 Dear students, in this topic we shall discuss the excretion of uric acid and uricotillic animals. The animals which excrete uric acid as their major nitrogenous waste are known as the uricotillic animals. These animals may also use a closely related compound called guanine as their major excretive product. The advantage of uric acid excretion is that each uric acid molecule carries with it 4 nitrogen atoms. So excreting one uric acid molecule means excreting 4 nitrogen containing waste atoms. Uric acid is used by the animals which are generally adapted to conditions of limited water availability. That is most terrestrial arthropods, birds and reptiles. Dear students, now we shall discuss the formation of uric acid. Uric acid is formed by the conversion of ammonia and jewellery in uricotillic animals. It is also formed by the breakdown of amino acids, glycine, aspartate and glutamine. It is also formed by the metabolism of pyrimidine and purine bases of nucleic acids. Dear students, the uric acid once formed is transported from the blood into the cells of renal tubule through a urate anion exchanger or through a urate uniporter. When this uric acid comes into tubular cells, from here it moves into the lumen of the tubule down an electrochemical gradient. In the lumen of the kidney tubule, it precipitates because of its low solubility. This is why it does not remain dissolved in water. It precipitates in the lumen of the tubule. And then it is exited out with urine without any major water loss.