Haemostasis Flashcards
what are the components of normal haemostasis system
Formation of platelet plug
- Primary Haemostasis
Formation of fibrin clot
- Secondary Haemostasis
Fibrinolysis
Anticoagulant Defences
how do platelets know where the site of injury is
Endothelial (vessel wall) damage exposes collagen and releases Von Willebrand Factor (VWF), and other proteins to which platelets have receptors
what are potential causes of a failure of platelet plug formation
vascular
- if we lose collagen in the vessel walls it makes them easier to break down
platelets
- reduced number (thrombocytopenia)
- reduced function (adequate numbers)
VWF
- reduced levels or not functioning
what are consequences of a failure of platelet plug formation
spontaneous bruising and purpura
mucosal bleeding
- epistaxes, GI, conjunctival, menorrhagia
intracranial haemorrhage
retinal haemorrhage
when is menorrhagia particularly a key presenting complaint
Von Willebrand problems
what is the screening test for primary haemostats
platelet count
what three things are needed for formation of a platelet plug
platelets
VWF
Collagen in vessel wall
what is secondary haemostasis
formation of a fibrin clot
what attracts tissue factor to platelets and starts secondary haemostats
platelets full of phospholipid which are negatively charged
calcium on the wall makes it positively charged
clotting factors are negatively charged and come stick to it
how is a fibrin clot formed
1 - tissue factor is released from damaged vessels wall
activating the first clotting factor = factor 7.
2 - this then activates clotting factor 5 and 10
3 - they turn prothrombin into thrombin
4 - thrombin then turns fibrinogen into fibrin
5 - thrombin also activates factor 8 and 9
6 - they then activate more clotting factor 5 and 10
7 - rapid feedback loop established
what step in forming the fibrin clot is initiation
when TF is released and activates factor 7
what step in forming the fibrin clot is propagation
clotting factor 5 and 10 converting prothrombin into thrombin
what step in forming the fibrin clot is amplification
thrombin activating factor 8 and 9 which go on to activate more 5 and 10.
what are causes of failure of fibrin clot formation
Single clotting factor deficiency
- eg Haemophilia (missing one of the clotting factors)
- usually hereditary
Multiple clotting factor deficiencies
- usually acquired
- eg Disseminated Intravascular Coagulation
Increased fibrinolysis
- usually part of complex coagulopathy
how does fibrinolysis occur
1 - plasminogen converted to plasmin by Tissue Plasminogen Activator (tPA)
2 - plasmin converts fibrin to Fibrin Degradation Products (FDP)
