Platelet function tests

Platelets play an essential role in arresting bleeding. Following vascular injury they adhere to subendothelial collagen via the ligand vWF, then stick to each other to form a cohesive mass. Release of internal factors— serotonin, ADP, TXA2, and platelet factor 4 (PF4) induces vascular constriction, and coagulation cascade activation. Finally, together with fibrin they form a thrombus, plugging the hole in the vessel. Within the platelet prostaglandin synthetic pathway, arachidonic acid forms thromboxane A2, a potent platelet aggregant and vasoconstrictor. From platelet activation cessation of bleeding takes 3-5 minutes.

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