Haemostasis and Blood Coagulation

Haemostasis and Blood Coagulation

Haemostasis the physiologic process that stops bleeding – it is reliant on the co-ordinated action of vascular factors, platelet factors and coagulation factors.

Three events/phases of haemostasis – vascular spasm, formation of platelet plug and clotting of the blood (coagulation).

Vascular spasm:
Blood vessels undergo immediate vasoconstriction following damage

Platelet plug formation:
Normally platelets do not adhere to each other or to vessel wall, but when collagen fibres are exposed by damage  platelets adhere to each other and exposed collagen. Platelets become activated  aggregation (complex process that builds fibrinogen links between adjacent platelets)  “plug” of platelets to stop bleeding

Coagulation:
3 phase process that clots blood:
1) Prothrombin activator is formed
2) Prothrombin activator converts prothrombin to thrombin
3) Thrombin catalyses fibrinogen molecules  fibrin mesh to trap blood cells

Two pathways mediate this process:
1) Intrinsic (all clotting factors are present in vascular system)
2) Extrinsic (requires thromboplastin from outside the vascular system)

Coagulation Factors (12):
I Fibrinogen
II Prothrombin
III Tissue factor
IV Calcium
V Proaccelerin
VII Proconvertin
VIII Antihaemophilic factor
IX Plasma thromboplastin component
X Stuart-Prower factor
XI Plasma thromboplastin antecedent
XII Hageman factor
XIII Fibrin stabilising factor

Clot retraction and repair:
Platelets contain actinomysin  contracts to draw edges of vessel together and serum squeezed out  repaired by smooth muscle and connective tissue and endothelial cell migration

Fibrinolysis:
Digestion of clot

We have not yet got to this page. We will eventually. Please contact us if you have something to contribute to it or sign up for our newsletter or like us on Facebook and Instagram or follow us on Twitter.

Page last updated: @ 12:39 am