Final answer:
The major function of the proximal tubule, specifically the proximal convoluted tubule (PCT), is to reabsorb ions, water, and nutrients from the filtrate. It also removes toxins and adjusts the filtrate's pH. The PCT's structure, including its microvilli, enhances its efficiency in solute reabsorption and secretion.
Step-by-step explanation:
The major function of the proximal tubule is to reabsorb ions, water, and nutrients from the filtrate into the interstitial fluid. Additionally, it removes toxins and adjusts the filtrate's pH. This portion of the nephron, known as the proximal convoluted tubule (PCT), plays a crucial role in the reabsorption and secretion of solutes. The PCT's simple cuboidal cells possess a brush border with numerous microvilli, maximizing the surface area for efficient absorption and secretion.