Which statement explains why metabolic acidosis develops with kidney failure?

• A. Inability of the renal tubules to secrete hydrogen ions and conserve bicarbonate.
• B. Depressed respiratory rate due to metabolic wastes, causing carbon dioxide retention.
• C. Inability of the renal tubules to reabsorb water to dilute the acid contents of blood.
• D. Impaired glomerular filtration, causing retention of sodium and metabolic waste products.

Answer: (A)

Metabolic acidosis from kidney failure happens because the kidneys lose their ability to handle acid-base balance: the renal tubules are normally responsible for secreting hydrogen ions into the urine and reclaiming, and generating, bicarbonate to buffer acids. When tubule function declines, hydrogen ions aren’t effectively secreted and bicarbonate isn’t adequately reabsorbed or produced, so hydrogen ions accumulate and bicarbonate levels fall. That buildup of acid and loss of base leads to metabolic acidosis.

The other ideas miss the key mechanism: retaining CO2 would cause a respiratory form of acidosis, not metabolic; simply failing to reabsorb water doesn’t directly explain acid-base imbalance; and while impaired filtration affects waste buildup, the direct cause here is the tubules’ reduced ability to excrete acid and conserve bicarbonate.