Obligatory Urine Volume

The maximal concentrating ability of the kidney decides to a minimum how much urine volume must be excreted each day to eliminate the body of waste products of metabolism and ions that are ingested. A normal 70 kg human being excretes about 600 mOsm solute in 1 day. Maximal urine concentra­tion is 1200 mOsm/L, characterised by the minimal volume of urine called the obligatory urine volume. It can be calculated as 600 mOsm/day/1200 mOsm/L = 0.5 L/day. This minimal loss of volume in the urine contributes to dehydration and water loss from the skin, respiratory tract and gastrointestinal tract, especially when the animal is deprived of water.

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