What is the principal inhibitor of thrombin and Factor Xa?

The principal inhibitor of thrombin and Factor Xa is Antithrombin III. This protein plays a crucial role in the regulation of blood coagulation by inhibiting serine proteases, which are enzymes crucial for the clotting process. Thrombin is a key enzyme in the coagulation cascade that converts fibrinogen to fibrin, and Factor Xa is essential for the conversion of prothrombin to thrombin.

Antithrombin III binds to these enzymes, significantly slowing their activity and thereby preventing excessive clotting. This action is enhanced by heparin, a substance commonly used as an anticoagulant in clinical settings.

Understanding the function of Antithrombin III is vital in hematology as deficiencies or dysfunctions of this inhibitor can lead to increased risk of thrombosis, underscoring its importance in maintaining hemostasis and preventing inappropriate clot formation.

The other options, while important in the coagulation process and regulation, do not serve as principal inhibitors for thrombin and Factor Xa in the same manner as Antithrombin III does.