Question

Define renal net acid excretion and the processes involved (the importance of new HCO₃^- formation) in paragraph form.

Answer 1

The net acid excretion (NAE) is defined as the net total amount of the excreted acid in the urine per single unit time.The value of the NAE depends on the following factors:

1. Urine Acid Concentration
2. Urine flow rate
3. Bicarbonate concentration in urine.

This term has a unit of milliliters per minute (ml/min). The NAE can be expressed as the following equation:

Where

• NAE: net acid excretion
• V: Volume of urine produced per single unit time
• UNH4: concentration of ammonium in urine
• UTA: concentration of titratable acid in urine
• UHCO3: concentration of bicarbonatein urine

Process Involved:

Within the cell, H2O gets dissociated and forms OH- and H+. This in turn gets promoted by CO2 hydroxylation given as: (OH- + CO2 => HCO3-). This reaction generates bicarbonate and it gets catalysed by type II solubles carbonic anhydrase.With the help of a high capacity isoform (NHE3) the H+ gets exchanged for Na+ . Under the conditions of normal acid-base, the urine excretes almost 50% of the NH4 produced,and the rest 50% is delivered to the renal veins. During ureagenesis, HCO3- is consumed by the NH4+ that is being delivered to renal veins.