Haemostasis Intro

Question 1

What are the components of normal haemostatic system?

Answer 1

1. Formation of platelet plug
   - primary haemostasis
2. Formation of fibrin clot
   - secondary haemostasis
3. Fibrinolysis
4. Anticoagulant defences

Question 2

Platelet

Answer 2

• live for only 7-10 days as they have no nucleus
• platelet adhesion at site of endothelial wall injury due to presence of receptors
• platelet aggregation due to chemicals secreted by adhered platelets

Question 3

What are consequences in primary haemostasis failure (can’t form platelet plug)?

Answer 3

Spontaneous bruising and purpura
Mucosal bleeding (epistaxes, gastrointestinal, conjunctival, menorrhagia)
Intracranial haemorrhage
Retinal haemorrhages

Question 4

How to screen for primary haemostasis?

Answer 4

Platelet count

Question 5

How do fibrin clots form?

Answer 5

prothrombin (factor II) –> thrombin [catalysed by factor V/Xa]
Thrombin catalyses fibrinogen –> fibrin
Thrombin also activates VIII/IXa, which is a pathway to activate V/Xa, hence amplifying the pathway
Tissue factor and factor VIIa can also activate V/Xa

DO NOT think about coagulation pathway, it is out-dated

Question 6

What might cause failure of fibrin clot formation (secondary haemostasis)?

Answer 6

• Single clotting factor deficiency (eg haemophilia)
  *Usually hereditary
• Multiple clottin gfactor deficiency
  *Usually acquired
  eg Disseminated intravascular coagulation
• Increased fibrinolysis
  *Usually part of complex coagulopathy

Question 7

Describe fibrinolysis

Answer 7

Fibrin is broken down by plasmin to fibrin degradation products (two of these bound together is called D-dimer)

Plasmin is converted from plasminogen by tissue plasminogen activator (tPA)

Question 7

How to screen for fibrin clot formation?

Answer 7

Prothrombin time testing the TF/VIIa pathway

Activated partial thromboplastin time testing the VIII/IXa pathway

Question 7

What are some naturally occurring anticoagulants and how do they work?

Answer 7

1. Serine protease inhibitor (Anti-thrombin)
2. Protein C/Protein S

Question 7

What are consequences of fibrin clot formation failure (secondary haemostasis failure)?

Answer 7

No characteristic clinical syndrome
May be combined primary/secondary haemostatic failure

Pattern of bleeding depends on:
- Single/multiple abnormalities
- The clotting factors involved