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CR 2 > Haemostasis intro > Flashcards

Haemostasis intro Flashcards

1
Q

What is primary haemostasis?

A

Platelets and vasoconstriction for platelet plug

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2
Q

What cells do platelets develop from

A

Megakaryocytes

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3
Q

Diameter of platelets?

A

1-4um

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4
Q

Define thrombocytopenia

A

Low platelet count

<150*10^9

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5
Q

Normal platelet count?

A

150-400*10^9

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6
Q

Define thrombocytosis

A

> 450*10^9

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7
Q

Function of the various proteins found inside platelets

A

Surface proteins: help platelets stick to breaks in vessel wall and to eachother
Granule proteins: help make plug
Contained proteins: Allow platelet to change shape

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8
Q

What causes platelet migration initially?

A

The collagen that is exposed when blood vessel breaks causes platelet migration and structural change

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9
Q

Describe structural changes that occur when platelets form initial clot

A 
Originally flat (look like plates)
Then extend long filaments and filaments from different platelets interlock to make a clot
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10
Q

What is secondary haemostasis

A

The use of fibrin to stabilise platelet clot

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11
Q

What is the first thing to trigger coagulation cascade

A

Tissue factor

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12
Q

Where is tissue factor found?

A

Outside of endothelium

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13
Q

When does extrinsic pathway of coagulation cascade occur?

A

When a vessel is injured

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14
Q

Describe the extrinsic pathway (excluding common pathway)

A
  • Factor VII is converted to VIIa via tissue factor

- VIIa converts factor X to factor Xa complex (complex including factor Xa, calcium and more)

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15
Q

Describe the common pathway of coagulation cascade?

A
  • Factor Xa converts prothrombin to thrombin
  • Thrombin converts fibrinogen to fibrin
  • Fibrin forms stable clot
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16
Q

What is the rate limiting step in extrinsic pathway

A

X->Xa

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17
Q

What measurment is used to test extrinsic and common pathways?

A

Prothrombin time

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18
Q

When does the intrinsic pathway of coagulation cascade occur?

A

occurs without injury to vessels

19
Q

Describe the instrinsic pathway exclusing the common pathway

A

Factor XII–> Factor XIIa
XIIa converts XI to XIa
XIa converts IX to IXa
IXa converts X to Xa

20
Q

What tests the intrinsic and common pathway

A

Activated partial prothrombin time

21
Q

Describe bleeding time test

A

Shallow incision made on underside of forearm
Time taken for bleeding to fully stop in measured
Normal is 3-10 minutes

22
Q

What is INR?

A

Derived from prothrombin time

Healthy is 0.8-1.2

23
Q

What is the INR to aim for in patients taking warfarin and heparin

A

2.0-3.0

24
Q

What type of feedback loop regulates thrombin production

A

Positive feedback

25
Q

What activates the positive feedback loop

A

Release of tissue factor causes small amount of thrombin to be produced
Thrombin activates feedback loop

26
Q

What three factors does the thrombin made by tissue factor activate in the amplification phase?

A

Va
VIIIa
XIa

27
Q

How does factors Va, VIIa and XIa produce more thrombin

A

VIIa and XIa combine to increase conversion of X to Xa
Va increases efficiency of Xa
Therefore more thrombin made by coagulation cascade

28
Q

How does fibrin make the clot more stable

A

Polymerases inside the clot.

29
Q

How does factor XIIIa increase clot stability

A

Increased crosslinking

30
Q

What is the main enzyme responsible for clot removal

A

plasmin

31
Q

How does plasmin circulate in the blood

A

Plasminogen

32
Q

What keeps plasminogen inactive within the clot

A

Alpha-2 antiplasmin

33
Q

What enzyme catalyses plasminogen–> plasmin

A

Tissue plasminogen activator

34
Q

Describe process by which tpa causes clot breakdown

A

Tpa production is suppressed at injury site
Once healed tpa is released
this converts plasminogen to plasmin
clot breakdown

35
Q

What product of clot breakdown can be measured to test for people with DVT?

A

D-dimer

36
Q

Deficiency of which factor causes haemophillia A?

A

Factor VIII

37
Q

Describe haemophillia A

A

Factor VIII levels low

Reduces effectiveness of positive feedback loop manufactoring thrombin

38
Q

Deficiency of which factor causes haemophillia b?

A

Factor IX

39
Q

Describe haemophillia B?

A

Deficiency of factor IX

IXa is essential component o tenase complex which converts X to Xa

40
Q

What is released by platelets to aid vasoconstriction in formation of primary haemostatic plug

A

Serotonin

41
Q

What is released by platelets to cause aggregation

A

TXA2

ADP

42
Q

Arer there more erythrocytes or platelets in a clot

A

Erythrocytes

43
Q

What does tissue plasminogen activator prevent?

A

Clot extending too far along blood vessel into health tissue

CR 2 (33 decks)

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