Acid Base Function - Know the concepts not the Exact numbers

• Bicarbonate is an important buffer and is maintained at 25mEg/l

  • Important to the normal metabolic processes - it is small and can pass through the glomerular wall

  • It can be recovered though

• GFR = about 180L/day

• Therefar, the filtered load of bicarbonate = about 4,500 mEg/day

• About 90% of this is reabsorbed in the proximal convoluted tubule (by mechanism of H+ secretion by the tubule, which titrates bocarbonate

• In the distal tubule H+ secretion reclaims the remainder of bicarbonate (the requirements of Acid-base balance are also met here by H+ secretion in the form of titratable acidity plus ammonium ion secretion

• Acid output by the kidney is limited by two factors:

• The Maximum number of moles of H+ which may be secreted by the tubules

• The minimum pH to which the urine may be driven

• 24 hour urine check:

  • 5 to 10 gm NH4Cl is given by mouth to stimulate maximum acidification. Analysis of the 24 hour specimen is then undertaken. Failure to excrete a total of more than 100 mEq of titrate acid + NH3 constitutes reduced capacity for acid excretion.

Category: Biochemistry Notes