Physiology & Biochemistry · single question
When the CO2 level in the blood DECREASES, what happens to respiration?
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Correct answer: C. Respiratory rate decreases
- A. Increased tidal volume is likewise a response to rising, not falling, CO2.
- B. An increase in rate is the response to HYPERcapnia (rising CO2), not to falling CO2.
- C. Correct. CO2 is the PRIMARY driver of respiration via central chemoreceptors in the medulla, which sense CSF pH. When CO2 falls (hypocapnia), the stimulus to breathe is REMOVED — respiratory rate and depth DECREASE until CO2 rises back to normal. This is exactly what happens after hyperventilation, and it is why the classic management of hyperventilation syndrome in the dental chair is to have the patient rebreathe their own exhaled air into cupped hands or a bag to restore CO2.
- D. Oxygen demand is set by metabolic activity and is not the respiratory response to changing CO2.
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