Which part of the kidney reabsorbs glucose and amino acids?

• A. Distal tubule
• B. Loop of Henle
• C. Collecting duct
• D. Proximal tubule

Answer: (D)

Glucose and amino acids are carried back into the blood mainly in the proximal tubule. The reabsorption process starts at the apical membrane, where glucose is taken into the tubular cell by sodium-glucose co-transporters: most of it is reabsorbed by the early proximal tubule via SGLT2, with the remainder handled by SGLT1 in the later part. Amino acids are reabsorbed by dedicated sodium-dependent amino acid transporters. In both cases, the driving force is the sodium gradient maintained by the Na+/K+-ATPase on the basolateral membrane, which keeps Na+ low inside the cell and powers the transporters to move solutes from the filtrate into the cells and then into the bloodstream.

The other nephron segments—Loop of Henle, distal tubule, and collecting duct—primarily handle water and various ions and adjust acid-base balance; they do not normally reabsorb significant amounts of glucose or amino acids. If the filtered glucose load is high enough to saturate the proximal transporters, glucose spills into the urine, illustrating where reabsorption capacity is located.