Haemostasis

Question 1

What is haemostasis?

Answer 1

The sequence of physical and biochemical changes induced by tissue/blood vessel damage that leads to clotting

Question 2

What are the four components needed for haemostasis to occur?

Answer 2

The vascular response, primary haemostatic plug, secondary haemostatic plug and total clot lysis

Question 3

What is the vascular response in haemostasis?

Answer 3

When blood endothelium is damaged, endothelin is released. Endothelin causes vasoconstriction in the vessels, reducing bleeding and allowing clotting factors to be initiated

Question 4

What are the four stages of the formation of the primary haemostatic plug?

Answer 4

Platelet adhesion
- Platelets stick together at the site of endothelium damage
Platelet activation

• Platelets become activated when exposed to collagen from the injured blood vessel

Secretion
- Platelets secrete chemicals to further encourage more platelets to gather to the broken blood vessel

Aggregation
- Platelets stick together to form clumps

Question 5

What is involved in the creation of the secondary haemostatic plug?

Answer 5

The activation of the clotting/coagulation cascade which adds fibrin to the primary platelet clot

Question 6

What are the two different clotting pathways? How do they differ?

Answer 6

The intrinsic pathway is triggered by collagen exposure from blood vessel damage

The extrinsic pathway is triggered by tissue factor extravascularly from damaged tissues

Question 7

What is the most important common clotting factor between the extrinsic and intrinsic pathways?

Answer 7

Factor 10

Question 8

What process in the coagulation cascade requires factor 10?

Answer 8

The conversion of Prothrombin (II) into Thrombin

Question 9

What are the purposes of thrombin?

Answer 9

To further activate more platelets and cleave soluble Fibrinogen (I) into insoluble Fibrin (XIII) strands to stabilise the clot

Question 10

What is thrombocytopenia?

Answer 10

A reduction of platelet (thrombocyte) levels

Question 11

What is haemophilia? What are the two types?

Answer 11

X-linked recessive genetic disorder caused by a defective or deficient coagulation factor.

Haemophilia A

• Factor 8 deficiency
• 85-90% of cases
• Affects both intrinsic and extrinsic pathways

Haemophilia B

• Factor 9 deficiency
• 10-15% of cases
• Only affects intrinsic pathway