Regulation of Stroke Volume and Heart Rate

Question 1

What neurotransmitter do sympathetic nerves release on adrenergic receptors?

Answer 1

Noradrenaline

Question 2

What hormone is released by the sympathetic system and where from?

Answer 2

Adrenaline from the adrenal medulla

Question 3

Where do the noradrenaline and adrenalin act on in the heart?

Answer 3

Beta 1 receptors on the sinoatrial node

Question 4

What effect does the sympathetic system have on heart rate?

Answer 4

It increases the slope of the pacemaker potential and so increases heart rate

Question 5

What neurotransmitter do the parasympathetic nerves release?

Answer 5

ACh

Question 6

Which parasympathetic nerve regulates heart rate?

Answer 6

Vagus nerve

Question 7

Where does the ACh act on the heart?

Answer 7

Muscarinic receptors on the sinoatrial node

Question 8

What effect does the parasympathetic system have on the heart rate?

Answer 8

It hyperpolarises the cells and decreases the pacemaker potential which deceases the heart rate

Question 9

What effects preload?

Answer 9

End diastolic volume

Question 10

What is afterload?

Answer 10

The load against which the muscle tries to contract

Question 11

What determines the afterload?

Answer 11

The total peripheral resistance

Question 12

If TPR increases, what will happen to stroke volume?

Answer 12

It will decrease

Question 13

How does the sympathetic system affect contractility?

Answer 13

Noradrenaline and adrenaline bind to beta 1 receptors on the myocytes and increase contractility

Question 14

What effect does the parasympathetic system have on contractility?

Answer 14

Very little effect

Question 15

What effect does hypercalcaemia do to the stroke volume?

Answer 15

It shifts the curve up and to the left

Question 16

What effect does hypocalcaemia have on stroke volume?

Answer 16

It shifts the curve down and to the right

Question 17

What effect does ischaemia have on stroke volume?

Answer 17

It shifts the curve down and to the right

Question 18

What effect do barbiturates have on stroke volume?

Answer 18

They shift the curve down and to the right

Question 19

Why does increasing the heart rate cause a decrease in stroke volume?

Answer 19

The shortened cardiac interval cuts into the rapid filling phase and reduced the EDV, which in turn reduces the SV

Question 20

How does the body counteract the decrease in SV that occurs when HR increases?

Answer 20

When HR rate increases, contractility and venous return increases and TPR falls causing an increase in the CO