Mechanisms of platelet activation with vascular injury

Endothelial cells normally release inhibitors of platelet aggregation, including nitric oxide and prostacyclin (PGI2) (Panel A). Disruption of the intact endothelium exposes the subendothelium and leads to the adherence of platelets. Once activated (Panel B), platelets degranulate, thereby releasing platelet aggregation agonists such as ADP and thromboxane A2. Degranulation also promotes surface thrombin generation and the recruitment of additional platelets, leading to thrombus formation.