Coagulation Factor XIIa, also known as Hageman factor, is a component of the blood coagulation system that plays a crucial role in the intrinsic pathway of blood coagulation. It is an enzyme that is responsible for the activation of the coagulation cascade, ultimately leading to the formation of a blood clot.
Factor XIIa is produced in the liver and circulates in the blood in an inactive form known as factor XII. Upon activation by contact with damaged blood vessels, foreign surfaces, or negatively charged substances, factor XII undergoes autoactivation and is converted into its active form, Factor XIIa. This activation step is facilitated by the presence of substances such as negatively charged surfaces, prekallikrein, and high molecular weight kininogen.
Once activated, Factor XIIa initiates a series of enzymatic reactions that result in the conversion of prothrombin to thrombin, which in turn converts fibrinogen to fibrin. The formation of fibrin creates a mesh-like network that helps to stabilize the blood clot, promoting hemostasis.
In addition to its role in blood clotting, Factor XIIa is also involved in other physiological processes, such as inflammation and complement activation. It has been suggested that Factor XIIa may participate in the regulation of blood pressure, blood vessel permeability, and angioedema, although these functions are not yet fully understood.
Abnormalities or deficiencies in Factor XIIa can lead to various bleeding disorders, such as hereditary angioedema or factor XII deficiency, while excessive activation of this enzyme can promote thrombosis and clotting disorders.
