How does heparin keep blood from clotting?

How does heparin keep blood from clotting?

• A. It activates platelets to form a plug
• B. It activates antithrombin III to inactivate thrombin and other clotting factors, preventing fibrin formation
• C. It directly destroys fibrin
• D. It acidifies plasma to prevent clotting

Answer: (B)

Heparin works by enhancing the activity of antithrombin III, a natural anticoagulant in the blood. When heparin binds to antithrombin III, it greatly accelerates its ability to inhibit key clotting proteins, especially thrombin and factor Xa. Without thrombin, fibrinogen cannot be converted into fibrin, so the blood doesn’t form a solid clot. This mechanism blocks the coagulation cascade rather than promoting clot formation. Heparin does not activate platelets, does not directly destroy fibrin, and does not acidify plasma, so those options don’t describe how it prevents clotting.

Heparin works by enhancing the activity of antithrombin III, a natural anticoagulant in the blood. When heparin binds to antithrombin III, it greatly accelerates its ability to inhibit key clotting proteins, especially thrombin and factor Xa. Without thrombin, fibrinogen cannot be converted into fibrin, so the blood doesn’t form a solid clot. This mechanism blocks the coagulation cascade rather than promoting clot formation. Heparin does not activate platelets, does not directly destroy fibrin, and does not acidify plasma, so those options don’t describe how it prevents clotting.