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ESA 2- Cardiovascular System > Special Circulations > Flashcards

Special Circulations Flashcards

1
Q

What circulations do the lungs have?

A

Bronchial circulation and Pulmonary circulation

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2
Q

What is the bronchial circulation part of?

A

The systemic circulation

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3
Q

What is the purpose of the bronchial circulation?

A

It meets the metabolic and oxygen requirements of lungs

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4
Q

What does the bronchial circulation ensure?

A

That those parts that are not readily perfused with oxygen are close to an oxygen supply

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5
Q

How is the pulmonary circulation related to the systemic circulation?

A

It is in series

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6
Q

What is the purpose of the pulmonary circulation?

A

It supplies blood to the alveoli, which is required for gas exchange

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7
Q

What gas exchange needs to occur at the lungs?

A

Needs to oxygenate blood, and allow for removal of carbon dioxide

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8
Q

What must the pulmonary circulation accept?

A

The entire cardiac output

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9
Q

Are the equal amounts of blood in the pulmonary and systemic circulations?

A

No

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10
Q

What is cardiac output at rest?

A

~5l/min

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11
Q

What does cardiac output have the ability to do?

A

Increase when exercising

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12
Q

What is the maximum cardiac output?

A

~20-25l/min

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13
Q

Is flow the same in systemic and pulmonary circulations?

A

Yes

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14
Q

How does the pulmonary circulation differ from the systemic?

A

It works with a much lower pressure and resistance

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15
Q

What is the pressure in the right ventricle?

A

15–30mmHg in systole

0-8mmHg in diastole

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16
Q

What is the pressure in the pulmonary artery?

A

15-30mmHg systole

4-12mmHg diastolic

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17
Q

Why is pulmonary artery pressure higher in diastole than right ventricle?

A

Due to elastic recoil and closure of valve

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18
Q

What is the pressure in the left atrium?

A

1-10mmHg

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19
Q

Why is left atrial pressure a bit higher than right atrial pressure?

A

Because pulmonary circulation is at low resistance, so you don;t get as much of a drop in pressure

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20
Q

How does the pressure of the left ventricle differ from the right?

A

It is higher

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21
Q

Why is the pressure in the left ventricle higher than in the right ventricle?

A

Because the wall of the left ventricle is much thicker so it’s able to squeeze the blood around at a higher pressure

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22
Q

What is the pressure in the aorta?

A

100-140mmHg systolic

60-90mmHg diastolic

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23
Q

Why is the pressure high in the aorta?

A

Because the wall is thicker

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24
Q

What is the pressure in the right atrium?

A

0-8mmHg

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25
Q

Why is the pressure in the RA and RV the same during diastole?

A

Because during diastole, the tricuspid valve is open, and so RA and RV are continuous

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26
Q

What happens to the right ventricles in systole?

A

It contracts, and so pressure goes up

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27
Q

What are the features of the pulmonary circulation?

A

Low pressure

Low resistance

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28
Q

What is the mean arterial pressure in the pulmonary circulation?

A

12-15mmHg

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29
Q

What is the mean capillary pressure in the pulmonary circulation?

A

9-12mmHg

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30
Q

What is the mean venous pressure in the pulmonary circulation?

A

5mmHg

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31
Q

Describe the vessels in the pulmonary circulation

A

Short, wide

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32
Q

What is the result of the pulmonary circulation having lots of capillaries?

A

There are many parallel elements, because there is lots of branching. This leads to resistors in parallel, and therefore lower resistance

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33
Q

How do the arterioles in the pulmonary circulation differ from those in the systemic?

A

They have relatively little smooth muscle

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34
Q

What adaptations does the pulmonary circulation have to promote efficient gas exchange?

A

Very high density of capillaries in alveoli wall

Short diffusion distance

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35
Q

What is the result of the very high density of capillaries?

A

Large capillary surface area

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36
Q

What separates the gas phase from the plasma in the pulmonary circulation?

A

A very thin layer of tissue

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37
Q

What is the combined endothelium and epithelium thickness?

A

~0.3µm

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38
Q

Why do pressures need to be low in the pulmonary circulation?

A

Because of the very short diffusion distance- if the pressure gets too high, can rupture the membrane

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39
Q

What do the adaptations of the pulmonary circulation produce?

A

A high oxygen and carbon dioxide transport capacity

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40
Q

What needs to be matched for efficient oxygenation?

A

Ventilation of alveoli (V) with perfusion of alveoli (Q)

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41
Q

What is the optional V/Q ratio?

A

0.8

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42
Q

What determines perfusion?

A

Cardiac output

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43
Q

What determines ventilation?

A

Amount you breath

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44
Q

What does maintaining the optimal V/Q ratio require?

A

Diverting blood from alveoli that are not well ventilated

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45
Q

What ensures the optimal V/Q ratio?

A

Hypoxic pulmonary vasoconstriction

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46
Q

What is hypoxic pulmonary vasoconstriction important for?

A

Regulating pulmonary vascular tone

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47
Q

What does alveolar hypoxia result in?

A

Vasoconstriction of pulmonary vessels

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48
Q

What is the result of hypoxic pulmonary vasoconstriction?

A

Poorly ventilated alveoli are less well perfuse, and so deoxygenated blood is not returning to the left side of the heart, which helps optimise gas exchange

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49
Q

How is hypoxic pulmonary vasoconstriction different to what happens in the systemic circulation?

A

It is the opposite effect

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50
Q

What can chronic hypoxic vasoconstriction cause?

A

Right ventricular failure, as it puts strain on the right side of the heart

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51
Q

Where can chronic hypoxia occur?

A

At altitude, or as a consequence of lung disease such as emphysema

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52
Q

What happens if someone is it altitude for a long time?

A

Get constriction of pulmonary vessels that increases blood pressure in the pulmonary artery

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53
Q

What can result from the increase in blood pressure in the pulmonary artery caused by prolonged altitude?

A

Pulmonary hypertension

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54
Q

What can lung disease lead to?

A

Poor ventilation, and then hypoxic vasoconstriction, leading to an increase in pulmonary artery pressure

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55
Q

What can high afterload on the right ventricle lead to?

A

Right ventricular heart failure

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56
Q

What are pulmonary vessels strongly influenced by?

A

Gravity

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57
Q

Why are pulmonary vessels strongly influenced by gravity?

A

Because they are low pressure and relatively thin vessels

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58
Q

What happens to pulmonary vessels when in the upright position?

A

There is greater hydrostatic pressure on the vessels in the lower part of the lung, and so the vessels near the base are distended

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59
Q

Why are the vessels near the base of the lung distended?

A

Due to increased hydrostatic pressure, because of column of liquid and effect of gravity

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60
Q

What happens to vessels near the apex of the lung?

A

They collapse during diastole

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61
Q

What happens to vessels at the level of the heart?

A

They are continuously patent

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62
Q

What effect does exercise have on cardiac output?

A

It increases it

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63
Q

What is the effect of exercise on the pulmonary blood flow?

A

There is a small increase in pulmonary arterial pressure

Capillary transit time reduced as blood flow increases

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64
Q

What is the effect of the increase in pulmonary arterial pressure?

A

It opens apical capillaries, and so means capillaries are better perfused so there is better matching of ventilation and perfusion

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65
Q

What is transit time?

A

The time it takes for RBCs to get through the capillaries

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66
Q

What is transit time in the pulmonary circulation at rest?

A

~1s

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67
Q

How far can transit time in the pulmonary circulation fall without compromising gas exchange?

A

~0.3s

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68
Q

Where can fluid move?

A

Through capillaries, and through capillaries into tissues

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69
Q

What determines tissue formation?

A

Starlings forces

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70
Q

What are Starlings forces?

A 
Hydrostatic pressure of blood within capillary
 Oncotic pressure (colloid osmotic pressure)
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71
Q

What does hydrostatic pressure of blood within the capillary do?

A

Pushes fluid out of capillary

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72
Q

What is oncotic pressure?

A

The pressure exerted by large molecules such as plasma proteins

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73
Q

What does oncotic pressure do?

A

Draws fluid into the capillary, because there aren’t many proteins outside

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74
Q

What is capillary hydrostatic pressure influenced by?

A

More venous pressure than arterial pressure

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75
Q

Why is capillary pressure influenced more by venous pressure?

A

Because between arteries and capillaries, there are very thick arterioles with lots of resistance, and so there is a drop of pressure across this, meaning that it’s not influenced as much by arterial pressure

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76
Q

Does hypertension result in peripheral oedema?

A

No

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77
Q

What does low capillary pressure in the lungs minimise?

A

Formation of lung lymph

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78
Q

What drives fluid into the capillary?

A

Plasma oncotic pressure

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79
Q

What drives fluid out of the capillary?

A

Interstital oncotic pressure and hydrostatic pressure

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80
Q

Why does not much lung lymph form?

A

Because filtration is roughly equal to reabsorption- they balance out well

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81
Q

Why is the minimisation of lung lymph formation important?

A

Because if you get too much fluid going out, get pulmonary oedema, which can impair gas exchange

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82
Q

How does oncotic pressure differ in the tissue fluid of the lungs compared to the periphery?

A

It is higher

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83
Q

How does the capillary hydrostatic pressure differ in the lungs compared to the periphery?

A

It is less

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84
Q

How does plasmic oncotic pressure differ in the lungs compared to the periphery?

A

It doesn’t

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85
Q

What does increased capillary pressure lead to?

A

Oedema

86
Q

Why can an increase in arterial pressure have an influence on capillary pressure in the lungs?

A

Because of the low resistance

87
Q

What prevents pulmonary oedema?

A

Low capillary pressure

88
Q

What is pulmonary capillary pressure normally?

A

9-12mmHg

89
Q

How much fluid leaves the capillaries in the lungs at normal pressure?

A

Only a small amount

90
Q

What can happen if capillary pressure in the lungs rises?

A

Can get pulmonary oedema

91
Q

How high does pressure have to rise to get pulmonary oedema?

A

If left atrial pressure rises to 20-25mmHg

92
Q

When can left atrial pressures reach levels that may give pulmonary oedema?

A

Mitral valve stenosis

Left ventricular failure

93
Q

Why does mitral valve stenosis cause an increase in left ventricular pressure?

A

More difficult for blood to move from left atrium to ventricle, so build up in left atrial pressure

94
Q

Why does an increase in left atrial pressure lead to pulmonary oedema?

A

Harder for pulmonary veins to drain

95
Q

Why does left ventricular failure cause pulmonary oedema?

A

If left ventricle can’t pump out as much, higher pressure in left ventricle, so harder for blood to move in from left atrium, so harder for pulmonary veins to drain

96
Q

What is the problem with pulmonary oedema?

A

It impairs gas exchange

97
Q

What affects pulmonary oedema?

A

Posture

98
Q

Why does posture affect pulmonary oedema?

A

Due to changes in hydrostatic pressure due to gravity

99
Q

Where does pulmonary oedema form when upright?

A

Mainly at bases

100
Q

Where does pulmonary oedema form when lying down?

A

Throughout the lungs

101
Q

What does the formation of pulmonary oedema throughout the lungs when lying down cause?

A

Symptoms that are worse at night

102
Q

How are the symptoms of pulmonary oedema relieved?

A

Diuretics, which reduce blood volume

Treat underlying cause if possible

103
Q

How much of the cardiac output does the brain receive?

A

About 15%

104
Q

Why does the brain receive so much of the cardiac output?

A

Because it has high oxygen demands

105
Q

What % of oxygen consumption does grey matter account for at rest?

A

20%

106
Q

What is important due to the high oxygen demands of the brain?

A

Must provide a secure oxygen supply

107
Q

How are the brains oxygen demands met?

A

High capillary density
High basal flow rate
High oxygen extraction

108
Q

What does high capillary density provide?

A

A large surface area for gas exchange, and a reduced diffusion distance

109
Q

What is the diffusion distance in the brain?

A

~10µm

110
Q

How does the basal flow rate in the brain compare to the rest of the body?

A

It’s about 10x the average

111
Q

How does oxygen extraction in the brain differ from the rest of the body?

A

35% above average

112
Q

Why is secure oxygen supply to the brain vital?

A

Neurones are very sensitive to hypoxia

Interruption to blood supply causes neuronal death

113
Q

How long can neurones be without oxygen?

A

Loss of consciousness occurs after a few seconds of cerebral ischaemia
Begin to get irreversible damage to neurones after about 4 minutes

114
Q

What happens when you get neuronal death?

A

Stroke

115
Q

How is a secure blood supply to the brain ensured?

A

Structurally

Functionally

116
Q

How is blood supply secured structurally?

A

Circles of Willis

117
Q

What are circles of Willis?

A

Anastomoses between basilar and internal carotid arteries

118
Q

How do circle of Willis ensure a secure blood supply?

A

Means there’s more than one route for blood to get there, so if you get a blockage in one, doesn’t prevent flow to the whole brain

119
Q

How is secure blood supply to the brain ensured functionally?

A

Myogenic autoregulation maintains perfusion during hypertension
Metabolic factors control blood flow

120
Q

What is myogenic autoregulation generated by?

A

Smooth muscle cells

121
Q

What does myogenic autoregulation respond to?

A

Changes to transmural pressure

122
Q

How does the brain respond to changes in transmural pressure?

A

High blood pressure causes vasoconstriction

Low blood pressure causes vasodilation

123
Q

What does myogenic autoregulation serve to do?

A

Maintain cerebral blood flow when BP changes

124
Q

When does myogenic autoregulation fail?

A

Between 50mmHg

125
Q

What are cerebral vessels very sensitive too?

A

Changes in arterial P CO2

126
Q

When does CO2 rise?

A

When theres a lot of activity in the brain, and therefore more demand

127
Q

What does hypercapnia cause?

A

Vasodilation

128
Q

What does hypocapnia cause?

A

Vasoconstriction

129
Q

What can cause hypocapnia?

A

Panic hyperventilation

130
Q

What can panic hyperventilation cause?

A

Dizziness or fainting

131
Q

How is panic hyperventilation treated?

A

Give bag to rebreathe into, to prevent blowing off too much CO2

132
Q

What regulates circulations?

A

Brainstem

133
Q

What is the result of the brainstem regulating other circulations?

A

The brain can prioritise its own circulation

134
Q

What does regional activity cause?

A

Local increases in blood flow

135
Q

Why does regional activity cause local increases in blood flow?

A

Things that are produced through breakdown of ATP cause vasodilation

136
Q

What metabolic factors cause vasodilation?

A

Increase in P CO2 Increase in [K+]
Increase in adenosine
Decrease in P O2

137
Q

What is the result of the rigid cranium?

A

It protects the brain, but does not allow for volume expansion

138
Q

What do increases in intracranial pressure do?

A

Impair cerebral blood flow

139
Q

What can cause increases in intracranial pressure?

A

Cerebral tumour or haemorrhage

140
Q

What is the result of the impairment of cerebral blood flow?

A

It makes it more difficult to perfuse the brain

141
Q

What is Cushing’s reflex?

A

The impaired blood flow to the vasomotor control regions of the brainstem due to an increase in intracranial pressure increases sympathetic vasomotor activity, which increases arterial blood pressure due to vasoconstriction in peripheral vessels

142
Q

What is the result of Cushing’s reflex?

A

Helps maintain cerebral blood flow

143
Q

What do the cerebral capillaries form?

A

A tight blood-brain barrier

144
Q

What can diffuse through the blood-brain barrier?

A

Lipid soluble molecules such as oxygen and carbon dioxide

145
Q

What can’t diffuse through the blood-brain barrier?

A

Lipid insoluble molecules such as K and catecholamines

146
Q

Why doesn’t the blood-brain barrier allow lipid insoluble molecules through?

A

Don’t want them, as they may cause too much activity

147
Q

What must the coronary circulation deliver?

A

Oxygen at a high basal rate

148
Q

What must the coronary circulation meet?

A

An increased demand, as work rate can increase five-fold

149
Q

What do the right and left coronary arteries arise from?

A

The right and left aortic sinuses

150
Q

When does blood flow in the left coronary artery mainly occur?

A

During diastole

151
Q

Why does left coronary artery flow mainly occur during diastole?

A

Because in systole, the left ventricle is contracting, which squeezes capillaries and small vessels, so difficult for coronary blood flow to take place

152
Q

When is it most difficult for coronary blood flow to take place?

A

At the start of isovolumetric contraction

153
Q

What happens to coronary blood flow at the start of isovolumetric contraction?

A

It drops to basically 0

154
Q

What is cardiac muscle adapted to do?

A

Receive lots of oxygen

155
Q

How is the cardiac muscle adapted to receive oxygen?

A

Muscle fibres 18µm in diameter
Capillary density 3000/mm 2
Capillaries continuously perfused

156
Q

What diameter are the muscle fibres in skeletal muscle?

A

50µm

157
Q

What is the result of the small muscle fibres in cardiac muscle?

A

The diffusion distance is always >9µm

158
Q

What is the capillary density in skeletal muscle?

A

3000/mm 2

159
Q

What is the result of the high capillary density in cardiac muscle?

A

It facilitates efficient oxygen delivery

160
Q

Are all capillaries perfused at rest in skeletal muscle?

A

No

161
Q

How are all capillaries perfused at rest in cardiac muscle?

A

Continuous production of nitric oxide by coronary endothelium keeps the capillaries open, which maintains a high basal flow

162
Q

What does coronary blood flow increase to meet?

A

Myocardial demand

163
Q

How is extra oxygen required at high work load supplied?

A

By increased blood flow

164
Q

What kind of relationship exists between oxygen demand and blood flow?

A

Almost linear relationship until very high oxygen demand, and then only a small increase in amount of oxygen extracted

165
Q

What can cause vasodilation of cardiac vessels?

A

Extra blood flow in response to metabolites

166
Q

What metabolites can cause myocardial vasodilation?

A

Increase in [K+]

Decrease in pH

167
Q

What kind of arteries are coronary arteries?

A

Functional end arteries

168
Q

What is the result of the coronary arteries being functional end arteries?

A

Few arterio-arterial anastomoses

169
Q

What is meant by their being few artero-arterial anastomoses?

A

Different arteries don’t join with each other, as they do in some tissues

170
Q

What are coronary arteries prone to?

A

Atheromas

171
Q

What do narrowed coronary arteries lead to?

A

Angina on exercise

172
Q

Why do narrowed coronary arteries lead to angina on exercise?

A

Due to increased oxygen demand
Made worse because coronary blood flow mainly during diastole, but diastole duration reduced as heart rate increases, compromising blood flow even further

173
Q

What does stress and cold cause?

A

Sympathetic coronary vasoconstriction and angina

174
Q

What does sudden obstruction by thrombus cause?

A

Myocardial infarction

175
Q

Why may skeletal muscle circulation need to increase?

A

To meet oxygen and nutrient delivery demands, and remove metabolites during exercise

176
Q

What does skeletal muscle have an important role in?

A

Regulating arterial pressure

177
Q

Why does skeletal muscle circulation help regulate arterial pressure?

A

Because it constitutes 40% of adult body mass, and so there is a lot of circulation going to skeletal muscle

178
Q

What do resistance vessels in skeletal muscle have?

A

Rich innervation by sympathetic vasoconstriction fibres

179
Q

What does the baroreceptor reflex do?

A

Maintains blood pressure

180
Q

What does capillaries density depend on?

A

Muscle type

181
Q

What kind of muscle has a higher capillary density?

A

Postural muscle

182
Q

Why do skeletal muscles have very high vascular tone?

A

Permites lots of dilation, and so flow can increase >20 times in active muscle

183
Q

How much of the capillaries are perfused at any one time at rest?

A

Only half

184
Q

What does only half the capillaries being perfused at rest allow for?

A

Increased recruitment

185
Q

What allows more capillaries to be perfused?

A

Opening of precapillary sphincters

186
Q

What is the result of more capillaries being perfused?

A

Increased blood flow and reduced diffusion distance

187
Q

What does flow in skeletal muscle increase in response to?

A

Metabolic hyperaemia

188
Q

What agents are thought to act as vasodilators?

A 
Increase in [K+]
 Increase in osmolarity
 Inorganic phosphates
 Adenosine
 Increase in [H+]
 Adrenaline
189
Q

How does adrenaline act in arterioles in skeletal muscle?

A

Through ß2 receptors

190
Q

What effect does noradrenaline have?

A

Vasoconstrictor response

191
Q

How does NA exert its vasoconstrictor response?

A

Via α1 receptors

192
Q

Does the skin have a high metabolic requirement?

A

No

193
Q

Where does the cutaneous circulation have a special role?

A

In temperature regulation

194
Q

What is core temperature maintained around?

A

Around 37 degrees

195
Q

What is core temperature a balance between?

A

Heat production and heat loss

196
Q

What is the main heat dissipating surface?

A

Skin

197
Q

What is heat dissipation from the skin regulated by?

A

Cutaneous blood flow

198
Q

Where does the cutaneous circulation have a role?

A

In maintain blood pressure

199
Q

How does the cutaneous circulation maintain blood pressure?

A

Vasoconstriction in cutaneous circulation can maintain blood pressure

200
Q

What specialised structures does acral (apical) skin have?

A

Arteriovenous anatomoses (AVAs)

201
Q

Where do AVAs tend to be?

A

In skin where you have a high surface area to volume ratio

202
Q

Give 4 examples of skin that has a lot of AVAs?

A

Ears
Nose
Fingers
Toes

203
Q

What kind of structure do AVAs have?

A

Coiled like

204
Q

What control are AVAs under?

A

Sympathetic

205
Q

How can heat be lost rapidly?

A

Bypass capillary bed and get blood to venous supply through low resistance shunt to venous plexus, which allows a large increase in blood flow just below the skin, allowing the skin temp to rise and so dissipating heat

206
Q

What effect does a decrease in core temperature have?

A

Increase in sympathetic tone in AVAs, and so decreases blood flow to the skin

207
Q

How can heat be lost through apical skin?

A

Due to dilation of capillary beds

208
Q

What happens if you’re hot?

A

Get increase in sympathetic outflow to sweat glands, which is thought to cause vasodilation

209
Q

What may sweat glands release?

A

Bradykinin

210
Q

What does bradykinin do?

A

Cause vasodilation

ESA 2- Cardiovascular System (18 decks)

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