Haemostasis Flashcards
Define haemostasis
- the arrest of bleeding and the maintenance of vascular patency
What are the components of haemostasis?
- formation of a platelet plug
- formation of a fibrin clot
- fibrinolysis
- anticoagulant defences
Where do platelets arise from?
- they are formed from budding of cytoplasm from the megakarytocyte in the bone marrow
What is the lifespan of a platelet?
- 7-10days
What causes platelet formation?
- endothelial damage
- expression of collagen and von willebrand factors
- platelet glycoproteins stick (platelet adhesion)
- release of other chemicals causing more recruitment (platelet aggregation)
causes of failures of a platelet plug?
- vascular loss of collagen
- thrombocytopenia
- von willerband reduced function
Define platelet adhesion?
- platelet glycoproteins bin to the receptors
define platelet aggregation
- release of other chemicals causing more platelet recruitment
What are consequences of platelet failure?
- spontaneous bruising and purpura
- mucosal bleeding
- haemorrhage
How can primary haemostasis be investigated?
- platelet count
Primary vs secondary haemostasis?
- primary = platelet formation
- secondary = fibrin coat
How is a fibrin clot formed?
- TF/ VIIa and VIII/IXa form V/Xa
- prothrombin converted to thrombin
- fibrinogen to fibrin
Where are clotting factors made?
- in the liver
Define fibrinolysis?
- once bleeding is controlled, the clot is broken down
- releasing fibrin degradation products
What is the reaction of fibrinolysis?
- plasminogen -> plasmin which causes fibrin to breakdoqn
How can fibrin breakdown be measured?
- d-dimers
Screening for Prothrombin time?
- TF
- VIIa
Screening for activated partial thromboplastin time?
- VIII
- IXa
Name some naturally occurring anticoagulants?
- antithrombin
- protein c
- protein s
Define thrombophilia
- deficiency of naturally occurring anticoagulants
- increased tendency to develop venous thrombosis
