ABSTRACT
Thrombin can be found and formed in both the intravascular and extravascular space. Thrombin has a critical role in the hemostatic response within the intravascular space. The primary mechanism for the formation of thrombin for hemostasis in the intravascular space uses the prothrombinase complex; there may be some other mechanisms, such as the MASP protease mechanism, which might participate in disease states. Prothrombin, the precursor of thrombin, is one of the several vitamin K–dependent proteins present in blood plasma. The vitamin K–dependent proteins are characterized by requirement for vitamin K for synthesis of functional protein containing. Factor Xa is the enzyme responsible for the conversion of prothrombin to thrombin in the vascular system. It is possible factor Xa also functions in the extravascular space, but as shown later, there are mechanisms for the generation of thrombin in the extravascular space.
