Renal Acid Exretion; Take Home Points
1. The net quantity of H+ ions excreted in the urine is equal to the amount of H+ excreted as titratable acidity and NH4+ minus any H+ added to the body because of urinary HCO3- loss.
Net acid excretion(NAE) = titratable acidity + NH4+ - urinary HCO3-
Note that normally there is no urinary HCO3- and therefore:
Net acid excretion(NAE) = titratable acidity + NH4+
2. Titratable acidity is dependent on the dietary intake of phosphate and cannot be regulated to increase acid excretion
3. The kidney 's main response to an increased acid load is to increase ammonium production and excretion
4. A very important feature of titrable acidity and ammonium excretion is the regeneration of bicarbonate ions.
5. The kidney must reabsorb all filtered HCO3- in order to maintain acid base balance.
6. Hydrogen ion secretion in the collecting tubule is very important in maximally acidifying the urine.
7. In states of acidosis, maximal acidification of the urine in the collecting tubule must occur for adequate ammonium excretion.
8. In states of acidosis, ammonium excretion is increased by increasing ammonium production and increased hydrogen ion secretion in the collecting duct.
9. Aldosterone stimulates secretion of hydrogen ion in the collecting duct .
10. Although the extracellular pH is the primary physiologic regulator of net acid excretion, in pathophysiologic states, the effective circulating volume, Aldosterone, and the plasma K+ concentration all can affect acid excretion, independent of the systemic pH.