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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
What does mean velocity depend on?
Viscosity of fluid  | Radius of tube
26
How does fluid move in laminar flow?
In concentric layers, with middle edges moving faster than the outer layers, and therefore the layers must slide over one another
27
What is the extent to which fluid layers resist sliding over one another known as?
Viscosity
28
What does a higher viscosity result in?
Slower flow of central layers, and a lower average velocity
29
What does viscosity determine?
The slope of the gradient of velocity
30
What does a wider tube result in at a constant gradient?
A faster middle layer
31
What is the relationship between mean velocity and cross sectional area of the tube?
Proportional
32
What is flow the product of?
Mean velocity and cross sectional area
33
How can flow be calculated?
Poiseuille’s Law
34
What is Poiseuille’s Law?
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
What does Poiseuille’s Law say that flow is, when blood flow is steady and laminar in blood vessels larger than arterioles ?
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
Why does Poiseuille’s Law only work in vessels larger than arterioles?
Because otherwise the vessel is so small that the flow doesn’t work fully for them
37
Whos airways are particularly prone to compromised flow?
Childrens, as they are narrow
38
What is childrens airways being narrow relevant to?
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
Why is the narrower childs airway relevant in intubation?
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
What can hyper-viscosity syndrome (HVS) be caused by?
Abnormally high plasma protein levels  | Abnormally high RBC or WBC count
41
Give an example of a HVS caused by abnormally high plasma protein levels
High IgM in Waldenstrom macroglobulinaemia
42
What % of HVS cases does Waldenstrom macroglobulinaemia account for?
85%
43
How is Waldenstrom macroglobulinaemia treated?
Plasmapheresis
44
Give an example of a HVS caused by abnormally high RBC or WBC count
Polycythemia
45
How is polycythemia treated?
Phlebotomy
46
What must be done to fully stop HVS?
The underlying condition must be treated, otherwise HVS reoccurs
47
When can functional cardiac murmurs occur?
In severe anaemias, as a result of high blood flow velocities and reduced viscosity of blood
48
Why do severe anaemias cause functional cardiac murmurs?
Because of the low blood cell count
49
What does flow of fluid along tubes obey?
Ohms law
50
What is Ohms law?
V = IR
51
What happens to resistance as viscosity increases?
It increases
52
What happens to resistance as the radius increases?
It decreases to the fourth power the radial increase
53
What happens to resistance when blood vessels are connected together?
They combine
54
How do you work out the total resistance for vessels in series?
The total resistance equals the sum of all the individual resistances
55
What is the effective resistance for vessels in parallel?
Lower for that in series
56
How do you work out the total resistance for vessels in parallel?
The reciprocal of the total resistance equals the sum of the resistance of the individual resistances
57
Why do capillaries offer little collective resistance?
On account of their parallel arrangement
58
What happens to the pressure change at a higher resistance, if the flow is fixed?
There is a greater pressure change from one end of the vessel to the other
59
What happens to flow at higher resistances, if the pressure is fixed?
The lower the flow
60
How does the flow change over the whole circulation?
It doesn’t- over the whole circulation, flow is the same at all points
61
What resistance are arteries?
Low
62
How big is the pressure drop over arteries?
Small
63
What resistance are arterioles?
High
64
How big is the pressure drop over arterioles?
High
65
What resistance are capillaries?
Individual capillaries are high resistance, but many are connected in parallel and so the overall resistance is low
66
How big is the pressure drop over capillaries?
Small
67
What resistance are veins and venules?
Low
68
Why is pressure within arteries high?
Because of the high resistance of arterioles
69
What does a higher arteriolar resistance cause for a given total flow?
Higher arterial pressure
70
When does flow become turbulent?
If flow velocity is high  If viscosity is low If lumen of vessel irregular
71
What can cause irregularity of the lumen?
Irregular narrowing, e.g. atherosclerosis
72
Give an example of where flow may become turbulent
Aorta
73
What does turbulent flow generate?
Sound
74
What is sound caused by turbulent flow called?
Bruit
75
How can a bruit be heard?
On auscultation
76
When can a bruit be heard?
If cardiac valves become stenoic (narrowed) | When atherosclerotic blockages obstruct a carotid artery, a renal artery, a hepatic artery, or a femoral artery
77
What can blood vessel walls?
Distend
78
What does pressure within vessels generate?
Transmural pressure between inside and outside
79
What is the result of the transmural pressure?
It tends to stretch the tube
80
What happens as a blood vessel stretches?
Resistance falls
81
What is the result of a higher pressure in a distensible vessel?
The easier it is for blood to flow through it
82
What happens as vessels widen with increasing pressure?
More blood transiently in than out
83
What can distensible vessels do?
Store blood- they have capacitacnce
84
What are the most distensible blood vessels?
Veins

ESA 2- Cardiovascular System (18 decks)

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