Acid-base homeostasis · USMLE Step 1

What happens to intracellular hydrogen ion concentration when extracellular pH drops (acidemia), if buffers and cellular mechanisms cannot fully compensate?

  1. Intracellular pH rises sharply
  2. Intracellular pH falls, impairing enzymes
  3. Intracellular pH remains unchanged
  4. Intracellular pH becomes strongly alkaline
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Correct answer: Intracellular pH falls, impairing enzymes

A drop in extracellular pH increases extracellular H⁺; if buffering is overwhelmed, H⁺ enters cells, lowering intracellular pH and potentially disrupting enzyme activity and cellular function.

Difficulty: Medium Question 13 of 19

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