis. It is released by mast cells, basophils, and activated eosinophils.

platelet-derived growth factor

A polypeptide that stimulates collagen synthesis, smooth muscle formation, tissue repair, and the proliferation of fibroblasts and microglia.

platelet tissue factor


pre-B cell growth factor

A polypeptide that stimulates collagen synthesis, smooth muscle formation, tissue repair, and the proliferation of fibroblasts and microglia.

predictive factor

A characteristic of a patient that indicates a greater or lesser likelihood of responding to a specific treatment regimen.

procoagulant factor

A lymphokine that can assume the role of factor VIII (antihemophilic factor) in coagulation cascade.

prognostic factor

Any feature of a disease or of a patient's presentation that suggests that he or she will be affected for better or worse by an illness.

quality factor

Abbreviation: Q
In radiology, a scale used to account for the biological effects of different radiations. Factors include beta, electron, and gamma x-radiation (Q = 1), thermal neutrons (Q = 5), and alpha neutrons and protons (Q = 20).

R factor

Resistance transfer factor.

resistance transfer factor

Abbreviation: RTF
A genetic factor in bacteria that controls resistance to certain antibiotic drugs. The factor may be passed from one bacterium to another. This makes it possible for nonpathogenic bacteria to become resistant to antibiotics and to transfer that resistance to pathogens, thereby establishing a potential source for an epidemic.
Synonym: R factor See: plasmid

Rh factor

An antigen found on the membranes of the red blood cells. It was discovered in 1940 by Karl Landsteiner and Alexander S. Wiener, who prepared anti-Rh serum by injecting red cells from Rhesus monkeys into rabbits and other animals. They found that the red cells of 85% of Caucasians agglutinates in contact with anti-Rh serum. These people are called Rh-positive. The remaining 15%, whose red cells are not agglutinated by anti-Rh serum, are called Rh-negative. More than 25 blood factors are known to belong to the Rh system. Rh incompatibility between mother and fetus is the cause of hemolytic disease of the newborn.

rheumatoid factor

Antibodies raised by the body against immunoglobulins. They are present in roughly 80% of patients with rheumatoid arthritis and in many patients with other rheumatological and infectious illnesses. This factor is used, with other clinical indicators, in the diagnosis and management of rheumatoid arthritis.

risk factor

An environmental, chemical, psychological, physiological, or genetic element that predisposes someone to the development of a disease. Risk factors for coronary artery disease include hypertension, high circulating blood lipids and cholesterol, obesity, cigarette smoking, diabetes mellitus, physical inactivity, microalbuminuria, chronic kidney disease, and an early family history of atherosclerosis.
Synonym: risk marker

spreading factor

The hyaluronidase made by Bacillus anthracis. See: hyaluronidase

stable factor

Serum prothrombin conversion accelerator.

susceptibility factor

A condition that increases a person's likelihood of acquiring a disease. The propensity to develop disease is often the result of a genetic mutation in a single base DNA base pair.

stem cell factor

Abbreviation: SCF
A cytokine glycoprotein that influences the development of sperm and egg cells, the production of melanin, and mast cell development.

Stuart-Prower factor

Coagulation factor X, a vitamin-K–dependent protease, synthesized by the liver, that, when activated to factor Xa, is the first coagulation factor in the common final pathway of blood coagulation that generates thrombin from prothrombin. The factors that lead to it are limited to the extrinsic or intrinsic coagulation pathways. The Stuart-Prower factor was formerly called “thrombokinase.”
See: blood coagulation; coagulation factor

T-cell growth factor


T-cell growth factor II


thyroid-stimulating hormone-releasing factor

Abbreviation: TSH-RF
An obsolete term for
Thyrotropin-releasing hormone.

tissue factor

Abbreviation: TF

transfer factor

Any of the low-molecular-weight chemicals extracted from immune cells activated to respond to specific antigens. These products can be taken from a sensitized person and given to another. The recipient will react to the same antigen originally used to sensitize the lymphocytes of the donor. The factor can be transferred by injecting the recipient with either intact lymphocytes or extracts of disrupted cells. It has been studied as adjunctive therapy to modulate the immune system in several clinical trials.

transforming growth factor

Abbreviation: TGF
A polypeptide growth factor that competitively binds to epidermal growth factor (EGF) receptors. This molecule can promote growth of fibroblasts in cell cultures, thus transforming normal cells into those with the abnormal properties of malignant cells.

tubal factor

Any abnormality of the fallopian tubes that produces infertility.

tumor angiogenesis factor

Abbreviation: TAF
A protein in animal and human cancer tissue that in experimental studies appears to be essential to growth of the cancer. This factor is thought to act by stimulating the growth of new blood capillaries that supply the tumor with nutrients and remove waste products.

tumor necrosis factor

Abbreviation: TNF
A polypeptide protein mediator or cytokine released primarily by macrophages and T lymphocytes. It helps regulate the metabolism of fats, the immune response, and some hematopoietic functions. There are two factors: alpha (TNFa), also called cachectin, produced by macrophages; and beta (TNFß), called lymphotoxin, produced by activated CD4+ T cells. The functions of TNF are similar to those of interleukin-1. A monoclonal antibody against TNFa, infliximab, is used to treat rheumatoid arthritis and other diseases in which TNFa causes inflammatory damage. Antagonists to tumor necrosis factor, e.g., adalimumab, etanercept, and infliximab, are used to treat diseases affected by TNF, such as rheumatoid arthritis or Crohn's disease.
See: cytokine; interleukin-1

uterine factor

Any abnormality of the uterus that produces infertility.

V factor

Nicotinamide adenine dinucleotide.

vascular endothelial growth factor

Abbreviation: VEGF
A growth factor produced by endothelial cells that promotes angiogenesis and increases microvascular permeability Inhibitors of VEGF are used to treat a variety of cancers. Their use is associated with hypertension, which sometimes may be severe.

virulence factor

A substance released by a microorganism that allows it to evade host defenses or cause serious injury to its host. Although most virulence factors are released by bacteria for their own benefit, sometimes factors released by one microorganism foster another disease-causing organism.

windchill factor

Loss of heat from exposure of skin to wind. Heat loss is proportional to the speed of the wind. Thus, skin exposed to a wind velocity of 20 mph (32 km/hr) when the temperature is 0°F (-17.8°C) is cooled at the same rate as in still air at -46°F (-43.3°C). Similarly, when the temperature is 20°F (-6.7°C) and the wind is 10, 20, or 35 mph (16.1, 32.2, or 56.3 km/hr), the equivalent skin temperature is -4°, -18°, or -28°F (-20°, -27.8°, or -33.3°C), respectively.

The windchill factor is calculated for dry skin; skin that is wet from any cause and exposed to wind loses heat at a much higher rate. Wind blowing over wet skin can cause frostbite, even on a comfortably warm day as judged by the thermometer.

X factor

A growth factor, identified as hemin, that is needed to grow Haemophilus influenzae in culture.
See: hemin

leukemia inhibitory factor

Abbreviation: LIF
A cytokine that regulates the growth and differentiation of many cells throughout the body, including endothelial cells, fat cells, embryonic stem cells, germ cells, osteoblasts, and peripheral nerve cells.
See also: factor


leukocyte inhibitory factor.
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