The Peripheral Circulation Flashcards Preview

ESA 2- Cardiovascular System > The Peripheral Circulation > Flashcards

Flashcards in The Peripheral Circulation Deck (92):
1

What are the main components of the CVS?

Heart, Arteries, Arterioles, Capillaries, Veins

2

What is the function of the heart?

Cyclic muscular pump that enables circulation of the blood

3

What is the function of arteries?

Gross conduction and distribution of blood supply

4

What is the purpose of arterioles?

Local distribution and fine control of defined tissue volume

5

What is the function of capillaries?

Microdiffusion and filteration

6

What is the function of veins?

Collection and return, and capacitance

7

What is compliance?

Ability to distend and increase volume due to pressure increase

8

What is capacitance?

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

9

What is pressure?

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

10

What does cyclic muscular contraction produce?

Pressure waves to move blood into circulation

11

How is cardiac output calculated?

Stroke volume x heart rate

12

What is the average cardiac output?

~5l/min

13

What happens with each beat of the heart?

Stroke volume is delivered to the major arterial tree

14

What is the resistance of the major arterial tree?

Low

15

What is the compliance of the major arterial tree?

~1-2% change / mmHg 
Still very important

16

What is the pressure of the major arterial tree?

High

17

What needs to be true of arterial pressures?

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

18

How much can resistance very from arteriole to arteriole?

Greatly

19

What is total peripheral resistance?

The sum of all arteriolar resistance

20

What does compliance affect?

Pulsatile pressure flow in arteries

21

In what manner does the heart eject blood?

Cyclically

22

When does blood flow into arteries?

Systole

23

What does compliance act to do?

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

24

What would happen if arteries were very rigid walled?

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

25

What effect does aortic compliance have?

Dampens the pulsatile nature of the systolic pressure wave

26

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

Aorta and elastic arteries and less smooth muscle

27

What is the Windkessel Effect?

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

28

What is systolic pressure?

The maximum arterial pressure that is reached during systole

29

What is diastolic pressure?

The minimum arterial pressure that is reached during diastole

30

What does the blood pressure gradient do?

Drives flow all all time points in the cardiac cycle

31

What is blood pressure measured in?

mmHg

32

What is systolic pressure typically said to be?

120mmHg

33

What is diastolic pressure typically said to be?

88mmHg

34

What factors affect systolic and diastolic pressure?

Cardiac output 
Arterial compliance

35

How is cardiac output calculated?

SV x HR

36

What determines cardiac ouput?

How hard the heart is pumping

37

What is meant by arterial compliance?

The stretchiness of elastic arteries

38

What is the compliance of elastic arteries?

1.5-2% /mmHg

39

What is pulse pressure?

The difference between systolic and diastolic pressure

40

What is pulse pressure at rest?

About 40mmHg, but varies

41

How is the average pressure calculated?

Calculated as diastole + 1/3 pulse pressure

42

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

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

43

What causes a decrease in pulse pressure?

Summated resistance and capacitance of arteriolar network

44

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

It decreases

45

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

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

46

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

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

47

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

40mmHg

48

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

Get ischaemia

49

What is the role of arterioles?

Control flow to capillary beds

50

What are the resistance vessels?

Arterioles and pre-capillary sphincters

51

What is the resistance of arterioles?

High

52

Why are arterioles high resistance?

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

53

What governs flow to capillary beds?

Arteriolar vasomotor tone

54

How does arteriolar vasomotor tone govern flow to capillary beds?

By vasoconstriction and vasodilation

55

What do vasoconstriction and vasodilation work together to do?

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

56

How does metabolic demand differ?

From tissue to tissue through the body

57

Is vasomotor tone high or low at rest?

High

58

What causes high vasomotor tone at rest?

Tonic contraction of muscle

59

Why is vasomotor tone being high at rest good?

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

What is vasomotor done most centrally controlled by?

The autonomic SNS

61

How does the SNS control vasomotor tone?

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

62

What modulates vasomotor tone?

Circulating hormones

63

What impact can local factors on vasomotor tone?

They can reduce it by increasing vasodilation

64

What effect does vasodilation have on flow?

It reduces resistance to flow

65

How can local factors reduce vasomotor tone?

Achieved by local vasodilator factors

66

What produces local vasodilator factors?

Metabolically active tissues produce vasodilator metabolites

67

Give 5 examples of vasodilator metabolites

H+
CO2
K+
Adenosine 
Lactate

68

How do vasodilator metabolites act?

To relax vascular smooth muscle

69

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

It is usually acute

70

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

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

71

What locally mediates vasomotor tone?

Myogenic factors 
Endothelial factors

72

What myogenic factors locally mediate vasomotor tone?

Arteriolar smooth muscle exposed to rapid intraluminal pressure rise

73

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

It causes a pressure spike of >200mmHg

74

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

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

75

Where are endothelial factors released from?

Arteriolar endothelium

76

What do autacoids do?

Modulate an increase or decrease in vasomotor tone

77

What are blood flow changes to tissue governed by?

Acute metabolic demands in local tissue

78

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

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

79

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

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

80

What is the total peripheral resistance?

The summation of all arteriolar resistances in the body

81

What is the total peripheral resistance inversely proportional do?

The total body demand for blood flow

82

What is the result of veins being very stretchy?

The provide a large circulatory reservoir
They have a very high compliance

83

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

65%

84

What is the compliance of the veins?

10%+ in volume /mmHg

85

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

The can accommodate change in blood volume very quickly

86

What is the resistance of veins?

Total total resistance relative to arterial system

87

What is the pressure in veins determined by?

The volume of blood they contain 
Depends on balance between flow in from body and out via heart

88

What does the central venous pressure range between?

-10 to +10 mmHg

89

Where is central venous pressure measured?

Great veins

90

What is central venous pressure required for?

Filling in diastole

91

Usually, what is central venous pressure?

2-6mmHg

92

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

Get blood into RA