Hemostasis involves three major phases. The first phase is platelet plug formation, in which platelets become "sticky" and cling to the site of injury. The second phase is the vascular spasm phase, in which serotonin released by the platelets causes the blood vessels to spasm and constrict, thus decreasing blood loss. The third phase is coagulation wherein thromboplastin interacts with PF3 and calcium, as well as other blood proteins, to form prothrombin activator. Prothrombin activator converts prothrombin to thrombin, which then joins with fibrinogen to form fibrin, the basis of the
