Haemostasis Flashcards
What is coagulation?
Solidification of blood to form a gel
What is platelet aggregation?
Stimulated shape change and activation of fibrinogen; platelets form clumps linked by fibrinogen
Inactive clotting factors need to be carboxylated and for this which vitamin is needed?
Vitamin K
Which pathway (intrinsic/extrinsic) initiates coagulation?
Extrinsic
Which pathway (intrinsic/extrinsic) sustains coagulation?
Intrinsic
Which factors are modified by carboxylation and so require vitamin K?
2 (prothrombin), 7, 9, 10
Haemophilia A is due to a loss of which factor?
8
Haemophilia B is due to loss of which factor?
9
Vitamin K deficiency can lead to coagulation problems. Why?
Because vitamin K is needed for carboxylation of factor 7,9, 10 and prothrombin (2)
Platelet aggregation is mediated by a fibrinogen receptor. What is it called?
GPIIb/IIIa
Describe the platelet activation process.
Prostacyclin in vessel walls suppresses the activation of platelets - leading to an increase in cAMP
Presence of thrombin activates platelets leading to a change in their shape
Platelets synthesise thromboxane A2, adrenaline, ADP
On activation, these are released from vesicles
Platelet aggregation is mediated by a fibrinogen receptor called GPIIb/IIIa and creates links between platelets
Fibrinogen is cleaved to fibrin which causes platelets to contract and tighten the plug
Exposure of platelets to acidic phospholipids promotes coagulation
How can atherosclerosis promote platelet activation?
Damage to vessel wall will disrupt prostacyclin production and so prostacyclin will not be able to suppress activation of platelets and so this promotes inappropriate activation
Venous pooling is a risk factor for thrombosis. True or false?
True
Is targeting coagulation, in the prevention of thrombosis more effective in venous or arterial thrombosis?
Venous
Is targeting platelet activation, in the prevention of thrombosis more effective in venous or arterial thrombosis?
Arterial
Heparins occur naturally in the body. True or false?
True
Heparins are oral anti-coagulants. True or false?
False - parenteral
How do heparins work?
They act via binding antithrombin III - they increase the rate of ATIII formation by 1000 fold
Unfractionated heparins are the most commonly used heparins. True or false?
False - less commonly used - mainly used with patients with renal failure
Which factor do low molecular weight heparins work on?
Factor X
Low molecular weight heparins affect thrombin. True or false?
False - only factor Xa
Enoxaparin, tinzaparin and dalteparin are examples of which type of anti-coagulant?
Low molecular weight low molecular weight heparins
Low molecular weight heparins have a longer duration of action and better bioavailability than unfractionated heparins. True or false?
True
Which factor does fondaparinux effect?
Factor Xa