| gray wing | A prominence in the floor of the inferior fovea of the fourth ventricle that overlies the dorsal motor nucleus of the vagus. Synonym: trigonum nervi vagi, ala cinerea, ashen wing, gray wing, trigone of vagus nerve, va'gi eminentia. (05 Mar 2000) |
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| middle gray layer of superior colliculus | See: gray layer of superior colliculus. Molecular layer, term applied to any layer of brain tissue that contains few nerve-cell bodies and is composed largely of terminal arborizations of dendrites and axons; notable examples are the superficial layer (first layer) of the cerebral cortex and the molecular layer of cerebellum. Synonym: plexiform layer, stratum moleculare. (05 Mar 2000) |
| 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) |
| platelet activation | A series of progressive, overlapping events triggered by exposure of the platelets to subendothelial tissue. These events include shape change, adhesiveness, aggregation, and release reactions. When carried through to completion, these events lead to the formation of a stable haemostatic plug. (12 Dec 1998) |
| platelet actomyosin | The contractile protein of platelets, responsible for clot retraction, platelet aggregation, and release of ADP and other biologic amines essential to platelet function. Synonym: thrombosthenin. (05 Mar 2000) |
| platelet adhesiveness | The process whereby platelets adhere to something other than platelets, e.g., collagen, basement membranes, microfibrils, or other "foreign" surfaces. (12 Dec 1998) |
| platelet-aggregating 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) |
| 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) |
| 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) |
| 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) |
| platelet basic protein | <protein> Protein that is the precursor of connective tissue activating peptide III and _ thromboglobulin. (18 Nov 1997) |
| platelet cofactor I | A coagulation (clotting) factor. Classic haemophilia (haemophilia A) is due to a congenital deficiency in the amount (or activity) of factor VIII. Factor VIII is also known as antihemophiliac factor (AHF) or antihemophiliac globulin (AHG). The gene for factor VIII (that for classic haemophilia) is on the X chromosome so females can be silent carriers without symptoms and males can be haemophiliacs. (12 Dec 1998) |
| platelet cofactor II | <chemical> Storage-stable blood coagulation factor acting in the intrinsic pathway. Its activated form, ixa, forms a complex with factor viii and calcium on platelet factor 3 to activate factor x to xa. Deficiency of factor ix results in christmas disease (haemophilia b). Chemical name: Blood-coagulation factor IX (12 Dec 1998) |
| platelet count | <haematology> The number of platelets per cubic millimetre of blood. The normal range is 150,000-400,000 platelets per cubic mm. Platelet counts under 10,000 per cubic millimetre place the patient at risk for spontaneous haemorrhage. Platelets are produced in the bone marrow in increased quantities in response to stress. (27 Sep 1997) |