Multiple choice

Which of the following statements concerning the excretion of acid by the nephrons are true?

  1. Acid can be excreted as NH3 ions.

  2. Acid excretion mainly occurs in the early nephron.

  3. In the distal nephron, secreted hydrogen ions mainly contribute to bicarbonate reabsorption.

  4. Sodium phosphate is a urinary buffer.

  5. Urine is usually alkaline.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Sodium phosphate can exist as Na2HPO4 or NaH2PO4 and the two form a buffer pair. The form NaHPO4 is a weak base which can accept a hydrogen ion to become NaH2PO4. Similarly NaH2PO4 is a weak acid which can donate a hydrogen ion to become Na2HPO4.

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