Which factor is associated with the intrinsic pathway of coagulation, specifically when activated by exposed collagen?

The intrinsic pathway of coagulation is initiated when blood comes in contact with negatively charged surfaces, such as exposed collagen from damaged blood vessels. This pathway is crucial in the formation of a stable fibrin clot and involves a series of clotting factors that are largely present in the blood in their inactive forms.

Hageman factor, also known as Factor XII, plays a pivotal role in the intrinsic pathway. Upon activation, it initiates the cascade by converting Factor XI to its active form. This process subsequently activates Factor IX and leads to the activation of Factor X, which is the common point for both the intrinsic and extrinsic pathways.

The other factors mentioned, while important in the coagulation process, do not specifically initiate the intrinsic pathway when collagen is exposed. Factor II is prothrombin, which is activated later in the clotting process. Factor X serves as a common factor for both pathways but is not involved in the initial interaction with collagen. Factor VII activates the extrinsic pathway, being directly triggered by tissue factor rather than by collagen exposure.

Thus, the intrinsic pathway’s activation through Hageman factor (Factor XII) is critical and illustrates the body's response to vascular injury, highlighting the importance of this factor in coagulation.