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ESA 2- Cardiovascular System > Flow through Tubes > Flashcards

Flow through Tubes Flashcards

1
Q

What are the two major subdivisions of the vascular system?

A

Systemic circulation and Pulmonary circulation

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2
Q

How are the systemic and pulmonary circulations arranged?

A

In series with one another

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3
Q

What is each subdivision of the circulation composed of?

A 
Arteries
 Arterioles
 Capillaries
 Venules
 Veins
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4
Q

How are most vessels of a given type arranged?

A

In parallel with each other

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5
Q

What must happen in order for blood to keep flowing?

A

Blood pressure must fall all the way from the aorta to the venae cavae

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6
Q

How is flow of blood driven through vessels?

A

By the gradient of pressure

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7
Q

What is flow proportional too?

A

The pressure difference between the ends of a vessel

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8
Q

What is the result of a higher pressure difference on flow?

A

Higher flow

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9
Q

What is the flow for a given pressure gradient determined by?

A

The resistance of a vessel

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10
Q

What is the resistance of a vessel determined by?

A

The nature of the fluid and the vessel

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11
Q

Define flow

A

The volume of fluid passing a given point per unit time

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12
Q

Define velocity

A

The rate of movement of fluid particles along the tube

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13
Q

How does flow differ at different points along a vessel?

A

It doesn’t

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14
Q

When can velocity vary along the length of a vessel?

A

If the radius of the tube changes

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15
Q

What is the relationship between velocity and cross sectional area at a given flow?

A

They are inversely proportional

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16
Q

What is the velocity of vessels with a small cross sectional area at a given flow?

A

High

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17
Q

What is the velocity of vessels with a large collective cross sectional at a given flow?

A

Low

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18
Q

What vessels have a large cumulative cross sectional area?

A

Capillaries

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19
Q

What happens as arteries branch?

A

The total cross sectional area of the vascular bed increases, and thus so does flow

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20
Q

How can the flow be described in most blood vessels?

A

Laminar

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21
Q

What happens in laminar flow?

A

There is a gradient of velocity from the middle (highest), to the edge, where fluid is stationary

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22
Q

What happens as mean velocity increases?

A

Flow eventually becomes turbulent

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23
Q

What happens in turbulent flow?

A

The velocity gradient breaks down as fluid tumbles over, and the flow resistance greatly increases

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24
Q

What is flow determined by in a vessel with constant pressure?

A

Mean velocity

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25
Q

What does mean velocity depend on?

A

Viscosity of fluid

Radius of tube

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26
Q

How does fluid move in laminar flow?

A

In concentric layers, with middle edges moving faster than the outer layers, and therefore the layers must slide over one another

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27
Q

What is the extent to which fluid layers resist sliding over one another known as?

A

Viscosity

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28
Q

What does a higher viscosity result in?

A

Slower flow of central layers, and a lower average velocity

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29
Q

What does viscosity determine?

A

The slope of the gradient of velocity

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30
Q

What does a wider tube result in at a constant gradient?

A

A faster middle layer

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31
Q

What is the relationship between mean velocity and cross sectional area of the tube?

A

Proportional

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32
Q

What is flow the product of?

A

Mean velocity and cross sectional area

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33
Q

How can flow be calculated?

A

Poiseuille’s Law

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34
Q

What is Poiseuille’s Law?

A

Q = π.∆P.r 4

8.n.L

Where

·
Q=
flow

·
π/8 =
constant of proportionality

·
∆P =
inflow and outflow pressure difference

·
r =
radius of tube

·
n =
viscosity of fluid

·
L =
length of tube

35
Q

What does Poiseuille’s Law say that flow is, when blood flow is steady and laminar in blood vessels larger than arterioles ?

A

Proportional to the difference between inflow and outflow pressures
Proportional to the fourth power of the radius
Inversely proportional to the length of vessel
Inversely proportional to the viscosity of the blood

36
Q

Why does Poiseuille’s Law only work in vessels larger than arterioles?

A

Because otherwise the vessel is so small that the flow doesn’t work fully for them

37
Q

Whos airways are particularly prone to compromised flow?

A

Childrens, as they are narrow

38
Q

What is childrens airways being narrow relevant to?

A

Narrowing of airways in childhood asthma
Bronchiolitis being primarily a disease of children
The need to avoid emotionally upsetting a sick child who is already fighting for breath, as upsetting them leads to more narrowing of airways
The need to ventilate an intubated child during surgery

39
Q

Why is the narrower childs airway relevant in intubation?

A

Because a 2mm reduction in diameter of a child’s trachea caused by an inserted tube reduces the flow more than a 2mm reduction in diameter of an adults trachea, as it’s smaller and so 2mm is a larger proportional reduction

40
Q

What can hyper-viscosity syndrome (HVS) be caused by?

A

Abnormally high plasma protein levels

Abnormally high RBC or WBC count

41
Q

Give an example of a HVS caused by abnormally high plasma protein levels

A

High IgM in Waldenstrom macroglobulinaemia

42
Q

What % of HVS cases doesWaldenstrom macroglobulinaemia account for?

A

85%

43
Q

How isWaldenstrom macroglobulinaemia treated?

A

Plasmapheresis

44
Q

Give an example of a HVS caused by abnormally high RBC or WBC count

A

Polycythemia

45
Q

How is polycythemia treated?

A

Phlebotomy

46
Q

What must be done to fully stop HVS?

A

The underlying condition must be treated, otherwise HVS reoccurs

47
Q

When can functional cardiac murmurs occur?

A

In severe anaemias, as a result of high blood flow velocities and reduced viscosity of blood

48
Q

Why do severe anaemias cause functional cardiac murmurs?

A

Because of the low blood cell count

49
Q

What does flow of fluid along tubes obey?

A

Ohms law

50
Q

What is Ohms law?

A

V = IR

51
Q

What happens to resistance as viscosity increases?

A

It increases

52
Q

What happens to resistance as the radius increases?

A

It decreases to the fourth power the radial increase

53
Q

What happens to resistance when blood vessels are connected together?

A

They combine

54
Q

How do you work out the total resistance for vessels in series?

A

The total resistance equals the sum of all the individual resistances

55
Q

What is the effective resistance for vessels in parallel?

A

Lower for that in series

56
Q

How do you work out the total resistance for vessels in parallel?

A

The reciprocal of the total resistance equals the sum of the resistance of the individual resistances

57
Q

Why do capillaries offer little collective resistance?

A

On account of their parallel arrangement

58
Q

What happens to the pressure change at a higher resistance, if the flow is fixed?

A

There is a greater pressure change from one end of the vessel to the other

59
Q

What happens to flow at higher resistances, if the pressure is fixed?

A

The lower the flow

60
Q

How does the flow change over the whole circulation?

A

It doesn’t- over the whole circulation, flow is the same at all points

61
Q

What resistance are arteries?

A

Low

62
Q

How big is the pressure drop over arteries?

A

Small

63
Q

What resistance are arterioles?

A

High

64
Q

How big is the pressure drop over arterioles?

A

High

65
Q

What resistance are capillaries?

A

Individual capillaries are high resistance, but many are connected in parallel and so the overall resistance is low

66
Q

How big is the pressure drop over capillaries?

A

Small

67
Q

What resistance are veins and venules?

A

Low

68
Q

Why is pressure within arteries high?

A

Because of the high resistance of arterioles

69
Q

What does a higher arteriolar resistance cause for a given total flow?

A

Higher arterial pressure

70
Q

When does flow become turbulent?

A

If flow velocity is high
If viscosity is low
If lumen of vessel irregular

71
Q

What can cause irregularity of the lumen?

A

Irregular narrowing, e.g. atherosclerosis

72
Q

Give an example of where flow may become turbulent

A

Aorta

73
Q

What does turbulent flow generate?

A

Sound

74
Q

What is sound caused by turbulent flow called?

A

Bruit

75
Q

How can a bruit be heard?

A

On auscultation

76
Q

When can a bruit be heard?

A

If cardiac valves become stenoic (narrowed)

When atherosclerotic blockages obstruct a carotid artery, a renal artery, a hepatic artery, or a femoral artery

77
Q

What can blood vessel walls?

A

Distend

78
Q

What does pressure within vessels generate?

A

Transmural pressure between inside and outside

79
Q

What is the result of the transmural pressure?

A

It tends to stretch the tube

80
Q

What happens as a blood vessel stretches?

A

Resistance falls

81
Q

What is the result of a higher pressure in a distensible vessel?

A

The easier it is for blood to flow through it

82
Q

What happens as vessels widen with increasing pressure?

A

More blood transiently in than out

83
Q

What can distensible vessels do?

A

Store blood- they have capacitacnce

84
Q

What are the most distensible blood vessels?

A

Veins

ESA 2- Cardiovascular System (18 decks)

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