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FM1020 Physiology > Arterial Blood Pressure > Flashcards

Arterial Blood Pressure Flashcards

1
Q

What do we mean by resistance vessels?

A

Provide high resistance to blood flow and pressure falls - arterioles

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2
Q

What is the equation for mean arterial pressure?

A

Pa = Pd + (Ps - Pd)/3

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3
Q

What is the actual normal Pa and what is this usually rounded up to?

A

93mmHg
100mmHg

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4
Q

What is the main physical determinant of MAP?

A

Arterial blood volume (Va)

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5
Q

What are the physiological determinants of MAP?

A

Rate of inflow of blood into arteries during systole (Qh) - Cardiac output (Q)
Rate of outflow through arterioles into capillaries (peripheral runoff) - (Qr)

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6
Q

When is the MAP constant?

A

Qh = Qr

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7
Q

When does MAP increase?

A

Qh > Qr

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8
Q

When does MAP decrease?

A

Qh < Qr

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9
Q

What does increased resistance do to the rate of blood flow?

A

Decreases it

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10
Q

What is Total peripheral resistance?

A

Resistance to blood flow through entire arteriolar system

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11
Q

What does total peripheral runoff determine?

A

The rate of blood flow out of the arterial system

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12
Q

What raises arterial blood pressure?

A

Increase in total peripheral resistance
Vasoconstriction of arterioles

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13
Q

If there is constriction in the system, what happens to blood pressure in both upstream and downstream vessels?

A

Upstream - increased
Downstream - decreased

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14
Q

What is mean arterial pressure calculated by?

A

Cardiac output * total peripheral resistance = MAP

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15
Q

How do you calculate cardiac output?

A

Cardiac rate * Stroke volume

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16
Q

What determines the rate of change of arterial blood pressure (Pa)?

A

Compliance

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17
Q

How does compliance determine the rate of change of Pa?

A

Rigid arteries attain higher Pa level rapidly
In elastic arteries, increases in Pa occur at a slower rate

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18
Q

What will result in long term effects on Pa?

A

Long term increases in either CO or TPR

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19
Q

What are the physical factors that affect arterial blood pressure?

A

Arterial blood volume
Arterial compliance

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20
Q

What are the physiological factors that affect Arterial blood pressure?

A

Peripheral resistance
Cardiac output

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21
Q

Why is stroke volume a major determinant of pulse pressue?

A

During ventricular ejection, arterial blood volume increases to V2 and blood pressure increases to P2
During diastole, peripheral runoff reduces volume to V1, and pressure falls to P1
(V2 - V1) directly proportional to (P2 - P1) pulse pressure

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22
Q

What would an increase in stroke volume do to pulse pressure?

A

Increase it

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23
Q

Do lower compliant arteries have higher or lower pulse pressures?

A

Higher

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24
Q

Why do lower compliant arteries have higher pulse pressures?

A

Ejected blood exerts a higher pressure on rigid walls
Systolic pressure is increased in rigid arteries, so pulse pressure also increases

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25
Q

How does aortic compliance change as we age and what effect does this have on pulse pressure?

A

Compliance decreases so pulse pressure increases

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26
Q

What gives a measure of stroke volume clinically?

A

Magnitude of pulse pressure assuming normal arterial compliance in the patient

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27
Q

What condition may cause a diminished pulse pressure?

A

Cardiac failure as it reduces stroke volume

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28
Q

When is there increased pulse pressure?

A

Aortic valve regurgitation - drops diastolic pressure

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29
Q

What is used clinically to measure systolic and diastolic pressure?

A

Inflatable cuff and sphymomanometer

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30
Q

What happens when the cuff pressure supersedes systolic pressure?

A

Artery is entirely closed and blood flow drops

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31
Q

What happens after the cuff pressure overtakes systolic pressure?

A

Cuff pressure is slow dropped which partially opens the artery, restarting blood flow in a turbulent fashion through the pinched artery

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32
Q

What can be heard by auscultation during the measurement of blood pressure as the cuff pressure slow drops?

A

Thumping noise called Korotkoff sounds

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33
Q

What happens when cuff pressure is less than diastolic pressure?

A

Artery is fully open; blood flow is smooth and Korotkoff sounds disappear

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34
Q

Where is the stethoscope placed when listening for Korotkoff sounds?

A

Immediately distal to the cuff

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35
Q

What is the pressure displayed during the first Korotkoff sound taken to be?

A

Systolic pressure

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36
Q

How do we know the diastolic pressure?

A

When Korotkoff sounds disappear

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37
Q

How can MAP be modulated?

A

Altering stroke volume, total peripheral resistance, heart rate

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38
Q

What is important in maintenance of arterial blood pressure?

A

Arterioles

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39
Q

What increases and decreases blood flow in arterioles?

A

Contraction reduces blood flow
Relaxation increases blood flow

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40
Q

What controls total peripheral resistance?

A

Regulation of smooth muscle contraction and relaxation in arterioles

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41
Q

What is the Ca++ sensor in smooth muscle?

A

Calmodulin

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42
Q

What is the role of Ca++/calmodulin complex?

A

Binding and activating myosin light chain kinase

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43
Q

What determines the strength of contraction of vascular smooth muscle?

A

Degree of opening of Ca++ channels

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44
Q

What is myogenic regulation?

A

Rapid increase in blood pressure increases transmural pressure induces reflex contraction of arterioles
Rapid reduction in blood pressure induces a reflex dilation of these vessels

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45
Q

What is the mechanism of myogenic regulation?

A

Unclear, but stretching of vascular smooth muscle increase [Ca++]i inducing contraction of VSM cells

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46
Q

Explain how myogenic regulation helps blood flow when someone moves from a lying to standing position.

A

This movement causes rapid flow of blood to lower extremities causing a rise in both venous and arterial pressure
Increased stretch triggers reflex constriction of arterioles reducing blood flow into lower leg capillaries

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47
Q

What would happen while someone is standing up in the absence of myogenic regulation?

A

Increased capillary blood pressure (hydrostatic pressure)
Elevated hydrostatic pressure increases capillary filtration causing oedema in feet and lower legs

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48
Q

What does endothelial-mediated regulation do?

A

Releases substances that trigger contraction/relaxation of VSM

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49
Q

What does increased blood flow result in by endothelial-mediated regulation?

A

Increased blood flow causes shear stress to endothelium and induces release of nitric oxide

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50
Q

What is nitric oxide synthesised from?

A

L-arginine

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51
Q

What does NO do once diffused to VSM cells?

A

Activates guanylyl cyclase increasing the intracellular concentration of cGMP

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52
Q

What does cGMP do to VSM?

A

Decreases [Ca++]i inducing dilation of blood vessels

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53
Q

What is release of NO induced by?

A

Accelerated blood flow

54
Q

What does metabolic activity regulate in the circulatory system?

A

Capillary blood flow

55
Q

What happens if O2 levels are inadequate in capillaries?

A

Metabolites with vasodilator activity are produced

56
Q

What do metabolites with vasodilator activity do?

A

Diffuse to VSM inducing relaxation and increasing capillary blood flow

57
Q

What is active hyperemia?

A

Rise in blood flow caused by increased tissue activity

58
Q

What are the possible metabolites responsible in metabolic regulation?

A

Phosphate
K+
Adenosine
(Breakdown products of ATP)

59
Q

What innervates VSM of arterioles and veins?

A

Post-ganglionic sympathetic nerves

60
Q

What does norepinephrine bind to on VSM cells and what does this induce? (Most prominent)

A

Alpha 1 adrenergic receptors
Induces vasoconstriction

61
Q

What does adrenaline bind to on VSM cells and what does it induce?

A

Beta 2 adrenergic receptors in skeletal blood vessels
Induces vasodilation

62
Q

What do alpha 1 adrenergic receptors do when activated?

A

Activate phospholipase C produces IP3 which increases [Ca++]i
Results in contraction

63
Q

What do activated beta 2 adrenergic receptors do?

A

Activates adenylyl cyclase and increases [cAMP]i which inhibits MLCK

64
Q

Is there a high level of sympathetic neural activity delivered to arterioles?

A

Yes

65
Q

How often is noradrenaline released from sympathetic nerves and why?

A

Constantly to induce a degree of vasoconstriction
Tonically active/vasoconstrictor tone

66
Q

What does increased sympathetic nerve activity do to peripheral blood flow?

A

Induces further vasoconstriction increasing TPR, decreasing rate of blood flow from arteries into tissues

67
Q

What is the purpose of sympathetic neural vasoconstriciton?

A

To increase MAP

68
Q

Where is a high percentage of blood?

A

Venules and small veins in tissue

69
Q

At basal SN activity, what is the degree of venous vascular tone?

A

Low in most tissue, especially skin

70
Q

What does sympathetic nerve stimulation do to arteries?

A

Reduces blood flow into tissues by constriction of arterioles

71
Q

What does sympathetic nerve stimulation do to venous circulation?

A

Decreases tissue blood volume by constriction of venules
Increases venous return
Redistribution of blood from venous into arterial system

72
Q

What does sympathetic nerve stimulation do to capillaries?

A

Reduces capillary hydrostatic pressure
Absorption of interstitial fluid into capillaries increases

73
Q

What does vasoconstriction do?

A

Mobilises blood from capacitance vessels and returns it to heart

74
Q

Physiologically, what is very important during exercise?

A

Increased venous return
Increased EDV
Increased SV
Increased CO

75
Q

What maintains normal arterial pressure during severe haemorrhage?

A

Vasoconstriction of resistance and capacitance vessels

76
Q

Do parasympathetic nerves have high or low vasodilatory effects?

A

Low

77
Q

What is regulation of peripheral resistance mediated by?

A

Sympathetic nerves

78
Q

Where is the vasomotor centre located?

A

Reticular substance of the medulla and the lower third of the Pons

79
Q

What does the vasomotor centre do?

A

Regulates impulses of the vagus nerve

80
Q

What section of the vasomotor centre regulates sympathetic nerve fibers?

A

Rostral ventrolateral medulla (RVLM)

81
Q

What does the RVLM do?

A

Sends fibers to spinal cord which excite pre-ganglionic neurons of the SNS
Maintains both sympathetic cardiac and vasoconstrictor tone

82
Q

What does stimulation of the RVLM do?

A

Increases BP and HR

83
Q

What happens if the RVLM is destroyed?

A

BP decreases to 40mmHg
Essential for maintaining normal BP

84
Q

What are other names for the RVLM?

A

Pressor region
Vasoconstrictor area

85
Q

What is the role of the caudal ventrolateral medulla?

A

Fibres project to the RVLM and inhibit its activity causing vasodilation

86
Q

What is the role of the caudal ventrolateral medulla?

A

Fibres project to the RVLM and inhibit its activity causing vasodilation

87
Q

What other names exist for the CVLM?

A

Depressor region
Vasodilator area

88
Q

What are the nucleus ambiguus (NA, AMB) and dorsal motor nucleus of vagus?

A

Origin of vagal projections to the heart
Vagal centre

89
Q

What is the role of the nucleus of the tractus solitarius?

A

Receives sensory signals from circulatory system mainly through the vagus and glossopharyngeal nerves

90
Q

What are the vagus and glossopharyngeal nerves stimulated by?

A

Baroreceptors and cardiopulmonary recpetors

91
Q

Where does the NTS send output to?

A

CVLM
NA

92
Q

What does stimulation of the NTS do?

A

Reduces sympathetic outflow and increases vagal outflow

93
Q

Where does the NTS receive sensory impulses from?

A

Baroreceptors
cardiopulmonary receptors
Chemoreceptors
Other brain regions

94
Q

Name an example of a detrimental effect of blood pressure diverging from normal limits.

A

Perfusion of cerebral circulation

95
Q

What are baroreceptors?

A

Stretch-sensitive mechanoreceptors

96
Q

Where are baroreceptors located?

A

Walls of the carotid artery and the aortic arch

97
Q

How do baroreceptors become more active?

A

An increase in blood pressure causing the walls of the carotid artery and the aortic arch

98
Q

Where exactly are stretch receptors located?

A

Carotid sinuses and aortic arch

99
Q

What are the afferent pathways of the arterial baroreceptors?

A

Carotid sinus nerve (Hering’s nerve) > Glossopharyngeal nerve > NTS
Vagus nerve > NTS
“Buffer nerves” as they buffer abrupt changes in BP

100
Q

At what values of BP is vagal activity depressed/activated?

A

Activated - >100mmHg
Depressed - <100mmHg

101
Q

What do increases in arterial pressure enhance?

A

Firing of baroreceptor terminals

102
Q

How is firing of baroreceptor terminals diminished?

A

Reductions in arterial pressure

103
Q

What does the baroreceptor reflex allow the cardiovascular system to do?

A

Respond to rapid pulsatile changes in blood pressure

104
Q

Which baroreceptors are more important for regulating arterial pressure?

A

Carotid sinus baroreceptors

105
Q

What viscus is responsible for long term regulation of blood pressure?

A

Kidney

106
Q

Can the baroreceptor reflex correct long term changes in arterial pressure?

A

No, they are only responsible for acute regulation of BP

107
Q

At 100mmHg does a slight change in pressure cause a weak or strong change in the baroreflex signal?

A

Strong as it wants to readjust arterial pressure back toward normal

108
Q

What will a sudden reduction in blood pressure do?

A

Rapid increase of sympathetic nerve activity
Reduction in vagal activity will diminish inhibitory effect of HR

109
Q

What will an increase in sympathetic nerve activity do?

A

Increase cardiac output
Contract venous smooth muscle promoting venous return
Stimulate contraction of arterial smooth muscle to increase peripheral resistance
Vasoconstriction in kidney arterioles also minimises urine formation

110
Q

What will a sudden elevation in blood pressure do?

A

Stimulate the vagus nerve
Inhibit sympathetic nerves
Kidneys are also stimulated to excrete more water as urine, thereby reducing total blood volume

111
Q

What does stimulation of the vagus nerve do?

A

Reduce cardiac output by slowing heart rate

112
Q

What does inhibiting sympathetic nerve activity do?

A

Reduces cardiac output
Causes relaxation of arterial smooth muscle to decrease peripheral resistance aka vasodilation

113
Q

What do cardiopulmonary baroreceptors do?

A

Initiate a reflex that lowers arterial blood pressure in response to changes in blood volume

114
Q

What does the reflex of cardiopulmonary baroreceptors mainly act on and to do what?

A

Kidneys to reduce blood volume by increasing urine output

115
Q

How does the reflex of the cardiopulmonary baroreceptors achieve this?

A

Reduction of sympathetic nerve activity to kidneys
Inhibition of angiotensin, aldosterone and ADH

116
Q

What is the Bainbridge reflex?

A

Increased blood volume increases atrial pressure causing a rapid increase in HR

117
Q

What is the Bainbridge reflex mediated by?

A

Atrial stretch receptors

118
Q

Where are the signals for the Bainbridge reflex transmitted in to and from the NTS?

A

vagus nerve afferently
vagal and sympathetic nerves efferently

119
Q

What do the sympathetic and vagal nerves do in the Bainbridge reflex?

A

Increases HR and contractility
Transfer of blood into arterial circulation
Prevents damming of blood in veins, atria and pulmonary circulation

120
Q

Are Bainbridge and baroreceptor reflexes agonistic or antagonistic?

A

Antagonistic

121
Q

If the blood volume is high which reflex predominates?

A

Bainbridge reflex

122
Q

If the blood volume is low which reflex predominates?

A

Baroreceptor reflex

123
Q

What makes the decision of whether the Bainbridge reflex or the Baroreceptor reflex predominates?

A

NTS

124
Q

Where are chemoreceptors located?

A

Medulla
Sinuses
Aortic arch

125
Q

What do chemoreceptors do and what is their role?

A

Respond to changes in arterial PO2, PCO2 and pH
Set appropriate rate and depth of ventilation

126
Q

What may peripheral chemoreceptor afferents do?

A

Increase blood pressure
Increase heart rate

127
Q

What does the hypothalamus do?

A

Regulates appetite, body temperature, fluid balance, endocrine secretion

128
Q

What does the anterior/preoptic hypothalamus do?

A

Decreases HR and BP

129
Q

What does the posterior and lateral hypothalamus do?

A

Involved in the alerting reaction in response to impending danger
Increases BP, HR
Vasodilation in skeletal muscle
Vasoconstriction in skin and splanchnic organs

130
Q

How does the cerebral cortex affect the circulatory system?

A

Vasoconstriction of skin, splanchnic and renal vessels
Vasodilation in skeletal muscles

131
Q

What does the limbic area of the cerebral cortex do?

A

Vasodilation of facial blood vessels
Triggers cardiovascular responses to pain and anxiety

132
Q

What is meant by compliance?

A

The ability of the blood vessels to distend (swell) in response to blood pressure

FM1020 Physiology (12 decks)

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