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ESA 2- Cardiovascular System > Special Circulations > Flashcards

Flashcards in Special Circulations Deck (210):
1

What circulations do the lungs have?

Bronchial circulation and Pulmonary circulation

2

What is the bronchial circulation part of?

The systemic circulation

3

What is the purpose of the bronchial circulation?

It meets the metabolic and oxygen requirements of lungs

4

What does the bronchial circulation ensure?

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

5

How is the pulmonary circulation related to the systemic circulation?

It is in series

6

What is the purpose of the pulmonary circulation?

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

7

What gas exchange needs to occur at the lungs?

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

8

What must the pulmonary circulation accept?

The entire cardiac output

9

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

No

10

What is cardiac output at rest?

~5l/min

11

What does cardiac output have the ability to do?

Increase when exercising

12

What is the maximum cardiac output?

~20-25l/min

13

Is flow the same in systemic and pulmonary circulations?

Yes

14

How does the pulmonary circulation differ from the systemic?

It works with a much lower pressure and resistance

15

What is the pressure in the right ventricle?

15–30mmHg in systole
0-8mmHg in diastole

16

What is the pressure in the pulmonary artery?

15-30mmHg systole
4-12mmHg diastolic

17

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

Due to elastic recoil and closure of valve

18

What is the pressure in the left atrium?

1-10mmHg

19

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

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

20

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

It is higher

21

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

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

22

What is the pressure in the aorta?

100-140mmHg systolic 
60-90mmHg diastolic

23

Why is the pressure high in the aorta?

Because the wall is thicker

24

What is the pressure in the right atrium?

0-8mmHg

25

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

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

26

What happens to the right ventricles in systole?

It contracts, and so pressure goes up

27

What are the features of the pulmonary circulation?

Low pressure
Low resistance

28

What is the mean arterial pressure in the pulmonary circulation?

12-15mmHg

29

What is the mean capillary pressure in the pulmonary circulation?

9-12mmHg

30

What is the mean venous pressure in the pulmonary circulation?

5mmHg

31

Describe the vessels in the pulmonary circulation

Short, wide

32

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

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

33

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

They have relatively little smooth muscle

34

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

Very high density of capillaries in alveoli wall 
Short diffusion distance

35

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

Large capillary surface area

36

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

A very thin layer of tissue

37

What is the combined endothelium and epithelium thickness?

~0.3µm

38

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

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

39

What do the adaptations of the pulmonary circulation produce?

A high oxygen and carbon dioxide transport capacity

40

What needs to be matched for efficient oxygenation?

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

41

What is the optional V/Q ratio?

0.8

42

What determines perfusion?

Cardiac output

43

What determines ventilation?

Amount you breath

44

What does maintaining the optimal V/Q ratio require?

Diverting blood from alveoli that are not well ventilated

45

What ensures the optimal V/Q ratio?

Hypoxic pulmonary vasoconstriction

46

What is hypoxic pulmonary vasoconstriction important for?

Regulating pulmonary vascular tone

47

What does alveolar hypoxia result in?

Vasoconstriction of pulmonary vessels

48

What is the result of hypoxic pulmonary vasoconstriction?

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

49

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

It is the opposite effect

50

What can chronic hypoxic vasoconstriction cause?

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

51

Where can chronic hypoxia occur?

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

52

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

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

53

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

Pulmonary hypertension

54

What can lung disease lead to?

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

55

What can high afterload on the right ventricle lead to?

Right ventricular heart failure

56

What are pulmonary vessels strongly influenced by?

Gravity

57

Why are pulmonary vessels strongly influenced by gravity?

Because they are low pressure and relatively thin vessels

58

What happens to pulmonary vessels when in the upright position?

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

59

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

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

60

What happens to vessels near the apex of the lung?

They collapse during diastole

61

What happens to vessels at the level of the heart?

They are continuously patent

62

What effect does exercise have on cardiac output?

It increases it

63

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

There is a small increase in pulmonary arterial pressure 
Capillary transit time reduced as blood flow increases

64

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

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

65

What is transit time?

The time it takes for RBCs to get through the capillaries

66

What is transit time in the pulmonary circulation at rest?

~1s

67

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

~0.3s

68

Where can fluid move?

Through capillaries, and through capillaries into tissues

69

What determines tissue formation?

Starlings forces

70

What are Starlings forces?

Hydrostatic pressure of blood within capillary 
Oncotic pressure (colloid osmotic pressure)

71

What does hydrostatic pressure of blood within the capillary do?

Pushes fluid out of capillary

72

What is oncotic pressure?

The pressure exerted by large molecules such as plasma proteins

73

What does oncotic pressure do?

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

74

What is capillary hydrostatic pressure influenced by?

More venous pressure than arterial pressure

75

Why is capillary pressure influenced more by venous pressure?

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

76

Does hypertension result in peripheral oedema?

No

77

What does low capillary pressure in the lungs minimise?

Formation of lung lymph

78

What drives fluid into the capillary?

Plasma oncotic pressure

79

What drives fluid out of the capillary?

Interstital oncotic pressure and hydrostatic pressure

80

Why does not much lung lymph form?

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

81

Why is the minimisation of lung lymph formation important?

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

82

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

It is higher

83

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

It is less

84

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

It doesn’t

85

What does increased capillary pressure lead to?

Oedema

86

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

Because of the low resistance

87

What prevents pulmonary oedema?

Low capillary pressure

88

What is pulmonary capillary pressure normally?

9-12mmHg

89

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

Only a small amount

90

What can happen if capillary pressure in the lungs rises?

Can get pulmonary oedema

91

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

If left atrial pressure rises to 20-25mmHg

92

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

Mitral valve stenosis 
Left ventricular failure

93

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

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

94

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

Harder for pulmonary veins to drain

95

Why does left ventricular failure cause pulmonary oedema?

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

What is the problem with pulmonary oedema?

It impairs gas exchange

97

What affects pulmonary oedema?

Posture

98

Why does posture affect pulmonary oedema?

Due to changes in hydrostatic pressure due to gravity

99

Where does pulmonary oedema form when upright?

Mainly at bases

100

Where does pulmonary oedema form when lying down?

Throughout the lungs

101

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

Symptoms that are worse at night

102

How are the symptoms of pulmonary oedema relieved?

Diuretics, which reduce blood volume 
Treat underlying cause if possible

103

How much of the cardiac output does the brain receive?

About 15%

104

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

Because it has high oxygen demands

105

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

20%

106

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

Must provide a secure oxygen supply

107

How are the brains oxygen demands met?

High capillary density 
High basal flow rate 
High oxygen extraction

108

What does high capillary density provide?

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

109

What is the diffusion distance in the brain?

~10µm

110

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

It’s about 10x the average

111

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

35% above average

112

Why is secure oxygen supply to the brain vital?

Neurones are very sensitive to hypoxia 
Interruption to blood supply causes neuronal death

113

How long can neurones be without oxygen?

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

114

What happens when you get neuronal death?

Stroke

115

How is a secure blood supply to the brain ensured?

Structurally 
Functionally

116

How is blood supply secured structurally?

Circles of Willis

117

What are circles of Willis?

Anastomoses between basilar and internal carotid arteries

118

How do circle of Willis ensure a secure blood supply?

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

How is secure blood supply to the brain ensured functionally?

Myogenic autoregulation maintains perfusion during hypertension 
Metabolic factors control blood flow

120

What is myogenic autoregulation generated by?

Smooth muscle cells

121

What does myogenic autoregulation respond to?

Changes to transmural pressure

122

How does the brain respond to changes in transmural pressure?

High blood pressure causes vasoconstriction 
Low blood pressure causes vasodilation

123

What does myogenic autoregulation serve to do?

Maintain cerebral blood flow when BP changes

124

When does myogenic autoregulation fail?

Between 50mmHg

125

What are cerebral vessels very sensitive too?

Changes in arterial P CO2

126

When does CO2 rise?

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

127

What does hypercapnia cause?

Vasodilation

128

What does hypocapnia cause?

Vasoconstriction

129

What can cause hypocapnia?

Panic hyperventilation

130

What can panic hyperventilation cause?

Dizziness or fainting

131

How is panic hyperventilation treated?

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

132

What regulates circulations?

Brainstem

133

What is the result of the brainstem regulating other circulations?

The brain can prioritise its own circulation

134

What does regional activity cause?

Local increases in blood flow

135

Why does regional activity cause local increases in blood flow?

Things that are produced through breakdown of ATP cause vasodilation

136

What metabolic factors cause vasodilation?

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

137

What is the result of the rigid cranium?

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

138

What do increases in intracranial pressure do?

Impair cerebral blood flow

139

What can cause increases in intracranial pressure?

Cerebral tumour or haemorrhage

140

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

It makes it more difficult to perfuse the brain

141

What is Cushing’s reflex?

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

What is the result of Cushing’s reflex?

Helps maintain cerebral blood flow

143

What do the cerebral capillaries form?

A tight blood-brain barrier

144

What can diffuse through the blood-brain barrier?

Lipid soluble molecules such as oxygen and carbon dioxide

145

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

Lipid insoluble molecules such as K and catecholamines

146

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

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

147

What must the coronary circulation deliver?

Oxygen at a high basal rate

148

What must the coronary circulation meet?

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

149

What do the right and left coronary arteries arise from?

The right and left aortic sinuses

150

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

During diastole

151

Why does left coronary artery flow mainly occur during diastole?

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

152

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

At the start of isovolumetric contraction

153

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

It drops to basically 0

154

What is cardiac muscle adapted to do?

Receive lots of oxygen

155

How is the cardiac muscle adapted to receive oxygen?

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

156

What diameter are the muscle fibres in skeletal muscle?

50µm

157

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

The diffusion distance is always >9µm

158

What is the capillary density in skeletal muscle?

3000/mm 2

159

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

It facilitates efficient oxygen delivery

160

Are all capillaries perfused at rest in skeletal muscle?

No

161

How are all capillaries perfused at rest in cardiac muscle?

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

162

What does coronary blood flow increase to meet?

Myocardial demand

163

How is extra oxygen required at high work load supplied?

By increased blood flow

164

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

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

165

What can cause vasodilation of cardiac vessels?

Extra blood flow in response to metabolites

166

What metabolites can cause myocardial vasodilation?

Increase in [K+]
Decrease in pH

167

What kind of arteries are coronary arteries?

Functional end arteries

168

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

Few arterio-arterial anastomoses

169

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

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

170

What are coronary arteries prone to?

Atheromas

171

What do narrowed coronary arteries lead to?

Angina on exercise

172

Why do narrowed coronary arteries lead to angina on exercise?

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

What does stress and cold cause?

Sympathetic coronary vasoconstriction and angina

174

What does sudden obstruction by thrombus cause?

Myocardial infarction

175

Why may skeletal muscle circulation need to increase?

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

176

What does skeletal muscle have an important role in?

Regulating arterial pressure

177

Why does skeletal muscle circulation help regulate arterial pressure?

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

178

What do resistance vessels in skeletal muscle have?

Rich innervation by sympathetic vasoconstriction fibres

179

What does the baroreceptor reflex do?

Maintains blood pressure

180

What does capillaries density depend on?

Muscle type

181

What kind of muscle has a higher capillary density?

Postural muscle

182

Why do skeletal muscles have very high vascular tone?

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

183

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

Only half

184

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

Increased recruitment

185

What allows more capillaries to be perfused?

Opening of precapillary sphincters

186

What is the result of more capillaries being perfused?

Increased blood flow and reduced diffusion distance

187

What does flow in skeletal muscle increase in response to?

Metabolic hyperaemia

188

What agents are thought to act as vasodilators?

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

189

How does adrenaline act in arterioles in skeletal muscle?

Through ß2 receptors

190

What effect does noradrenaline have?

Vasoconstrictor response

191

How does NA exert its vasoconstrictor response?

Via α1 receptors

192

Does the skin have a high metabolic requirement?

No

193

Where does the cutaneous circulation have a special role?

In temperature regulation

194

What is core temperature maintained around?

Around 37 degrees

195

What is core temperature a balance between?

Heat production and heat loss

196

What is the main heat dissipating surface?

Skin

197

What is heat dissipation from the skin regulated by?

Cutaneous blood flow

198

Where does the cutaneous circulation have a role?

In maintain blood pressure

199

How does the cutaneous circulation maintain blood pressure?

Vasoconstriction in cutaneous circulation can maintain blood pressure

200

What specialised structures does acral (apical) skin have?

Arteriovenous anatomoses (AVAs)

201

Where do AVAs tend to be?

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

202

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

Ears
Nose
Fingers
Toes

203

What kind of structure do AVAs have?

Coiled like

204

What control are AVAs under?

Sympathetic

205

How can heat be lost rapidly?

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

What effect does a decrease in core temperature have?

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

207

How can heat be lost through apical skin?

Due to dilation of capillary beds

208

What happens if you’re hot?

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

209

What may sweat glands release?

Bradykinin

210

What does bradykinin do?

Cause vasodilation