Haemostasis Flashcards

1
Q

what are the components of normal haemostasis system

A

Formation of platelet plug
- Primary Haemostasis

Formation of fibrin clot
- Secondary Haemostasis

Fibrinolysis

Anticoagulant Defences

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2
Q

how do platelets know where the site of injury is

A

Endothelial (vessel wall) damage exposes collagen and releases Von Willebrand Factor (VWF), and other proteins to which platelets have receptors

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3
Q

what are potential causes of a failure of platelet plug formation

A

vascular
- if we lose collagen in the vessel walls it makes them easier to break down

platelets

  • reduced number (thrombocytopenia)
  • reduced function (adequate numbers)

VWF
- reduced levels or not functioning

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4
Q

what are consequences of a failure of platelet plug formation

A

spontaneous bruising and purpura

mucosal bleeding
- epistaxes, GI, conjunctival, menorrhagia

intracranial haemorrhage
retinal haemorrhage

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5
Q

when is menorrhagia particularly a key presenting complaint

A

Von Willebrand problems

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6
Q

what is the screening test for primary haemostats

A

platelet count

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7
Q

what three things are needed for formation of a platelet plug

A

platelets
VWF
Collagen in vessel wall

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8
Q

what is secondary haemostasis

A

formation of a fibrin clot

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9
Q

what attracts tissue factor to platelets and starts secondary haemostats

A

platelets full of phospholipid which are negatively charged

calcium on the wall makes it positively charged

clotting factors are negatively charged and come stick to it

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10
Q

how is a fibrin clot formed

A

1 - tissue factor is released from damaged vessels wall
activating the first clotting factor = factor 7.

2 - this then activates clotting factor 5 and 10

3 - they turn prothrombin into thrombin

4 - thrombin then turns fibrinogen into fibrin

5 - thrombin also activates factor 8 and 9

6 - they then activate more clotting factor 5 and 10

7 - rapid feedback loop established

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11
Q

what step in forming the fibrin clot is initiation

A

when TF is released and activates factor 7

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12
Q

what step in forming the fibrin clot is propagation

A

clotting factor 5 and 10 converting prothrombin into thrombin

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13
Q

what step in forming the fibrin clot is amplification

A

thrombin activating factor 8 and 9 which go on to activate more 5 and 10.

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14
Q

what are causes of failure of fibrin clot formation

A

Single clotting factor deficiency

  • eg Haemophilia (missing one of the clotting factors)
  • usually hereditary

Multiple clotting factor deficiencies

  • usually acquired
  • eg Disseminated Intravascular Coagulation

Increased fibrinolysis
- usually part of complex coagulopathy

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15
Q

how does fibrinolysis occur

A

1 - plasminogen converted to plasmin by Tissue Plasminogen Activator (tPA)

2 - plasmin converts fibrin to Fibrin Degradation Products (FDP)

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16
Q

how is FDP measured

A

by measuring there cross linked product

- D-Dimers

17
Q

what are the screening tests for Fibrin Clot Formation

A

Prothrombin Time (PT)

Activated Partial Thromboplastin Time (APTT)

18
Q

how does measuring PT work

A

push pathway through TF

if prolonged suggests a problem with TF or VIIa

19
Q

how does measuring APTT work

A

pushing pathway through factor 8 and 9

if prolonged suggests a problem with factor 8 or 9

20
Q

how is warfarin monitored

A

measure PT

as it affects factor 7 the most

21
Q

how is heparin monitored

A

measure APTT

22
Q

how does anticoagulation occur

A

1 - Anti-Thrombin III binds to thrombin

2 - AT-III also switches off TF, VIIa, V, Xa, VIII, IX

23
Q

what are Protein C and Protein S

A

co-factors activated by thrombin

switch off factor 5, 10 and 8