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Maintaining Water Balance

Biology (Year 12) - Osmoregulation

Ben Whitten

How do the kidneys maintain water balance? ADH (antidiuretic hormone) is the key hormone involved in the maintenance of water levels in mammals, and it acts to decrease urine output. ADH is produced by the hypothalamus, and is stored in the posterior pituitary gland. ADH reduces the level of urine output via its action on the distal convoluted tubule and collecting ducts of the kidney in the nephrons. The main functions of the collecting ducts include the reabsorption of water back into the blood, and the carrying of urine to the ureter. Osmoreceptors in the hypothalamus detect deviations from water trolerance limits, where ADH secretion will either be increased or decreased. Negative feedback loop: Osmoregulation The negative feedback loops shown above demonstrate two different scenarios, each displaying either an increase in blood water plasma levels, or a decrease in blood water plasma levels.

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