Which factor activates the extrinsic pathway of coagulation?

The factor that activates the extrinsic pathway of coagulation is Tissue Factor (TF). Tissue Factor is a glycoprotein expressed on the surface of subendothelial tissue, especially at sites of vascular injury. When blood vessels are damaged, Tissue Factor comes into contact with circulating Factor VII, which then gets activated to Factor VIIa. The complex of Tissue Factor and activated Factor VII (TF/VIIa) subsequently activates Factor X, leading to the formation of thrombin and ultimately the development of a fibrin clot.

This pathway is crucial for the initiation of hemostasis and plays a significant role in both normal and pathological conditions, including those related to thrombosis and bleeding disorders. Understanding the role of Tissue Factor emphasizes its importance in the coagulation cascade, specifically in the extrinsic pathway, which is the first to be activated in response to vascular injury.