What is the primary functional unit of the kidney?

• A. Glomerulus
• B. Bowmans capsule
• C. Collecting duct
• D. Nephron

Answer: (D)

The kidney’s basic functional unit is the nephron. Each nephron carries out filtration, reabsorption, and secretion to form urine and regulate fluid and electrolyte balance. Filtration occurs at the glomerulus, and the resulting filtrate is collected in Bowman's capsule, then processed along the tubule system (proximal tubule, loop of Henle, distal tubule, and collecting duct). While the glomerulus is the filtration site and Bowman's capsule collects filtrate, and the collecting duct conducts final urine and concentration, none of these alone handles the full sequence of filtration plus processing that defines kidney function. That integrated unit is the nephron, making it the correct answer.