kidneys Role in acid base balance

• kidneys play a crucial role in maintaining the body’s acid-base balance, a vital aspect of homeostasis, by regulating the pH of the blood.
• The normal pH range of blood is tightly regulated between 7.35 and 7.45, and the kidneys contribute to maintaining this balance by excreting acid or base and reabsorbing bicarbonate (HCO3-) from the urine.

Excretion of Hydrogen Ions from kidneys

• The kidneys help maintain acid-base balance primarily through the excretion of hydrogen ions (H+) in the urine. Nephrons, the functional units of the kidney, contain cells that can secrete H+ into the tubular fluid.
• This process is essential for removing excess acid from the body.
• The excretion of hydrogen ions is facilitated through several mechanisms:

1. Ammonia Buffering

   • Process: Ammonia (NH3) binds with H+ to form ammonium (NH4+), which is excreted in urine.

2. Phosphate Buffering

   • Process: Dihydrogen phosphate (H2PO4-) binds with H+ to form monohydrogen phosphate (HPO4^2-), which is excreted in urine.

Reabsorption and Production of Bicarbonate

1. Reabsorption

   • Process: Most filtered bicarbonate is reabsorbed in the proximal tubule, helping maintain the body’s base balance.

2. Production

   • Process: Kidneys generate new bicarbonate through glutamine metabolism and the excretion of ammonium (NH4+) and titratable acids, which adds new bicarbonate to the blood.

Compensation for Acid-Base Imbalances in kidneys

1. Metabolic Acidosis

   • Response: The kidneys increase H+ excretion and bicarbonate reabsorption to raise blood pH.

2. Metabolic Alkalosis

   • Response: The kidneys reduce H+ excretion and bicarbonate reabsorption to lower blood pH.

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