Intro to haemostasis Flashcards
What is haemostasis?
arrest of bleeding and maintenance of vascular patency
What are the requirements of haemostasis?
permanenent state of readiness; prompt response; localised response; protection against unwated thrombosis
What is primary haemostasis?
formation of a platelet plug
What is secondary haemostasis?
formation of fibrin clot
What are the components of normal haemostatic system?
primary and secondary haemostasis; fibrinolysis and anticoagulant defences
What is the lifespan of platelets?
7-10 days
What is the result of endothelial damage?
exposing of collagen and release of von willebrand factor
What are the consequences of failure of platelet plugs?
spontaneous bruising and purpura (esp. in lowerl imbs); mucosal bleeding; intracranial haemorrhage; retinal haemorrhage
What is the screening test for primary haemostasis?
platelet count
Why might vitamin C deficiency result in increased bleeding?
need to make collagen
What is found on the outside of platelets?
negatively charged phospholipid with calcium stuck on
What is released with tissue damage that begins the fibrin clot?
tissue factor
What does tissue factor activate?
factor VII
What is the action of TF/VII?
activates factors V and Xa
What is the function of V/Xa complex?
changes prothrombin to thrombin
What are the actions of thrombin?
converts fibrinogen to fibrin; and activates VII/IXa
What is the purpose of VIII/Xa?
activates V/Xa and amplifies the response from TF
What is the difference between single and multiple clotting factor deficiencies?
single:usually hereditary whereas multiple are usually acquired
What other name is prothrombin known by?
factor II
What converts plasminogen to plasmin?
tissue plasminogen activator
What is the action of plasmin?
convert fibrin to FDPs
How are fibrin degredation products detected clinically?
d-dimers: cross-linked version of FDPs
What does prothrombin time measure?
pathway through TF/VIIa ( intrinsic pathway)
What does activated partial thromboplastin time measure?
pathway though VIII/IXa (extrinsic pathway)
What are the naturally occurring anticoagulants?
anti-thrombin; protein C and S
What are the functions of anti-thrombin?
inhibits TF/VIIa; V/Xa; VIII/IXa and thrombin
How are Protein S and C activated?
thrombomodulin on endothelium binds to thrombin which activates PC and PS
Waht are the actiosn of protein C and S?
inhibit V/Xa and VIII/IXa
What is thrombophilia?
deficiency of naturally occurring anticoagulants
