Hemostasis blood coagulation pathway

Hemostasis is the process that stops bleeding in a blood vessel. Normal hemostasis involves a complex process of extrinsic and intrinsic factors. Figure 44-1 shows the coagulation pathway and factors involved. The copulation cascade is so named because as each factor is activated it acts as a catalyst that enhances the next reaction, with the net result being a large collection of fibrin that forms a plug in the vessel. Fibrin is the insoluble protein that is essential to clot formation. 

We shall first describe the coagulation pathway leading to the formation of fibrin. Then we shall briefly describe some aspects of the involvement of platelets and blood vessel walls in the overall process. This separation of clotting factors and platelets is artificial, since both play intimate and often mutually interdependent roles in hemostasis and thrombosis, but it facifitates description of the overall processes involved. 

Mackman N, Tilley RE, Key NS. Role of the extrinsic pathway of blood coagulation in hemostasis and thrombosis. Arterioscler Thromb Vase Biol 2007 27(8) 1687-93. 

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. 

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