Question:
Heparin exerts its anticoagulant effect by enhancing the activity of which of the following endogenous inhibitors of coagulation?
Heparin exerts its anticoagulant effect by enhancing the activity of which of the following endogenous inhibitors of coagulation?
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Heparin is one of the oldest and most widely used parenteral anticoagulants. It does not directly dissolve clots; instead it works indirectly by boosting the body's own natural anticoagulant proteins.
Updated On: Jun 24, 2026
- Antithrombin III
- Protein C
- Protein S
- Calcium
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The Correct Option is A
Solution and Explanation
Concept:
Heparin is one of the oldest and most widely used parenteral anticoagulants. It does not directly dissolve clots; instead it works indirectly by boosting the body's own natural anticoagulant proteins.
How it works: Heparin binds to and dramatically accelerates the activity of Antithrombin III (a circulating plasma protein). Once activated, Antithrombin III neutralises thrombin (factor IIa) and factor Xa, switching off the clotting cascade. Heparin can speed up this inhibition by about a thousandfold.
Why the other choices are wrong: Protein C and Protein S are also natural anticoagulants, but they are activated by the thrombin–thrombomodulin complex, not by heparin. Calcium (factor IV) is actually required to promote clotting, so it is the opposite of an inhibitor.
Answer: Option (1) — Heparin works by enhancing the activity of Antithrombin III. (1)
Heparin is one of the oldest and most widely used parenteral anticoagulants. It does not directly dissolve clots; instead it works indirectly by boosting the body's own natural anticoagulant proteins.
How it works: Heparin binds to and dramatically accelerates the activity of Antithrombin III (a circulating plasma protein). Once activated, Antithrombin III neutralises thrombin (factor IIa) and factor Xa, switching off the clotting cascade. Heparin can speed up this inhibition by about a thousandfold.
Why the other choices are wrong: Protein C and Protein S are also natural anticoagulants, but they are activated by the thrombin–thrombomodulin complex, not by heparin. Calcium (factor IV) is actually required to promote clotting, so it is the opposite of an inhibitor.
Answer: Option (1) — Heparin works by enhancing the activity of Antithrombin III. (1)
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