DBC Flashcards
Why does clotting occur?
→Blood loss is stopped by formation of a plug composed of platelets and fibrin
What does the endothelium maintain in blood vessels?
→maintains an anticoagulant surface
What are the two main processes of haemostasis?
→primary and secondary
What is primary haemostasis of clotting?
→when platelet adheres, activation
What is secondary haemostasis of clotting?
→activation of fibrin formation
Describe primary haemostasis
→Endothelial cells also store von Willebrand Factor in Weibel-Palade bodies for release when appropriately stimulated
→If collagen becomes exposed to blood von Willebrand Factor binds to it
→Platelets express receptors for both collagen and von Willebrand Factor and become activated when these proteins bind to them
→Activated platelets express functional fibrinogen receptors, which are required for aggregation.
Describe secondary haemostasis
→Tissue factor (TF), activates the coagulation cascade to initiate a minor burst of thrombin
→Factor FVIIa binds to Tissue Factor, which ultimately leads to conversion of prothrombin to thrombin
→Thrombin activates receptors on platelets and endothelium
→amplifies platelet aggregation and initiating release of stored von Willebrand Factor from endothelial cells.
Which cell express tissue factor?
→by nearly all sub-endothelial cells
When would collagen become exposed?
→because the endothelium is damaged
Describe the amplification process in clotting
→Thrombin activates Factor VIIIa and Factor Va
→subsequently form calcium ion-dependent complexes on the surface of platelets with Factor IXa and Factor Xa
→accelerate production of Factor Xa and thrombin, respectively
Which factors does thrombin activate?
→Factor VIIIa and Factor Va
Where are the calcium dependent complexes found?
→surface of platelets with Factor IXa
What is the tenase complex?
→Factor IXa and Factor VIIIa
→substrate is Factor X
What is the prothrombinase complex?
→Factor Xa
What does thrombin convert?
→convert fibrinogen to the fibrin mesh
Describe fibro lysis
→Plasminogen in activated to plasmin by tissue plasminogen activator, t-PA
→Plasmin degrades the fibrin mesh to fibrin degradation products which can be cleared
What is plasmin?
→proteolytic and very potent
What is antithrombin?
→a serpin
serine protease inhibitor