Haematosis

Question 1

What is Haemostasis?

Answer 1

The stoppage of bleeding from cut vessels to prevent excessive blood loss.

Question 2

What are the 3 phases in haemostasis?

Answer 2

1.Formation of temporary haemostatic platelet aggregate.
2.Formation of fibrin mesh
3.Dissolution of haemostatic plug

Question 3

How is the temporary haemostatic plug formed?

Answer 3

1.Reflex vasoconstriction
Endothelin release for vasoconstriction
2.Platelets binds to collagen via von Willebrand Factor
3.Platelets activated,they change shape & release granules(ADP,Thromboxane A2
4.The granules induce platelet aggregation

Question 4

How is the secondary haemostatic plug formed?

Answer 4

1.Coagulation cascade occurs
2Thrombin acts to convert fibrinogen to fibrin

Question 5

How does the coagulation cascade occur?

Answer 5

*Activation of factor 10a which binds to 5a
It turns prothrombin to thrombin,this enzyme catalyses the formation of fibrin from fibrinogen.
1.INTRINSIC pathway-12,11,9&8….9a+8a acts on factor 10
2.EXTRINSIC pathway-7……7a+TISSUE FACTOR acts on factor 10

*THROMBIN also converts factor 13 to 13a which stabilizes the fibrin clot

Question 6

How does the breakdown of the fibrin clot occur?

Answer 6

*Tissue plasminogen activator is produced by endothelial cells
*Plasminogen is converted into PLASMIN,
This degrades the fibrin into fibrin degradation products(FDP) e.g D-Dimers