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Cardiovascular system > Regulation of stroke volume & heart rate > Flashcards

Regulation of stroke volume & heart rate Flashcards

1
Q

what are the effects of the sympathetic system on heart rate

A

the sympathetic nervous system releases the hormones to accelerate the heart rate

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2
Q

what are the effects of the parasympathetic system on heart rate

A

stimulating the parasympathetic nervous system increases the resting potential and decreases the rate of diastolic depolarisation; under these circumstances the heart rate slows

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3
Q

what is the effect of the sympathetic system on stroke volume

A

stroke volume increases,

heart rate and contractility also increases

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4
Q

what activates the sympathetic nervous system

A

exercise

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5
Q

what are the effects of preload on stroke volume

A

increase in stroke volume

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6
Q

what are the effects of after load on stroke volume

A

increasing after-load reduces stroke volume

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7
Q

what is after-load

A

it is the stress in the wall of the left ventricle during ejection, i.e. it is the end load against which the heart contracts to eject blood

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8
Q

what are the components after-load is broken into

A

one factor is the aortic pressure the left ventricular muscle must overcome to eject blood

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9
Q

what are factors that affect after-load

A

age
increased blood pressure
hypertension
constriction of the arteries

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10
Q

what else does increasing after-load effect, apart from reducing stroke volume

A

increasing after-load also increases left ventricular end-diastolic pressure

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11
Q

what does preload refer to

A

the end diastolic volume that stretches the right or left ventricle of the heart to its greatest dimensions under variable physiologic demand

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12
Q

what does after load to

A

it is the end load against which the heart contracts to eject blood

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13
Q

after load is readily broken into components, describe one factor

A

it is the aortic pressure the left ventricular muscle must overcome to eject blood

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14
Q

what forms the atrioventricular node

A

pacemaker cells

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15
Q

where is the atrioventricular node

A

the area between the ventricles

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16
Q

describe how sympathetic nerves control heart rate

A

sympathetic nerves release noradrenaline, which acts on beta receptors on the sinoatrial node, which increases pacemaker potential - leading to tachycardia - an increased heart rate

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17
Q

how do sympathetic nerves control heart rate

A

sympathetic nerves increase heart rate

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18
Q

describe parasympathetic and sympathetic activity whilst you are doing exercise

A

parasympathetic activity decreases

sympathetic activity increases

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19
Q

describe parasympathetic and sympathetic activity at rest

A

parasympathetic and sympathetic nerves always have ongoing activity at rest

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20
Q

where are beta 1 receptors present

A

on the sinoatrial node

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21
Q

describe how parasympathetic nerves control heart rate

A

parasympathetic nerves hyperpolarise the cells in the sinoatrial node

  • resulting in it taking longer for the pacemaker potential to reach threshold
  • making the interval between each heart beat longer
  • resulting in bradycardia
  • the heart rate is slowing down
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22
Q

how does the parasympathetic nerves control heart rate

A

parasympathetic nerves act to decrease heart rate

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23
Q

what does acetylcholine bind to

A

muscarinic receptors

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24
Q

what is the vagus

A

each of the 10 pairs of cranial nerves

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25
Q

what does the vagus supply

A

the heart, lungs, upper digestive tract, and other organs of the chest and abdomen

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26
Q

what do the 10 pairs of cranial nerves release

A

acetylcholine

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27
Q

describe how the vagus controls heart rate

A
  • the vagus releases acetylcholine
  • acetylcholine acts on muscarinic receptors on the sinoatrial node
  • the pacemaker cells in the sinoatrial node hyper-polarise
  • the slope of the pacemaker potential decreases
  • resulting in the heart rate decreases
    = bradycardia
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28
Q

how does the vagus control heart rate

A

the vagus decreases the heart rate

activity of the 10 pairs of cranial nerves = bradycardia

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29
Q

describe starling’s law

A

the energy of contraction is proportional to the initial length of the cardiac muscle fibre

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30
Q

how is tension formed

A

by the myosin cross bridges

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31
Q

what is the result of more cross bridges

A

the stronger contraction you can produce

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32
Q

what is the result of a shorter acting muscle length

A

the actin filaments start interfering with one another,
therefore there is not as good cross bridge formation,
therefore there is a weaker strength of contraction

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33
Q

in cardiac muscle what does stretching of a muscle fibre depend on

A

the end diastolic volume - how much blood is in the ventricle at the end of the filling phase

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34
Q

describe the ventricle filling phase and contraction relationship

A

the more blood you have squeezed into the ventricle during the filling phase will stretch that muscle more, therefore the more contraction you are going to get

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35
Q

describe preload

A

the amount of stretch put on a muscle before it starts to contract

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36
Q

in life what is preload affected by

A

the end diastolic volume

37
Q

because preload is affected by the end diastolic volume, what can end diastolic volume plotted against

A

stroke volume

38
Q

what is stroke volume

A

the amount of blood pumped by the left ventricle of the heart in one contraction

39
Q

what is the volume of stroke volume normally

A

NOT all the blood contained in the left ventricle

it is normally 2/3s of the blood in the ventricle

2/3s of the blood in the ventricle is expelled with each beat

40
Q

what is end diastolic volume

A

it is the volume of blood in the right and/or left ventricle at end load i.e. the end of the filling phase

41
Q

what is the end diastolic volume essentially

A

the amount of blood in the ventricles just before systole

42
Q

what is systole

A

the phase of the heartbeat when the heart muscle contracts and pumps blood from the chambers into the arteries

43
Q

what is the result if stronger tension is induced

A

the heart will eject more blood

44
Q

what is the result if you squeeze more blood into the heart

A

you get more stretch on the muscle, therefore the strength of contraction is stronger

45
Q

what is the consequence of preload being affected by the end diastolic volume

A

stroke volume is resultantly affected

46
Q

what does stroke volume increase in response to

A

an increase in the end diastolic volume when all other factors remain constant

47
Q

what does the starling curve describe

A

that the amount of blood pumped by the left ventricle of the heart on one contraction increases as the volume of blood filing the heart increases, this is when all other factors remain constant

48
Q

how does cardiac muscle respond to more/excess blood coming back to the heart resulting in a bigger end diastolic volume

A

the cardiac muscle is just going to contract harder and you will get a bigger stroke volume

49
Q

what is the result if less blood comes back to the heart?

A

decreased end diastolic volume
decreased preload
decreased stroke volume

50
Q

what is the result of an increased end diastolic volume

A

an increased stroke volume

51
Q

what is the result of a decreased end diastolic volume

A

aa decreased stroke volume

52
Q

describe the blood pumped on both sides of the heart

A

the left and right sides of the heart always pump the same amount of blood

53
Q

why is the heart rate on both sides of the heart the same?

A

because they share the same pacemaker, so stroke volume has to be the same as well

54
Q

what is venous return

A

it is the rate of blood flow back to the heart

55
Q

what does venous return limit

A

cardiac output

56
Q

what is after load in relation to the heart

A

it is the force that the muscle is trying to work against

57
Q

describe afterload

A

it is the pressure against which the heart must work to eject blood during systole

58
Q

what is stopping the pushing of the opening of the aortic valve

A

the mean arterial pressure

59
Q

what does total peripheral resistance affect

A

the aortic pressure

60
Q

what is aortic pressure

A

the blood pressure at the root of the aorta

61
Q

what does an increase in total peripheral resistance result in

A

increase in aortic pressure
decrease in stroke volume

as the ventricle will have to work harder to push open the aortic valve therefore there is less energy to eject blood

62
Q

what is afterload set by

A

the arterial pressure

63
Q

what does arterial pressure depend on

A

the total peripheral resistance

64
Q

what types of vessels are venules/veins

A

capacitance vessels - hold blood

65
Q

what do venules/veins affect

A

preload

66
Q

what types of vessels are arterioles

A

resistance vessels

they stop the blood getting out,
they redirect blood to different regions of the body when you want to

67
Q

what do arterioles affect

A

afterload

68
Q

what do you affect each time you are contracting the capacitance vessels

A

you are affecting the preload

69
Q

what is the affect on stroke volume when arterioles are constricted

A

stroke volume decreases

70
Q

in relation to the sympathetic system describe how sympathetic nerves regulate stroke volume

A
  • sympathetic nerves release noradrenaline and adrenaline from the adrenal medulla
  • both then act on beta 1 receptors on the myocytes
  • this increases contractility
  • this gives a stronger but shorter contraction
  • therefore increases stroke volume
71
Q

describe how sympathetic nerves affect stroke volume

A

stroke volume increases by increasing contractility

72
Q

describe how parasympathetic nerves affect stroke volume

A

can be increased or decreased

these nerves really have very little effect on stroke volume as they have very little to do with contractility

73
Q

where do parasympathetic nerves innervate

A

parasympathetic nerves innervate at the top of the heart and nodes quite a lot but don’t quite get down to the ventricles therefore stimulating these nerves does next to nothin to the strength of contraction

74
Q

state four ways of pathological regulation of stroke volume

A

hypercalcemia
hypocalcemia
ischaemia
barbiturates

75
Q

describe how hypercalcemia can regulate stroke volume

A

as there is more calcium coming in during the cardiac action potential more cross bridges are being formed

76
Q

what is hypercalcemia

A

high calcium concentration in plasma

77
Q

describe how hypocalcemia can regulate stroke volume

A

less calcium coming in curing the cardiac action potential results in weaker cardiac contraction
starling curve shifts down and to the right

78
Q

describe how ischaemia can regulate stroke volume

A

due to poor bloody supply, the effected side of the heart is going to contract less strongly
starling curve shifts down and to the right

79
Q

how do barbiturates regulate stroke volume

A

they depress the action of the heart and shift the starling curve down and to the right

80
Q

what is cardiac output equal to

A

it is heart rate multiplied by stroke volume

81
Q

what is the average cardiac output equal to

A

5 lites a minute

82
Q

what is the result of an electronic pacemaker

A

increase heart rate
decrease cardiac output
decrease stroke volume

because

decrease end diastolic volume
decrease preload
decrease stroke volume

83
Q

what is the result of a physiological pacemaker

e.g. exercise
natural reaction

A 
increase heart rate
decrease vagal tone
increase sympathetic tone
increase venous return
increase contractility
decrease systole
decrease total peripheral resistance
decrease afterload
increase cardiac output
84
Q

how do sympathetic nerves regulate heart rate

A

increases heart rate

85
Q

how do parasympathetic nerves regulate heart rate

A

decreases heart rate

86
Q

in terms of stroke volume regulation, what is the result when preload is equal to end diastolic volume

A

increase in stroke volume

87
Q

in terms of stroke volume regulation, what is the result when after load is equal to end diastolic volume

A

decrease stroke volume

88
Q

describe neural regulation of stroke volume

A

sympathetic nerves increase stroke volume

Cardiovascular system (34 decks)

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