The frog is also able to use its urinary bladder to aid water conservation. When in water, the frog's bladder quickly fills up with a hypotonic urine. On land, this water is reabsorbed into the blood helping to replace water lost through evaporation through the skin. The reabsorption is controlled by a hormone similar to mammalian ADH . Among the many adaptations to such environments is their ability to convert waste nitrogen compounds into uric acid .
Uric acid is quite insoluble and so can be excreted using only a small amount of water.
Thus we find that reptile glomeruli are quite small and, in fact, some reptiles have no glomeruli at all. Those with glomeruli filter just enough fluid to wash the uric acid, which is secreted by the tubules, into the cloaca . Most of this moisture is reabsorbed in the cloaca. These water conservation mechanisms can allow the reptile to forgo drinking water. The water content of its food plus the water produced by cellular respiration is usually sufficient.