A delicate balance exists between the hemostatic sequence, designed to maintain blood within injured vessels, and the fibrinolytic system, designed to prevent excessive occlusion of clotted vessels. The hemostatic process is initiated by local vascular reaction aimed at reducing blood loss and includes vasoconstriction, shunting of blood to uninjured vessels, and local tissue swelling. Within seconds of vessel injury, a temporary plug is formed by platelets. Platelets adhere to the exposed subendothelial connective tissue, spread to cover the damaged surface, and release a multitude of compounds, notably ADP, that promote aggregation of many platelets to form a barrier. In addition to serving as a physical plug to the break in vascular integrity,aggregated platelets expose phospholipid-3 on their surface, which is required to initiate and support the enzymatic reactions of the coagulation cascade that will eventually stabilize the platelet plug by formation of fibrin.
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