Blood Clotting and Hemophilia

04-19-2019 Blood Clotting and Hemophilia When an injury occurs that causes the rapture of a blood vessel, hemostasis is the process that prevents blood loss by slowing the blood flow and forming a clot. The process involves three steps that occur in rapid succession: vasoconstriction, the platelet plug formation, and blood clotting. Once blood flow stops, the healing process begins. When there is a rupture in the endothelium of a blood vessel, hemostasis begins with vasoconstriction, also known as vascular spasm. Blood vessels briefly and intensely contract to reduce the flow of blood. Under normal circumstances, endothelial cells of intact blood vessels regulate blood’s clotting tendency by preventing platelet aggregation and stopping the coagulation cascade. But when a rupture occurs, the endothelial cells stop secreting aggregation and coagulant inhibitors and in their place secrete von Willebrand factor that makes platelets adhere to each other during the initial formation of a clot. Almost immediately after a rupture occurs in a blood vessel, platelets create the ‘platelet plug.’ Coagulation is initiated within twenty seconds of a disruption of the epithelial wall of the blodd vessels. In about sixty seconds the fibrin strands start to intersperse the affected area and forms a platelet plug after several minutes. Blood clotting is caused by platelet adherence and activation by collagen in the epithelial cells. The activated platelets degranulate releasing their contents, responsible for more platelet activation and enhancing the hemostatic process. Exposure of the subendothelial collagen proteins a rupture triggers thromboxane which causes platelets to swell, grow filaments and start aggre...