Physiology & Biochemistry · single question
A decrease in carbon dioxide (CO2) in the blood will lead to:
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Correct answer: B. Decrease in respiration rate
CO2 is the primary driver of respiration (not O2). CO2 dissolves in blood to form carbonic acid, lowering pH. Chemoreceptors detect rising CO2/falling pH and stimulate increased breathing. When CO2 DECREASES (e.g., hyperventilation, or reduced metabolism), there is less stimulus to breathe → DECREASED RESPIRATION RATE. This is why hyperventilation can cause temporary apnea — blowing off CO2 reduces the drive to breathe.
- A. INCORRECT. Increased tidal volume would occur in response to HIGH CO2 (to blow off excess). Low CO2 would decrease tidal volume and rate.
- B. CORRECT. Low blood CO2 (hypocapnia) reduces the stimulus to the respiratory center (chemoreceptors in the medulla and carotid bodies), leading to DECREASED RESPIRATION RATE. The body has less CO2 to 'blow off,' so it breathes less.
- C. INCORRECT. Oxygen demand is determined by metabolic rate, not CO2 levels. Decreased CO2 does not directly reduce oxygen demand.
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