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Haematology > Haemostasis > Flashcards

Haemostasis Flashcards

1
Q

What is haemostasis?

A

The arrest of bleeding and the maintenance of vascular patency.

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2
Q

What are the requirements of 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 haemostasis?

A

Formation of platelet plug
Fibrin clot formation
Fibrinolysis

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4
Q

What is primary haemostasis?

A

Formation of platelet plug

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5
Q

What prevents primary haemostasis in undamaged blood vessels?

A

Negative charge
Vasodilation (NO and prostocyclins- also inhibit platelet aggregation)
Plasminogen activators.

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6
Q

How are platelets formed?

A

Budding off megakaryocytes

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7
Q

Describe platelets

A

Small anucleate discs

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8
Q

How long to platelets last for?

A

7-10 days

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9
Q

How do platelets stop bleeding?

A

Adhere to collagen in damaged endothelium (vessel walls).
Damaged walls causes release of Von Willebrand Factor (VWF) which attaches to exposed collagen and platelets have receptors for.

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10
Q

What can cause failure of platelets/primary haemostasis?

A

Vascular
Platelets
vWF

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11
Q

What is a reduced number of platelets called?

A

Thrombocytopenia

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12
Q

What are the consequences of platelet failure?

A

Spontaneous Bruising and Purpura
Mucosal Bleeding
Intracranial haemorrhage
Retinal haemorrhages

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13
Q

What are common locations of mucosal bleeding?

A

Epistaxes
Gastrointestinal
Conjunctival
Menorrhagia

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14
Q

How do you investigate primary haemostasis?

A

Platelet count

No simple screening tests for other components of primary haemostasis

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15
Q

What is secondary haemostasis?

A

Fibrin clot formation

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16
Q

Describe fibrin clot formation

A

1) VII from circulation combines with tissue factor (TF) (III) on platelets.
2) Tf/VII converts X to Xa (initiation)
3) Xa and cofactor V (V/Xa) convert prothrombin (II) to thrombin (propagation)
4) Thrombin converts fibrinogen (I) to fibrin.
5) Thrombin activates VIII/IXa which further induces V/Xa (amplification)

17
Q

What is extrinsic coagulation?

A

Factor VII and TF -> Fibrinogen to fibrin

Propogation

18
Q

What is intrinsic coagulation?

A

Thrombin activates VIII/IXa which further induces V/Xa (amplification)

19
Q

How do you measure extrinsic coagulation?

A

Prothrombin time

20
Q

How do you measure intrinsic coaguation?

A

Activated partial thromboplastin time

21
Q

What are the fibrinogen receptors on platelets called?

A

Glycoprotein IIb-IIIa

22
Q

What additional molecule is needed for GPIIb-IIIa to bind fibriongen and aggregate platelets?

A

ADP

23
Q

What can cause secondary haemostasis failure?

A

Single clotting factor deficiency
Multiple clotting factor deficiencies
Increased fibrinolysis

24
Q

Are single clotting factor deficiencies usually hereditary or acquired?

A

Hereditary

25
Q

What can cause increased fibrinolysis?

A

Complex coagulopathies

26
Q

What are the consequences of secondary haemostasis failure?

A

No characteristic clinical syndrome
May be combined primary/secondary haemostatic failure
Pattern of bleeding depends on: Single/multiple abnormalities, the clotting factors involved

27
Q

What is fibrinolysis?

A

Breakdown of fibrin

28
Q

Describe fibrinolysis

A

Fibrin converted to fibrin degradation products (FDP) by plamsmin.

29
Q

What does plasmin do?

A

Breakdown fibrin

30
Q

Describe production of plasmin

A

Plasminogen converted to plasmin by Tissue Plasminogen Activator (tPA) (released from endothelial cells).

31
Q

Why do we have natural anticoagulant defences?

A

To control coagulation

32
Q

What are three natural anticoagulats we have?

A

Antithrombin
Protein C
Protein S

33
Q

What does antithrombin block?

A

Thrombin
Tf/VIIa
V/Xa
VIII/IXa

34
Q

What does Protein C block?

A

Blocks VIII/IXa

35
Q

What does Protein S block?

A

Blocks V/Xa

36
Q

What can a failure of natural anticoagulation cause?

A

Thrombophilia

37
Q

What activated Protein C and S?

A

Thrombin

Haematology (12 decks)

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