Chemical control of breathing

Question 1

Is plasma pO2 or pCO2 controlled more? Why?

Answer 1

pCO2

Because pCO2 affects plasma pH

Question 2

Is plasma pO2 or pCO2 controlled less? Why?

Answer 2

pO2

Because pO2 can fall up to 8kPa with haemaglobin still having high % saturation

Question 3

What detects pO2 and pCO2 in the plasma?

Answer 3

Peripheral chemoreceptors detect pO2 and pCO2, but mostly pO2

Central chemoreceptors detect pCO2 only

Question 4

Where are peripheral chemoreceptors located?

Answer 4

Aortic body

Carotid body

Question 5

What stimulates the peripheral chemoreceptors?

Answer 5

Mostly decreased plasma pO2

Increased plasma pCO2

Question 6

What carries sensory information from the peripheral chemoreceptors?

Answer 6

From aortic body, vagus nerve

From carotid body, glossopharyngeal nerve

Question 7

Where is sensory information from the peripheral chemoreceptors carried to?

Answer 7

Respiratory control centre in the medulla of the brainstem

Question 8

What does the respiratory control centre in the medulla stimulate in response to decreased plasma pO2?

Answer 8

Increased alveolar ventilation

Question 9

Where are central chemoreceptors located?

Answer 9

Medulla of brainstem

Question 10

What stimulates the central chemoreceptors?

Answer 10

Changes in arterial plasma pCO2

Question 11

How do changes in plasma pCO2 and hydrogen ion concentration stimulate the central chemoreceptors?

Answer 11

Carbon dioxide diffuses across the blood brain barrier into the CSF
in the CSF, it reacts with water to form bicarbonate and hydrogen ions
hydrogen ions stimulate the central chemoreceptors

Changes in pCO2 leads to changes in the amount of carbon dioxide diffusing across the blood brain barrier…

Question 12

Why do changes in plasma bicarbonate and plasma hydrogen ion concentrations not stimulate the central chemoreceptors?

Answer 12

Because the blood brain barrier is impermeable to them

Question 13

What do the central chemoreceptors stimulate in response to an increased arterial plasma pCO2? Why?

Answer 13

Increased alveolar ventilation

to expire more carbon dioxide

Question 14

What do the central chemoreceptors stimulate in response to a decreased arterial plasma pCO2? Why?

Answer 14

Decreased alveolar ventilation

to expire less carbon dioxide

Question 15

How long are central chemoreceptors stimulated by a change in arterial plasma pCO2?

Answer 15

Few days

Question 16

Why are central chemoreceptors stimulated by a change in arterial plasma pCO2 only for a few days?

Answer 16

Because after that, choroid plexus cells change the bicarbonate ion concentration of the CSF
so that the bicarbonate:carbon dioxide ratio is normal
changed arterial pCO2 seen as normal