Which process rapidly returns glucose filtered into Bowman's capsule back to the tissue fluid along the proximal tubule?

• A. Active transport
• B. Facilitated diffusion
• C. Osmosis
• D. Simple diffusion

Answer: (A)

Glucose reabsorption in the proximal tubule relies on energy to move glucose against its gradient, using a sodium-glucose cotransporter that couples glucose uptake to the Na+ gradient. Sodium pumped out by Na+/K+-ATPase on the basolateral side keeps intracellular Na+ low, so Na+ flows from the tubule lumen into the epithelial cell and drags glucose along with it into the cell. This is secondary active transport—energy from the sodium gradient drives glucose uptake. Inside the cell, glucose exits into tissue fluid via GLUT transporters by facilitated diffusion.

That’s why active transport best explains rapid return of filtered glucose: it moves against a gradient with help from energy. Facilitated diffusion or simple diffusion wouldn’t reclaim glucose efficiently against its gradient, and osmosis is about water movement, not solute transport.