What are the functional units of the kidney called?

• A. The glomerulus
• B. Nephrons
• C. The renal pelvis
• D. The ureter

Answer: (B)

Nephrons are the functional units of the kidney. Each nephron acts as a tiny filtration and processing unit that turns blood into urine. Blood first enters a glomerulus, a small knot of capillaries where filtration happens, producing a filtrate that is free of large proteins and blood cells. This filtrate then moves through a sequence of tubules—the proximal tubule, loop of Henle, distal tubule, and collecting duct—where essential substances like water, glucose, and ions are reabsorbed back into the bloodstream, and waste products are secreted into the filtrate. The final urine is collected in the renal pelvis and then travels down the ureter, but the critical site of filtration and urine formation is the nephron itself. There are about a million nephrons in each kidney, providing the extensive capacity needed to regulate fluid balance, electrolytes, and waste removal.