Haemostasis Flashcards Preview

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Flashcards in Haemostasis Deck (34)
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1

Summarise the mechanisms of normal haemostasis

Vessel constriction
Platelet plug formation
Plug stabilisation with fibrin
Dissolution of clot

2

What clotting factors are synthesised by the vascular endothelium?

PGI2
Thrombomodulin
vWF
Plasminogen activators

3

How many platelets are produced by each megakaryocte?

about 4000

4

What is the lifespan of a platelet?

10 days

5

Where are 1/3 of platelets stored?

Spleen

6

What receptors are present on the platelet surface?

Thrombin
Glycoprotein

7

Recall the types of granule present in platelets and the composition of each type

Dense: ADP, ATP, serotonin, Ca++
Alpha: vWF and Factor V
Glycogen

8

Describe the cytoskeleton of platelets

Actomyosin, microtubules

9

Recall the 2 mechanisms by which a platelet can adhere to the endothelium

Direct binding to Gp1a
Binding to Gp1b which binds vWF

10

What happens when a platelet adheres to the endothelium?


GpIIa and GpIIb activated on platelet surface
ADP and TXA2 are released
Thrombin activates coagulation

11

How are the platelets aggregated when the plug forms?

Fibrinogen AND Ca++ connects platelets via GpIIa and GpIIb

12

Recall the mechanism of PG metabolism that leads to PGI2 and TXA2 production

1. Membrane phospholipid converted to arachdionic acid via phospholipase
2. Conversion to endoperoxidases (eg PGH2) via COX1
3. Converted to PGI2/ TXA2 via synthetases

13

Where are most coagulation factors synthesised?

Liver

14

Where is vWF synthesised?

Vascular endothelium

15

What clotting factors are synthesised in megakaryocytes?

Factor V and vWF

16

Recall the successive activation of factors in the coagulation cascade

12
11
9
10
prothrombin
fibrinogen

17

Which coagulation factors are activated by tissue factor? What is the cofactor in each case?

9 (8a)
10 (calcium)

18

Recall the mechanism of fibrinolysis

Plasminogen and tPA simultaneously encounter a fibrin clot
Plasminogen converted to plasmin
Plasmin degrades fibrin producing FDP

19

What is an elevated FDP indicative of?

DIC

20

What are the main inhibitory mechanisms in the clotting cascade?

Antithrombin III
Protein C with protein S

21

Where in the coagulation cascade does anti-thrombin have inhibitory action?

9a
10a
thrombin

22

What is the other name for factor IIa?

Thrombin

23

What is a normal platelet count?

150-400 x 10^9

24

What platelet count would cause common spontaneous bleeding?

<40 x 10^9

25

Recall 3 clinical features of AI thrombocytopenia

Purpura
Multiple bruises
Eccymoses

26

What are the 3 main tests for coagulation?

APTT (activated partial thromboplastin time)
PT (prothrombin time)
TCT (thrombin clotting time)

27

Describe the function and use of APTT

Initiates coagulation through factor XII therefore detects abnormalities in intrinsic and common pathways

28

What abnormalities can be detected by PT

Extrinsic and common pathway faults

29

What test is used to test for haemophilia?

TCT

30

What coagulation test is used to monitor heparin therapy?

APTT

31

What coagulation test is used to monitor warfarin therapy?

PT

32

Which enzyme is inhibited by warfarin and why does this inhibit coagulant?

Vit K epoxide
clotting factors are reacted with vit K in liver

33

Recall the mechanism of action of heparin

Accelerates antithrombin action

34

Recall the 3 classes of antiplatelet agent

ADP receptor agonists
COX antagonist
GpIIa/GpIIb antagonists