Factor XIIa, also known as activated Factor XII or FXIIa, is a serine protease that plays a crucial role in the coagulation cascade, specifically the intrinsic pathway. It is a zymogen, which means it is in an inactive form until it is cleaved and activated into its active form.
Factor XIIa is produced in the liver and circulates in the blood plasma. Upon tissue injury or contact with certain surfaces (such as collagen or negatively charged substances), factor XII becomes activated by autoactivation, triggered by conformational changes induced by these surfaces. Once activated, Factor XIIa initiates a complex cascade of molecular events leading to blood clot formation.
One of the key functions of Factor XIIa is the activation of Factor XI, which subsequently activates Factor IX. This sequential activation ultimately leads to the conversion of prothrombin to thrombin and the subsequent formation of fibrin, resulting in the formation of a blood clot to prevent excessive bleeding.
Factor XIIa also interacts with other components of the coagulation system, including factor XI, prekallikrein, and high molecular weight kininogen, forming a complex network that amplifies coagulation responses.
Notably, Factor XIIa is also involved in the activation of the kallikrein-kinin system, playing a role in inflammation and blood pressure regulation.
Understanding the precise mechanisms and role of Factor XIIa is of significant importance in both physiological clot formation essential for hemostasis and pathological clot formation leading to thrombotic disorders.
