A trekker ascends rapidly to 4500 m. Within hours he hyperventilates and his arterial pH is 7.48. Which adjustment restores his pH toward normal over the following several days?

• A Immediate fall in cerebrospinal fluid bicarbonate
• B Renal excretion of bicarbonate ✓
• C Increase in haemoglobin concentration within 24 hours
• D Reduction in peripheral chemoreceptor sensitivity

Explanation

Acute hypobaric hypoxia drives hyperventilation through the carotid bodies, washing out CO2 and producing respiratory alkalosis. Over days the kidneys compensate by excreting bicarbonate, lowering plasma bicarbonate and restoring pH, which in turn permits further ventilation to rise. Haemoglobin concentration rises only after weeks via erythropoietin, and peripheral chemosensitivity increases rather than decreases with acclimatisation.

Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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