Extrinsic System
Rapidly active system of blood coagulation
It begins with the release of a tissue factor (tissue thrombokinase, Factor III) by the destruction of tissue cells. This activates the plasmatic factor VII which is bound at the site of the injury. Factor VII in turn activates Factor X, which together with the activated Factor V in the presence of Ca2+ (Factor IV) causes the conversion of prothrombin into thrombin.