The body temporarily buffers hydrogen ions (H+) with plasma proteins, hemoglobin, and bicarbonate (HCO3), but H+ must be excreted to prevent acidosis. The major functions of the kidneys in acid-base homeostasis are to excrete H+ and reabsorb HCO3. Failure to perform these functions results in HCO3 wasting, leading to renal tubular acidosis (RTA), which is categorized into 3 major groups: distal (type I), proximal (type II), and hyperkalemic (type IV) RTA.

Excretion of H+ to balance acid production is primarily the function of the distal convoluted tubule and collecting duct (DCT/CD), where α-intercalated cells actively transport H+ into the tubule. Secreted H+ combines with ammonia to form ammonium in the DCT/CD lumen. Because of its positive charge, ammonium cannot diffuse out of the tubular lumen, and it is passed in the urine.

In distal RTA,...

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