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One of a pair of organs that maintain water balance and expel metabolic wastes.
Human kidneys are bean-shaped organs about 4 in. (10 cm) long, in the small of the back. They filter the entire 5-quart (about 4.5-liter) water content of the blood every 45 minutes. Glucose, minerals, and needed water are returned to the blood by reabsorption. The remaining fluid and wastes pass into collecting ducts, flowing to the ureter and bladder as urine. Each kidney has over 1 million functional units ( kidney failure , kidney stones , and {{link=nephritis">nephritis . See also urinary system .
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[c mediumvioletred] (as used in expressions)
kidney failure
kidney stone
kidney transplant