Which structure of the nephron is primarily responsible for salt and water reabsorption?

The Proximal Convoluted Tubule (PCT) is the primary site for salt and water reabsorption in the nephron. This segment of the nephron reabsorbs approximately 65-70% of filtered sodium and a similar percentage of water, alongside other solutes like bicarbonate, glucose, and amino acids. The reabsorption in the PCT is facilitated by various transport mechanisms, including active transport for sodium ions and co-transport for other solutes, which enhances water reabsorption through osmosis.

In contrast, while the Distal Convoluted Tubule and Collecting Duct do have roles in the fine-tuning of sodium and water reabsorption, their contributions are not as significant as those of the PCT. The Loop of Henle is important for generating a concentration gradient in the renal medulla, but it mainly focuses on concentrating urine rather than the initial reabsorption of salt and water. Hence, the PCT stands out as the primary structure for these processes.