Final answer:
Bicarbonate (HCO3−) reabsorption mainly takes place in the proximal convoluted tubule (PCT) of the kidney, facilitated by carbonic anhydrase enzyme, Na+/H+ antiporter, and Na+/K+ pump, ensuring the recovery of bicarbonate and maintenance of the acid-base balance.
Step-by-step explanation:
The reabsorption of bicarbonate (HCO3−) primarily occurs in the proximal convoluted tubule (PCT) of the kidney. This process is critical for maintaining the body's acid-base balance. During reabsorption, the enzyme carbonic anhydrase (CA) catalyzes the conversion of HCO3− and H+ into carbonic acid (H2CO3), which then dissociates into CO2 and H2O. These components diffuse across the cell membrane into the tubular cells. Inside the cells, the reaction reverses to regenerate HCO3−, which is then transported along with Na+ into the surrounding interstitial space and is eventually taken up by the peritubular capillaries, returning to the bloodstream.
Furthermore, a Na+/H+ antiporter plays a role by exchanging Na+ for H+ ions in the filtrate, which is essential for conserving Na+ and promoting the removal of acid through urine. This mechanism also displays the conservation of bicarbonate, as H+ ions are continually recycled to permit the recovery of HCO3−. The Na+/K+ pump helps establish a Na+ gradient that further facilitates these processes within the kidney's complex filtration system.
At systemic levels, the bicarbonate buffering system also interacts with pulmonary functions, where CO2 produced from the bicarbonate reaction is eventually exhaled during respiratory processes.