The intrinsic pathway is initiated when blood comes into contact with exposed collagen from damaged endothelium. This activates Factor XII (Hageman factor), which in turn activates Factor XI. Activated Factor XI then activates Factor IX in the presence of calcium ions. Factor IX, along with its cofactor Factor VIII and calcium ions, activates Factor X. The activation of Factor X is a crucial step that leads to the conversion of prothrombin to thrombin, ultimately resulting in the formation of a fibrin clot.
