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Hematology > Introduction to Haemostasis > Flashcards

Introduction to Haemostasis Flashcards

1
Q

What is haemostasis?

A

The arrest of bleeding and maintenance of vascular patency

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2
Q

List the requirements for haemostasis

A

Permanent state of readiness
Prompt response
Localised response
Protection against unwanted thrombosis

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3
Q

What are the components of normal haemostatic system?

A
  1. formation of platelet plug
  2. Formation of fibrin clot
  3. Fibrinolysis - breaking down of the clot
  4. Anti-coagulant defence - switching off the clotting systen
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4
Q

What stabilises a clot and enhances it?

A

Fibrin meshwork

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5
Q

What are primary and secondary haemostasis?

A

primary - platelet plug

secondary - fibrin clot

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6
Q

Where are platelets formed?What are the precursor cells?

A

Bone marrow

Budding from megakryocytes

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7
Q

Describe a megakaryocyte

A

Large, multi nucleated cell seen only in the bone marrow

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8
Q

Why do megakaryocytes have a short lifespan?

A

Enucleated

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9
Q

What is the lifespan of a platelet cell?

A

7-10 days

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10
Q

Which drug stops platelets from working?

A

Aspirin

Clopidogrel

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11
Q

What is the function of a platelet cell?

A

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

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12
Q

What causes failure of platelet plug formation?

A

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

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13
Q

What are the consequences of failed platelet plug formation?

A

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

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14
Q

Collagen deficiency, elderly patient, bruising. What is this called?

A

Senile purpura

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15
Q

What are the screening tests for primary hemostasis?

A

Platelet count

No simple screening tests for other components of primary haemostasis

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16
Q

When does fibrin clot formation/secondary hemostasis occur?

A

More extensive bleeding where a stronger plug is needed

17
Q

Describe fibrin clot formation

A

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

18
Q

What are the two roles of fibrin in clotting mechanism?

A

a) causes fibrinogen to become fibrin

b) activation of VIII/IX

19
Q

What causes failure of fibrin clot formation?

A

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

20
Q

What are the consequences of secondary hemostasis failure?

A

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

21
Q

Name the test for excess fibrinolysis in the bosy

A

D-dimer

22
Q

What clinical features are seen in single clotting factor deficiency?

A

Single clotting factor deficiency shows bleeding into joints

23
Q

What are the screening tests for fibrin clot formation?

A

Prothrombin time

Activated partial thromboplastin time

24
Q

What to cover in history taking for a bleeding disorder?

A

Bleeding/bruising
Duration (life-long?)
Previous surgery/dental extractions

Drug history - NSAIDS and aspirin interefere with platelet function

25
Q

What are some of the things to look for in PE?

A

fundal hemorrhage, mucosal bleeding, skin of lower bleeding, splenomegaly (low platelet

26
Q

What are the naturally occurring anti-coagulants?

A
  1. serine protease inhibitors

2. Protein C and Protein S - switch off factor VIII and V

Hematology (9 decks)

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