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ESA2 > CVS 5 (Control of cardiac output + peripheral circulation) > Flashcards

CVS 5 (Control of cardiac output + peripheral circulation) Flashcards

1
Q

How does the pressure difference between the ends of a vessel affect the flow of blood?

A

Pressure difference is proportional to flow:

- the greater the pressure difference, the greater the flow

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2
Q

Define flow:

A

The volume of fluid passing a given point per unit time

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3
Q

Define velocity:

A

The rate of movement of fluid particles along the tube

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4
Q

At a given flow, how is velocity related to the cross sectional area of a tube?

A

Velocity is inversely proportional to the cross sectional area (at a given flow):
-As the cross sectional area increases, velocity decreases

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5
Q

What kind of vessel has a small cross sectional area, but high velocity?

A

Large arteries or veins

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6
Q

What kind of vessel has a large cross sectional area, but low velocity?

A

Capillaries

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7
Q

What is the approx. cross sectional area of the aorta (in cm)?

A

~ 2.5 cm

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8
Q

Describe laminar flow:

A

Fluid travels in thin parallel layers, which each pass over each other.
Velocity is greatest in the middle of the vessel, and decreases towards the edges, where flow is stationary.

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9
Q

Where in a healthy body is laminar flow most likely to become turbulent flow, and why?

A

Ascending aorta, due to the high velocity of blood.

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10
Q

What kind of flow generates sound waves?

A

Turbulent flow

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11
Q

Define turbulent flow:

A

A fluid flow in which the velocity at a given point varies erratically in magnitude and direction

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12
Q

What is the relationship between viscosity and velocity?

A

Velocity is inversely proportional to viscosity:

- as viscosity increases, velocity decreases

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13
Q

How is the cross sectional area of a tube related to velocity?

A

Velocity is proportional to the cross sectional area of a tube:
- As cross sectional area increases, velocity increases

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14
Q

Whose Law relates flow (Q) to the viscosity (n) of the fluid, the pressure gradient across the tubing (P), and the length (L) and diameter(r) of the tubing?

A

Poiseuille’s Law

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15
Q

When does Poiseuille’s Law NOT apply?

A

In vessels smaller than arterioles

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16
Q

What may cause Hyperviscosity Syndrome?

A
  • High plasma protein levels
  • High RBC count
  • High WBC count
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17
Q

How may Hyperviscosity Syndrome be treated?

A
  • Plasmapheresis (if high plasma protein levels)

- Phlebotomy (if high WBC/RBC count)

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18
Q

How can pressure be calculated from flow and resistance?

A

Pressure = Flow x Resistance

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19
Q

How is resistance related to viscosity?

A

Resistance is proportional to viscosity:

- as viscosity increases, resistance increases

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20
Q

Do arteries have high or low resistance? Why?

A

Low resistance - small pressure difference between the ends of the vessels

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21
Q

Do arterioles have high or low resistance? Why?

A

High resistance - large pressure difference between the ends of the vessels

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22
Q

Do capillaries have high or low resistance?

A

Individually - high resistance

In total - low resistance (as connected in parallel)

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23
Q

Do veins and venues have high or low resistance?

A

Low resistance

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24
Q

When does flow tend to become turbulent?

A
  • High flow velocity
  • Low viscosity
  • Irregular lumen of vessel
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25
Q

Define bruit:

A

An audible vascular sound associated with turbulent blood flow

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26
Q

Define capacitance:

A

The ability to store blood

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27
Q

Which blood vessels have the highest capacitance? Why?

A

Veins - most distensible

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28
Q

What is meant by the ‘Windkessel effect’?

A

The elastic arteries of the body smooth the pressure wave between systole and diastole, by storing blood between heart beats (capacitance)

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29
Q

What is the approx. pressure in arteries? (in mmHg)

A

95 mmHg

30
Q

What is the approx. pressure in arterioles? (in mmHg)

A

60 mmHg

31
Q

What is the approx. pressure in capillaries? (in mmHg)

A

35 mmHg

32
Q

What is meant by ‘pulse pressure’?

What is the typical pulse pressure? (in mmHg)

A

The difference between systolic and diastolic blood pressures
~ 40 mmHg

33
Q

What is the time period of systole (approx.)?

A

~ 0.3 s

34
Q

What is the time period of diastole (approx.)?

A

~ 0.55 s

35
Q

What is the time period of the cardiac cycle (approx.)?

A

~ 0.85 s

36
Q

Why is vasomotor tone high at rest?

A

Low demand = low blood flow

37
Q

Which branch of the nervous system controls vasomotor tone?

A

Sympathetic branch of Autonomic Nervous System

38
Q

Which neurotransmitter is released on blood vessels to control vasomotor tone? Which receptor does it bind to?

A

Noradrenaline

alpha-1 adrenoceptors

39
Q

How is vasodilation achieved?

A
  • Reduce sympathetic innervation of blood vessel

- Production of vasodilator metabolites by metabolically active tissues (H+/K+/CO2/Adenosine/Lactate)

40
Q

Name 5 vasodilator metabolites produced by metabolically active tissues:

A

1) H+
2) K+
3) CO2
4) Adenosine
5) Lactate

41
Q

Why is vasodilation caused by local mediators very short-lived?

A

Vasodilation increases blood flow, which disperses and removes the local vasodilator metabolites

42
Q

What is Reactive Hyperaemia?

A

The transient increase in blood flow following a brief period of ischaemia, due to increased amounts of vasodilator metabolites produced locally (to try to restore blood flow)

43
Q

What is TPR?

A

Total Peripheral Resistance: sum of arteriolar resistances throughout body

44
Q

What is the usual range of Central Venous Pressure (in mmHg)?

A

~ 2-6 mmHg

45
Q

What 2 main factors determines arterial pressure?

A

1) Cardiac output

2) Total Peripheral Resistance

46
Q

How does total-body exercise (initially) affect the Total Peripheral Resistance?

A

TPR falls as muscles require more blood = vasodilation of arterioles

47
Q

If TPR falls and cardiac output remains constant, what happens to the arterial and venous pressures?

A

Arterial pressure falls

Venous pressure rises

48
Q

If TPR rises and cardiac output remains constant, what happens to the arterial and venous pressures?

A

Arterial pressure rises

Venous pressure falls

49
Q

If cardiac output rises and TPR remains constant, what happens to the arterial and venous pressures?

A

Arterial pressure rises

Venous pressure falls

50
Q

If cardiac output falls and TPR remains constant, what happens to the arterial and venous pressures?

A

Arterial pressure falls

Venous pressure rises

51
Q

Cardiac output is calculated via:

A

Heart Rate x Stroke Vol.

52
Q

Define Stroke Volume:

A

The amount of blood pumped out of the left ventricle per beat:
End Diastolic Vol. - End Systolic Vol.

53
Q

Describe the relationship between venous pressure and ventricular volume:

A

Venous pressure is directly proportional to ventricular volume:
- If venous pressure increases, the ventricular volume will increase

54
Q

How is End-Diastolic Volume related to the Stroke Volume?

A

EDV is proportional to Stroke volume:

- If EDV increases, the Stroke volume increases (to a limit set by actin+myosin filaments)

55
Q

What is Starling’s Law of the heart?

A

The Stroke volume increases with the filling of the heart (End-Diastolic vol.)

56
Q

Define contractility:

A

The capability of causing contraction

57
Q

Which 2 factors determines the force of contraction of the heart?

A

1) End-Diastolic Volume

2) Contractility

58
Q

Which branch of the nervous system can affect cardiac contractility? What is its effects?

A

Sympathetic system

Increases cardiac contractility

59
Q

What happens to the stroke volume if arterial pressure falls?

A

Stroke volume increases

60
Q

During heart failure, HR automatically increases. Why should beta-blockers be administered?

A

Beta-blockers reduce sympathetic innervation
= slows HR
= increases diastolic time
= increases stroke volume

61
Q

What is meant by ‘heart failure’ (or left ventricular failure)?

A

Left ventricle fails to contract forcefully enough to maintain a normal cardiac output and peripheral perfusion.

62
Q

Where are the arterial baroreceptors located?

A

1) Carotid sinus (bifurcation of internal and external carotid arteries)
2) Aortic arch

63
Q

Where are the low-pressure baroreceptors located?

A

1) Great veins
2) Pulmonary vessels
3) Walls of right atria and ventricles of heart

64
Q

Describe the Bainbridge reflex:

A

Low pressure baroreceptors detect change in venous pressure:

  • Alter parasympathetic and sympathetic innervation to SA node
  • Alter heart rate
65
Q

In which 2 ways can low pressure baroreceptors offset a change in venous pressure?

A

1) Bainbridge reflex (alter autonomic innervation of SA node)
2) Renal reflex (hormonal control of salt and water)

66
Q

What will happen to the arterial and venous pressures if the heart stops?

A

Arterial pressure falls

Venous pressure increases

67
Q

What is the physiological range for central venous pressure?

A

3 - 8 mmHg

68
Q

Which 2 factors can change central venous pressure?

A

1) Cardiac output

2) Total peripheral resistance

69
Q

Why do some people faint if they stand up too quickly?

A

Hypotension due to mass movement of blood to lower extremities
- Venomotor tone is not altered quickly enough to maintain adequate cerebral perfusion

70
Q

Define pre-load:

A

The end diastolic volume that stretches the right or left ventricle of the heart prior to contraction

71
Q

Define after-load:

A

The “load” that the heart must eject blood against, dependant on aortic and pulmonary pressures

72
Q

In which area of the brain are the cardiac an vasomotor centres?

A

Medulla oblongata

ESA2 (27 decks)

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