Hemostasis
Hemostasis is the physiologic process which results in the cessation of bleeding in most animals with a closed circulatory system.
When a wound occurs in a blood vessel, several interconnected steps occur to staunch the flow of blood.
- vasoconstriction constricts the blood vessel, minimizing vessel diameter and slowing bleeding.
- primary hemostasis occurs, wherein platelets, one of the formed elements of the blood, bind to collagen in the exposed walls of the blood vessel to form a hemostatic plug within seconds after an injury.
- secondary hemostasis or coagulation occurs. This is a complex cascade of coagulation factors ultimately resulting in the transformation of fibrinogen, a blood protein, into polymerized fibrin, making a clot. This process takes several minutes.
- The clot attracts and stimulates the growth of fibroblasts and smooth muscle cells within the vessel wall, and begins the repair process which ultimately results in the dissolution of the clot (clot lysis).
Disorders of hemostasis can be roughly divided into platelet disorders, such as idiopathic thrombocytopenic purpura, and disorders of coagulation, such as hemophilia.
