<prompt> Answer this question truthfullyWhat is the major anion that is reabsorbed in the early proximal convoluted tubule PCT of the nephron?  <response>: <reason> The major anion that is reabsorbed in the early PCT of the nephron is HCO3-. The PCT is the first segment of the renal tubule and is responsible for the reabsorption of most of the filtered bicarbonate HCO3- from the glomerular filtrate. HCO3- reabsorption is critical for maintaining acid-base balance in the body, as it helps to neutralize excess acid in the blood. The reabsorption of HCO3- in the PCT is accomplished through the action of the enzyme carbonic anhydrase, which converts HCO3- to CO2 and water, and then back to HCO3- inside the tubule cells. This process generates H ions, which are then transported out of the tubule cells and into the lumen of the tubule, where they combine with filtered HCO3- to form H2CO3, which is then converted back to CO2 and water by carbonic anhydrase. The CO2 is then reabsorbed into the tubule cells, where it is converted back to HCO3-, which is then transported into the bloodstream. 