Figure 1. Model for tissue factor (TF) dependent blood coagulation. The coagulation cascade is a series of reactions in which the sequential activation of serine proteases amplify the generation of thrombin, which then converts soluble fibrinogen in to an insoluble fibrin clot. The coagulation factors are identified by roman numerals, with a small "a" following the numeral to indicate the activated form. The membrane-bound enzyme complexes of coagulation are indicated by the circles. The initiation phase is triggered by formation of the TF-FVIIa complex. The propagation phase amplifies the response through the FIXa-FVIIIa complex (intrinsic tenase). FX activation by the intrinsic tenase complex is the rate-limiting step for thrombin generation in tissue factor dependent blood coagulation.