Haemostasis

Question 1

Describe primary haemostasis

Answer 1

Platelets respond to injury on vessel wall by adhering to it and forming a primary platelet plug.

Question 2

Describe secondary haemostasis

Answer 2

Intrinsic, extrinsic and common coagulation pathways are activated, and fibrin strand is formed, strengthening the platelet plug.

Question 3

Why are the endothelial cells of the intima anti-thrombotic?

Answer 3

The endothelial cells of the intima are anti-thrombotic, due to several factors: secretion of platelet inhibitors like prostacyclin and nitric oxide, negatively charged heparin-like glycosaminoglycans and fibrinolysis activators (Palta et al., 2014).

Question 4

Why is the subendothelial layer highly thrombogenic?

Answer 4

It contains collagen, fibronectin, elastin and actin as well as Von Willebrand Factor (vWF).
It also contains proteins involved in platelet adhesion such as thrombospondin, laminin and vitronectin (Palta et al., 2014).

Question 5

Describe what happens in primary haemostasis.

Answer 5

The prothrombotic subendothelial layer of blood vessels is exposed when injury occurs, causing arteriolar vasospasm, leading to vasoconstriction.
This is mediated by local mediators such as endothelin and thromboxane A2 (TxA2) (Palta et al., 2014).