Hemostasis is derived from two words. These are HEMO and STASIS. HEMO means BLOOD and STASIS means STANDING STILL. So Hemostasis is defined as the stopping of bleeding or the arrest of bleeding.
WHAT ARE THE VARIOUS STAGES OF HEMOSTASIS?
When there is an injury in the blood vessels , initiations of series of reactions takes place which results in the HEMOSTASIS. All these things takes place in three stages. These are as follows:-
- VASOCONSTRICTION
- PLATELET PLUG FORMATION
- COAGULATION OF BLOOD
VASOCONSTRICTION :-
Just after the injury , there is constriction of blood vessels and blood loss decreases from the damaged area. Here the constriction of arterioles and small arteries takes place. After the cut in blood vessels , endothelium get damaged and there collagen get exposed. Now the platelets get attached to these collagens and gets activated. Now there is secretion of serotonin and others vasoconstrictor substances and it causes the constriction of blood vessels. The attachments of platelets to the collagen is accelerated by VON WILLEBRAND FACTOR. This factor now acts as a factor between a specific glycoprotein present on the surface of platelet and collagen fibres.
FORMATION OF PLATELET PLUG:-
Here the attachment of platelets to the collagen of ruptured blood vessels takes place. It secretes ADP and THROMBOXANE A2. Now there is attraction of more and more platelets by these two substances. This also helps in activation. Aggregation of platelets takes place together and there is formation of a loose temporary platelet plug or temporary hemostatic plug, it closes the vessel and prevents further blood loss. The acceleration of platelet aggregation takes place by platelet – activating factor {PAF}.
COAGULATION OF BLOOD :-
In this process , there is conversion of fibrinogen to fibrin. There is attachment of the fibrin threads to the loose platelet plugs. It blocks the ruptured part of blood vessels. It helps in preventing the further loss of blood completely.
Coagulation or clotting of blood is defined as the process in which the blood loses its fluidity and forms a jelly like structure.
The substances necessary for clotting are called clotting factors. There are total 13 clotting factors which are identified .
CLOTTING FACTORS
I FIBRINOGEN
II PROTHOMBIN
III THROMBOPLASTIN
IV CALCIUM
V LABILE FACTOR
VI NOT BEEN APROVED
VII STABLE FACTOR
VIII ANTEHEMOPHILIC FACTOR
IX CHRISTMAS FACTOR
X STUART PROWER FACTOR
XI PLASMA THROMBOPLASTIN
ANTECEDENT
XII HAGEMAN FACTOR
XIII FIBRIN-STABILIZING FACTOR
VARIOUS SEQUENCE OF CLOTTING MECHANISM:-
- ENZYME CASCADE THEORY
- STAGE 1: FORMATION OF PROTHROMBIN ACTIVATOR – INTRINSIC PATHWAY , EXTRINSIC PATHWAY
- STAGE 2 : CONVERSION OF PROTROMBIN TO THROMBIN
- STAGE 3: CONVERSION OF FIBRINOGEN TO FIBRIN
INTRINSIC PATHWAY FOR THE FORMATION OF PROTHOMBIN ACTIVATOR :-
In this process , the formation of prothrombin activator takes which is initiated by the platelets and these are present within the blood itself.
EXTRINSIC PATHWAY FOR THE FORMATION OF PROTHOMBIN ACTIVATOR :-
In this process , the formation of prothrombin activator which is initiated by the tissue thromboplastin which is formed from the injured tissues.
Contributor- Medico Abinash Jena
