What is the primary mechanism by which antithrombin III exerts its anticoagulant effect in the coagulation cascade?

A By binding to and inhibiting the activity of thrombin
B By binding to and inhibiting the activity of factor Xa
C By binding to heparin and enhancing its anticoagulant activity ✓
D By activating protein C, which then inhibits factors Va and VIIIa

Explanation

Antithrombin III is a serine protease inhibitor that primarily exerts its anticoagulant effect by binding to heparin, which greatly enhances its ability to inhibit thrombin and other coagulation factors, particularly factor Xa.

Source

Guyton and Hall Textbook of Medical Physiology
Hematology Hematology: Coagulation Disorders Hematology: Coagulation Disorders Medium MEDICAL Confidence: high