1.3 The Mechanism of Blood Clotting

What is blood clotting?

• A body mechanism to stop or minimise blood loss from damaged blood vessels

The necessity for blood clotting

• Prevent blood loss when a person is injured

• Maintain blood pressure

• Maintain the circulation of blood

• Prevent the entry of microorganisms and foreign substances into the body

Blood Clotting Mechanism

• A complex series of biochemical reaction in the blood to prevent excessive bleeding after an injury

• The chain reactions transform fibrinogen to fibrin (self-sealing material) to plug leaks.

The mechanism of blood clotting.doc

Formation of fibrin from fibrinogen.doc

Problems related to blood clotting

• Defect at any step in the blood clotting process can impaired blood clotting.

• Two problems:

1. Haemophilia

2. Thrombosis

1. Haemophilia

• A heredity disease

• The afflicted person lack certain clotting factors in his blood.

• Cause excessive bleeding even from small cut and can lead to death.

• They even may experience spontaneous internal bleeding without being injured

2. Thrombosis

• Formation of blood clot inside an unbroken blood vessel

• The clot - thrombus • A blood clot moving in bloodstream -

embolus • Clot form in coronary artery can lead to

heart attack• A clot blocks blood flows to the brain can

cause stroke

Exercise

1. Give two reasons why blood clotting is necessary when blood vessels are damaged following an injury.

A: To prevent blood loss when a person is injured and maintain blood pressure.

2. Explain briefly how platelet plug is formed.

A: When the blood vessel damaged, the connective tissues will expose to the blood. Platelets from the blood will stick to the connective tissue and release clotting factors that make the platelet sticky. These platelet will aggregate and form the platelet plug

3. Name the activator that converts prothrombin into thrombin.

A: Thromboplastins

4. Give one example of a disease that is due to an impaired blood clotting mechanism.

A: Haemophilia /Thrombosis