Which site is associated with the reabsorption of nutrients and water in the nephron?

• A. Bowman’s capsule
• B. Collecting duct
• C. Proximal convoluted tubule
• D. Glomerulus

Answer: (C)

Reabsorbing nutrients and most of the water from the filtrate happens mainly in the proximal convoluted tubule. Its cells have a brush border of microvilli that greatly increases surface area, so nutrients can be taken back into the body efficiently. Sodium-dependent transporters on the apical surface move glucose and amino acids together with sodium from the filtrate into the cells. The basolateral Na+/K+ ATPase pumps sodium into the interstitial fluid, maintaining the gradient that drives continued reabsorption. Water follows this reabsorbed solute load by osmosis through aquaporin channels, so a large amount of water is reclaimed and the filtrate becomes isotonic with the blood. Overall, this region reabsorbs about two-thirds of filtered water and most filtered nutrients, making it the primary site for nutrient and water reabsorption. Bowman’s capsule and the glomerulus are involved in filtration, not reabsorption, while the collecting duct handles final water reabsorption under hormonal control and does not reclaim nutrients to the same extent.