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ESA 2- Cardiovascular System > Flow through Tubes > Flashcards

Flashcards in Flow through Tubes Deck (84):
1

What are the two major subdivisions of the vascular system?

Systemic circulation and Pulmonary circulation

2

How are the systemic and pulmonary circulations arranged?

In series with one another

3

What is each subdivision of the circulation composed of?

Arteries 
Arterioles 
Capillaries 
Venules 
Veins

4

How are most vessels of a given type arranged?

In parallel with each other

5

What must happen in order for blood to keep flowing?

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

6

How is flow of blood driven through vessels?

By the gradient of pressure

7

What is flow proportional too?

The pressure difference between the ends of a vessel

8

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

Higher flow

9

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

The resistance of a vessel

10

What is the resistance of a vessel determined by?

The nature of the fluid and the vessel

11

Define flow

The volume of fluid passing a given point per unit time

12

Define velocity

The rate of movement of fluid particles along the tube

13

How does flow differ at different points along a vessel?

It doesn't

14

When can velocity vary along the length of a vessel?

If the radius of the tube changes

15

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

They are inversely proportional

16

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

High

17

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

Low

18

What vessels have a large cumulative cross sectional area?

Capillaries

19

What happens as arteries branch?

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

20

How can the flow be described in most blood vessels?

Laminar

21

What happens in laminar flow?

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

22

What happens as mean velocity increases?

Flow eventually becomes turbulent

23

What happens in turbulent flow?

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

24

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

Mean velocity

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