What is the primary functional unit of the kidney?

• A. Nephron
• B. Glomerulus
• C. Collecting Duct
• D. Renal Pelvis

Answer: (A)

The essential unit responsible for making urine and shaping its composition is the nephron. It’s the kidney’s basic structural and functional unit, with each kidney containing roughly a million of them. A nephron starts with the renal corpuscle, where filtration happens in the glomerulus and is collected by Bowman's capsule. Then it continues through a tubular system—proximal tubule, loop of Henle, distal tubule—that reabsorbs substances and secretes others to fine-tune the filtrate. All of this tubular processing leads to urine, which is finally collected in the collecting duct. The collecting duct itself is part of the nephron’s tubule system and aggregates urine from many nephrons, but it isn’t the unit that carries out filtration and reabsorption on its own. The renal pelvis is simply the chamber that drains urine into the ureter, not a functional unit of urine formation.