10.4 - Mechanism of Blood Clotting

Necessity of Blood Clotting

• Stops or minimises blood loss from an injured blood vessel.
• Prevents microorganisms such as bacteria from entering the bloodstream through the damaged vessel.
• Maintains blood pressure; excessive blood loss can lower it to a dangerous level.

Mechanism of Blood Clotting

Step 1: Formation of an Activator

• Coagulated platelets, damaged cells and clotting factors in blood plasma form an activator called thrombokinase.

Step 2: Conversion of Prothrombin

• Thrombokinase, aided by calcium ions and vitamin K, converts inactive plasma protein prothrombin into active plasma protein thrombin.

Step 3: Formation of Fibrin

• Thrombin acts as an enzyme and catalyses the conversion of soluble fibrinogen into insoluble fibrin.

Step 4: Clot Formation

• Threadlike fibrin fibres form a network over the wound.
• The network traps erythrocytes and closes the wound, preventing blood loss.

Health Issues Related to Blood Clotting

Thrombosis

• Thrombosis is the formation of a blood clot (thrombus).
• It results from damage in blood vessels or sluggish blood flow that causes clotting factors to accumulate.

Embolism

• A blood clot transported by blood flow is an embolus.
• If an embolus becomes lodged in a tiny blood vessel, blood flow stops.

Haemophilia

• Haemophilia is a hereditary illness caused by a deficiency of certain clotting factors in the blood.
• Blood fails to clot normally; excessive bleeding from small wounds or bruises can cause death.