Wednesday, December 22, 2010


Our blood is exposed to the air when there is a wound. We do not want harmful microorganisms to infect the wound, nor do we wish to lose blood at the site of injury.

The good news is this: our blood contains platelets, which help blood to clot. A clot closes the wound and disallows blood loss.

Question & Answer

1. Which cells and proteins/enzymes are involved in the mechanism of blood clotting? What are their function?
Platelet (cell) - initiates the clotting of blood.
Thrombokinase (enzymes)
- catalyses the conversion of prothrombin to thrombin.

Thrombin (enzymes)
- catalyses the conversion of fibrinogen to fibrin.

Prothrombin (plasma protein)
- produces thrombin when activated.

Fibrinogen (plasma protein)
- produces fibrin when activated.

Fibrin (thread-like structures)
- traps red blood cell to produce a clot.

2. State the characteristics of blood platelets.
No regular shape, mere cell fragments, no nucleus, no haemoglobin.

3. Where are the plasma proteins involved in clotting of blood
a) synthesised?
b) found?
Blood plasma.

4. What happens if:
i) clotting does not happen?

Loss of blood and blood pressure, and infection at the site of the wound due to exposure to microorganisms.
ii) a wounded person suffers from haemophilia?
Blood will not clot when there is a wound, resulting in loss of blood and possible death.

5. Name the factors that may affect the clotting of blood.
Presence of platelets; presence of plasma proteins (prothrombin and fibrinogen); presence of Vit K, calcium and other clotting factors.

6. How does the mechanism of blood clotting work?
i) Cut/wound/exposure of blood to the air.
ii) Platelets release the enzymes thrombokinase.

iii)Thrombokinase converts prothrombin to thrombin.
iv) Thrombin catalyses the conversion of fibrinogen to fibrin.

v) Fibrin traps red blood cells and a clot is then formed.

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