Identify the protein that is activated by thrombin as part of the coagulation cascade.

Identify the protein that is activated by thrombin as part of the coagulation cascade.

• A. Factor II
• B. Factor VII
• C. Factor V
• D. Factor XIII

Answer: (C)

Thrombin not only makes more thrombin, it also feeds back to activate cofactors that amplify the cascade. A central example is Factor V, which thrombin cleaves to form Factor Va. Va then partners with Factor Xa on a phospholipid surface to create the prothrombinase complex, dramatically speeding up the conversion of prothrombin into thrombin. This rapid amplification is what drives a robust and focused clot at the site of injury. While thrombin can activate other players, Factor II is the substrate that thrombin acts on to generate more thrombin, not a factor activated by thrombin. Factor VII is part of the initial extrinsic trigger and is not primarily activated by thrombin in the amplification sense. Factor XIII is also activated by thrombin to XIIIa, which crosslinks fibrin to stabilize the clot, but it’s about stabilization rather than boosting thrombin production.

Thrombin not only makes more thrombin, it also feeds back to activate cofactors that amplify the cascade. A central example is Factor V, which thrombin cleaves to form Factor Va. Va then partners with Factor Xa on a phospholipid surface to create the prothrombinase complex, dramatically speeding up the conversion of prothrombin into thrombin. This rapid amplification is what drives a robust and focused clot at the site of injury.

While thrombin can activate other players, Factor II is the substrate that thrombin acts on to generate more thrombin, not a factor activated by thrombin. Factor VII is part of the initial extrinsic trigger and is not primarily activated by thrombin in the amplification sense. Factor XIII is also activated by thrombin to XIIIa, which crosslinks fibrin to stabilize the clot, but it’s about stabilization rather than boosting thrombin production.