Haemostasis Flashcards
Haemostasis 3 processes
Vasoconstriction
Formation of unstable platelet plug at site of vessel wall damage (primary haemostasis)
Formation of a stable fibrin clot (secondary haemostasis/coagulation)
Platelet definition
Discoid,non nucleated, granule containing cells
Derived from myeloid SCs
Platelet lifespan
10 days
How to platelets become activated
Following injury to vessel walls platelets stick to damaged endothelium to collagen. The adhesion of platelets causes them to activate and changes their shape from a disc to a more rounded form with spicules to encourage platelet-platelet interaction
3 Important components of platelet granules released
ADP
fibrinogen
Von Willebrand factor
Thromboxane 2 function
Vasoconstriction
Platelet aggregation
What produces thromboxane A2
Platelets
What 2 chemicals have +ve feedbacks on platelet recruitment activation and aggregation
How
ADP and thromboxane A2 binding respectively to P2Y12 and thromboxane A2 receptors on platelets
Fibrinogen role
Binds to GPIIb/IIIa receptors which further activates platelets
Linking platelets together to form platelet plug
Aspirin mechanism
Inhibits production of thromboxane A2 by irreversibly (effects last till platelets are replaced~7days) blocking action of cyclo-oxygenase resulting in reduced platelet aggregation.
Clopidogrel
Irreversibly blocking p2y12 (ADP) receptor on platelets.
Last 7 days
Von Willebrand Factor (VWF)
Glycoprotein synthesised by endothelial cells and megakaryocytes. Circulates in plasma. Mediates adhesion of platelets to sites of injury and promotes platelet aggregation
site of majority of clotting factor production
Liver
How is coagulation initiated
A tissue factor (TF) mainly located on sites not usually exposed to blood. Interaction between blood and TF leads to activation of prothrombin and an initial small amount of thrombin.
Amplification phase
Small amount of thrombin mediates activation of co-factors, zygomen (preenzyme) factor XI and platelets
