Final answer:
The highest percentage of sodium and water reabsorption occurs in the proximal tubule. This segment of the nephron is primarily responsible for reabsorbing 65% of filtered sodium and water, with hormones like aldosterone and ADH regulating the reabsorption process.
Step-by-step explanation:
The location where the highest percentage of sodium and water are reabsorbed back into the bloodstream is the proximal tubule (B. Proximal tubule). In the proximal convoluted tubule (PCT), a majority of water, along with electrolytes and other substances, are reabsorbed into the bloodstream. It is estimated that approximately 65% of the filtered sodium and water are reabsorbed in this segment, mainly through passive and active transport mechanisms tightly regulated by hormones like aldosterone and antidiuretic hormone (ADH).
Various portions of the nephron, which include the PCT, loop of Henle, distal convoluted tubule (DCT), and the collecting ducts, differ in their capacity to reabsorb water and specific solutes. While the distal convoluted tubule (DCT) and collecting ducts play a significant role in the fine-tuning of water and sodium reabsorption, under the influence of ADH and aldosterone, most of the reabsorption occurs in the proximal convoluted tubule, making it the primary site for these processes.