Question

The respiratory centre in the brain is stimulated by
A. $C{O_2}$ concentration in venous blood
B. ${O_2}$ concentration in venous blood
C. ${O_2}$ concentration in arterial blood
D. $C{O_2}$ concentration in arterial blood

Answer 1

Hint: The various metabolism in our body have their counter-reactions to alter their amount. The excess and less of each compound are harmful, there needs a certain balance. So the body will react to such changes and get triggered. The whole metabolic functioning is controlled by the brain.

Complete answer:
The brain coordinates every function in the body. The increase and decrease of any production are counterbalanced when sensed. The various parts of the brain like the cerebrum, cerebellum, medulla oblongata etc., all perform particular functions.

The centre responsible for respiration will get triggered by the altering levels of carbon dioxide. We, humans, take in oxygen and breathe out the carbon dioxide.
The arteries carry the oxygenated blood that means the artery will have more concentration of the oxygen than carbon dioxide while the venous blood will have more carbon dioxide than oxygen.

So the brain should check the arterial blood to know whether the concentrations of both the gases have been altered or not. This will help to respire the correct gas.

> Option A: $C{O_2}$ concentration in venous blood: The venous blood already has the carbon dioxide more in it so it will not be able to help the brain respiratory centre.

> Option B: ${O_2}$ concentration in venous blood: The venous blood is not pure that means it is not oxygenated so should not matter in the respiratory mechanisms.

> Option C: ${O_2}$ concentration in arterial blood: The arteries have a high amount of oxygen already.

> Option D: $C{O_2}$ concentration in arterial blood: This could be helpful in the way that increases in the carbon dioxide gas amount in the oxygenated pure blood will trigger the brain to respire more oxygen to increase the oxygen level. Thus this could act as a stimulator.

Hence, the correct answer is option (D).

Note: There are some special receptors in the carotid artery and aortic artery to sense the decrease in the blood pH thus increased carbon dioxide levels. The brain’s respiratory centre signals the muscles of the lungs to expand and contract accordingly.