Renal Filtration and Electrolyte Balance · USMLE Step 1

Which of the following best describes how the kidneys contribute to acid–base balance?

  1. By filtering plasma proteins into the urine
  2. By reabsorbing bicarbonate and secreting H⁺ ions
  3. By generating carbon dioxide in tubular cells
  4. By secreting urea into the filtrate
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Correct answer: By reabsorbing bicarbonate and secreting H⁺ ions

The kidneys maintain acid–base homeostasis by reabsorbing filtered bicarbonate (HCO₃⁻) and secreting H⁺ ions into the urine; this adjusts blood pH over time.

Difficulty: Medium Question 8 of 20

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