Which pathway of coagulation begins when collagen fibers of the basement membrane are exposed to blood?

The intrinsic pathway of coagulation is initiated when blood comes into contact with exposed collagen fibers, which typically occurs when there is vascular injury. This pathway involves several clotting factors that are activated in a series of steps, ultimately leading to the formation of a fibrin clot. The exposure of collagen activates Factor XII, which sequentially activates other factors, leading to the production of thrombin and fibrin. This pathway is crucial for hemostasis, particularly in situations where the vascular integrity is compromised.

In contrast, the extrinsic pathway is initiated by tissue factor (thromboplastin) released from damaged tissue, and the common pathway is where both intrinsic and extrinsic pathways converge. The fibrinolytic pathway is involved in the breakdown of the fibrin clot after its formation, rather than initiating the coagulation process. Therefore, the intrinsic pathway is clearly the correct response, as it directly relates to the exposure of collagen in the basement membrane to blood, setting off the coagulation cascade.