Platelets and primary haemostasis.

Platelets have a critical role in haemostasis when vessel wall is injured. Platelet receptors are involved in sequence in this process by slowing platelets down via GPIb/von Willebrand factor to bring them into contact with exposed collagen, then activating them via GPVI to release granule contents and express integrins in a matrix protein binding state. More platelets are incorporated into the growing thrombus and a series of events are set off that finishes with the exposed subendothelium protected by a non-thrombogenic platelet surface and tissue repair underway and the blood flow through the vessel maintained. GPIb is also involved in thrombin activation and, together with GPVI, in the formation of COAT platelets. In thrombosis, pathological changes occur that may lead to life-threatening blockage of vessels. Prevention of thrombosis while maintaining haemostasis remains a major goal of medical research.