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==Platelet factors==
==Platelet factors==
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Platelet responses are critical in maintaining haemostasis. When platelets are activated, the haemostatic plug is formed. Regulation by thrombosthenin gives clot organisation and fibrin formation; the clot continues to organise and contract over the 3-5 days following formation.
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==Platelet Release==
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A series of events activates platelets to allow them to form the haemostatic plug:
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===Adhesion===
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The first stage in platelet activation is an increase in the adhesiveness of platelets which may be initiated by several scenarios:
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*The release of ADP from damaged endothelial cells.
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*Platelet contact with collagen or basement membrane.
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*Platelet contact with some denatured proteins and antibody-antigen complexes.
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A friable and leaking plug is formed within 1 minute by this adhesion stage.
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===Agglutination===
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More ADP is released, bringing and linking more platelets into the clot.
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===Aggregation===
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This is also known as viscous metamorphosis - platelets aggregate to form a tightly packed mosaic which results in compaction of the plug. This gives a good temporary seal to the injured vessel in about 5-30 minutes.
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===Disruption===
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Further aggregation of platelets is stimulated by prostaglandin endoperoxide (PGG2) release. Platelet breakdown produces phospholipids (platelet factors 3 and 4).
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Platelet factors catalyse the conversion of soluble fibrinogen to insoluble fibrin resulting in a progessive infiltration of the initial thrombocyte plug by strands of fibrin, leading to the formation of a composite plug. The fibrin also polymerises, causing coagulation of the blood and clot formation.
Platelet factors catalyse the conversion of soluble fibrinogen to insoluble fibrin resulting in a progessive infiltration of the initial thrombocyte plug by strands of fibrin, leading to the formation of a composite plug. The fibrin also polymerises, causing coagulation of the blood and clot formation.