Lecture notes
Haemostasis
- Module
- Blood Science (6H5Z1003)
- Institution
- Manchester Metropolitan University (MMU)
Lectures notes on Haemostasis
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Haemostasis II - Coagulation and secondary haemostasisSecondary haemostasis:
- Platelet plug alone is not enough to stem the blood loss
- Needs to be reinforced
- This is where the coagulation pathways come into play
- Secondary haemostasis (coagulation) is usually initiated simultaneously with primary haemostasis upon
endothelial damage
- Result of activation of coagulation pathways is that soluble fibrinogen is converted to insoluble fibrin
Coagulation cascade - key complexes: Coagulation factors:
Coagulation Cascade:
- Circulating inactive zymogens are
sequentially activated to the
active enzyme forms
- Intrinsic pathway – requires
enzymes and factors all present in
the plasma.
- Extrinsic pathway- requires
enzymes and factors present in
the plasma as well as an activator
- Both pathways converge on a
common pathway to generate the
fibrin clot
, Events of coagulation:
1. Endothelial injury exposes tissue factor (TF) – factor which
binds its circulating ligand in plasma, the pro-enzyme FVII
2. Binding to TF activates FVII and promotes activity
3. The TF-FVIIa complex then activates the pro-enzyme FX
4. FXa is able to cleave its substrate prothrombin (FII) to
thrombin
5. Only a small amount of FXa is generated by this reaction
Extrinsic pathway:
1. FXa + FVa
2. Need phospholipids (PL) and Ca2+ ions
3. This is the prothrombinase complex
4. It is able to cleave its substrate prothrombin (FII) to thrombin
5. Only small amounts of thrombin are generated by this
reaction
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