Functional unit of the kidney that removes waste and excess substances from the blood to produce urine .
Each of the million or so nephrons in each kidney is a tubule 1.2–2.2 in. (30–55 mm) long. At one end it is closed, expanded, and folded into a double-walled cuplike structure (Bowman's capsule) enclosing a cluster of electrolytes such as sodium and potassium are balanced in several distinct sections along its length. The final concentrated product is urine. See also {{link=urinary system">urinary system .