Factor X is in what pathway?

• A. Intrinsic
• B. Extrinsic
• C. Common
• D. Fibrinolytic

Answer: (C)

The main idea is where Factor X fits in the coagulation cascade. Factor X sits at the convergence point of the intrinsic and extrinsic pathways—the common pathway. Factor X is activated to Xa by both the intrinsic tenase complex (IXa with VIIIa on a phospholipid surface) and the tissue factor–FVIIa complex from the extrinsic pathway. Once activated, factor Xa combines with factor V to form the prothrombinase complex, which converts prothrombin (factor II) to thrombin, and thrombin then converts fibrinogen to fibrin to form the clot. This makes Factor X a component of the common pathway, the stage after the two initial pathways have joined. The fibrinolytic system is a separate pathway and not where Factor X operates as a component in the coagulation cascade.