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ESA 2- Mechanisms of Disease > Haemostasis, Thrombosis and Embolism > Flashcards

Haemostasis, Thrombosis and Embolism Flashcards

1
Q

What does haemostasis do?

A

Stop blood

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2
Q

What does successful haemostasis depend on?

A

The vessel wall
Platelets
Coagulation system
Fibrinolytic system

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3
Q

What does the coagulation system do?

A

Promotes the formation of a solid mass of blood

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4
Q

What does the fibrinolytic system do?

A

Acts against the coagulation system to make sure that you don’t end up with too much blood clotting

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5
Q

Why are tight control mechanisms required?

A

To ensure that there’s no over- or under- activity

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6
Q

How to blood vessels contribute to haemostasis?

A

They constrict to reduce blood loss

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7
Q

How does constriction of blood levels contribute to haemostasis?

A

If the hole is made smaller, they reduce the volume of blood coming out

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8
Q

Which vessels can contribute to reducing the amount of blood loss?

A

All

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9
Q

What are platelets?

A

Subcellular fragments

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10
Q

What are platelets derived from?

A

Cells in the bone marrow called megakaryocytes

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11
Q

What to platelets do?

A

Adhere to one another and to the damaged vessel wall, promoting the coagulation of blood.
They participate in the platelet release reaction.

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12
Q

What is the purpose of the platelet release reaction?

A

Once the platelets are stuck, they release certain molecules that are helpful in forming and expanding the platelet plug, and activating the coagulation system

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13
Q

What happens in the platelet release reaction?

A

ATP is converted to ADP (and therefore this is an energy dependant reaction). The ADP, along with thromboxane A2, cause platelet aggregation. 5HT and platelet factor 3 are also released

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14
Q

Why is PF3 important in coagulation?

A

It activates the cascade mechanism aiming to produce fibrin

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15
Q

What happens to platelets after aggregation?

A

They coalesce

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16
Q

How does coagulation occur?

A

As a cascade, with amplification

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17
Q

What happens in the coagulation cascade?

A

A series of inactive components are converted to active components.
Prothrombin is converted to thrombin, which is then used to convert fibrinogen to fibrin

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18
Q

What is fibrin?

A

A solid mass that’s formed at the end of coagulation cascade, that has a major contribution to the process of haemostasis

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19
Q

How can the coagulation cascade be useful therapeutically?

A

It can be manipulated to have the desired effect

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20
Q

How much blood is needed to produce enough thrombin to convert all the fibrinogen in the body to fibrin?

A

1ml

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21
Q

Why is tight regulation of the clotting cascade required?

A

If left unchecked, the blood would go solid

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22
Q

What is needed to regulate coagulation?

A

A balance of procoagulant and anticoagulant forces

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23
Q

What controls coagulation?

A

Thrombin inhibitors
Fibrinolysis
Endothelium

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24
Q

What are thrombin inhibitors?

A

Things that reduce the action of thrombin

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25
Q

Give 5 examples of thrombin inhibitors

A 
Antithrombin III
 α1 anti-trypsin
 α2 macroglobulin
 Protein C
 Protein S
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26
Q

What may inherited deficiency of antithrombin III lead to?

A

Thrombosis

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27
Q

What may inherited deficiency of protein C and S lead to?

A

Thrombosis

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28
Q

What is fibrinolysis?

A

The breakdown of fibrin

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29
Q

How is plasminogen converted to plasmin?

A

By plasminogen activators

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30
Q

Where is fibrinolytic therapy used?

A

To enhance the fibrinolytic mechanism, getting stuff to break down

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31
Q

Give 2 examples of fibrinolytic factors

A

Streptokinase

tPA

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32
Q

What anti-coagulation mechanisms does endothelium have?

A

Plasminogen activators
Prostacyclin
Nitric oxide
Thrombomodulin

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33
Q

What is thrombosis?

A

The formation of a solid mass of blood within the circulatory system during life

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34
Q

Why can thrombosis be hard to identify?

A

Can sometimes be hard to tell if thrombus formed before or after death

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35
Q

What can thrombosis occur due to?

A

Abnormalities in vessel wall
Abnormalities in blood flow
Abnormalities of blood components

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36
Q

What abnormalities in the vessel wall can cause thrombosis?

A

Atheroma
Direct injury
Inflammation

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37
Q

What abnormalities in blood flow can cause thrombosis?

A

Stagnation

Turbulence

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38
Q

What abnormalities of blood components can lead to thrombosis?

A

Alteration of coagubility of blood

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39
Q

What can alter the coagubility of blood?

A

Smokers
Post-partum
Post-op

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40
Q

Why is the coagubility of blood altered post-partum?

A

There needs to be a good haemostatic mechanism, as after a baby, there is a raw area where the placenta has come away that’s prone to haemorrhage

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41
Q

How to arterial thrombi appear?

A 
Pale
 Granular
 Lines of Zahn
 Lower cell content
 Still have residual lumen
 Curved shape on either side
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42
Q

What produces lines of Zahn?

A

The tendency to get lying down of layers

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43
Q

How does the cell content of arterial thrombi differ from arterial?

A

Arterial have lower cell content, but more fibrin

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44
Q

What does the appearance of arterial thrombi depend on?

A

Particular constituents of blood

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45
Q

Why do arterial thrombi have a curved shape on either side?

A

Where the artery has swollen and bulged out

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46
Q

How do venous thrombi appear?

A

Soft
Gelatinous
Deep red
Higher cell content

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47
Q

What are the potential outcomes of thrombosis?

A 
Lysis
 Propagation
 Organisation
 Recanalistion
 Embolism
48
Q

What is likely to be happening with regards to thrombi at all times in the body?

A

They are being formed, but get dealt with so don’t get bigger

49
Q

What happens in lysis of thrombi?

A

Complete dissolution

50
Q

When does lysis of thrombi occur?

A

When the fibrinolytic system is active

51
Q

What happens when lysis of thrombi occur?

A

Blood flow is re-established

52
Q

When is lysis of thrombi likely?

A

When thrombi are small

53
Q

What is propagation of thrombi?

A

The progressive spread of thrombosis

54
Q

What happens in propagation of thrombi?

A

It gets bigger in the direction of blood flow, so away from the starting point

55
Q

What is the result in propagation of thrombi?

A

The thrombi spreads distally in arteries, and proximally in veins

56
Q

What happens when you get a thrombus in a vein?

A

Up until the next vein joints, there is stagnation of the blood- no movement, as there is a blockage, so nothing pushing it. When you get the next branch coming in, there is turbulent flow, due to there being no normal flow behind, so there if formation of a new thrombus. This starts a chain reaction, giving an increase in size of thrombus

57
Q

What is the problem with thrombi in veins?

A

As you move back towards the heart, the veins get bigger, so ones that are blocked get bigger, and so does the thrombus. This means that you can get a thrombus that occludes the femoral veins

58
Q

What happens to the size of the thrombus in propagation?

A

It gets wider, not longer

59
Q

What can happen to a propagated thrombus?

A

It can become detached, forming an embolus

60
Q

What happens in organisation of thrombi?

A

Reparative process, where you get an ingrowth of fibroblasts and capillaries

61
Q

What does organisation of thrombi lead to?

A

The formation of scar tissue

62
Q

What is the problem with organisation of thrombi?

A

The lumen continues to be obstructed, and there is no restoration of flow

63
Q

What happens in recanalisation of thrombi?

A

Blood flow is re-established, but incompletely, as one or more channels is formed through organising thrombus

64
Q

What is the result of recanalisation?

A

Means you don’t get the same level of flow as you would through normal lumen

65
Q

What happens in embolism?

A

Part of the thrombus breaks off, travels through blood stream and lodges at a distant site

66
Q

When does a pulmonary embolism occur?

A

When a thrombus starts in deep veins, breaks off, gets to heart and lodges in lungs

67
Q

What does arterial thrombosis lead to?

A

Ischaemia and infarction

68
Q

Why does arterial thrombosis lead to ischaemia and infarction?

A

Because there is reduced flow to artery, so eventually the tissue supplied by that artery will die

69
Q

What does the final outcome of arterial thrombosis depend on?

A

The exact site

If collateral circulation has developed

70
Q

When is the development of collateral circulation more likely to have occurred?

A

When there’s been a progressive increase in arterial disease

71
Q

What is more likely with a sudden occlusion of a previously healthy artery?

A

The outcome of ischaemia and infarction

72
Q

What is the problem with functional end arteries?

A

They have no collateral circulation, so if they get blocked, theres nothing else that can supply blood

73
Q

What does venous thrombosis lead to?

A

Congestion and oedema

74
Q

Why do venous thrombosis lead to congestion and oedema?

A

Because they’re unable to drain the tissue, so there’s an increase in hydrostatic pressure in the vessels, eventually producing stagnant flow

75
Q

What must happen before veins can push fluid out of them?

A

There must be sufficient hydrostatic pressure for blood to get to tissue via veins

76
Q

What happens if pressure builds reaching arterial pressure?

A

There will be no flow, and therefore ischaemia and infarction will occur

77
Q

What is an embolism?

A

A blockage of a blood vessel by a solid, liquid or gas at a site distant from it’s origin

78
Q

What types of emboli are there?

A 
Thrombo-emboli
 Air
 Amniotic fluid
 Nitrogen
 Medical equipment
 Tumour cells
 Cholesterol
79
Q

What % of emboli are thrombo-emboli?

A

> 90%

80
Q

How much air is needed to give an air embolism?

A

About 150ml

81
Q

When can a large amount of air enter the bloodstream?

A

If the jugular is cut

82
Q

What can a jugular cut lead to?

A

It can produce froth, which cannot be pumped around the circulatory system

83
Q

When do amniotic fluid embolisms occur?

A

In illegal terminations of pregnancies

Can also occur after normal pregnancies or miscarriage

84
Q

When do nitrogen emboli occur?

A

When you come up to quickly after diving

85
Q

Why do nitrogen emboli occur when you come up too quickly after diving

A

Because the nitrogen comes out of the blood, giving gaseous nitrogen which can get stuck

86
Q

How can medical equipment cause an embolus?

A

Can break off, circulate and get stuck somewhere

87
Q

What happens when you block an arterial channel?

A

There is always a risk damage

88
Q

What happens to thrombo-emboli from systemic veins?

A

They pass to the lungs, causing pulmonary emboli

89
Q

What happens to thrombo-emboli from the heart?

A

They pass via the aorta to renal, mesenteric, or any other artery

90
Q

What happens to thrombo-emboli from atheromatous carotid arteries?

A

They pass to the brain

91
Q

What happens to thrombi-emboli from an atheromatous abdominal aorta?

A

They pass to the arteries of the legs

92
Q

What are the predisposing factors to a deep vein thrombosis?

A

Loosing the calf pump, so if legs aren’t moving normally
Things causing hypercoagubility
Cardiac failure
Disseminated cancer

93
Q

What can cause the loss of the calf pump

A

Immobility/bed rest

Any long journey where legs are compressed

94
Q

What causes hypercoagubility?

A

Pregnancy Post-partum
Oral contraceptive
Severe burns

95
Q

Why does the oral contraceptive cause hypercoagubility?

A

Oestrogen affects coagulation

96
Q

What must happen if a patient is at high risk of DVT?

A

They must be identified and offered prophylaxis

97
Q

What prophylaxis might a patient at high risk of DVT be given?

A

Sub-cutaneous heparin

98
Q

How can DVT be prevented during surgery?

A

Using leg compression, which mimics the muscular pump of the calves, expelling blood from the venous circulation so you don’t get a stagnation effect

99
Q

How are DVTs treated?

A

IV heparin

Warfarin

100
Q

What does IV heparin do?

A

Prevents the thrombus from getting bigger, but doesn’t dissolve it

101
Q

What does warfarin do?

A

Inhibits certain coagulation factors

Reduces opportunity for thrombus to get bigger

102
Q

What constitutes a massive pulmonary embolism?

A

> 60% reduction in blood flow

103
Q

What is the outcome of a massive PE?

A

It’s rapidly fatal

104
Q

What constitutes a major PE?

A

When medium sized vessels are blocked

105
Q

What are the symptoms of a major PE?

A

Shortness of breath
May cough
Blood stained sputum

106
Q

What constitutes a minor PE?

A

When a small peripheral pulmonary artery is blocked

107
Q

What are the symptoms of a minor PE?

A

May be asymptomatic

Present with minor shortness of breath

108
Q

Who do minor PE’s occur particularly in?

A

Young, fit people

109
Q

When may minor PE’s have an impact?

A

If already have CVS or pulmonary problems

110
Q

What do recurrent minor PE’s lead to?

A

Pulmonary hypertension

111
Q

What does cerebral embolisms occur with?

A

Carotid atheroma

112
Q

What happens in a cerebral embolism?

A

Piece of thrombus formed on atheromatous plaque moves up into cerebral circulation

113
Q

What gives a warning of a cerebral embolism?

A

Where really tiny bits of thrombus produces a transient ischaemic attack

114
Q

What must be done if someone has a TIA?

A

They must be anti-coagulated to reduce risk of stroke

May have carotid surgery

115
Q

When do fat embolisms occur?

A

When a long bone gets broken, and some of the fat (sometimes bone marrow) gets into the circulation

116
Q

How can fat embolisms present?

A

Profound neurological problems

Confusion

ESA 2- Mechanisms of Disease (11 decks)

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