When thrombin binds to thrombomodulin on the endothelial cell surface, thrombin activates which pathway?

When thrombin binds to thrombomodulin on the endothelial cell surface, thrombin activates which pathway?

• A. Activate the protein C pathway
• B. Activate factor V and factor VIII
• C. Convert fibrinogen to fibrin
• D. Stimulate platelet aggregation

Answer: (A)

When thrombin binds to thrombomodulin on the endothelial surface, its role shifts from promoting clot formation to activating an anticoagulant pathway. The thrombin–thrombomodulin complex activates protein C to activated protein C (APC). APC, with its cofactor protein S, then inactivates factors Va and VIIIa, key accelerants of the coagulation cascade, thereby reducing thrombin generation and limiting clot formation. This endothelial anticoagulant mechanism helps keep clotting in check on blood vessels. The other typical actions of thrombin—cleaving fibrinogen to fibrin to form a clot and stimulating platelet aggregation via PAR receptors—are not the primary outcomes of the thrombin–thrombomodulin interaction, which is why the protein C pathway is the best answer here.

When thrombin binds to thrombomodulin on the endothelial surface, its role shifts from promoting clot formation to activating an anticoagulant pathway. The thrombin–thrombomodulin complex activates protein C to activated protein C (APC). APC, with its cofactor protein S, then inactivates factors Va and VIIIa, key accelerants of the coagulation cascade, thereby reducing thrombin generation and limiting clot formation. This endothelial anticoagulant mechanism helps keep clotting in check on blood vessels.

The other typical actions of thrombin—cleaving fibrinogen to fibrin to form a clot and stimulating platelet aggregation via PAR receptors—are not the primary outcomes of the thrombin–thrombomodulin interaction, which is why the protein C pathway is the best answer here.