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Bicarbonate

• what is bicarbonate?
• where does bicarbonate come from?
• bicarbonate needs
• bicarbonate absorption
• bicarbonate regulation
• bicarbonate and the kidney
• bicarbonate functions in the body

 

What is Bicarbonate?

 

 

Where does Bicarbonate Come from?

 

 

Bicarbonate Needs

 

 

Bicarbonate Absorption

 

 

Bicarbonate Regulation

 

 

 

The physiologic concentration of HCO₃ is 24 mmol/l, while the concentration of H+ is 40 nmol/l.

Bicarbonate Reabsorption in the Kidney

The kidney has the capacity to regulate blood pH by addition or secretion of bicarbonate.

Normally, all HCO₃ is reabsorbed, giving urine a pH of less than 7. Vegans have a more alkaline diet, and so some HCO₃ is excreted in the urine. Addition of large amounts of HCO₃^- to the blood will be dealt with rapidly by the kidney through excretion.

Loss of bicarbonate produces renal tubular acidosis.

Seventy percent of HCO₃ reabsorption occurs in the proximal tubule, with the rest in the LoH.

In the proximal tubule,

 

• HCO₃ reabsorption is coupled with H+ secretion the Na/H antiporter.
• CA works both in the lumenal brush border and inside the cell.
• HCO₃ reabsorption is coupled with NH₄ secretion, mediated by deamination of glutamine from the liver.

Transport defects, or inhibition of any of the above pumps, can result in renal tubular acidosis.

The drug acetazolamide inhibits CA and therefore reduces bicarbonate reabsorption.

 

 

Bicarbonate and the Kidney

 

After filtration, almost all bicarbonate is reabsorbed by the proximal tubule.

 

 

 

Bicarbonate's Functions in the Body