Week 6 - Control of the Cardiovascular System

Question 1

Give the formula for cardiac output, and state a typical value for this at rest (for a 70 kg male).

Answer 1

Cardiac output = Heart Rate x Stroke Volume

At rest: 5 litres/minute

Question 2

Which factors regulate the heart rate?

Answer 2

The autonomic nervous system and some hormones can modulate heart rate (although, this is independently determined by the SA node).

Question 3

Why does the Starling curve reach a plateau at the top (i.e. why does force of contraction not increase beyond a certain point)?

Answer 3

The sarcomeres become undigitated and therefore, cannot produce more contraction.

Question 4

Outline the locations of baroreceptors in the body and state what pressures they increase firing at.

Answer 4

1. Aortic arch: Increase firing at pressures greater than 100 mmHg
2. Carotid body: Increase firing at pressures greater than 50 mmHg

Question 5

State the range of values for central venous pressure.

Answer 5

+2 to +10 mmHg

Question 6

State the value of mean arterial blood pressure (MABP) at rest.

Answer 6

Approximately 95 mmHg

Question 7

Briefly describe the response of the cardiovascular system to haemorrhage.

Answer 7

1. Baroreceptors signal severe drop in blood pressure.
2. Very large SNS output to increase heart rate and stroke volume
3. Very large SNS output to arterioles to increase TPR to increase MABP
4. Very large SNS output to veins to increase CVP and therefore, SV
5. Tachycardia: 120-140 beats per minute
6. Except the heart and brain, all systems experience decreased supply
7. Can result in kidney failure

Question 8

Briefly describe the response of the cardiovascular system to haemorrhage.

Answer 8

1. Baroreceptors signal severe drop in blood pressure.
2. Very large SNS output to increase heart rate and stroke volume
3. Very large SNS output to arterioles to increase TPR to increase MABP
4. Very large SNS output to veins to increase CVP and therefore, SV
5. Tachycardia: 120-140 beats per minute
6. Except the heart and brain, all systems experience decreased supply
7. Can result in kidney failure