Module 3: Mechanisms of Normal Hemostasis

Question 1

Define hemostasis

Answer 1

Prevention and arrest of bleeding by rapid repair of any ruptures in blood vessels
Occurs continuously to deal with wear and tear on the vascular endothelium and whenever the vessel is injured by outside trauma

Question 2

What are the 5 major components of hemostasis?

Answer 2

1. Vascular component - blood vessels and surrounding sub-endothelium
2. Platelet component
3. Coagulation system
4. Fibrinolytic system
5. Natural anticoagulants and inhibitors

The last 3 are plasma components

Question 3

How are vascular endothelial cells thromboresistant?

Answer 3

They secrete:

• heparin sulphate (inhibits coagulation)
• prostacyclin (inhibits platelet adhesion and aggregation)
• nitrous oxide / endothelium derived relaxing factor (EDRF) (relaxes smooth muscle and prevents vasoconstriction)

Question 4

What causes hemostasis activation when an injury occurs?

Answer 4

Platelets and plasma components are exposed to subendothelial tissues including collagen and thromboplastin