Haemostasis

Response to Blood Vessel Injury

Haemostasis:

Haemostasis:

The process of forming clots in the walls of damaged blood vessels and preventing blood loss while maintaining blood in a fluid state within the vascular system.

or.defined as the process in which blood loses its fluidity and becomes a jelly-like mass.

A collection of complex interrelated systemic mechanisms operates to maintain this balance between coagulation and anticoagulation.

When a small blood vessel is damaged, the injury initiates a series of events that lead to the formation of a clot (haemostasis).

This seals off the damaged region and prevents further blood loss

In general, blood clotting occurs in three stages:

• 1. Formation of prothrombin activator
• 2. Conversion of prothrombin into thrombin

3. Conversion of fibrinogen into fibrin.

1. FORMATION OF PROTHROMBIN ACTIVATOR

• Blood clotting commences with the formation of a

substance called prothrombin activator, which converts prothrombin into thrombin. Its formation is initiated by substances produced either within the blood or outside the blood.

• Thus, formation of prothrombin activator occurs through two pathways:
• i. Intrinsic pathway

ii. Extrinsic pathway.

Intrinsic pathway

In this pathway, the formation of prothrombin activator is initiated by platelets, which are within the blood itself Extrinsic pathway.

In this pathway, the formation of prothrombin activator is initiated by the tissue thromboplastin, which is formedfrom the injured tissues.

2. CONVERSION OF PROTHROMBIN

INTO THROMBIN

Prothrombin activator that is formed in intrinsic and extrinsic pathways converts prothrombin into thrombin 3. CONVERSION OF FIBRINOGEN INTO FIBRIN The final stage of blood clotting involves the conversion of fibrinogen into fibrin by thrombin.

ANTICLOTTING MECHANISM IN THE BODY

Under physiological conditions, intravascular clotting does not occur. It is because of the presence of some physicochemical factors in the body

Physical Factors

• i. Continuous circulation of blood.

ii. Smooth endothelial lining of the blood vessels

Chemical Factors – Natural Anticoagulants

• i. Presence of natural anticoagulant called heparin that is produced by the liver

iii. All the clotting factors are in inactive state.