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The human hemostatic system provides a natural balance between procoagulant and anticoagulant forces. The procoagulant forces include platelet adhesion and aggregation and fibrin clot formation; anticoagulant forces include the natural inhibitors of coagulation and fibrinolysis. Under normal circumstances, hemostasis is regulated to promote blood flow; however, it is also prepared to clot blood rapidly to arrest blood flow and prevent exsanguination. After bleeding is successfully halted, the system remodels the damaged vessel to restore normal blood flow. . | Chapter 059. Bleeding and Thrombosis The human hemostatic system provides a natural balance between procoagulant and anticoagulant forces. The procoagulant forces include platelet adhesion and aggregation and fibrin clot formation anticoagulant forces include the natural inhibitors of coagulation and fibrinolysis. Under normal circumstances hemostasis is regulated to promote blood flow however it is also prepared to clot blood rapidly to arrest blood flow and prevent exsanguination. After bleeding is successfully halted the system remodels the damaged vessel to restore normal blood flow. The major components of the hemostatic system which function in concert are 1 platelets and other formed elements of blood such as monocytes and red cells 2 plasma proteins the coagulation and fibrinolytic factors and inhibitors and 3 the vessel wall itself. Steps of Normal Hemostasis Platelet Plug Formation On vascular injury platelets adhere to the site of injury usually the denuded vascular intimal surface. Platelet adhesion is mediated primarily by von Willebrand factor vWF a large multimeric protein present in both plasma and in the extracellular matrix of the subendothelial vessel wall which serves as the primary quot molecular glue quot providing sufficient strength to withstand the high levels of shear stress that would tend to detach them with the flow of blood. Platelet adhesion is also facilitated by direct binding to subendothelial collagen through specific platelet membrane collagen receptors. Platelet adhesion results in subsequent platelet activation and aggregation. This process is enhanced and amplified by humoral mediators in plasma e.g. epinephrine thrombin mediators released from activated platelets e.g. adenosine diphosphate serotonin and vessel wall extracellular matrix constituents that come in contact with adherent platelets e.g. collagen vWF . Activated platelets undergo the release reaction during which they secrete contents that further promote .
