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Haematology > Haemostasis > Flashcards

Haemostasis Flashcards

1
Q

What is the lifespan of platelets?

A

7 - 10 days

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2
Q

What is haemostasis?

A

The arrest of bleeding and

the maintenance of vascular patency

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3
Q

What cells produce platelets?

A

Megakaryocytes

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4
Q

Describe platelet plug formation in response to an injury.

A
  1. Vasospasm (blood vessels contract to reduce flow) - contraction of smooth muscles brought about by signals from endothelial and nerve cells
    Platelet adhesion (Platelets form a temporay plug
    Platelet adhesion; Von Willebrand factor assist platelets to attach to the injured site where they bind easily onto exposed collagen. Erythroctes also bind get caught in the matrix. Von Willebrand factors help platelets bind to exposed collagen.
    Platelet release reaction
    Platelets release chemicals to attract more platelets (adenosine bisphosphate) and increase vasoconstriction (seratonin and thromboxine A2)
    Platelet aggregation
    Platelets all stick together
    Healthy cells secrete NO and prostoglandins to stop platelet aggregation in the wrong place.
    Plug formation
    This plug is not very strong and requires strenghtheing.
    This is done by formation of a fibrin clot (secondary haemostasis)
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5
Q

What is the main component of the vessel wall?

A

Collagen

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6
Q

Why do old people and people of steroids bruise easily?

A

Less collagen in the vessel wall

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7
Q

Deficiency of which vitamin causes a reduction in vessel wall collagen

A

Vitamin C - Scurvy

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8
Q

What is the most common inherited bleeding disorder?

A

Von Willebrand factor disease

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9
Q

What are the symptoms of failure of the platelet plug?

A
  1. Spontaneous bleeding and Purpura
  2. Mucosal bleeding
    - Epistaxis
    - GI
    - Conjunctaval
    - Menorhhagia
  3. Retinal hammorhagge
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10
Q

What is the simple screening test to look for primary haemostasis?

A

Platelet count

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11
Q

Briefly describe secondary haemostasis? (Not including clotting factorr)

A

Platelet aggregation stimulates the intrinsic and extrinsic pathway which both lead to the production of prothrombinase/ prothrombin activator (enzyme)
Prothrombinase and Ca2+ (calcium ions) catalyses the conversion of prothrombin into thrombin
Thrombin and Ca2+ acts as an enzyme to convert fibrinogen into fibrin
Fibrin sticks to everything else to form a meshwork that will go on to form a stable clot.

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12
Q

What substance starts off the coagulation cascade?

A

Tissue factore

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13
Q

What substance converts fibrinogen to fibrin?

A

Thrombin

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14
Q

Is the intrinsic of extrinsic pathway more involved in initiation of coagulation?

A

Extrinsic

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15
Q

Describe the extrinsic pathway in secondary haemostasis

A

Triggered by the release of tissue factor from damaged tissue
Tissue factor and Factor VIIa combine to convert factor X to Xa
Then carries on with the intrinsic pathway

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16
Q

Describe the intinsic pathway in secondary haemostasis

A

Important for the amplification of the clotting cascade
Factor VIII and Factor V are activated
Factor VIIIa and Factor IXa cause further activation of factor Xa

17
Q

What two factors can be affected in haemophillia

A

8 (Hamophillia A)

9 (Hameophilia B)

18
Q

Why do you get multiple clotting factor deficiency?

A

Aquired usually

  • Liver disease (liver produces clotting factors)
  • DIC
19
Q

What three disease mechanisms cause failure of the fibrin clot?

A
  1. Single factor deficiency
  2. Multiple factor deficiency
  3. Increase in fibrinolysis
20
Q

What substance activates fibrinolysis? How?

A

Tissue Plasminogen Activator (tPA) It converts plasminogen to plasmin which breaks down fibrin to FDP.

21
Q

What does Tissue Plasminogen Activator (tPA) do?

A

Converts plasminogen to plasmin

22
Q

Where do you get increased bleeding most often in secondary haemostatic failure?

A

Large joints.

23
Q

What are the tests used when assessing secondary haemostasis

A

PT

APPT

24
Q

If the prothrombin time is prolonged where is the problem likely to be in the clotting cascade?

A

Tissue Factor

Factor 7a

25
Q

If the activated partial prothrombin time is prolonged where is the problem likely to be in the clotting cascade?

A

Factor 8a

Factor 9a

26
Q

What two factors are important in the conversions of prothrombin to thrombin?

A

Va

Xa

27
Q

What does the prothromin time measure?

A

How long it takes blood to clot

28
Q

What factors are affected in prolonged APTT

A

Factor 8

Factor 9a

29
Q

What hereditable condition causes prolonged APTT?

A

Hameophillia

30
Q

What switches of thrombin?

A

Anti thrombin III

31
Q

What proteins stop coagulation by switching off facto V and VIII?

A

Protein C

Protein S

Haematology (21 decks)

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