What is the basic functional unit of the human kidney?

The nephron is the basic functional unit of the human kidney.

Each nephron filters blood and modifies the resulting fluid to form urine. Its renal corpuscle contains a glomerulus, a tuft of capillaries, and Bowman's capsule. Filtrate then passes through the proximal tubule, loop of Henle, distal tubule, and collecting duct, although the collecting duct is often considered part of the urinary system rather than the nephron proper.

The kidney uses filtration, reabsorption, and secretion to regulate the body's internal environment. Useful substances such as much of the water, glucose, and selected ions are reclaimed, while wastes and excess substances remain in the urine. The loop of Henle helps establish a concentration gradient that permits water conservation.

Human kidneys contain roughly one million nephrons each, though the exact number varies. Nephrons also support blood-pressure regulation and red-blood-cell production indirectly through kidney hormones. A nephron is not the same as a neuron: a neuron is a nerve cell, whereas a nephron is a kidney structure.