Which of the following factors is primarily involved in the extrinsic pathway of coagulation?

The factor primarily involved in the extrinsic pathway of coagulation is Factor VII. In the coagulation cascade, the extrinsic pathway is triggered by tissue factor (also known as thromboplastin), which is exposed at the site of vascular injury. When tissue factor interacts with Factor VII in the presence of calcium ions, it forms the tissue factor-Factor VII complex, which is crucial for initiating the coagulation process. This complex then activates Factor X, leading to the common pathway of coagulation.

Understanding the roles of different factors helps clarify why Factor VII is essential in this pathway. Factor X, Factor II (prothrombin), and Factor V play roles in other aspects of the coagulation process, particularly in the common pathway leading to fibrin formation, but they are not primary initiators in the extrinsic pathway. Thus, recognizing the function of Factor VII in conjunction with tissue factor is key to understanding how the extrinsic pathway operates in hemostasis.