Coagulation of Blood Neet Notes

Clotting of Blood or Haemostasis

When a blood vessel is damaged, it results in coagulation or clotting of blood.
A blood clot is a network of thread like protein fibers, called fibrin, that traps blood cells, platelets and fluid.
The clotting depends on several proteins in the plasma.
They are called coagulation factors. Normally these factors are in an inactive state. After injury they are activated to produce a clot.
The activation can happen in three stages.
Stage 1 - Formation of thrombokinase - Damaged tissues release a mixture of lipoproteins and phospholipids called tissue factor (TF) or thromboplastin. This factor in the presence of certain factors in the blood form a complex called prothrombinase or thrombokinase.
Stage 2 - Formation of thrombin - During this stage soluble plasma protein prothrombin is converted into the enzyme thrombin by prothrombinase. Prothrombin synthesis in liver requires vitamin K.
Stage 3 - The soluble plasma protein fibrinogen is converted to insoluble protein, fibrin by thrombin. The fibrin forms the fibrous network of the clot.

The formation of a thrombus or blood clot within an intact blood vessel is called thrombosis. Clotting is a normal response that prevents bleeding when a blood vessel wall is injured. However thrombus formation is abnormal if it occurs in an intact vessel.
A thrombus within an artery may block the artery preventing blood and oxygen from reaching the organ or tissue supplied by an artery.
A thrombus that forms within one of the coronary arteries supplying heart muscle is known as coronary thrombosis.
This is the cause for heart attack . A thrombus within arteries supplying the brain is known as cerebral thrombosis. It causes stroke.
When a portion of a thrombus clot becomes fragmented and enters the circulating blood, it is called embolus.
Embolus may block a circulation to vital parts resulting in serious consequences such as stroke.