7. Haemostasis - Coagulation Cascade Flashcards
what initiates coagulation cascade
Tissue factor (TF)
what does TF bind to when it comes into contact with circulating blood
binds with factor VII
= factor VIIa
what is a tenase complex
complex that allows cleavage of X into Xa
2 forms = extrinsic and intrinsic
what is extrinsic complex made up of
- Factor VIIa (from before)
- TF (from before as well)
- FX (the thing that needs to be activated)
- Ca2+ (as per usual)
- Phospholipid (idek why)
= CONVERTS X INTO Xa
and also smalllll amount of factor IX made
after factor Xa is made, what else needs to be made
(trace) thrombin
how is thrombin made
Factor Xa with some Ca2+
and Prothrombin
how is the initiation process down regulated
by action of tissue factor pathway inhibitor
= inhibits FXa and TF/FVIIa complex
what needs to happen after initiation
amplification
amplification process
- thrombin activates:
> platelets - to enhance platelet plug
> FVIII
> FV
what is factor 5 a cofactor for
10
what is factor 8 a cofactor for
factor 9
what comes after amplification
propogation
first step of propgation
formation of intrinsic tenas complex
what is intrinsic tenase complex made up of
- IXa
- VIIIa (cuz is 9s cofactor)
- FX (duh)
- Ca2+
- phospholipid
= produces lots more Xa
with no specific inhibitor unlike in the extrinsic
prothrombinase complex
after intrinsic tenase:
- Xa
- and its cofactor Va
- Prothrombinase
- Ca2+
- phospholipid
= forms THROMBIN in larger amounts than before
after burst of thrombin by prothrombinase complex, what does it activate
- platelets
- 5, 8 and 7 (which feedback into coagulation process)
- factor 11
- factor 13 into 13a
what does 13a do
crosslinking of fibrin = stable fibrin clot
which coagulation factors are vitamin K dependent
prothrombin
7
9
10
what is the contact activation pathway
occurs alongside coagulation pathway
exposure of clotting fators to collagen
what factors bind to collagen in the contact activation pathway
- high molecular weight kinogen (HMWK)
- prekallikrein
- factor 11 = 11a (which has feedback effect of 9)
- factor 12 = 12a
thrombin’s cofactor
thrombomodulin
what is platelet plug clot retraction
- as platelet plug degranulates, fibrin will increase
- and after few hrs, the plug is entirely made up of cross linked fibrin
what is clot retraction mediated by
glycoproteins
(same ones that were involved in platelet adhesion)