Which factors are part of the extrinsic pathway of coagulation?

The extrinsic pathway of coagulation is primarily initiated by tissue factor (also known as thromboplastin), which is released by damaged tissues and interacts with factor VII. This interaction is critical for the initiation of the coagulation cascade in response to vascular injury. Therefore, the factors that specifically comprise the extrinsic pathway include factor VII and factor III (tissue factor).

Factor III is not typically numbered in the same way as the clotting factors, but it is crucially involved in this pathway as it triggers the pathway upon release during tissue injury. The combined action of these factors leads to the activation of factor X, subsequently progressing the clotting process.

The other options consist of factors that are part of different pathways. Factors I (fibrinogen) and II (prothrombin) are central to the common pathway but do not initiate coagulation. Factors VIII and IX are part of the intrinsic pathway, involved with the amplification of the clotting cascade, while factors X and XI include factors from the common and intrinsic pathways, respectively. Thus, only the inclusion of factor VII and factor III accurately represents the extrinsic pathway.