Water, Electrolyte, And Acid-Base Balance
Explain the role of the kidney in acid-base balance
Answer:
Role of Kidney in Acid-Base Balance:
- The renal regulation of pH occurs by the following mechanism
1. Excretion of H+ ions
- Carbonic acid is formed from carbon dioxide & water by carbonic anhydrase
- Carbonic acid then dissociates to H+ & bicarbonate ions
- H+ ions are secreted into the tubular lumen in exchange for Na+
- Na+ along with bicarbonate ions is reabsorbed
- Bicarbonate ions add up to the alkali reserve, while H+ combines with a noncarbonate base & is excreted in urine
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2. Reabsorption of bicarbonate
- Bicarbonate diffuses from the plasma into the tubular lumen
- Here it combines with H+ to form carbonic acid
- By carbonic anhydrase enzyme, it dissociates to carbon dioxide & water
- Carbon dioxide diffuses into the tubular cells
- Here it again combines with water & forms carbonic acid
- Then it dissociates into H+ & bicarbonate ions
- H+ is secreted into the lumen in exchange for Na+
- The bicarbonate ion is reabsorbed into plasma along with Na+
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3. Excretion of titrable acid
- H+ ion is secreted into the tubular lumen in exchange for Na+ ion
- Na+ is formed from disodium hydrogen phosphate
- This combines with H+ & forms sodium dihydrogen phosphate
- As the tubular fluid moves down the renal tubules, more & more H+ ions are added
- This causes acidification of urine
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4. Excretion of ammonium ions
- H+ ions secreted into tubular fluid combines with NH3 to form an ammonium ion
- In the tubular cells, deamidation of glutamine to glutamate & NH3 occurs by the enzyme glutaminase
- NH3 diffuses into the tubular lumen where it combines with H+ to form an ammonium ion
- Ammonium ions cannot diffuse back into tubular cells & therefore are excreted into the urine.
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