alleryStart learning →What buffers the hydrogen ions pumped into the forming urine?
ABicarbonate, dihydrogen phosphate and ammonia
BAlbumin, globulin and haemoglobin molecules
CSodium, potassium and magnesium ions
DGlucose, lactate and amino acid residues
Answer & Solution
Correct answer: A. Bicarbonate, dihydrogen phosphate and ammonia
1. Proximal tubule cells secrete hydrogen ions as sodium is reabsorbed, and intercalated cells pump more in downstream.
2. Free hydrogen ions would drive urine pH below its working range almost immediately.
3. They are buffered instead by bicarbonate, by dihydrogen phosphate and by ammonia, which forms ammonium.
4. Plasma proteins do buffer within the blood, but they are not filtered, so they cannot buffer the tubular fluid.
5. That buffering is what keeps urine pH inside its normal range of 4.5 to 8.0.
_Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 25 "The Urinary System", section 25.9 Regulation of Fluid Volume and Composition_
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