Introduction to Haemostasis Flashcards
(26 cards)
What is haemostasis?
The arrest of bleeding and maintenance of vascular patency
List the requirements for haemostasis
Permanent state of readiness
Prompt response
Localised response
Protection against unwanted thrombosis
What are the components of normal haemostatic system?
- formation of platelet plug
- Formation of fibrin clot
- Fibrinolysis - breaking down of the clot
- Anti-coagulant defence - switching off the clotting systen
What stabilises a clot and enhances it?
Fibrin meshwork
What are primary and secondary haemostasis?
primary - platelet plug
secondary - fibrin clot
Where are platelets formed?What are the precursor cells?
Bone marrow
Budding from megakryocytes
Describe a megakaryocyte
Large, multi nucleated cell seen only in the bone marrow
Why do megakaryocytes have a short lifespan?
Enucleated
What is the lifespan of a platelet cell?
7-10 days
Which drug stops platelets from working?
Aspirin
Clopidogrel
What is the function of a platelet cell?
Endothelial damage
Exposure of collagen - signal
Release of von-willebrand factor (VWF) and other proteins for which platelets have receptors
Platelet adhesion to site of injury
Once there, platelets secrete granules which allow them to aggregate at site of injury
What causes failure of platelet plug formation?
a) Vascular causes - blood vessel wall (collagen deficient, scurvy)
b) Platelets: reduced no. (increased destruction, reduced production) or reduced function
c) Von Willebrand Factor - deficiency
What are the consequences of failed platelet plug formation?
Spontaneous bruising and purpura (purpura rashes mostly on lower limb)
Mucosal bleeding:
- epistaxis
- GI
- Conjunctival
- Menorrhagia (presentation in women of VWF def.)
Intracranial haemorrhage
Retinal haemorrhage
Collagen deficiency, elderly patient, bruising. What is this called?
Senile purpura
What are the screening tests for primary hemostasis?
Platelet count
No simple screening tests for other components of primary haemostasis
When does fibrin clot formation/secondary hemostasis occur?
More extensive bleeding where a stronger plug is needed
Describe fibrin clot formation
Platelets release Ca2+ which sits on negatively charged phospholipids
When tissue is damaged, TF is released which activates clotting factor VII. This begins hemostasis
Clotting factor V and X are activate prothrombin to thrombin.
Thrombin causes fibrinogen to change to fibrin
Thrombin also activates VII and IX which positively feedbacks the activation of fibrinogen to fibrin
What are the two roles of fibrin in clotting mechanism?
a) causes fibrinogen to become fibrin
b) activation of VIII/IX
What causes failure of fibrin clot formation?
Single clotting factor deficiency - usually factor VIII/IX (loss of amplification)
Ex. haemophillia
Multiple clotting factor deficiencies - usually acquired, ex. DIC
Increased fibrinolysis - part of complex coagulopathy
What are the consequences of secondary hemostasis failure?
No characteristic clinical syndrome
May be combined secondary and primary haemostatic failure - ex. DIC
Pattern of bleeding depends on:
a) single/multiple abnromalities
b) clotting factors involved
Name the test for excess fibrinolysis in the bosy
D-dimer
What clinical features are seen in single clotting factor deficiency?
Single clotting factor deficiency shows bleeding into joints
What are the screening tests for fibrin clot formation?
Prothrombin time
Activated partial thromboplastin time
What to cover in history taking for a bleeding disorder?
Bleeding/bruising
Duration (life-long?)
Previous surgery/dental extractions
Drug history - NSAIDS and aspirin interefere with platelet function
