Haemostasis, Thrombosis and Embolism Flashcards Preview

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

Flashcards in Haemostasis, Thrombosis and Embolism Deck (116):
1

What does haemostasis do?

Stop blood

2

What does successful haemostasis depend on?

The vessel wall
Platelets 
Coagulation system 
Fibrinolytic system

3

What does the coagulation system do?

Promotes the formation of a solid mass of blood

4

What does the fibrinolytic system do?

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

5

Why are tight control mechanisms required?

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

6

How to blood vessels contribute to haemostasis?

They constrict to reduce blood loss

7

How does constriction of blood levels contribute to haemostasis?

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

8

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

All

9

What are platelets?

Subcellular fragments

10

What are platelets derived from?

Cells in the bone marrow called megakaryocytes

11

What to platelets do?

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

12

What is the purpose of the platelet release reaction?

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

13

What happens in the platelet release reaction?

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

14

Why is PF3 important in coagulation?

It activates the cascade mechanism aiming to produce fibrin

15

What happens to platelets after aggregation?

They coalesce

16

How does coagulation occur?

As a cascade, with amplification

17

What happens in the coagulation cascade?

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

18

What is fibrin?

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

19

How can the coagulation cascade be useful therapeutically?

It can be manipulated to have the desired effect

20

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

1ml

21

Why is tight regulation of the clotting cascade required?

If left unchecked, the blood would go solid

22

What is needed to regulate coagulation?

A balance of procoagulant and anticoagulant forces

23

What controls coagulation?

Thrombin inhibitors 
Fibrinolysis 
Endothelium

24

What are thrombin inhibitors?

Things that reduce the action of thrombin

25

Give 5 examples of thrombin inhibitors

Antithrombin III
α1 anti-trypsin 
α2 macroglobulin 
Protein C
Protein S

26

What may inherited deficiency of antithrombin III lead to?

Thrombosis

27

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

Thrombosis

28

What is fibrinolysis?

The breakdown of fibrin

29

How is plasminogen converted to plasmin?

By plasminogen activators

30

Where is fibrinolytic therapy used?

To enhance the fibrinolytic mechanism, getting stuff to break down

31

Give 2 examples of fibrinolytic factors

Streptokinase 
tPA

32

What anti-coagulation mechanisms does endothelium have?

Plasminogen activators
Prostacyclin
Nitric oxide
Thrombomodulin

33

What is thrombosis?

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

34

Why can thrombosis be hard to identify?

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

35

What can thrombosis occur due to?

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

36

What abnormalities in the vessel wall can cause thrombosis?

Atheroma 
Direct injury
Inflammation

37

What abnormalities in blood flow can cause thrombosis?

Stagnation 
Turbulence

38

What abnormalities of blood components can lead to thrombosis?

Alteration of coagubility of blood

39

What can alter the coagubility of blood?

Smokers 
Post-partum 
Post-op

40

Why is the coagubility of blood altered post-partum?

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

41

How to arterial thrombi appear?

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

42

What produces lines of Zahn?

The tendency to get lying down of layers

43

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

Arterial have lower cell content, but more fibrin

44

What does the appearance of arterial thrombi depend on?

Particular constituents of blood

45

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

Where the artery has swollen and bulged out

46

How do venous thrombi appear?

Soft
Gelatinous 
Deep red
Higher cell content

47

What are the potential outcomes of thrombosis?

Lysis 
Propagation 
Organisation 
Recanalistion
Embolism

48

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

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

49

What happens in lysis of thrombi?

Complete dissolution

50

When does lysis of thrombi occur?

When the fibrinolytic system is active

51

What happens when lysis of thrombi occur?

Blood flow is re-established

52

When is lysis of thrombi likely?

When thrombi are small

53

What is propagation of thrombi?

The progressive spread of thrombosis

54

What happens in propagation of thrombi?

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

55

What is the result in propagation of thrombi?

The thrombi spreads distally in arteries, and proximally in veins

56

What happens when you get a thrombus in a vein?

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

What is the problem with thrombi in veins?

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

What happens to the size of the thrombus in propagation?

It gets wider, not longer

59

What can happen to a propagated thrombus?

It can become detached, forming an embolus

60

What happens in organisation of thrombi?

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

61

What does organisation of thrombi lead to?

The formation of scar tissue

62

What is the problem with organisation of thrombi?

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

63

What happens in recanalisation of thrombi?

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

64

What is the result of recanalisation?

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

65

What happens in embolism?

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

66

When does a pulmonary embolism occur?

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

67

What does arterial thrombosis lead to?

Ischaemia and infarction

68

Why does arterial thrombosis lead to ischaemia and infarction?

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

69

What does the final outcome of arterial thrombosis depend on?

The exact site 
If collateral circulation has developed

70

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

When there’s been a progressive increase in arterial disease

71

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

The outcome of ischaemia and infarction

72

What is the problem with functional end arteries?

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

73

What does venous thrombosis lead to?

Congestion and oedema

74

Why do venous thrombosis lead to congestion and oedema?

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

75

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

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

76

What happens if pressure builds reaching arterial pressure?

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

77

What is an embolism?

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

78

What types of emboli are there?

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

79

What % of emboli are thrombo-emboli?

>90%

80

How much air is needed to give an air embolism?

About 150ml

81

When can a large amount of air enter the bloodstream?

If the jugular is cut

82

What can a jugular cut lead to?

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

83

When do amniotic fluid embolisms occur?

In illegal terminations of pregnancies
Can also occur after normal pregnancies or miscarriage

84

When do nitrogen emboli occur?

When you come up to quickly after diving

85

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

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

86

How can medical equipment cause an embolus?

Can break off, circulate and get stuck somewhere

87

What happens when you block an arterial channel?

There is always a risk damage

88

What happens to thrombo-emboli from systemic veins?

They pass to the lungs, causing pulmonary emboli

89

What happens to thrombo-emboli from the heart?

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

90

What happens to thrombo-emboli from atheromatous carotid arteries?

They pass to the brain

91

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

They pass to the arteries of the legs

92

What are the predisposing factors to a deep vein thrombosis?

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

93

What can cause the loss of the calf pump

Immobility/bed rest
Any long journey where legs are compressed

94

What causes hypercoagubility?

Pregnancy Post-partum
Oral contraceptive
Severe burns

95

Why does the oral contraceptive cause hypercoagubility?

Oestrogen affects coagulation

96

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

They must be identified and offered prophylaxis

97

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

Sub-cutaneous heparin

98

How can DVT be prevented during surgery?

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

How are DVTs treated?

IV heparin
Warfarin

100

What does IV heparin do?

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

101

What does warfarin do?

Inhibits certain coagulation factors
Reduces opportunity for thrombus to get bigger

102

What constitutes a massive pulmonary embolism?

>60% reduction in blood flow

103

What is the outcome of a massive PE?

It’s rapidly fatal

104

What constitutes a major PE?

When medium sized vessels are blocked

105

What are the symptoms of a major PE?

Shortness of breath
May cough
Blood stained sputum

106

What constitutes a minor PE?

When a small peripheral pulmonary artery is blocked

107

What are the symptoms of a minor PE?

May be asymptomatic 
Present with minor shortness of breath

108

Who do minor PE’s occur particularly in?

Young, fit people

109

When may minor PE’s have an impact?

If already have CVS or pulmonary problems

110

What do recurrent minor PE’s lead to?

Pulmonary hypertension

111

What does cerebral embolisms occur with?

Carotid atheroma

112

What happens in a cerebral embolism?

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

113

What gives a warning of a cerebral embolism?

Where really tiny bits of thrombus produces a transient ischaemic attack

114

What must be done if someone has a TIA?

They must be anti-coagulated to reduce risk of stroke
May have carotid surgery

115

When do fat embolisms occur?

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

116

How can fat embolisms present?

Profound neurological problems
Confusion