Physiology & Biochemistry · single question
A decrease in CO₂ levels in the blood (hypocapnia) will lead to which of the following?
Show answer and explanation
Correct answer: A. Decreased respiratory rate
CO₂ is the primary driver of respiration. LOW CO₂ (hypocapnia) decreases the respiratory drive — the body breathes less because CO₂ is already low.
- A. CORRECT. Decreased CO₂ (hypocapnia) decreases the respiratory drive — brainstem chemoreceptors detect low CO₂ and reduce respiratory rate. This is why hyperventilation (lowering CO₂) causes dizziness and eventually apnea.
- B. Increased tidal volume occurs in response to HIGH CO₂ (hypercapnia), not low CO₂. Low CO₂ suppresses respiratory drive.
- C. Oxygen demand relates to metabolic activity, not directly to CO₂ levels in this context.
- D. Hypocapnia does cause vasoconstriction (CO₂ is a vasodilator), but decreased respiratory rate is the primary answer being tested here.
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