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Cardiovascular System > Regulation of Stroke Volume and Heart Rate > Flashcards

Regulation of Stroke Volume and Heart Rate Flashcards

1
Q

Regulation of the heart rate is _______.

A

neural

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2
Q

The sympathetic nervous system has what effect on regulation of heart?

A

Tachycardia

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3
Q

What does the sympathetic nervous system release?

A

Noradrenaline released from sympathetic nerves and;

adrenaline released from the adrenal medulla.

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4
Q

What does noradrenaline and circulating adrenaline act on?B1 receptors on sinoatrial node

A

Beta-1 receptors on sinoatrial node

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5
Q

What impact does the sympathetic nervous system have on the SA node?

A

Increase slope of the pacemaker potential, pacemaker cells reach threshold quicker.

Increases heart rate (tachycardia)

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6
Q

What does the parasympathetic system release?

A

Acetylcholine (ACh)

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7
Q

What nerve from the parasympathetic system acts on the heart?

A

Vagus nerve (CN X)

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8
Q

What does the parasympathetic system act on?

A

Muscurinic receptors on sinoatrial node

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9
Q

What effect does the parasympathetic system have on the sinoatrial node?

A

Hyperpolarises cells and decreases slope of pacemaker potential.

Decreases heart rate (bradycardia)

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10
Q

What are the 4 things that can alter the strength of contraction (stroke volume) of the heart?

A

Preload

Afterload

Neural

Pathological

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11
Q

What does Starling’s Law state?

A

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

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12
Q

How does tension of cardiac muscle fibres change with length (preload)?

A

Tension increases until it reaches a maximum then it decreases as the length increases.

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13
Q

What is the relationship between tension and length (preload) due to?

A

Because the over lap of the actin and myosin filaments changes, therefore the number of potential cross bridges changes also.

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14
Q

What is the curve of tension against length (preload) essentially the same as?

A

End diastolic volume against stroke volume

EDV v SV

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15
Q

In vivo, what affects preload?

A

EDV

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16
Q

What impact does increases venous return have on EDV and stroke volume?

A

EDV: increases
SV: increases

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17
Q

What effect does decreasing venous return have on EDV and stroke volume?

A

EDV: decreases
SV: decreases

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18
Q

What does the relationship between EDV and stroke volume ensure?

A

Self regulation so that the stroke volume of the left and right ventricles are the same.

Resting EDV is neither at the max or min SV.

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19
Q

What is afterload?

A

The load against which a muscle tries to contract.

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20
Q

What is the aortic pressure impacted by?

A

Total peripheral resistance (TPR)

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21
Q

What happens to the aortic pressure if total peripheral resistance increases?

A
  • aortic pressure increases
  • LV will have to use more work (energy) in opening the aortic valve
  • SV will decrease as there is less energy for the ejection phase of contraction.
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22
Q

What happens to stroke volume if total peripheral resistance increases?

A

It decreases

23
Q

What affects the afterload of the heart?

A

The aortic pressure which in turn is determined by TPR.

24
Q

What kind of vessels affect preload?

A

capacitance (veins/venules)

25
Q

What kind of vessels affect afterload?

A

resistance (arterioles)

26
Q

How is the stroke volume regulated neurally?

A

By the sympathetic nervous system

27
Q

What does the sympathetic system act on to impact stroke volume?

A

Beta-1 receptors on the myocytes

28
Q

What does the sympathetic system acting on B1 receptors of myocytes cause?

A

Increases contractibility (inotropic effect)

Gives stronger, but shorter contractions.

29
Q

What impact does the parasympathetic system have on stroke volume?

Why?

A

Little effect

Due to vagus nerve not innervating the ventricular muscle.

30
Q

What is preload?

A

How full the ventricle is before it starts contracting (EDV).

31
Q

What is afterload?

What is it affected by?

A

How difficult it is for the heart to pump out the blood (i.e. the TPR).

Affected by the state of contraction of arterioles.

32
Q

What happens to stroke volume when veins/venules contract?

Why?

A

It increases

  • increased venous return to the heart
  • increases EDV
  • increases preload therefore increasing stroke volume.
33
Q

Does vasoconstriction affect stroke volume?

A

No, just arteriole constriction.

34
Q

Describe how arteriole constriction affects stroke volume?

A

SV decreases because:

  • TPR increases
  • aortic pressure increases
  • afterload increases
  • LV needs to work harder
35
Q

What is an inotropic effect?

A

A change in the force or speed of contraction of muscle.

36
Q

What are examples of pathological impacts on stroke volume?

4 points

A

Hypercalcemia
Hypocalcemia
Ischaemia
Barbiturates

37
Q

How does hypercalcemia impact the stroke volume/EDV curve?

Why?

A

Shifts it up and left

  • more Ca outside myocytes
  • more actin-myosin cross bridge formation
  • increased SV
38
Q

How does hypocalcemia impact the stroke volume/EDV curve?

A

Shifts it down and right

39
Q

How does ischaemia impact the stroke volume/EDV curve?

A

Shifts it down and right

40
Q

How does barbiturates impact the stroke volume/EDV curve?

A

Shifts it down and right, producing an anaesthetic effect.

41
Q

What is ischaemia?

A

Restriction in blood supply to tissues.

42
Q

Why does ischaemia cause the stroke volume vs EDV curve to shift down and to the right?

A

Down: stroke volume decreases as there are less living myocytes to contract.

Right: As the other side of the heart is still healthy and has a higher SV. This means the EDV in the ischaemic side of the heart increases and SV increases again by preload.

43
Q

What are barbiturates?

A

Drug that acts on the CNS as a depressant.

44
Q

Cardiac output = _____ + ______

A

SV + HR

45
Q

Increasing HR with an electronic pacemaker, causes a small increase in ____, but then _____ decreases.

Why?

A

CO
SV

  • Shortened cardiac interval cuts into the rapid filling phase.
  • Reduced EDV, reduces preload
  • SV decreases (Starlings)
46
Q

How does the heart compensate for a reduced pumping ability?

A

By working around a bigger EDV, resulting in a lower ejection fraction and reduced exercise capacity.

47
Q

Outline the things that accompany physiological increases in heart rate to offset the effect of decreased stroke volume? (4)

A
  • HR increases
  • Contractility increases
  • Venous return increases
  • TPR falls
48
Q

What causes the HR to increase? (2)

A
  • increased sympathetic tone

- decreased vagal tone

49
Q

What causes contractility to increase? (2)

A
  • increased sympathetic tone

- alters inotropic state & shortens systole (shorter but stronger contractions)

50
Q

What causes the venous return to increase? (3)

A
  • vasoconstriction
  • skeletal/resp. pumps
  • maintains preload
51
Q

What causes the TPR to fall? (2)

A
  • arteriole dilation

- reduces afterload

52
Q

How much can a pacemaker increase the CO by?

A

2x

53
Q

How much can the physiological mechanisms increase the CO by?

A

4-6x

Cardiovascular System (37 decks)

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