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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 set by?

A

Pacemakers of the heart

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2
Q

Which type of nervous system regulates heart rate?

A

Autonomic NS

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3
Q

Which branch of the autonomic NS increases heart rate?

A

Sympathetic branch

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4
Q

Which branch of the autonomic NS reduces heart rate?

A

Parasympathetic branch

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5
Q

Describe how the sympathetic branch of the autonomic NS increases HR.

A

-Sympathetic nerves release noradrenaline
-Plus circulating adrenaline from adrenal medulla
-Both act on β1 receptors on sinoatrial node
-Increases slope of the pacemaker potential
-Increases heart rate

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6
Q

Describe how the parasympathetic branch of the autonomic NS decreases HR.

A

Vagus nerve releases acetylcholine
Acts on muscarinic receptors on sinoatrial node
Hyperpolarises cells and decreases slope of pacemaker potential
Decreases heart rate

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7
Q

What is the medical term for a decrease in HR?

A

Bradycardia

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8
Q

What is the medical term for an increase in HR?

A

Tachycardia

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9
Q

RECAP- what releases noradrenaline in the sympathetic ANS?

A

Sympathetic nerves

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10
Q

RECAP- what releases acetylcholine in the parasympathetic ANS?

A

Vagus nerve

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11
Q

RECAP- what does noradrenaline act on?

A

β1 receptors on sinoatrial node

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12
Q

RECAP- what does acetylcholine act on?

A

Muscarinic receptors on sinoatrial node

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13
Q

What is preload?

A

The force that stretches the cardiac muscle prior to contraction

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14
Q

What does Starling’s Law state regarding preload?

A

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

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15
Q

What happens at peak tension in the heart?

A

Optimal number of cross bridges forming between actin and myosin.
This means there is a strong muscle contraction.

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16
Q

In physiology, what stretches cardiac muscle?

A

End diastolic volume (volume of blood is filled into the ventricles before the contract)

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17
Q

If the ventricles are stretched, describe the size of the end diastolic volume, contraction and stroke volume.

A

Larger end diastolic volume
Larger contraction
Larger stroke volume

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18
Q

Describe what may happen to end diastolic volume and stroke volume upon exercise.

A

Exercise would increase venous return to the heart.
Ventricles would stretch more and EDV volume increases.
This means there is a larger contraction and therefore larger stroke volume.

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19
Q

Describe what would happen to end diastolic volume and stroke volume upon rest.

A

At rest, ventricles would not be stretched so lower EDV.
Smaller contraction and smaller stroke volume.

20
Q

Why is the regulation of stoke volume important?

A

Ensures self-regulation
Ensures blood volume is fairly equal on the left and right sides of the heart.

21
Q

Define stroke volume.

A

The volume of blood pumped out of the left ventricle of the heart during each systolic cardiac contraction.

22
Q

Define afterload.

A

Afterload is the load against which the muscle tries to contract

23
Q

What stops the muscle shortening during systole?

A

The mitral valve being closed due to pressure in the ventricle.

24
Q

What is aortic pressure affected by?

A

How easily blood gets out through the arterioles – i.e. the total peripheral resistance (TPR)

25
Q

Recap- Which vessels are the resistance vessels?

A

Arterioles.

26
Q

What is the main thing which influences total peripheral resistance?

A

How dilated the arterioles are.

27
Q

What happens to stroke volume if TPR increases?

A

Aortic pressure increases
Ventricle will have to work harder to push open the aortic valve and will have less energy left to do the useful bit of ejecting blood

Stroke volume decreases

28
Q

What is afterload determined by?

A

The arterial pressure against which the blood is ejected - this in turn depends on the total peripheral resistance (TPR)

29
Q

Describe how the sympathetic NS can regulate stroke volume.

A

Sympathetic nerves releasing noradrenaline
Plus circulating adrenaline from adrenal medulla
Both act on β1 receptors on the myocytes
Increases contractility (an inotropic effect)
Gives stronger, but shorter contraction

30
Q

Name the different places you can find beta 1 receptors.

A

Sinoatrial node of the heart
Myocytes

31
Q

What effect does the parasympathetic NS have on stroke volume?

A

Little effect as vagus nerve does not innervate ventricular muscle

32
Q

Define contractibility

A

How strong a contraction is produced for any given preload or afterload.

33
Q

What is contractibility affected by?

A

Sympathetic NS

34
Q

What is preload affected by?

A

The state of contraction of venules/veins i.e. contracted, relaxed, constricted, dilated etc.

35
Q

What is afterload affected by?

A

Affected by the state of contraction of arterioles i.e. contracted, relaxed, dilated, constricted etc.

36
Q

Which are resistance vessels- veins or arteries?

A

Arteries/ arterioles

37
Q

Which are capacitance vessels?

A

Veins/ venules

38
Q

At rest, how much blood is stored in the capacitance vessels?

A

2/3

39
Q

Cardiac volume= ?

A

heart rate x stroke volume

40
Q

What does cardiac volume determine?

A

How much blood is getting to your tissues

41
Q

What would happen if you used an electrical pacemaker to increase HR?

A

You cut into the filling phase which decreases end diastolic volume.
Cardiac muscle will be stretched less and there will be a smaller contraction.
This reduces stroke volume.

42
Q

Why does HR increase during exercise?

A

Decreased vagal tone
Increased sympathetic tone

43
Q

Why does contractibility increase during exercise?

A

Controlled via sympathetic NS via increased sympathetic tone
Alters inotropic state as stronger force of contraction due to formation of more myosin-actin cross bridges.
Short contraction and shortens systole

44
Q

Why does venous return increase during exercise?

A

Via venoconstriction and skeletal/respiratory pumps pushing more blood back to the heart.
Increases EDV and maintains preload

45
Q

Why does TBR fall during exercise?

A

Due to arteriolar dilation in muscle, skin and heart
Reduces afterload as easier to pump blood

46
Q

Name the three factors which affect stroke volume.

A

Preload
Afterload
Contractibility

Year 1-Cardiovascular System (41 decks)

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