Haemostasis, Thrombosis and Embolism Flashcards
(116 cards)
1
Q
What does haemostasis do?
A
Stop blood
2
Q
What does successful haemostasis depend on?
A
The vessel wall
Platelets
Coagulation system
Fibrinolytic system
3
Q
What does the coagulation system do?
A
Promotes the formation of a solid mass of blood
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
5
Q
Why are tight control mechanisms required?
A
To ensure that there’s no over- or under- activity
6
Q
How to blood vessels contribute to haemostasis?
A
They constrict to reduce blood loss
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
8
Q
Which vessels can contribute to reducing the amount of blood loss?
A
All
9
Q
What are platelets?
A
Subcellular fragments
10
Q
What are platelets derived from?
A
Cells in the bone marrow called megakaryocytes
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.
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
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
14
Q
Why is PF3 important in coagulation?
A
It activates the cascade mechanism aiming to produce fibrin
15
Q
What happens to platelets after aggregation?
A
They coalesce
16
Q
How does coagulation occur?
A
As a cascade, with amplification
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
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
19
Q
How can the coagulation cascade be useful therapeutically?
A
It can be manipulated to have the desired effect
20
Q
How much blood is needed to produce enough thrombin to convert all the fibrinogen in the body to fibrin?
A
1ml
21
Q
Why is tight regulation of the clotting cascade required?
A
If left unchecked, the blood would go solid
22
Q
What is needed to regulate coagulation?
A
A balance of procoagulant and anticoagulant forces
23
Q
What controls coagulation?
A
Thrombin inhibitors
Fibrinolysis
Endothelium
24
Q
What are thrombin inhibitors?
A
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
