Question

Coagulation of blood vessels is prevented during normal circulation by
(a) A heparin
(b) Prothrombin
(c) Plasminogen
(d) Thromplastin

Answer 1

Hint: Anticoagulant agent that is secreted by mast cells and basophils that activates antithrombin which combines with thrombin and prevents clot formation.

Complete answer:
Clotting of blood takes place when clotting factors in the blood activates which further activates thrombin. It results in the formation of fibrin mesh and aid coagulation. The molecules of substances that prevent the clotting of blood are called anticoagulants. The anticoagulant synthesized by mast cells and basophils is heparin. It activates antithrombin, a plasma protein, which combines with thrombin and activates it. This results in the prevention of clotting in normal circulation.

Additional Information: - Breakage of a blood vessel exposes collagen proteins to the blood which initiates three separate, but overlapping mechanisms- vasoconstriction, the formation of a platelet plug, and the production of a web of fibrin proteins(blood clot)
- Narrowing of the blood vessels when a blood vessel is damaged is vasoconstriction to prevent loss of blood. When the endothelium is ruptured, platelets adhere to collagen and release some secretions that aggregate other platelets form a platelet plug.
- Prothrombin activator in presence of sufficient amounts of calcium causes the conversion of prothrombin to thrombin which forms a web of fibrin and results in clot
- Anticoagulants like heparin activate antithrombin and prevent clot formation.
So, the correct answer is ‘heparin’.

Note: -Besides heparin, coumarin derivatives such as warfarin which is initially used as a rodenticide are used as an anticoagulant agent. They are antagonists to vitamin K that activates clotting factors such as factor II, VII, IX, and X.
-Aspirin is also used as an anticoagulant agent.