Secondary Haemostasis Flashcards
How is the extrinsic pathway activated?
Factor VII in plasma is exposed to tissue factor
Where is tissue factor found?
Endothelium and smooth muscle
What reaction does VIIa catalyse? What else is needed?
Tenase reaction. Needs calcium present
What does Xa do?
Converts a small amount of prothrombin to thrombin.
What is the clinical test for the extrinsic and common pathway?
Prothrombin time
How does the initial thrombin amplify itself?
Thrombin activates V, VIII, XI. VIIIa and IXa increase Xa. Va increases effectiveness of Xa
What is the order of factors in the intrinsic pathway?
XII- XI- IX- X
How is the intrinsic pathway activated?
XII can be activated by collagen and polyanions from activated platelets.
Can become activated when blood is stagnant.
Which reactions in the intrinsic pathway require calcium?
Activation of IX, tenase
What is the clinical test for the intrinsic and common pathway?
Activated partial thromboplastin time APTT
What is the INR?
Derived from PT- compensates for differences between manufacturers. Should be 0.8-1.2. Used to assess patients taking anticoags. Aim for 2-3.
What does thrombin do?
Fibrinogen-> fibrin. VIII activated which increases crosslinking.
