How does the phosphate buffer system aid in excretion of titratable acid?

Location
  • Starts in the proximal tubules, but continues up to the distal tubules
Process
  • Hydrogen ions are secreted into the tubular lumen in exchange for Na+ ions
  • Leads to the conversion of Na2HPO4 (basic phosphate) to NaH2PO4 (acid phosphate) - the phosphate buffer system
  • The maximum limit of acidification is a urinary pH of 4.5.
Result
  • Trapping of H+ ions in urine to allow excretion