The various proteins (coagulation factors) involved in blood clotting, numbered more or less in reverse order of their activation: the final step is the conversion of factor I, fibrinogen, into factor Ia (fibrin) by thrombin. Most of the factors are zymogens of serine peptidases that are cleaved and activated by the activated factor upstream in the cascade, the whole system providing amplification and thus rapid haemostasis. Blood clotting can be triggered through the contact activation pathway (formerly the intrinsic pathway), or the tissue factor pathway (formerly known as the extrinsic pathway) triggered by the trauma-induced production of tissue factor. See Hageman factor; protein-C; protein-S; von Willebrand factor. Deficiencies lead to various forms of haemophilia.
Subjects: Medicine and Health.