Factor XII

Factor XII

Diagram of the coagulation cascade, including Factor XII

Factor XII, also known as Hageman factor, is a serine protease enzyme of the coagulation cascade in the blood coagulation process. It is a crucial component of the intrinsic pathway of blood coagulation.

Structure and Function

Factor XII is synthesized in the liver and circulates in the blood plasma as an inactive zymogen. Upon contact with negatively charged surfaces, such as exposed collagen or kallikrein, Factor XII is activated to Factor XIIa. This activation is a key step in the initiation of the intrinsic pathway of coagulation.

Factor XIIa then activates Factor XI, which in turn activates Factor IX, leading to the activation of Factor X and the conversion of prothrombin to thrombin. Thrombin then converts fibrinogen to fibrin, forming a stable blood clot.

Clinical Significance

Deficiency in Factor XII is a rare condition and is usually asymptomatic, as it does not lead to bleeding disorders. However, it can prolong the activated partial thromboplastin time (aPTT) in laboratory tests. Factor XII deficiency is often discovered incidentally during routine coagulation screening.

Factor XII has also been implicated in the process of inflammation and angiogenesis, and its role in thrombosis is an area of active research.

History

Factor XII was first discovered in 1955 by Dr. Oscar Ratnoff and Dr. Jane Colopy, who identified it in a patient named John Hageman, after whom the factor is named. Despite its role in the coagulation cascade, individuals with Factor XII deficiency do not typically experience bleeding problems, which led to further investigations into its function.

Related Pages

• Coagulation cascade
• Factor XI
• Factor IX
• Thrombin
• Fibrinogen
• Intrinsic pathway