Regulation of SV and HR

Question 1

What regulates HR?

Answer 1

Neural

Question 2

What regulates stroke volume?

Answer 2

• Preload
• Afterload
• Neural
• Pathological

Question 3

What part of the nervous system controls HR?

Answer 3

Autonomic

Question 4

What neurotransmitter is released by the sympathetic system to increase HR?

Answer 4

Noradrenaline

Question 5

Where else can the noradrenaline come from that increases HR?

Answer 5

Adrenal medulla

Question 6

What receptors does the noradrenaline act on?

Answer 6

B1 receptors

Question 7

Where are the B1 receptors that the noradrenaline acts on?

Answer 7

Sinoatrial node

Question 8

What effect does the sympathetic this have on the pacemaker potential?

Answer 8

Increases slope

Question 9

What neurotransmitter is released by the parasympathetic system?

Answer 9

ACh

Question 10

What cranial nerve slows HR?

Answer 10

Vagus

Question 11

What receptors are acted on by the ACh released by the parasympathetic system?

Answer 11

Muscarinic receptors in the SA node

Question 12

What effect does the ACh have on pacemaker cells?

Answer 12

Hyperpolarises them

Question 13

What effect does ACh have on the slope of the pacemaker potential?

Answer 13

Decreases slope

Question 14

What does starlings law state?

Answer 14

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

Question 15

What is the length of the cardiac muscle fibre known as?

Answer 15

Preload

Question 16

What is preload affected by?

Answer 16

End diastolic volume

Question 17

What effect would an increased/decreased venous load have on EDV?

Answer 17

Increased load = higher EDV

Decreased load = lower EDV

Question 18

What happens to stroke volume as EDV increases/decreases?

Answer 18

• Stroke volume increases as EDV increases

- Stroke volume decreases as EDV decreases

Question 19

How does the directly proportional relationship of EDV and SV ensure self regulation?

Answer 19

Means the SV of the left and right ventricles is equal

Question 20

What is afterload?

Answer 20

The load against which the muscle fibre contracts

Question 21

In what two ways is aortic pressure affected?

Answer 21

• How much blood is pushed into the aorta (CA)

- How easy it is for the blood to get out of the aorta (TPR)

Question 22

If TPR increases what will happen to the ventricle and stroke volume?

Answer 22

• Ventricle will have to work harder to open the aortic valve
• Less energy will remain to actually inject the blood so STROKE VOLUME decreases

Question 23

What vessels affect preload?

Answer 23

Capacitance

Question 24

What vessels affect afterload?

Answer 24

Resistance

Question 25

What effect does the sympathetic system have on stroke volume?

Answer 25

Increases it

Question 26

What receptors does the sympathetic system release noradrenaline into to increase SV?

Answer 26

- B1 receptors on myocytes

Question 27

How does the sympathetic system effect contraction time?

Answer 27

Gives a shorter but stronger contraction (chronotropic effect)

Question 28

How does the parasympathetic system effect stroke volume

Answer 28

- Doesn't really | - Vagus doesn't innervate ventricular muscle

Question 29

What effect will hypercalcaemia have on SV?

Answer 29

- Shifts curve up and left (stronger shorter contraction)

Question 30

What effect will hypocalcaemia have on SV?

Answer 30

- Shifts curve down and right (longer weaker contraction)

Question 31

What effect will ischaemia have on SV?

Answer 31

- Shifts curve down and right (longer weaker contraction)

Question 32

How does starling's law allow the heart to compensate for a reduced pumping ability?

Answer 32

- Allows the heart to work around a bigger EDV | - Results in a lower ejection fraction and reduced exercise capacity

Question 33

What effect will barbiturates have on stroke volume?

Answer 33

Shifts curve down and right (longer weaker contraction)

Question 34

In what ways can the cardiac output be controlled?

Answer 34

- HR Increase - Contractility increase - Venous return increase - TPR fall

Question 35

How does an increase in contractility effect the CO?

Answer 35

Alters ionotropic state and shortens systole

Question 36

How does a venous return increase affect CO?

Answer 36

- Venoconstriction | - Maintains preload

Question 37

How does a fall in TPR control CO?

Answer 37

Reduces afterload