Haemostasis Flashcards
Define haemostasis
Body’s physiological response to prevent significant blood loss after vascular injury
List the 4 step process
- Localised vasoconstriction
- Primary haemostasis (platelet plug formation)
- Secondary haemostasis (coagulation)
- Tertiary haemostasis (fibrinolysis)
Describe each step of haemostasis
1st - Reduces blood flow to injury site + retards blood flow
2nd - Plugs breach in blood vessel
3rd - Strengthens + reinforces platelet plug
4th - dissolves clot once blood vessel integrity has been restored
List the 4 events that occur in primary haemostasis
Platelet adhesion + activation
Aggregation + plug formation
What changes occur during platelet activation
- Change shape
- Cytoplasmic granules released
- Increase thromboxane A2
- Activation + expression of GPIIb/IIIa receptors
Agonist - activated platelet GPIIb/IIIa receptors bind to ______ to form _____ with adjacent platelets to form a primary haemostatic plug. This can stop haemorrhage in _____ blood vessels.
Fibrinogen
Cross-bridges
Small
Activated + aggregated platelets form the phospholipid membrane surface for _____
Clotting
What are the 3 pathways of the coagulation cascade?
Extrinsic, intrinsic, common
Major activation of the cascade requires what?
- Very charged phospholipid-rich membrane
- Enzyme
- Substrate
- Cofactor
- Ca 2+
What is the coagulation cascade?
A sequence of enzymatic reactions involving blood borne coagulation factors
What is the final substrate of the cascade?
Fibrinogen
Fibrinogen is converted into ____ by the enzyme ____
Fibrin
Thrombin
Where are the main coagulation factors synthesised?
Liver
Is extrinsic a quick/slow response?
Quick
Is intrinsic a quick/slow response?
Slow
Which tissue factor is exposed at damaged tissue? (extrinsic pathway)
FIII
What does prothrombin FII require for synthesis?
Require vit K for synthesis
In the extrinsic pathway the released TF forms a complex with _____ and _____ which is called the _______. This activates _____ of the ________ and _______ pathway.
Activation of FX leads to the production of ______.
FVII Ca 2+ extrinsic tenase FX intrinsic common thrombin
In the intrinsic pathway, FXII forms a complex with ______ and ______ on collagen, activating _____.
FXIIa activates ____. FXIa activates ______.
HMW kininogen Prekallikrein FXII FXI FIX
The intrinsic tenase activates _____ in the ______ pathway, leading to the production of _______.
FX
common
thrombin
List the steps of the common pathway
- Activation of FX
- Conversion of prothrombin (FII) to thrombin (FIIa)
- Cleavage of fibrinogen (FI) to fibrin (FIa)
- Polymerisation + stabilisation of fibrin polymers by FXIII
The prothrombinase complex converts ______ to ______
prothrombin
thrombin
Give 2 limitations of the coagulation cascade
- Doesn’t explain how blood clots in vivo
- Assumes intrinsic + extrinsic are independently capable of clot formation
Name the 3 steps of the new proposed model
Initiation
Propagation
Amplification
