The kidneys have two main ways to maintain acid-base balance: one of the ways is that their cells reabsorb bicarbonate (HCO3−) from the urine back to the blood, and the other way is that they secrete hydrogen (H+) ions into the urine. By adjusting the amounts reabsorbed and secreted, they balance the bloodstream’s pH value.

1. The Role Of The Kidneys In
Maintaining The Acid-Base
Balance In The Human Body
Poznan University Of Medical Sciences

2. • The kidneys have two main ways to maintain acid-base
balance:
their cells reabsorb bicarbonate (HCO3−) from
the urine back to the blood and they secrete
hydrogen (H+) ions into the urine.
• By adjusting the amounts reabsorbed and
secreted, they balance the bloodstream’s pH.
**The pH of the extracellular fluid is normally
regulated between 7.32 and 7.42

4. • Many extracellular proteins are very sensitive to the
extracellular pH. Outside the acceptable range of pH,
proteins are denatured, causing enzymes and ion channels
to malfunction.
• Acidosis: the pH of the body's extracellular fluid is
acidic.
• Alkalosis: the pH of the body's extracellular fluid is
basic.

5. • First, the carbon dioxide (CO2) in the blood reacts with
water and produce Carbonic acid (H2CO3).
• Carbonic Anhydrase: an enzyme present in red blood cells,
aids in the conversion of carbon dioxide to carbonic acid
and bicarbonate ions.

6. • Then, the produced carbonic acid becomes bicarbonate
and hydrogen ion.
• Bicarbonate returns to bloodstream, and the hydrogen
ions enter filtrate.

7. • The urine must carry away the necessary quantity of
hydrogen ion without becoming excessively acidic.
Therefore, the hydrogen ion is tied up by the reaction
with dihydrogen phosphate (H2PO4-), or by the reaction
with ammonia (NH3).

8. • Then, the hydrogen ions secreted into the filtrate
combines with bicarbonate (HCO3-) to produce carbon
dioxide (CO2) and water.
• Upon returning to the bloodstream, the CO2 is
reconverted to bicarbonate.

9. Thank You For Your
Attention!