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FM1020 Physiology > Regional Circulations > Flashcards

Regional Circulations Flashcards

1
Q

What intrinsic mechanisms regulate blood flow?

A

Myogenic
Endothelial mediated
Metabolic

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2
Q

What extrinsic mechanisms regulate blood flow?

A

Neural
Hormonal

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3
Q

What supplies the myocardium?

A

Right and left coronary arteries

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4
Q

Where does the innermost section of myocardium receive blood from?

A

Directly from cardiac chambers via specialised vessels

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5
Q

Where does blood from the left ventricle drain to?

A

Coronary sinus

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6
Q

Where does blood from the right ventricle drain to?

A

Anterior cardiac veins

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7
Q

What is the resting coronary blood flow?

A

~225 ml/min
~5% of totatl cardiac output

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8
Q

How much may cardiac output increase by during exercise?

A

6-9 fold

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9
Q

How much may coronary blood flow increase by during exercise?

A

3-4 fold

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10
Q

What is unique to cardiac muscle?

A

Very high requirements of O2

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11
Q

How much O2 is extracted from blood in cardiac capillaries during one passage?

A

Near maximum amount possible

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12
Q

How would one increase coronary blood flow?

A

Increasing O2 delivery to myocaridal cells

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13
Q

What does increased cardiac O2 cosnumption do?

A

Triggers corresponding increase in coronary blood flow

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13
Q

What is the primary controller of resistance of coronary vessels?

A

Metabolic regulation

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14
Q

What is the rate of coronary blood flow determined by?

A

Constriction/dilation of resistance vessels

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15
Q

What is released when levels of O2 in coronary muscles become insufficient?

A

Vasodilatory metabolites

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16
Q

What triggers active hyperaemia?

A

Inadequate coronary blood flow
Decreased arterial O2
Increased metabolic activity

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17
Q

What are believed to be the mediators of active hyperaemia?

A

Adenosine
Nitric oxide

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18
Q

What does a reduction in ATP concentration do?

A

Opening of Katp (potassium-sensitive ATP) channels and a hyperpolarisation
Relaxation of coronary VSM

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19
Q

What does stimulation of autonomic nerves to heart affect?

A

Coronary blood flow both directly and indirectly

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20
Q

What do the direct effects of stimulation of autonomic nerve affect?

A

Blood vessels themselves

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21
Q

What does the activation of sympathetic nerves do?

A

Triggers vasoconstriction via alpha adrenergic receptors on coronary VSM

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22
Q

What are beta adrenergic receptors associated with in regard to VSM?

A

Dilation

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23
Q

What does vagal nerve stimulation do to coronary resistance vessels?

A

Slightly dilates them

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24
Q

How do indirect effects in coronary blood flow arise?

A

Changes in coronary blood flow by changes in the activity of cardiac muscle

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25
Q

What does sympathetic nerve activity do to cardiac muscle?

A

Increased contractility
Increased tachycardia

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26
Q

What does increased cardiac activity produce?

A

Metabolic vasodilatory metabolites

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27
Q

What do metabolic vasodilatory metabolites do?

A

Have the effect of increasing coronary blood flow

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28
Q

What does sympathetic activity indirectly cause?

A

Vasodilation in the coronary circulation

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29
Q

What does vagal activity indirectly result in?

A

Vasodilation in the coronary circulation

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30
Q

What is highly important in coronary circulation?

A

Metabolic regulation

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31
Q

Is extravascular compression a pathological or physiological phenomenon?

A

Physiological

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32
Q

What affect does contraction of the left ventricle on left coronary arterial blood flow?

A

May slow, halt or temporarily reverse the flow

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33
Q

Why is the effect of extravascular compression less apparent on the right coronary artery than the left coronary artery?

A

As there is a lower pressure found in the right ventricle than the left ventricle

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34
Q

What is ischaemia?

A

Restriction in blood supply to a tissue

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35
Q

What causes myocardial ischaemia?

A

Acute occlusion of a coronary artery by atherosclerotic plaque

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36
Q

How may myocardial infarction prove fatal?

A

Decreased cardiac output
Pulmonary oedema
Fibrillation of heart
Rupture of heart

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37
Q

What is blood flow i skeletal muscle determined by?

A

Contractile activity of the muscle

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38
Q

What are the factors that regulate skeletal blood flow?

A

Neural and intrinsic factors

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39
Q

What is the resting blood flow in skeletal muscle?

A

3ml/min/100g

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40
Q

What is the exercise blood flow in skeletal muscle?

A

60ml/min/100g

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41
Q

What is the predominant regulator of skeletal blood flow at rest?

A

Neural regulation

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42
Q

What is the predominant regulator of skeletal blood flow during exercise?

A

Local factors

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43
Q

What does tonic sympathetic nerve activity do?

A

Maintain a degree of vasoconstriction

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44
Q

What does noradrenaline bind to?

A

Alpha and beta 1 adrenergic receptors, little affinity for beta 2 receptors

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45
Q

What does the binding of noradrenaline do?

A

Exclusively triggers vasoconstriction

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46
Q

Are most skeletal capillary beds perfused at rest?

A

No

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47
Q

What is sympathetic nerve activity to skeletal muscle modulated by?

A

Baroreceptor reflex

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48
Q

What contributes greatly to total peripheral resistance?

A

Resistance in skeletal muscle blood vessels

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49
Q

What does carotid artery occlusion do?

A

Reduces baroreceptor firing

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50
Q

What reduces muscle blood flow in carotid artery occlusion?

A

Increased sympathetic nerve activity

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51
Q

What contributes to the large increase in mean arterial pressure?

A

Increased sympathetic nerve activity

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52
Q

What does releasing the carotid artery increase?

A

Baroreceptor firing

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53
Q

What causes vasodilation?

A

Reduced sympathetic nerve activity

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54
Q

What does vasodilation do?

A

Increases muscle blood flow
Reduces MAP

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55
Q

What is skeletal muscle blood flow closely coupled to?

A

Metabolic demand

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56
Q

In active muscle, what rapidly increases blood flow?

A

Vasodilatory metabolites

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57
Q

Name some vasodilatory metabolites.

A

Adenosine, K+, CO2, lactic acid

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58
Q

What does “unopposed” increased vasoconstriction in inactive muscles do?

A

Diverts blood flow to active muscles

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59
Q

What do beta 2 adrenergic receptors promote?

A

Vasodilation

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60
Q

What does adrenaline have a higher affiity for?

A

Beta 1 and beta 2 receptors

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61
Q

What do low concentrations of circulating adrenaline bind to?

A

Preferentially bind to beta 2 receptors triggering vasodilation

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62
Q

What do high concentrations of adrenaline bind to?

A

Alpha 1 adrenergic receptors?

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63
Q

What do alpha 1 adrenergic effects lead to?

A

Vasoconstrictor effects predominating

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64
Q

What nerves of the ANS release ACh?

A

Parasympathetic and sympathetic cholinergic nerves

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65
Q

What can ACh trigger from endothelial cells?

A

Nitric oxide release

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66
Q

What does acetylcholine activate?

A

Endothelial nitric oxide synthase

67
Q

What is the function of nitric oxide?

A

Potent vasodilator

68
Q

Where may ACh spillover from the NMJ diffuse to?

A

Local blood vessels

69
Q

What does ACh spillover promote in local blood vessels?

A

Endothelial NO production
VSM relaxation
Further vasodilation

70
Q

What induces dilation in the microcirculation?

A

Metabolites in actively contracting muscle

71
Q

What does dilation in the microcirculation promote?

A

A pressure gradient with upstream feed arteries

72
Q

What does the resulting increase in blood flow caused by a pressure gradient with upstream feed arteries do?

A

Elevates shear stress
Release of endothelial-derived NO
Further vasodilation

73
Q

What is functional sympatholysis?

A

Increased activity of tissue blocks sympathetic effects on that tissue

74
Q

What may nitric oxide inhibit?

A

Noradrenaline release from varicosities
Directly opposes alpha 2 mediated constriction of vascular smooth muscle

75
Q

What may skeletal muscle fibers contain?

A

Neuronal NOS

76
Q

What does contraction increase?

A

NO release

77
Q

What do strong contractions of skeletal muscle do to blood vessels?

A

Compress them

78
Q

What does compression do to the rate of venous return?

A

Increase it

79
Q

What may cause blood flow to almost cease in muscle?

A

Tetanic contraction

80
Q

What does tetanic contraction do to the contraction itself?

A

Rapid weakening of the strength of the muscle

81
Q

What is venous occlusion plethysmography?

A

Technique for measuring limb blood flow

82
Q

How does venous occlusion plethysmography work?

A

Venous return is interrupted by inflating cuff around upper arm at 40mmHg
Hand circulation is completely occluded with a wrist cuff higher than systolic pressure
Arterial inflow in unaltered and forearm volume increases
Changes in arm circumference is measured by strain-gauge plethysmogrpah

83
Q

What does VOP do?

A

Provide a measure of arterial blood flow to that part of the forearm enclosed by the two cuffs

84
Q

When is VOP used?

A

TO study the effect of vasoactive mediators or drugs in the forearm vascular bed in human clinical trials

85
Q

What is the path of capillaries in cutaneous circulation?

A

Loop under epidermis then flows into a venous plexus, acting as a blood resevoir

86
Q

What is responsible for colouration of skin?

A

Blood accumulation in venousn plexus

87
Q

What is the role of arteriovenous anastomoses?

A

Specialised shunts that feed blood into plexuses directly from subcutaneous arteries

88
Q

Where are AV anastomoses found?

A

Skin circulation of hands, ears, nose and lips

89
Q

What controls the tone of the thick VSM in AV anastomoses?

A

Sympathetic neural control

90
Q

What is the intrinsic regulation of AV anastomoses?

A

N/A

91
Q

What is the main purpose of skin circulation?

A

Regulation of body temperature

92
Q

What regulates cutaneous circulation?

A

SN activity - alpha adrenergic recepetors

93
Q

When is cutaneous circulation subject to a high degree of adrenergic tone?

A

Normal temperatures - high degree of vasoconstriction

94
Q

What does vasoconstriction of arterioles and AV anastomoses result in?

A

Reduction/blocking of flow into skin capillaries

95
Q

what is blushing/blanching caused by?

A

Inhibition/stimulation of SN in blood to skin of face

96
Q

What has a low degree of autoregulation in cutaneous circulation?

A

Resistance arterioles - produce vasodilatory metabolites

97
Q

What is reactive hyperaemia?

A

Increased blood flow following ischaemia

98
Q

What happens to resistance vessels when a region of the body is exposed to cold?

A

Causes vasoconstriction to capacitance/resistance vessels at that region (local axon reflex) and other extremities

99
Q

Where do temperature receptors send signals to?

A

Temperature regulating centre of the hypothalamus

100
Q

What happens to resistance/capacitance vessels when there is sustained exposure to cold?

A

Localised cold vasodilation

101
Q

What happens if the cold keeps persisting?

A

Alternating vasoconstriction and vasodilation caused by local axon reflexes

102
Q

What does an application of heat cause at an affected region and at other regions of the body?

A

Vasodilation of vessels

103
Q

What is the purpose of widespread vasodilation when excessive heat is present?

A

Increase flow of warm blood to sub-epidermal circulation which is cooled by proximity to external environment and perspiration

104
Q

What kind of nerves innervate sweat glands?

A

Cholinergic sympathetic nerves

105
Q

What does sweat production increase the production of in skin?

A

Bradykinin, a potent vasodilator, which further stimulates the formation of nitric oxide

106
Q

What does exercise do to cutaneous circulation?

A

Overall increase in sympathetic outflow resulting in vasoconstriction

107
Q

What allows counter-current heat exchange?

A

Close proximity of major arteries and veins

108
Q

What is counter-current heat exchange essential for?

A

Protecting the body core from extremes of heat

109
Q

Which arteries are responsible for cerebral circulation?

A

Internal carotid and vertebral arteries which supply the basilar artery

110
Q

What does the basilar artery supply and where is this structure found?

A

Circle of Willis which loops around the brain stem

111
Q

How does blood travel from the circle of Willis into brain tissue?

A

Cerebral arteries

112
Q

Which is higher: intercranial pressure and central venous pressure?

A

Intercranial pressure (0-10mmHg)

113
Q

What is affected by changes in intracranial pressure?

A

Cerebral perfusion

114
Q

What does elevated ICP (over 20mmHg) cause?

A

Compression of venous vessels and reduced blood flow by reducing cerebral perfusion pressure

115
Q

What is the equation for cerebral perfusion pressure?

A

Mean arterial pressure - intracranial pressure

116
Q

How can we describe the blood supply to the brain?

A

Remains constant i.e., the rate of inflow via arterioles = rate of outflow via venules resulting in a constant value of blood and tissue fluid

117
Q

What do neuronal cells have a high requirement for?

A

O2 and glucose

118
Q

How much O2 does the brain consume at rest and how much of the cardiac output does it receive?

A

consumes 20% of resting O2
Receives ~14% of cardiac output

119
Q

What is brain tissue very sensitive to?

A

Ischaemia

120
Q

How long must ischaemia last in brain tissue to cause unconsciousness and irreversible brain damage?

A

~5 sec for unconsciousness
~4 min for irreversible brain damage

121
Q

What is the driving force for brain perfusion?

A

MAP

122
Q

When does cerebral circulation exhibit autoregulation?

A

MAP between 60 and 160 mmHg

123
Q

What happens when there is an MAP below 60 mmHg?

A

Syncope

124
Q

What happens when there is an MAP above 160 mmHg?

A

Damage to blood brain barrier resulting in cerebral oedema

125
Q

What does increased blood flow in certain neuronal regions correlate with?

A

C14 glucose uptake in these regions

126
Q

What is paramount in regulating cerebral blood flow?

A

Local factors - metabolic regulation

127
Q

What effect does maximum SN activity have on cerebral resistance?

A

May increase it by ~20%

128
Q

What does metabolic regulation exert in cerebral blood flow?

A

Functional sympatholysis

129
Q

What doesn’t really effect cerebral blood flow?

A

Baroreceptor reflex

130
Q

How may cerebral blood flow be regulated?

A

Vasodilatory metabolites by inducing active hyperaemia

131
Q

What is the most important vasodilatory factor in cerebral blood flow?

A

Increased production of carbon dioxide by neuronal cells

132
Q

What can CO2 do in cerebral blood flow?

A

Diffuse across blood-brain barrier and reduce the pH of CSF triggering vasodilation of cerebral arterioles

133
Q

What reduces washout of CO2 from brain?

A

Reduction in CPP

134
Q

What can trigger vasodilation and vasoconstriction in cerebral blood flow?

A

Increased PCO2 (hypercapnia) and decreased PCO2 (hypocapnia) respectively

135
Q

What mediates hypercapnia and hypocapnia in cerebral blood flow?

A

Changes in pH of CSF

136
Q

What causes a strong vasodilation of vessels to maintain O2 supply to brain?

A

PO2 < 50mmHg

137
Q

What may cause an elevated ICP?

A

Brain trauma
Cerebral oedema

138
Q

What happens if ICP>MAP?

A

Severe cerebral ischaemia

139
Q

What may happen as a result of an elevated ICP?

A

Shift in brain tissue within skull aka herniation

140
Q

What does the cushing reflex do?

A

Activates the SNS causing peripheral vasoconstriction and increased cardiac output thereby increasing MAP
Increased MAP stimulates baroreceptors in carotid bodies resulting in bradycardia

141
Q

What is Cushing’s triad and what are they symptoms of?

A

Hypertension, bradycardia, irregular respirations - brain trauma and increased ICP

142
Q

What does splanchnic circulation refer to?

A

Blood supply to visceral organs:
GI tract
Spleen
Pancreas
Liver
Pancreas

143
Q

What feature is found in the circulation of villi?

A

Counter-current exchange of O2 directly form arterioles to venules

144
Q

What happens to blood at the base of microvilli?

A

Blood is shunted directly form arterioles to venules reducing O2 supply to mucosal cells at the tip - necrosis of villi may follow

145
Q

How is regulation of intestinal blood flow mediated?

A

Both by SN and intrinsic mechanisms

146
Q

When is vasoconstriction of mesenteric arterioles and capacitance vessels commonly seen?

A

During exercise

147
Q

What is intestinal blood flow increased by?

A

Functional hyperaemia

148
Q

What do all aspects of GI tract function have?

A

Vasodilatory properties

149
Q

Name a digestive hormone with vasodilatory properties.

A

Gastrin

150
Q

What increases metabolic activity of tissue in the GI?

A

Absorption of biomolecules

151
Q

What vasodilator is produced locally?

A

NO

152
Q

What do parasympathetic nerves innervate in the GI tract and why?

A

Intestinal smooth muscle and glands to increase motility and secretions - indirectly to blood flow by stimulating metabolic activity and by producing bradykinin and NO

153
Q

How much of cardiac output goes to hepatic circulation?

A

25%

154
Q

How does blood flow enter the liver?

A

Portal vein from GI tract, spleen and pancreas

155
Q

What are the functions of the liver?

A

Processing and storage of GI-derived nutrients
Re-entry of GI-derived nutrients into the general circulation
Clears blood of drugs and toxins
Blood reservoir

156
Q

What is O2 needed for in the hepatic artery?

A

Metabolic activity so the liver may perform its functions

157
Q

What may impact hepatic blood flow?

A

GIT, splenic and pancreatic blood flow

158
Q

How does an acinus work?

A

Portal venules and hepatic arterioles enter the centre of an acinus and deliver blood to sinusoids
Sinusoids are very leaky, permitting rapid exchange
These sinusoids radiate to the periphery of an acinus and connect with hepatic venules, hepatic veins and IVC

159
Q

Is there low or high oncotic pressure of plasma in hepatic circulation?

A

Relatively low

160
Q

What greatly affects filtration, lymph production and substance exchange in hepatic circulation?

A

Hydrostatic pressure in sinusoidal capillaries

161
Q

How are rates of blood flow in portal venules and hepatic arterioles regulated?

A

Reciprocally

162
Q

What may rapidly return half of liver blood into heart?

A

SNS-induced vasoconstriction of capacitance vessels

163
Q

What does heart failure increase?

A

Increase in CVP

164
Q

What does increased CVP cause?

A

Increases in hepatic venous and hepatic sinusoidal pressure leading to hepatic oedema

165
Q

What does hepatic oedema lead to?

A

Accumulation of fluid in the abdominal cavity - ascites

166
Q

When may ascites occur?

A

Heart failure
Liver cirrhosis as it causes portal hypertension

FM1020 Physiology (12 decks)

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