Gas Regulation

Question 1

List muscles for control of breathing including action and innervation.

Answer 1

Intercostal muscles
External intercostals pull ribcage up and out to increase thoracic cavity volume
Internal intercostals pull ribcage down and in to decrease thoracic cavity volume
Innervated by intercostal nerves

Diaphragm
Contracts to increase thoracic cavity volume
Relaxes to decrease thoracic cavity volume
Innervated by phrenic nerve

Question 2

Describe structure and function of respiratory centre

Answer 2

Respiratory centre located in the medulla oblongata
Two regions - one controlling inspiration and other controlling expiration. Impulses passed between regions.
Connected to phrenic and intercostal nerves.

Question 3

Which is the more sensitive regulator for breathing: CO2 or O2?

Answer 3

CO2 (through its effect on blood pH levels) is more sensitive

O2 requires a large decrease to trigger a response from the respiratory centre.

Question 4

Where are the chemoreceptors most sensitive to changes in CO2 found?

Answer 4

In the medulla oblongata

Question 5

Which chemoreceptors are stimulated by a decrease in blood pH?

Answer 5

The chemoreceptors on the aortic and carotid bodies

Question 6

Explain how blood pH levels regulate breathing

Answer 6

Increased levels of hydrogen ions in the blood lead to a lowered blood pH, which stimulates the aortic and carotid bodies to send impulses to the respiratory centre of the medulla oblongata to increase breathing rate.

Question 7

What is hyperventilation? Why is it dangerous when swimming underwater?

Answer 7

Rapid deep breathing which increases O2 levels and decreases CO2 levels.

Reduces CO2 levels, meaning that the slight increase needed to stimulate taking a breath will not occur until later than usual. This can lead to drowning, as the fall in O2 levels becomes so steep that it leads to loss of consciousness before the more sensitive CO2 mechanism is triggered.