Primary Hemostasis

Platelets play a central role in primary hemostasis. They are also important in pathological processes leading to thrombosis. Antiplatelet drugs are primarily directed against platelets and inhibit platelet activation by a number of different mechanisms. They are used for the prevention and treatment of thrombotic processes, especially in the arterial vascular system. 

Primary hemostasis is the first phase of hemostasis consisting of platelet plug formation at the site of injury. It occurs within seconds and stops blood loss from capillaries, arterioles, and venules. Secondary hemostasis, in contrast, requires several minutes to be complete and involves the formation of fibrin through the coagulation cascade. 

Prepro-opiomelanocortin Primary Hemostasis Primary Hyperparathyroidism Prodrug... 

The adhesion of platelets to the subendothelial matrix via specific adhesive GPs is the initial step in primary hemostasis. Binding of platelets to the matrix results in rapid (Fig, 2) morphological conversion of platelets from flat discs to spiny spheres. 

Sloan and Gore 1992). These risk factors are clearly difficult, if not impossible, to simulate in laboratory animals. Consequently, more general tests of anticoagulation and primary hemostasis have been employed. 

The development of parallel-plate perfusion chambers [67,68] made possible the study of platelet interaction with the extracellular matrix (ECM) generated by cells in culture or with isolated subendothelial components under defined experimental conditions. The use of the ECM produced by human umbilical vein endothelial cells (HUVEC) in culture as adhesive substrate has Su tated the understanding of the mechanisms involved in primary hemostasis [68]. HUVECs are immature and not subjected to flow conditions during their culture, two Ikctors which may influence the reactivity of their ECM towards platelets [69]. Interestingly, the properties and reactivity of the underlying ECM can be modified by exposure of HUVECs to different stimuli, an experimental approach which has fevored the investigation of basic mechanisms of thrombosis [33]. 

Primary Hemostasis, Cellular Components Platelet Count Direct determination of the number of platelets per unit volume Platelet number Diagnosis of thrombocytopenia Generally none, but insensitive to defective function... 

Blood vessel walls and activated platelets play central roles in primary hemostasis. Damage to a vessel wall initiates vasoconstriction and the exposure of collagen and tissue factor to blood. This exposure initiates coagulation via the tissue factor pathway. 

Stages of hemostasis (a) vasoconstriction, (b) primary hemostasis, (c) secondary hemostasis, and (d) thrombus and antithrombotic events. Source Adapted from Reference 26. 

Harrigan C, Lucas CE et al. (1985) Serial changes in primary hemostasis after massive transfusion. Surgery 98 836-844... 

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