Aldosterone , a hormone secreted by the kidneys, regulates the transfer of sodium from the nephron to the blood. When sodium levels in the blood fall, aldosterone is released into the blood, causing more sodium to pass from the nephron to the blood. This causes water to flow into the blood by osmosis. Renin is released into the blood to control aldosterone. Many kidney problems can be treated by dialysis, where a machine acts as a kidney.
Kidney transplants are an alternative to dialysis.
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