Physiologie de l’hémostase

Haemostasis is a physiological process triggered by a breach in a blood vessel. Haemostasis plugs the breach and stops the loss of blood via two distinct but intertwined and interdependent mechanisms: primary haemostasis and plasma coagulation. Primary haemostasis is an emergency mechanism in which circulating blood platelets adhere to the injured endothelium to produce a white thrombus or platelet plug. Then, the platelet plug is strengthened by the development of a fibrin network that entraps the aggregated platelets. Insoluble fibrin is produced when the soluble plasma protein fibrinogen is exposed to thrombin, the final product of a cascade of enzymatically activated reactions among clotting factors. The fibrin-platelet thrombus is eventually dissolved by the proteolytic enzyme plasmin, which is the main protein of the fibrinolytic system. The various phases of haemostasis are tightly regulated by a system of plasma activators and inhibitors that locally control the development of the clot and avoid activation of coagulation at a distance from the vascular injury.