Haemostasis Flashcards
What is primary haemostasis?
Formation of platelet plug
What is secondary haemostasis?
Formation of fibrin clot
How are platelets formed in bone?
marrow by ‘budding’ from megakaryocytes
Describe how endothelial wall damage lead to platelet adhesion?
endothelial wall damage exposes collagen
This causes Von Willebrand Factor and ther proteins to be released.
These factors/proteins have receptors for platelets, so platelets come and bind to them = platelet adhesion
How does platelet aggregation occur?
The platelets (which are now bound to the proteins at the site of endothelial damage) secrete chemicals
What are the 3 general causes of failure of platelet plug formation?
- Vascular cause
- Platelets
- Reduced number (thrombocytopenia)
- Reduced function - Von Willebrand Factor
List some consequences of a failure of platelet plug formation.
Spontaneous Bruising and Purpura Mucosal Bleeding, epistaxis, GI bleed, conjunctival bleed Menorrhagia Intracranial haemorrhage Retinal haemorrhages
Screening test for primary haemostasis?
Platelet count (No simple screening tests for other components of primary haemostasis)
What converts fibrinogen to fibrin?
thrombin
What converts prothrombin to thrombin (what is prothrombinase)?
Factor Xa, and the protein cofactor, Factor Va
What are the 3 causes of failure of formation of a fibrin clot (secondary haemolysis)?
- Single clotting factor deficiency, usually hereditary
eg Haemophilia - Multiple clotting factor deficiencies, usually acquired e.g. Disseminated Intravascular Coagulation
- Increased fibrinolysis, usually part of complex coagulopathy
Fibronolysis converts what to what?
fibrin to fibrin degradation products (FDPs)
What is the enzyme in fibrinolysis?
plasmin
What converts plasminogen to plasmin?
Tissue plasminogen activator (TPA)
What is the characteristic sign of fibrin clot formation failure?
No characteristic clinical syndrome
