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MCD Y2: Haematology > Haemostasis > Flashcards

Haemostasis Flashcards

1
Q

Summarise the mechanisms of normal haemostasis

A

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

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2
Q

What clotting factors are synthesised by the vascular endothelium?

A

PGI2
Thrombomodulin
vWF
Plasminogen activators

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3
Q

How many platelets are produced by each megakaryocte?

A

about 4000

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4
Q

What is the lifespan of a platelet?

A

10 days

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5
Q

Where are 1/3 of platelets stored?

A

Spleen

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6
Q

What receptors are present on the platelet surface?

A

Thrombin

Glycoprotein

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7
Q

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

A

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

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8
Q

Describe the cytoskeleton of platelets

A

Actomyosin, microtubules

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9
Q

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

A

Direct binding to Gp1a

Binding to Gp1b which binds vWF

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10
Q

What happens when a platelet adheres to the endothelium?

A

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

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11
Q

How are the platelets aggregated when the plug forms?

A

Fibrinogen AND Ca++ connects platelets via GpIIa and GpIIb

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12
Q

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

A
  1. Membrane phospholipid converted to arachdionic acid via phospholipase
  2. Conversion to endoperoxidases (eg PGH2) via COX1
  3. Converted to PGI2/ TXA2 via synthetases
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13
Q

Where are most coagulation factors synthesised?

A

Liver

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14
Q

Where is vWF synthesised?

A

Vascular endothelium

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15
Q

What clotting factors are synthesised in megakaryocytes?

A

Factor V and vWF

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16
Q

Recall the successive activation of factors in the coagulation cascade

A 
12
11
9
10
prothrombin
fibrinogen
17
Q

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

A

9 (8a)

10 (calcium)

18
Q

Recall the mechanism of fibrinolysis

A

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

19
Q

What is an elevated FDP indicative of?

A

DIC

20
Q

What are the main inhibitory mechanisms in the clotting cascade?

A

Antithrombin III

Protein C with protein S

21
Q

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

A

9a
10a
thrombin

22
Q

What is the other name for factor IIa?

A

Thrombin

23
Q

What is a normal platelet count?

A

150-400 x 10^9

24
Q

What platelet count would cause common spontaneous bleeding?

A

<40 x 10^9

25
Q

Recall 3 clinical features of AI thrombocytopenia

A

Purpura
Multiple bruises
Eccymoses

26
Q

What are the 3 main tests for coagulation?

A

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

27
Q

Describe the function and use of APTT

A

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

28
Q

What abnormalities can be detected by PT

A

Extrinsic and common pathway faults

29
Q

What test is used to test for haemophilia?

A

TCT

30
Q

What coagulation test is used to monitor heparin therapy?

A

APTT

31
Q

What coagulation test is used to monitor warfarin therapy?

A

PT

32
Q

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

A

Vit K epoxide

clotting factors are reacted with vit K in liver

33
Q

Recall the mechanism of action of heparin

A

Accelerates antithrombin action

34
Q

Recall the 3 classes of antiplatelet agent

A

ADP receptor agonists
COX antagonist
GpIIa/GpIIb antagonists

MCD Y2: Haematology (11 decks)

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