What is primarily reabsorbed in the tubules of the nephron?

In the nephron, the primary site for reabsorption occurs in the renal tubules, specifically the proximal convoluted tubule and the loop of Henle. Water is the primary substance that is reabsorbed in significant quantities throughout the nephron. This reabsorption process is critical for maintaining the body's fluid balance and preventing dehydration.

As the filtrate moves through the nephron, up to 65% to 70% of the water is reabsorbed back into the bloodstream in the proximal convoluted tubule. This is followed by additional water reabsorption in the loop of Henle, especially in the descending limb, which is permeable to water. The reabsorption of water is influenced by various factors, including the presence of antidiuretic hormone (ADH), which increases water permeability in the collecting ducts.

While glucose, amino acids, and uric acid are also reabsorbed to some extent, especially in the proximal convoluted tubule, the reabsorption of water is the most significant process in terms of volume. Therefore, water’s reabsorption is crucial for maintaining homeostasis and regulating blood pressure by controlling the concentration of urine.