Haemostasis Flashcards Preview

Haematology > Haemostasis > Flashcards

Flashcards in Haemostasis Deck (31):
1

What is the lifespan of platelets?

7 - 10 days

2

What is haemostasis?

The arrest of bleeding and
the maintenance of vascular patency

3

What cells produce platelets?

Megakaryocytes

4

Describe platelet plug formation in response to an injury.

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)

5

What is the main component of the vessel wall?

Collagen

6

Why do old people and people of steroids bruise easily?

Less collagen in the vessel wall

7

Deficiency of which vitamin causes a reduction in vessel wall collagen

Vitamin C - Scurvy

8

What is the most common inherited bleeding disorder?

Von Willebrand factor disease

9

What are the symptoms of failure of the platelet plug?

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

10

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

Platelet count

11

Briefly describe secondary haemostasis? (Not including clotting factorr)


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.

12

What substance starts off the coagulation cascade?

Tissue factore

13

What substance converts fibrinogen to fibrin?

Thrombin

14

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

Extrinsic

15

Describe the extrinsic pathway in secondary haemostasis

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

16

Describe the intinsic pathway in secondary haemostasis

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

What two factors can be affected in haemophillia

8 (Hamophillia A)
9 (Hameophilia B)

18

Why do you get multiple clotting factor deficiency?

Aquired usually
- Liver disease (liver produces clotting factors)
- DIC

19

What three disease mechanisms cause failure of the fibrin clot?

1. Single factor deficiency
2. Multiple factor deficiency
3. Increase in fibrinolysis

20

What substance activates fibrinolysis? How?

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

21

What does Tissue Plasminogen Activator (tPA) do?

Converts plasminogen to plasmin

22

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

Large joints.

23

What are the tests used when assessing secondary haemostasis

PT
APPT

24

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

Tissue Factor
Factor 7a

25

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

Factor 8a
Factor 9a

26

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

Va
Xa

27

What does the prothromin time measure?

How long it takes blood to clot

28

What factors are affected in prolonged APTT

Factor 8
Factor 9a

29

What hereditable condition causes prolonged APTT?

Hameophillia

30

What switches of thrombin?

Anti thrombin III

31

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

Protein C
Protein S