Questions: Which of these does NOT help to prevent blood loss? Synthesis of thromboxanes Blood vessel constriction Formation of a network of fibrin Release of heparin Formation of a platelet plug

The answer is the fourth one: Release of heparin.

Explanation for each option:

1. Synthesis of thromboxanes: Incorrect. Thromboxanes are involved in the process of platelet aggregation and vasoconstriction, both of which help prevent blood loss.

2. Blood vessel constriction: Incorrect. Constriction of blood vessels (vasoconstriction) reduces blood flow to the area of injury, helping to minimize blood loss.

3. Formation of a network of fibrin: Incorrect. Fibrin forms a mesh that traps blood cells, creating a stable clot that prevents further bleeding.

4. Release of heparin: Correct. Heparin is an anticoagulant, meaning it prevents blood clotting. Its release would not help prevent blood loss; instead, it would inhibit the clotting process.

5. Formation of a platelet plug: Incorrect. Platelets adhere to the site of a blood vessel injury and aggregate to form a plug, which is an initial step in preventing blood loss.

In summary, the release of heparin does not help to prevent blood loss because it acts as an anticoagulant, inhibiting the clotting process.