The initiation and propagation of blood coagulation. The reactions of blood coagulation take place on the surface of cell membranes where enzymes and cofactors form complexes that efficiently convert their respective proenzyme substrates to active enzymes. The reaction sequence is initiated by the exposure of tissue factor (TF) to blood with subsequent binding of FVII/FVIIa and activation of FIX and FX. The following assembly of tenase (FIXa/FVIIIa) and prothrombinase (FXa/FVa) complexes on the surface of negatively charged phospholipid membranes (provided mainly by platelets) results in amplification, propagation, and generation of high concentrations of thrombin (T). The initial thrombin that is formed feedback-activates FVIII (circulating with von Willebrand factor [VWF]) and FV. Illustration by Marie Dauenheimer.