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ESA 2- Cardiovascular System > The Peripheral Circulation > Flashcards

The Peripheral Circulation Flashcards

1
Q

What are the main components of the CVS?

A

Heart, Arteries, Arterioles, Capillaries, Veins

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2
Q

What is the function of the heart?

A

Cyclic muscular pump that enables circulation of the blood

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3
Q

What is the function of arteries?

A

Gross conduction and distribution of blood supply

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4
Q

What is the purpose of arterioles?

A

Local distribution and fine control of defined tissue volume

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5
Q

What is the function of capillaries?

A

Microdiffusion and filteration

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6
Q

What is the function of veins?

A

Collection and return, and capacitance

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7
Q

What is compliance?

A

Ability to distend and increase volume due to pressure increase

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8
Q

What is capacitance?

A

Effectively the same as compliance- a measure of relative volume increase per unit in pressure

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9
Q

What is pressure?

A

A measure of mechanical energy gradient in blood that drives flow around different parts of the system

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10
Q

What does cyclic muscular contraction produce?

A

Pressure waves to move blood into circulation

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11
Q

How is cardiac output calculated?

A

Stroke volume x heart rate

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12
Q

What is the average cardiac output?

A

~5l/min

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13
Q

What happens with each beat of the heart?

A

Stroke volume is delivered to the major arterial tree

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14
Q

What is the resistance of the major arterial tree?

A

Low

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15
Q

What is the compliance of the major arterial tree?

A

~1-2% change / mmHg

Still very important

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16
Q

What is the pressure of the major arterial tree?

A

High

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17
Q

What needs to be true of arterial pressures?

A

They need to be high enough to drive cardiac output through high resistance arterioles

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18
Q

How much can resistance very from arteriole to arteriole?

A

Greatly

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19
Q

What is total peripheral resistance?

A

The sum of all arteriolar resistance

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20
Q

What does compliance affect?

A

Pulsatile pressure flow in arteries

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21
Q

In what manner does the heart eject blood?

A

Cyclically

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22
Q

When does blood flow into arteries?

A

Systole

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23
Q

What does compliance act to do?

A

Store mechanical energy of rising pressure wave during systole, and so dissipates energy more gradually over diastole

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24
Q

What would happen if arteries were very rigid walled?

A

Pressure would rise enough in systole to force whole stroke volume through TPR, but fall to 0 in diastole

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25
Q

What effect does aortic compliance have?

A

Dampens the pulsatile nature of the systolic pressure wave

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26
Q

Which vessels act to smooth out the pressure wave during systole?

A

Aorta and elastic arteries and less smooth muscle

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27
Q

What is the Windkessel Effect?

A

The capacitance effect, whereby more blood flows in than out, so pressure doesn’t rise as rapidly because elastic arteries recoil in diastole to release energy, which smooths flow through arterioles

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28
Q

What is systolic pressure?

A

The maximum arterial pressure that is reached during systole

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29
Q

What is diastolic pressure?

A

The minimum arterial pressure that is reached during diastole

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30
Q

What does the blood pressure gradient do?

A

Drives flow all all time points in the cardiac cycle

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31
Q

What is blood pressure measured in?

A

mmHg

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32
Q

What is systolic pressure typically said to be?

A

120mmHg

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33
Q

What is diastolic pressure typically said to be?

A

88mmHg

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34
Q

What factors affect systolic and diastolic pressure?

A

Cardiac output

Arterial compliance

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35
Q

How is cardiac output calculated?

A

SV x HR

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36
Q

What determines cardiac ouput?

A

How hard the heart is pumping

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37
Q

What is meant by arterial compliance?

A

The stretchiness of elastic arteries

38
Q

What is the compliance of elastic arteries?

A

1.5-2% /mmHg

39
Q

What is pulse pressure?

A

The difference between systolic and diastolic pressure

40
Q

What is pulse pressure at rest?

A

About 40mmHg, but varies

41
Q

How is the average pressure calculated?

A

Calculated as diastole + 1/3 pulse pressure

42
Q

Why is average pressure calculated in the way that it is?

A

Because time in systole is shorter, and so diastole predominates in average pressure

43
Q

What causes a decrease in pulse pressure?

A

Summated resistance and capacitance of arteriolar network

44
Q

What happens to variation in pulse pressure as it goes down the arterial tree?

A

It decreases

45
Q

Why does variation in pulse pressure decrease as it goes down the arterial tree?

A

As energy gets lost due to increased resistance as it branches out

46
Q

What is the result of the decrease in difference in pulse pressure as you go down the arterial tree?

A

Can approach a smooth mean pressure prior to flowing to capillary circulation- the pressure gradient decreases significantly by the time it reaches capillaries

47
Q

What is the pressure gradient at the end of the arteriolar branches?

A

40mmHg

48
Q

What happens if the pressure gradient at the end of the arteriolar tree isn’t enough to push it through capillaries?

A

Get ischaemia

49
Q

What is the role of arterioles?

A

Control flow to capillary beds

50
Q

What are the resistance vessels?

A

Arterioles and pre-capillary sphincters

51
Q

What is the resistance of arterioles?

A

High

52
Q

Why are arterioles high resistance?

A

Because the lumen is narrow, due to proportionally large amount of smooth muscle in tunica media

53
Q

What governs flow to capillary beds?

A

Arteriolar vasomotor tone

54
Q

How does arteriolar vasomotor tone govern flow to capillary beds?

A

By vasoconstriction and vasodilation

55
Q

What do vasoconstriction and vasodilation work together to do?

A

Finely regulate very small tissue volumes, and so can precisely match substrate supply to metabolic demand

56
Q

How does metabolic demand differ?

A

From tissue to tissue through the body

57
Q

Is vasomotor tone high or low at rest?

A

High

58
Q

What causes high vasomotor tone at rest?

A

Tonic contraction of muscle

59
Q

Why is vasomotor tone being high at rest good?

A

Modest resource demand, as only need low blood flow
No need to employ large functional reserve
Increased SNS activity driving α1-GPCRs leads to further vasoconstriction

60
Q

What is vasomotor done most centrally controlled by?

A

The autonomic SNS

61
Q

How does the SNS control vasomotor tone?

A

Release of NA acts on α1-GPCRs, causing an increase in intracellular [Ca], and so contraction

62
Q

What modulates vasomotor tone?

A

Circulating hormones

63
Q

What impact can local factors on vasomotor tone?

A

They can reduce it by increasing vasodilation

64
Q

What effect does vasodilation have on flow?

A

It reduces resistance to flow

65
Q

How can local factors reduce vasomotor tone?

A

Achieved by local vasodilator factors

66
Q

What produces local vasodilator factors?

A

Metabolically active tissues produce vasodilator metabolites

67
Q

Give 5 examples of vasodilator metabolites

A 
H+
 CO2
 K+
 Adenosine
 Lactate
68
Q

How do vasodilator metabolites act?

A

To relax vascular smooth muscle

69
Q

What can be said of decreased vasomotor tone due to metabolic activity and local release of vasodilator factors?

A

It is usually acute

70
Q

What causes a return to vasomotor tone dominated by SNS after local mediators have caused vasodilation?

A

Increased blood supply removes metabolic factors, so there is a gradual return

71
Q

What locally mediates vasomotor tone?

A

Myogenic factors

Endothelial factors

72
Q

What myogenic factors locally mediate vasomotor tone?

A

Arteriolar smooth muscle exposed to rapid intraluminal pressure rise

73
Q

What happens when arteriolar smooth muscle is exposed to a rapid intraluminal pressure rise?

A

It causes a pressure spike of >200mmHg

74
Q

What is the purpose of the reaction of arteriolar smooth muscle to a rapid intraluminal pressure rise?

A

Acute contraction protects from excess pressure, as this would damage tissue if allowed to persist

75
Q

Where are endothelial factors released from?

A

Arteriolar endothelium

76
Q

What do autacoids do?

A

Modulate an increase or decrease in vasomotor tone

77
Q

What are blood flow changes to tissue governed by?

A

Acute metabolic demands in local tissue

78
Q

What does increased blood flow due to acute metabolic demands lead to?

A

Decreased metabolite concentration (positive control signal to dilate offsets SNS)

79
Q

What happens once the increased blood flow has decreased metabolite concentration?

A

Resistance in arterioles returns to default to supply baseline level of metabolism (negative control signal to constrict)

80
Q

What is the total peripheral resistance?

A

The summation of all arteriolar resistances in the body

81
Q

What is the total peripheral resistance inversely proportional do?

A

The total body demand for blood flow

82
Q

What is the result of veins being very stretchy?

A

The provide a large circulatory reservoir

They have a very high compliance

83
Q

How much of the blood volume is held in the veins at rest?

A

65%

84
Q

What is the compliance of the veins?

A

10%+ in volume /mmHg

85
Q

What is the result of the veins having high compliance and being a reservoir?

A

The can accommodate change in blood volume very quickly

86
Q

What is the resistance of veins?

A

Total total resistance relative to arterial system

87
Q

What is the pressure in veins determined by?

A

The volume of blood they contain

Depends on balance between flow in from body and out via heart

88
Q

What does the central venous pressure range between?

A

-10 to +10 mmHg

89
Q

Where is central venous pressure measured?

A

Great veins

90
Q

What is central venous pressure required for?

A

Filling in diastole

91
Q

Usually, what is central venous pressure?

A

2-6mmHg

92
Q

What does central venous pressure need to be enough to do?

A

Get blood into RA

ESA 2- Cardiovascular System (18 decks)

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