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05. Year 1: Cardiovascular System > Regulation of Stroke Volume and Heart Rate > Flashcards

Regulation of Stroke Volume and Heart Rate Flashcards

1
Q

What is heart rate regulated by?

A

Autonomic nervous system

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2
Q

What are the 2 components of the autonomic nervous system?

A

Sympathetic

Parasympathetic

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3
Q

What does the sympathetic nervous system release?

A

Noradrenaline

Circulating adrenaline from adrenal medulla

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4
Q

What does noradrenaline and circulating adrenaline act on?

A

B1 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

Increases heart rate (tachycardia)

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6
Q

What is tachycardia?

A

Increased heart rate

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7
Q

What is increased heart rate called?

A

Tachycardia

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8
Q

What does the parasympathetic system release?

A

Acetylcholine

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9
Q

What nerve from the parasympathetic system acts on the heart?

A

Vagus

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10
Q

What does the parasympathetic system act on?

A

Muscurinic receptors on sinoatrial node

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11
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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12
Q

What is bradycardia?

A

Decreased heart rate

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13
Q

What is decreased heart rate called?

A

Bradycardia

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14
Q

What is regulation of stroke volume done by?

A

Preload

Afterload

Neural

Pathological

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15
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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16
Q

How does tension of cardic 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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17
Q

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

A

Overlap of myosin in the muscle, impacting the amount of cross bridges that can be made

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18
Q

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

A

End diastolic volume against stroke volume

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19
Q

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

A

Increases EDV and so increases stroke volume

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20
Q

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

A

Decreases EDV and so decreases stroke volume

21
Q

What does the relationship between EDV and stroke volume ensure?

A

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

22
Q

What is afterload?

A

The load against which a muscle tries to contract

23
Q

What is the aortic pressure impacted by?

A

Total peripheral resistance (TPR)

24
Q

What happens to aortic pressure if total peripheral resistance increases?

A

Aortic pressure increases

25
Q

What happens to stroke volume if total peripheral resistance increases?

A

Ventricles need to work harder to push open the AV vale and so it will have less energy left to eject blood, so stroke volume will decrease

26
Q

What is afterload set by?

A

Arterial pressure against which blood is expelled, which in turn depends on the total peripheral resistance

27
Q

What affects preload?

A

Venules/veins

Capacitance vessels

28
Q

What affects afterload?

A

Arterioles

Resistance vessels

29
Q

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

A

B1 receptors on the myocytes

30
Q

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

A

Increases contractibility (inotropic effect)

Gives stronger, but shorter contractions

31
Q

What impact does the parasympathetic system have on stroke volume?

A

Little effect

Due to vagus nerve not innervating the ventricular muscle

32
Q

What is preload?

A

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

33
Q

What is afterload?

A

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

34
Q

What does TPR stand up for?

A

Total peripheral resistance

35
Q

What are examples of pathological impacts on stroke volume?

A

Hypercalcemia

Hypocalcemia

Ischaemia

Barbiturates

36
Q

How does hypercalcemia impact the stroke volume/EDV curve?

A

Shifts it up and left

37
Q

How does hypocalcemia impact the stroke volume/EDV curve?

A

Shifts it down and right

38
Q

How does ischaemia impact the stroke volume/EDV curve?

A

Shifts it down and right

39
Q

How does barbiturates impact the stroke volume/EDV curve?

A

Shifts it down and right

40
Q

What is ischaemia?

A

Restriction in blood supply to tissues

41
Q

What is restriction in blood supply to tissues called?

A

Ischaemia

42
Q

What are barbiturates?

A

Drug that acts on the CNS as a depressant

43
Q

How does the heart compensate for a reduced pumping ability?

A

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

44
Q

What does the heart working around a larger EDV result in?

A

Lower ejection fraction

Reduced exercise capacity

45
Q

What formula describes cardiac output?

A

Cardiac output = heart rate x stroke volume

46
Q

How does increasing heart rate with an electronic pacemaker impact cardiac output and stroke volume?

A

Small increase in cardiac output

But stroke volume decreases (because shortened cardiac interval cus into the rapid filling phase, reduced EDV reduces preload, in turn reduces stroke volume)

47
Q

Why does increasing heart rate with an electronic pacemaker cause a decrease in stroke volume?

A

Shortened cardiac interval cuts into rapid filling phase

Reduces EDV which reduces preloa

This reduces stroke volume by Starling’s law

48
Q

What are some things that accompany physiological increases in heart rate to offset the effect of decreased stroke volume?

A

Heart rate increases (decreased vagal tone and increases sympathetic tone)

Contractility increases (increases sympathetic tone, shortens systole)

Venous return increases (via vasoconstriction, maintains preload)

Total peripheral resistance falls (via arteriolar dilation in muscle, skin and heart reducing afterload)

Cardiac output increases 4-6 times

05. Year 1: Cardiovascular System (41 decks)

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