Hemostasis

Hemostasis is the physiological process that limits blood loss after vessel injury through vascular constriction, platelet activity, and blood coagulation.

Vasoconstriction: Narrowing of blood vessels through contraction of their smooth muscle. The injured vessel constricts early, reducing blood flow before a clot forms.
Platelets: Small blood-cell fragments that adhere to damaged vessels and help form clots. They provide the cellular surface and aggregation needed for the initial plug.
Hemophilia A: An inherited bleeding disorder caused by deficiency or dysfunction of coagulation factor VIII. Impaired coagulation weakens hemostasis and causes prolonged bleeding.
Thrombosis: Formation of a blood clot within a blood vessel or heart chamber during life. Thrombosis is clot formation inside vessels, unlike the localized response to vessel injury.
Clot retraction: Contraction of a platelet-rich clot that draws its edges together and expels fluid. Platelet contraction tightens the hemostatic seal and brings wound edges closer.
Primary hemostasis: Formation of a platelet plug at a site of vascular injury. Platelet adhesion and aggregation create the initial, temporary seal.
Endothelium: The layer of cells lining blood vessels and the heart. Intact endothelium suppresses clotting; injury exposes surfaces that promote it.
von Willebrand disease: An inherited bleeding disorder caused by deficient or defective von Willebrand factor. It disrupts platelet adhesion and can also reduce factor VIII levels.
Embolism: Obstruction of a blood vessel by material carried through the bloodstream from elsewhere. A clot formed during hemostasis can become dangerous if it detaches and travels.
Wound healing: The biological process by which damaged tissue is repaired and restored. Hemostasis creates the early provisional barrier that precedes tissue repair.

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