Platelets are produced in the bone marrow by highly specialized cells called megakaryocytes. About 70-80% of a person's total platelet count is circulating in the vasculature at any given time. The other 20-30% are pooled in the spleen.
The average lifespan of a platelet is 9-12 days.
Platelets play a significant role in primary hemostasis, as they are the “bricks”, or building blocks of the developing platelet plug, the forerunner to the end stage fibrin clot. Platelets have inherent adhesive properties which are essential for adherence to the site of vascular damage, and for binding to one another in aggregation activities.
Platelets must be present in sufficient number, and be functionally active for optimal clotting to occur. Platelet functionality tends to be more crucial than the number of platelets available, however, as patients with lower platelet counts can still clot relatively effectively as compared to those patients with intrinsic platelet defects.