| Approximately one million nephrons (right) compose each bean-shaped kidney (left). The filtration unit of the nephron, called the glomerulus, regulates the concentration within the body of important substances such as potassium, calcium, and hydrogen, and removes substances not produced by the body such as drugs and food additives. The filtrate, urine, leaves the nephron through the long renal tubule. Chemical signals triggered by the body’s need for water and salt cause the walls of the tubule to become more or less permeable to these substances, which are reabsorbed accordingly from the urine. |
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