| platelet aggregation test | A test of the ability of platelets to adhere to each other and hence form a haemostatic plug to prevent bleeding; failure to aggregate occurs in several conditions, e.g., thrombasthenia, Von Willebrand's disease, and following administration of aspirin, phenylbutazone, and indomethacin; the test is conducted by quantitating the decrease in turbidity that occurs in platelet-rich plasma following the in vitro addition of one or several platelet-aggregating agents (e.g., ADP, epinephrine, or serotonin). (05 Mar 2000) |
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| platelet aggregation | The attachment of platelets to one another. This clumping together can be induced by a number of agents (e.g., thrombin, collagen) and is part of the mechanism leading to the formation of a thrombus. (12 Dec 1998) |
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| platelet aggregation inhibitors | Drugs or agents which antagonise or impair any mechanism leading to blood platelet aggregation, whether during the phases of activation and shape change or following the dense-granule release reaction and stimulation of the prostaglandin-thromboxane system. (12 Dec 1998) |
| aggregation | Massing of materials together as in clumping. (18 Nov 1997) |
| receptor aggregation | Chemically stimulated aggregation of cell surface receptors, which potentiates the action of the effector cell. (12 Dec 1998) |
| cell aggregation | The phenomenon by which dissociated cells intermixed in vitro tend to group themselves with cells of their own type. (12 Dec 1998) |
| erythrocyte aggregation | Aggregation of erythrocytes probably resulting from changes in the negative surface charge (zeta potential) of the cells caused by the dielectric effect of proteins in the surrounding plasma, especially asymmetric macromolecules like fibrinogen and gamma-globulin. (12 Dec 1998) |
| erythrocyte aggregation, intravascular | The massing or clumping of erythrocytes in intact blood vessels in response to injury or in certain diseases, interfering with adequate blood flow. It is also called sludging of blood and intravascular agglutination. (12 Dec 1998) |
| familial aggregation | <genetics> The occurrence of a trait in more members of a family than can be readily accounted for by chance; presumptive but not cogent evidence of the operation of genetic factors. (05 Mar 2000) |
| acquired platelet function defect | <haematology> Platelet function can be affected by a number of different disease processes including polycythaemia vera, leukaemia, myelofibrosis, renal failure, multiple myeloma and some medications (for example penicillins, salicylates, phenothiazines). Disturbed blood clotting can be manifested by: easy bruising, bleeding gums, nosebleeds, abnormal vaginal bleeding, rectal bleeding, skin rash, vomiting blood, coughing up blood or blood in the urine. A measure of bleeding time and coagulation profile will be part of the evaluation. (29 Dec 1997) |
| antigens, human platelet | Human alloantigens expressed only on platelets, specifically on platelet membrane glycoproteins. These platelet-specific antigens are immunogenic and can result in pathological reactions to transfusion therapy. (12 Dec 1998) |
| anti-platelet agents | Medications that, like aspirin, reduce the tendency of platelets in the blood to clump and clot. (12 Dec 1998) |
| receptors, platelet-derived growth factor | Specific molecular sites or structures on cell membranes that react with platelet-derived growth factor, its analogs, or antagonists, to elicit or to inhibit the specific response of the cell to this factor. Pdgf binds with different affinities and specificities to two structurally related receptors, the alpha-receptor and the beta-receptor. Both of these receptors are transmembrane proteins with an intracellular, ligand-stimulatable protein kinase domain. (12 Dec 1998) |
| medication, anti-platelet | Platelet-blocking drugs. Drugs that, like aspirin, reduce the tendency of platelets in the blood to clump and clot. (12 Dec 1998) |
| platelet | <haematology> A discoid cell (3m diameter) found in large numbers in blood, important for blood coagulation and for haemostasis by repairing breaches (small breaks) in the walls of blood vessels. Platelet _ granules contain lysosomal enzymes, dense granules contain ADP (a potent platelet aggregating factor) and serotonin (a vasoactive amine). They also release platelet-derived growth factor which presumably contributes to later repair processes by stimulating fibroblast proliferation. Synonym: thrombocytes. (09 Oct 1997) |
| platelet-activating factor | <cytokine> Potent phospholipid activator and mediator of many leucocyte functions, including platelet aggregation, inflammation, and anaphylaxis. It is produced in response to specific stimuli by a variety of cell types, including neutrophils, basophils, platelets, and endothelial cells. Several molecular species of platelet-activating factor have been identified which vary in the length of the O-alkyl side chain. It is an important mediator of bronchoconstriction. Synonym: platelet-aggregating factor. Acronym: PAF (20 Sep 2002) |