Flashcards in Haemostasis Deck (31):
What is the lifespan of platelets?
7 - 10 days
What is haemostasis?
The arrest of bleeding and
the maintenance of vascular patency
What cells produce platelets?
Describe platelet plug formation in response to an injury.
1. Vasospasm (blood vessels contract to reduce flow) - contraction of smooth muscles brought about by signals from endothelial and nerve cells
Platelet adhesion (Platelets form a temporay plug
Platelet adhesion; Von Willebrand factor assist platelets to attach to the injured site where they bind easily onto exposed collagen. Erythroctes also bind get caught in the matrix. Von Willebrand factors help platelets bind to exposed collagen.
Platelet release reaction
Platelets release chemicals to attract more platelets (adenosine bisphosphate) and increase vasoconstriction (seratonin and thromboxine A2)
Platelets all stick together
Healthy cells secrete NO and prostoglandins to stop platelet aggregation in the wrong place.
This plug is not very strong and requires strenghtheing.
This is done by formation of a fibrin clot (secondary haemostasis)
What is the main component of the vessel wall?
Why do old people and people of steroids bruise easily?
Less collagen in the vessel wall
Deficiency of which vitamin causes a reduction in vessel wall collagen
Vitamin C - Scurvy
What is the most common inherited bleeding disorder?
Von Willebrand factor disease
What are the symptoms of failure of the platelet plug?
1. Spontaneous bleeding and Purpura
2. Mucosal bleeding
3. Retinal hammorhagge
What is the simple screening test to look for primary haemostasis?
Briefly describe secondary haemostasis? (Not including clotting factorr)
Platelet aggregation stimulates the intrinsic and extrinsic pathway which both lead to the production of prothrombinase/ prothrombin activator (enzyme)
Prothrombinase and Ca2+ (calcium ions) catalyses the conversion of prothrombin into thrombin
Thrombin and Ca2+ acts as an enzyme to convert fibrinogen into fibrin
Fibrin sticks to everything else to form a meshwork that will go on to form a stable clot.
What substance starts off the coagulation cascade?
What substance converts fibrinogen to fibrin?
Is the intrinsic of extrinsic pathway more involved in initiation of coagulation?
Describe the extrinsic pathway in secondary haemostasis
Triggered by the release of tissue factor from damaged tissue
Tissue factor and Factor VIIa combine to convert factor X to Xa
Then carries on with the intrinsic pathway
Describe the intinsic pathway in secondary haemostasis
Important for the amplification of the clotting cascade
Factor VIII and Factor V are activated
Factor VIIIa and Factor IXa cause further activation of factor Xa
What two factors can be affected in haemophillia
8 (Hamophillia A)
9 (Hameophilia B)
Why do you get multiple clotting factor deficiency?
- Liver disease (liver produces clotting factors)
What three disease mechanisms cause failure of the fibrin clot?
1. Single factor deficiency
2. Multiple factor deficiency
3. Increase in fibrinolysis
What substance activates fibrinolysis? How?
Tissue Plasminogen Activator (tPA) It converts plasminogen to plasmin which breaks down fibrin to FDP.
What does Tissue Plasminogen Activator (tPA) do?
Converts plasminogen to plasmin
Where do you get increased bleeding most often in secondary haemostatic failure?
What are the tests used when assessing secondary haemostasis
If the prothrombin time is prolonged where is the problem likely to be in the clotting cascade?
If the activated partial prothrombin time is prolonged where is the problem likely to be in the clotting cascade?
What two factors are important in the conversions of prothrombin to thrombin?
What does the prothromin time measure?
How long it takes blood to clot
What factors are affected in prolonged APTT
What hereditable condition causes prolonged APTT?
What switches of thrombin?
Anti thrombin III