Hemostasis or haemostasis (hemo- + -stasis) is a process which causes bleeding to stop, meaning to keep blood within a damaged blood vessel, either by physiologic (primary and secondary hemostasis) or surgical means.
Primary hemostasis is vasoconstriction and platelet plug formation.
Secondary hemostasis (coagulation cascades) is the process where the platelet plug is reinforced by the conversion of fibrinogen to fibrin.
Tertiary hemostasis is fibrinolysis.
Hemostasis is the first stage of wound healing. This involves coagulation, blood changing from a liquid to a gel. Endothelial cells of intact vessels prevent blood clotting with a heparin-like molecule and thrombomodulin and prevent platelet aggregation with nitric oxide and prostacyclin. When endothelial injury occurs, the endothelial cells stop secretion of coagulation and aggregation inhibitors and instead secrete von Willebrand factor which initiate the maintenance of hemostasis after injury.
Hemorrhage is the opposite of hemostasis.