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Semester 2 > CVS Session 5 > Flashcards

CVS Session 5 Flashcards

0
Q

What is flow proportional to?

A

Pressure difference b/w ends of the vessel

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1
Q

What is flow?

A

The volume of fluid (or gas) passing a given point per unit time

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2
Q

What limits flow?

A

Resistance of the vessel

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3
Q

What determines resistance of the vessel?

A

Interaction of the nature of the fluid and the vessel

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4
Q

What is velocity?

A

The rate of movement of fluid particles along a tube

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5
Q

What must remain constant and what can vary if the radius changes?

A

Flow must be constant

Velocity can vary

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6
Q

At a given flow, what is the relationship between velocity and cross sectional area?

A

Inversely proportional

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7
Q

How does the velocity of blood in the aorta compare to that of blood in the capillaries?

A

High in aorta

Low in capillaries

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8
Q

What is kept constant by having high velocity in narrow vessels and low velocity in wide vessels?

A

Number of particles delivered

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9
Q

What is laminar flow?

A

Gradient of velocity from centre to edge - velocity highest in centre, 0 immediately adjacent to wall

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10
Q

What is another name for laminar flow?

A

Silent flow

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11
Q

What is turbulent flow caused by?

A

Increased mean velocity causing velocity gradient to break down

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12
Q

What is turbulent flow?

A

Fluid tumbles over itself and flow resistance increases - net flow forwards but particle move randomly

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13
Q

What is a bruit?

A

Noise caused by turbulent flow

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14
Q

When is a bruit normal and when is it pathological?

A

Normal in heart

Pathological in BV

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15
Q

If a vessel has a constant pressure, what will determine flow?

A

Mean velocity

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16
Q

What is the relationship between mean velocity and viscosity?

A

Inversely proportional

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17
Q

What is flow a product of?

A

Mean velocity and cross sectional area

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18
Q

What two factors determine mean velocity?

A

Tube radius

Viscosity

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19
Q

What is Poiseulle’s law?

A

Flow is proportional to pressure difference divided by viscous resistance = (Pr^4)/(viscosity x length)

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20
Q

What two things is mean velocity proportional to?

A

Cross sectional area

r^2

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21
Q

Why does increasing the cross-sectional area of a tube increase velocity?

A

A wide tube allows for faster middle layers as the velocity gradient remains constant

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22
Q

What is viscosity?

A

The extent of resistance to layer sliding in laminar flow

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23
Q

How does fluid move in laminar flow?

A

In concentric layers w/middle faster than edges

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24
Q

How does increasing viscosity cause average velocity to decrease?

A

Causes central layers to move more slowly –> decreased velocity gradient therefore decreased average velocity

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25
Q

What does viscosity determine graphically in relation to velocity?

A

Slope of gradient of velocity

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26
Q

What law does flow resistance obey?

A

Ohm’s law

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27
Q

What two things is flow resistance proportional to?

A

Viscosity

1/(r^4)

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28
Q

What makes blood harder to push?

A

Small BV

Thicker blood

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29
Q

How does resistance compare in BV in series to those in parallel?

A 
Series = resistances add
Parallel = lower effective resistance as alternative pathways available
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30
Q

If flow is fixed and resistance is increased, what happens to the pressure change from one end of the vessel to another?

A

Increases

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31
Q

If pressure is fixed and resistance is increased, what happens to flow?

A

Decreases

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32
Q

Why do cells travel round the circulation faster than plasma?

A

They bounce off walls and congregate in the middle of flow so the apparent viscosity increases and they travel faster than the surrounding plasma

33
Q

What can be said about the flow in the whole circulation system?

A

Is it 5 l per minute at all points

34
Q

How does the pressure change across arteries?

A

Small drop

35
Q

Why is BP measured in the arm?

A

There is only a small drop in pressure between here and the heart therefore it is the most accurate and practical place to measure

36
Q

What is the magnitude of the pressure drop across arterioles?

A

Large

37
Q

Compare the resistance of single capillaries to their overall resistance.

A

Singularly are high resistance but in parallel so overall resistance is low

38
Q

Are venules and veins high or low resistance?

A

Low resistance

39
Q

What determines arterial pressure?

A

Cardiac output and TPR

40
Q

What will tip laminar flow into turbulent flow when on the edge of transition?

A

Stress

41
Q

How can distensible BV walls decrease resistance?

A

Transmural pressure changes –> stretches tube –> increases lumen

42
Q

How is capacitance achieved?

A

Vessels widen w/ increasing pressure causing more blood transiently in than out

43
Q

What happens to the lumen of BV with distensible walls in cases of sudden pressure changes?

A

Sudden increase = increase lumen –> more blood in than out

Sudden decrease = more blood out than in –> decrease lumen

44
Q

What is the critical closing pressure of a BV?

A

Pressure inside vessel

45
Q

Why must arteries have distensible walls?

A

So that blood can continue to flow in diastole and the entire cardiac output does not have to be pushed past TPR during systole

46
Q

How does the distensibility of artery walls allow blood to flow during diastole even though no blood is entering the arteries?

A

In systole: arteries stretch –> more blood in than out –> pressure does not increase much –> arteries recoil in diastole

47
Q

What is systolic pressure?

A

Maximum arterial pressure at the end of systole

48
Q

What is diastolic pressure?

A

Minimum arterial pressure at the end of diastole

49
Q

What determines systolic pressure?

A

How hard the heart pumps
TPR
Compliance (stretchiness) of arteries

50
Q

Why does systolic pressure increase with age?

A

Compliance of arteries decreases with age

51
Q

What is the approximate value of systolic pressure?

A

~120 mmHg

52
Q

What is the approximate value of diastolic pressure?

A

~80 mmHg

53
Q

What determines diastolic pressure?

A

TPR

Systolic pressure - determines start point of diastolic

54
Q

What is the better indicator of diastolic pressure and why?

A

TPR, it is not affected by compliance

55
Q

What is pulse pressure?

A

Systolic - diastolic

56
Q

What does pulse pressure tell you about?

A

Force of contraction of the heart e.g. adrenaline or exercise effects

57
Q

How is average pressure calculated?

A

Diastolic + 1/3 pulse
2/3 diastolic + 1/3 systolic
(Systole is shorter than diastole)

58
Q

What are the approximate values of pressure in the arteries, arterioles, capillaries, venules and veins?

A 
Arteries = 100 mmHg
Arterioles = 35 mmHg
Capillaries = 10 mmHg
Venules = 8 mmHg
Veins = 3 mmHg
59
Q

Why are arterioles coupled with pre-capillary sphincters in skeletal muscle?

A

It’s requirement for a variable blood flow

60
Q

What are pre-capillary sphincters?

A

Smooth muscle around arterioles which can contract/relax to alter resistance to blood flow

61
Q

What is vasomotor tone?

A

Tonic (continuous) contraction of smooth muscle

62
Q

How is vasoconstriction achieved?

A

NA on alpha 1 receptors in virtually every tissue causing increased resistance to flow

63
Q

How is vasodilation achieved?

A

Vasodilator factors antagonise vasomotor tone - BV do not actively relax, they contract less

64
Q

What is reactive hyperaemia?

A

Circulation cut off for 1-2 mins –> vasodilator metabolites not washed away –> transient large increase in bloodflow on reperfusion

65
Q

What does the effect of vasodilator metabolites depend on?

A

Balance b/w rate of production and rate of removal by blood flow

66
Q

Why does resistance usually increase without a decrease in blood supply resistance?

A

Due to metabolites

67
Q

What is autoregulation?

A

Constant metabolism –> constant [metabolite] –> supply pressure increases –> transient increase in blood flow –> metabolites washed away –> smooth muscle contracts increasing vasomotor tone

68
Q

What must occur for a tissue to automatically take what blood it needs irrespective of arterial supply?

A

Supply pressure to remain within certain limits

69
Q

What determines how much blood is pumped around the body?

A

If all tissues in the body alter the resistance of their arterioles to match their metabolism

70
Q

What determines the pressure of blood in the veins?

A

Capacitance - the volume of blood they contain

71
Q

What does capacitance depend on?

A

Balance b/w flow in from the body and out via the heart

72
Q

What is central venous pressure?

A

Pressure in the great veins that fills the heart in diastole

73
Q

What determines venous and arterial pressure?

A 
Venous = capacitance of veins
Arterial = resistance vessels
74
Q

What does central venous pressure depend on?

A

Return of blood from the body
Pumping of the heart
Gravity
Muscle pumping

75
Q

How does muscle pumping increase venous return?

A

Skeletal muscle compresses vein pushing blood out of veins to heart
Inhaling ‘sucks’ blood back to heart due to pressure changes

76
Q

What is central venous pressure balanced by?

A

Inflow and outflow of blood

77
Q

What must arterial pressure be high enough to ensure?

A

Tissues get what blood they need

78
Q

What happens as more blood is needed?

A

TPR decreases

79
Q

What fills the heart?

A

Central venous pressure

80
Q

What 4 variables can the CVS be reduced to?

A

Arterial pressure
Pressure in veins
Cardiac output
TPR

Semester 2 (45 decks)

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