Week 2- Haemostasis Flashcards
What is haemostasis the balance between?
Coagulating factors and platelets vs anticoagulating proteins and fibrinolytic factors
What are the aims of haemostasis?
- To allow stimulation of blood clotting (coagulation)
- To prevent excessive blood clotting (thrombosis)
- To allow the fibrin clot to break down (fibrinolysis)
What are the 3 stages of haemostasis?
- Construction of blood vessels
- Primary haemostasis: Formation of a temporary platelet plug (platelet aggregation and adhesion)
- Secondary haemostasis: Formation of a fibrin clot (coagulation)
Which cells do platelets come from?
Myeloid stem cells
What is the lifespan of an average platelet?
10 days
How are platelets made?
Via megakaryocyte fragmentation
Describe the structure of platelets
They are discoid, non nucleated, have glycoproteins on their cell surface, contain granules
How do platelets attach to endothelium cells?
Directly: to collagen via GP1a receptor
Indirectly: via Von Willebrand factor (VWF) and GP1b receptor
What granules do platelets contain and describe how granular contents are released from platelets
They contain alpha and dense granules, contents are released via cannicular system that is formed from invaginated surface
What do granules in platelets contain?
ADP, fibrinogen and VWF
How is thromboxane A2 synthesized?
From arachadonic acid that comes from the cell membrane
What is the function of thromboxane A2?
To help with platelet aggregation and vasoconstriction
Describe the process of platelet aggregation
- Granular release of ADP and thromboxane A2
- Conformational change in GPIIb/IIIa receptor
- Fibrinogen binds to receptor
- Fibrin clot can form
What is prostacyclin and where is it used?
It is a chemical vasodilator that is released during platelet aggregation to prevent excessive aggregation
Name the anti-platelet drugs and their mechanism of action
Aspirin- blocks thromboxane A2 synthesis
Clopidrogel- blocks ADP receptors on cell membrane