Tubular reabsorption of Na+ from the proximal tubule involves which of the following mechanisms?

• A. Active transport via Na+/K+ ATPase pumps
• B. Facilitated diffusion through aquaporins
• C. Simple diffusion across the tubular membrane
• D. Endocytosis into tubular cells

Answer: (A)

Verified step by step guidance

1. Understand that tubular reabsorption is the process by which the nephron removes water and solutes from the tubular fluid and returns them to the circulating blood.
2. Recognize that sodium (Na+) reabsorption in the proximal tubule is a crucial step in maintaining electrolyte balance and blood pressure.
3. Identify that active transport is a process that requires energy, typically in the form of ATP, to move substances against their concentration gradient.
4. Learn that the Na+/K+ ATPase pump is a type of active transport mechanism that moves Na+ out of the tubular cells into the interstitial fluid, while bringing K+ into the cells, using energy from ATP.
5. Differentiate between active transport and other mechanisms such as facilitated diffusion, which involves transport proteins but does not require energy, and simple diffusion, which is the passive movement of molecules down their concentration gradient.