Which statement describes the proximal tubule's role in reabsorption?

• A. Reabsorbs Na+, water, and glucose
• B. Secretes H+ into filtrate
• C. Produces renin
• D. Secretes bile

Answer: (A)

The proximal tubule is where most of the filtrate is reclaimed. It reabsorbs sodium, and because water follows sodium by osmosis, a large amount of water is reabsorbed there as well. It also reabsorbs glucose by sodium-dependent transport, so nearly all filtered glucose is recovered in this segment. This combination of Na+, water, and glucose reabsorption is the defining reabsorptive function of the proximal tubule. The other statements refer to processes outside this primary role—renin production occurs in juxtaglomerular cells, bile secretion is a liver function, and while H+ can be secreted to aid acid-base balance, that is a secretion process rather than reabsorption.