Question

Rate of breathing is controlled by

• A. The amount of freely available oxygen
• B. The amount of carbon dioxide present in the blood
• C. Muscular function of the body
• D. Stress

Answer 1

The correct option is B The amount of carbon dioxide present in the blood

The level of $C{O}_2$ in the blood is the most important influence on the regulation of ventilation. The blood level of $C{O}_2$ acts directly on the respiratory centres in the medulla. A rise in $PC{O}_2$ (a condition called hypercapnia) decreases the pH level of cerebrospinal fluid. This excites the central chemoreceptors resulting in an increase in the depth and rate of respiration, a condition called hyperventilation.