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SUMMARY
The coagulation cascade consists of a complex network of reactions that are essential for the conversion of zymogens into enzymes and of inactive procofactors into cofactors. Most of these reactions take place on a membrane surface, which restricts coagulation to the site of injury. Upon initiation, these reactions serve to produce the fibrin that is necessary for the formation of a stable hemostatic plug. In addition, these reactions provide feedback loops that limit and localize thrombus formation and regulate thrombus resolution. This chapter highlights key biochemical characteristics of the individual coagulation factors, essential aspects regarding their synthesis, and the clinical importance of acquired or inherited variations that affect their quantity or function. The coagulation factors are grouped as (1) the vitamin K–dependent zymogens (prothrombin, factor VII, factor IX, factor X, and protein C); (2) the procoagulant cofactors (factor V, factor VIII); (3) the soluble cofactors (protein S, von Willebrand factor); (4) factor XI and the contact system (factor XII, prekallikrein, and high-molecular weight kininogen); (5) the cell-associated cofactors (tissue factor, thrombomodulin, endothelial protein C receptor); (6) the fibrin network (fibrin[ogen], factor XIII, thrombin-activatable fibrinolysis inhibitor); and (7) inhibitors of coagulation (antithrombin, tissue factor pathway inhibitor, protein Z/protein Z–dependent protease inhibitor). Table 3–1 summarizes the major features of the coagulation factors addressed in this chapter. The final sections of this chapter present an overview of the coagulation cascade in which the pathways of hemostasis including the contribution of endothelial cells, blood platelets, and immune cells are described.
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