Renal acid handling: bicarbonate reabsorption, ammoniagenesis and renal tubular acidosis
How the kidney reclaims filtered bicarbonate and makes new bicarbonate through titratable acid and ammonium, how the urine anion and osmolal gaps estimate ammonium, and how each type of renal tubular acidosis follows from a defect in one step.
Tier 1Medical sciences concept
Written with AI assistance and fact-checked against the sources below. For exam study, not clinical decisions. How notes are made
At a glance
- The kidney has two jobs: reclaim nearly all filtered bicarbonate, and regenerate the 50 to 100 mmol of bicarbonate consumed daily by non-volatile acid.
- New bicarbonate comes from excreting H+ as titratable acid (mainly phosphate) and as ammonium. Ammonium is the adjustable part.
- Net acid excretion = NH4+ + titratable acid minus urinary HCO3.
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Sources
- Brenner and Rector's The Kidney (11th ed.)Elsevier (Yu et al., 2020), 2020
- Guyton and Hall Textbook of Medical Physiology (14th ed.)Elsevier (Hall and Hall, 2021), 2021
- Renal tubular acidosis: the clinical entityJournal of the American Society of Nephrology (Rodriguez Soriano, 2002;13(8):2160-2170), 2002
- Urea and ammonia metabolism and the control of renal nitrogen excretionClinical Journal of the American Society of Nephrology (Weiner, Mitch and Sands, 2015;10(8):1444-1458), 2015
- Last updated
- 14 November 2026
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