Acid-base homeostasis · USMLE Step 1

Why are small changes in plasma H⁺ concentration physiologically significant even though absolute H⁺ concentration is tiny (≈ 40 nmol/L)?

  1. Because H⁺ ions transport oxygen in blood
  2. Because enzymes and proteins are highly pH-sensitive
  3. Because H⁺ ions contribute to blood viscosity
  4. Because H⁺ ions determine plasma volume
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Correct answer: Because enzymes and proteins are highly pH-sensitive

Enzymes and structural proteins are very sensitive to pH changes; even slight variations in H⁺ concentration can alter protein conformation and impair cellular functions.

Difficulty: Medium Question 17 of 19

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