Final answer:
The generation of new bicarbonate ions in the kidney involves the reabsorption of sodium ions in exchange for hydrogen ions, conversion of carbon dioxide to bicarbonate ions, and transportation of these bicarbonate ions back into the blood. This process is facilitated by the enzyme carbonic anhydrase and is crucial for maintaining the acid-base balance of the body.
Step-by-step explanation:
The process that generates new bicarbonate ions in the kidney involves several steps critical for the maintenance of acid-base balance in the body. Initially, sodium ions are reabsorbed in exchange for hydrogen ions via an antiporter mechanism found in the renal tubule cells. The generated hydrogen ions are then secreted into the filtrate.
Within the cells, carbon dioxide converts to bicarbonate ions through a reaction that forms carbonic acid, which dissociates into a bicarbonate ion and a hydrogen ion. This reaction is catalyzed by the enzyme carbonic anhydrase (CA), which is largely located within the cell, and a small amount is bound to the brush border of the membrane on the apical surface of the cell. The bicarbonate ion is then shuttled to the peritubular capillaries and returns to the blood.
The recovery of bicarbonate is essential as it acts as a powerful buffer, resisting changes in pH levels within the body. Bicarbonate ions combine with hydrogen ions to form carbonic acid, which is then converted back into CO₂ and water. The CO₂ diffuses into cells while water moves across aquaporin channels, allowing the reverse reaction inside the cell to produce more bicarbonate ions. These ions are then transported along with sodium ions across the membrane to the interstitial space. Concurrently, the Na+/H+ antiporter excretes hydrogen ions into the lumen while recovering sodium ions, thus recycling the hydrogen ions and promoting the recovery of bicarbonate.