Haemostasis

Question 1

Summarise the mechanisms of normal haemostasis

Answer 1

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

Question 2

What clotting factors are synthesised by the vascular endothelium?

Answer 2

PGI2
Thrombomodulin
vWF
Plasminogen activators

Question 3

How many platelets are produced by each megakaryocte?

Answer 3

about 4000

Question 4

What is the lifespan of a platelet?

Answer 4

10 days

Question 5

Where are 1/3 of platelets stored?

Answer 5

Spleen

Question 6

What receptors are present on the platelet surface?

Answer 6

Thrombin

Glycoprotein

Question 7

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

Answer 7

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

Question 8

Describe the cytoskeleton of platelets

Answer 8

Actomyosin, microtubules

Question 9

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

Answer 9

Direct binding to Gp1a

Binding to Gp1b which binds vWF

Question 10

What happens when a platelet adheres to the endothelium?

Answer 10

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

Question 11

How are the platelets aggregated when the plug forms?

Answer 11

Fibrinogen AND Ca++ connects platelets via GpIIa and GpIIb

Question 12

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

Answer 12

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

Question 13

Where are most coagulation factors synthesised?

Answer 13

Liver

Question 14

Where is vWF synthesised?

Answer 14

Vascular endothelium

Question 15

What clotting factors are synthesised in megakaryocytes?

Answer 15

Factor V and vWF

Question 16

Recall the successive activation of factors in the coagulation cascade

Answer 16

12
11
9
10
prothrombin
fibrinogen

Question 17

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

Answer 17

9 (8a)

10 (calcium)

Question 18

Recall the mechanism of fibrinolysis

Answer 18

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

Question 19

What is an elevated FDP indicative of?

Answer 19

DIC

Question 20

What are the main inhibitory mechanisms in the clotting cascade?

Answer 20

Antithrombin III

Protein C with protein S

Question 21

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

Answer 21

9a
10a
thrombin

Question 22

What is the other name for factor IIa?

Answer 22

Thrombin

Question 23

What is a normal platelet count?

Answer 23

150-400 x 10^9

Question 24

What platelet count would cause common spontaneous bleeding?

Answer 24

<40 x 10^9

Question 25

Recall 3 clinical features of AI thrombocytopenia

Answer 25

Purpura Multiple bruises Eccymoses

Question 26

What are the 3 main tests for coagulation?

Answer 26

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

Question 27

Describe the function and use of APTT

Answer 27

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

Question 28

What abnormalities can be detected by PT

Answer 28

Extrinsic and common pathway faults

Question 29

What test is used to test for haemophilia?

Answer 29

TCT

Question 30

What coagulation test is used to monitor heparin therapy?

Answer 30

APTT

Question 31

What coagulation test is used to monitor warfarin therapy?

Answer 31

PT

Question 32

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

Answer 32

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

Question 33

Recall the mechanism of action of heparin

Answer 33

Accelerates antithrombin action

Question 34

Recall the 3 classes of antiplatelet agent

Answer 34

ADP receptor agonists COX antagonist GpIIa/GpIIb antagonists