In the extrinsic pathway of coagulation, which factor combines with Factor VII to initiate the process?

• A. Factor V
• B. Factor X
• C. Factor III (Tissue Factor)
• D. Factor IX

Answer: (C)

Verified step by step guidance

1. Understand the extrinsic pathway of coagulation: This pathway is initiated when blood comes into contact with tissue factor (Factor III), which is exposed due to tissue injury.
2. Identify the role of Factor III (Tissue Factor): Factor III is a membrane-bound protein that is not normally present in the blood but is exposed upon tissue damage.
3. Recognize the interaction between Factor III and Factor VII: In the extrinsic pathway, Factor III combines with Factor VII to form a complex.
4. Explain the activation process: The Factor III-Factor VII complex activates Factor X, which is a key step in the coagulation cascade leading to the formation of a blood clot.
5. Summarize the importance of Factor III: Factor III is crucial for the initiation of the extrinsic pathway, as it triggers the cascade that ultimately results in clot formation.