Regulation of Stroke Volume and Heart Rate

Question 1

What nervous system increases the slope of the pacemaker potential?

Answer 1

Sympathetic

Question 2

What nervous system causes bradycardia?

Answer 2

Parasympathetic

Question 3

What nervous system depolarises cells and decreases slope of pacemaker potential?

Answer 3

Parasympathetic

Question 4

What nervous system causes tachycardia?

Answer 4

Sympathetic

Question 5

What nervous system releases noradrenaline which acts on beta-1 receptors on the sinoatrial node?

Answer 5

Sympathetic

Question 6

Which nervous system releases ACh from the vagus nerve which acts on muscarinic receptors on the sinoatrial node?

Answer 6

Parasympathetic

Question 7

What does Starling’s Law state?

Answer 7

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

Question 8

What is meant by preload?

Answer 8

The end diastolic volume that stretches the ventricle of the heart to its greatest dimensions

Question 9

What is meant by peak tension?

Answer 9

The maximum overlap between myosin and actin on cross bridges, producing greater tension

Question 10

In vivo, preload is affected by

Answer 10

the EDV

Question 11

What effect would an increased venous return which increased EDV have on stroke volume?

Answer 11

Stroke volume would increase

Question 12

What effect would a decreased venous return which decreased EDV have on stroke volume?

Answer 12

Stroke volume would decrease

Question 13

What is afterload?

Answer 13

The load against which the cardiac muscle tries to contract

Question 14

What factors affect aortic pressure?

Answer 14

• cardiac output

- total peripheral resistance

Question 15

If total peripheral resistance increase, stroke volume would

Answer 15

decrease

Question 16

In vivo, after load is set by

Answer 16

the arterial pressure against which the blood is expelled

Question 17

What vessels affect preload?

Answer 17

Capacitance vessels

Question 18

What values affect afterload?

Answer 18

Resistance vessels

Question 19

What effect does the sympathetic nervous system have on contractility and contraction?

Answer 19

When adrenaline/noradrenaline is released and acts on beta-1 receptors

• contractility increases
• contraction is stronger but shorter

Question 20

What effect does the parasympathetic system have on the strength of contraction?

Answer 20

Generally, no effect

Question 21

On a Starling curve, what would shift the curve up and left?

Answer 21

Hypercalcaemia

Question 22

On a Starling curve, what would shift the curve down and right?

Answer 22

• Hypocalcaemia
• Ischaemia
• Barbiturates

Question 23

The heart will compensate for a reduced pumping ability by

Answer 23

working around a bigger EDV

Question 24

What results from the heart works at a higher point on the Starling curve?

Answer 24

• lower ejection fraction

- reduced exercise capacity

Question 25

What is the ejection fraction?

Answer 25

Stroke Volume / EDV

Question 26

What is the equation for calculating cardiac output?

Answer 26

Cardiac output = HR x SV

Question 27

What effect does increasing the heart rate with an electronic pacemaker have on cardiac output and stroke volume?

Answer 27

• Cardiac output increases slightly

- SV decreases

Question 28

Give one factor that, by Starling’s Law, reduce stroke volume

Answer 28

• shortened cardiac interval cutting into rapid filling phase
• reduced end diastolic volume reducing preload

Question 29

Give two ways in which heart rate is increased

Answer 29

• via decreased vagal tone

- increased sympathetic tone

Question 30

How does contractility increase?

Answer 30

Via increased sympathetic tone

Question 31

How does venous return increase?

Answer 31

Via vasoconstriction

Question 32

When venous return increases, what does it maintain?

Answer 32

Preload

Question 33

When total peripheral resistance falls, what is reduced?

Answer 33

Afterload