What are the functional units of the kidney called?

• A. Alveoli
• B. Nephrons
• C. Neurons
• D. Lobes

Answer: (B)

The functional unit of the kidney is the nephron. A nephron carries out the essential tasks of filtering blood and forming urine. It begins with a glomerulus where blood is filtered, and then fluid passes through a tubular system—the proximal tubule, loop of Henle, distal tubule, and collecting duct—where water and ions are reabsorbed, wastes are secreted, and the concentration of the urine is adjusted. This combination of filtration plus selective reabsorption and secretion is what lets the kidneys regulate fluid balance, electrolytes, and waste elimination.

Other terms you might hear refer to different parts of the body: alveoli are air sacs in the lungs for gas exchange, neurons are nerve cells, and lobes are subdivisions of organs like the brain or liver. None of these are the kidney’s functional unit.