Excreation is a process in which metabolic waste is eliminated from an organism. It is an essential process in all forms of life. During life activities such as cellular respiration, several chemical reactions take place in the body. These reactions are known as metabolism. These chemical reactions produce waste products like carbon dioxide, water, salts, urea and uric acid. Accumulation of these waste beyond the level inside the body is harmful to the organism. The excretary organs remove these waste. This process of removal of metabolic waste from the body is termed excretion. Metabolic waste or excretements are substances that are left over from the metabolic processes. They cannot be used by the organism. They are surplus and many times toxic. They therefore must be excreted. This includes nitrogen compounds, water, carbon dioxide, phosphates, sulfates etc. Animals treat these compounds as excretes. Plants also have their own chemical machinery to transform these compounds into useful substances or remove them from the organism. All the metabolic waste that are excreted in the form of water solutes through the excretary organs, nephridea, malphigian tubules, kidneys etc. With the exception of carbon dioxide which is excreted together with the water vapour through the lungs. The elimination of these compounds enables chemical homeostasis in the organism or maintenance of a equilibrium. The nitrogen compounds through which excess nitrogen is eliminated from the organism is called nitrogenous waste. They are ammonia, urea, uric acid and creatinine. All of these substances are produced from protein metabolism. In many animals, the urine is the main source of excretion for such waste. In some, feces is. In animals, the main excretary products vary. The liver and the kidneys clear many substances from the blood. The excreted substances are then removed from the body in the form of urine or feces. If an organism excretes ammonia as its nitrogenous waste product, it is grouped as ammonia or telly. These organisms need a lot of water as ammonia is very toxic. Most aquatic organisms excrete ammonia directly into the external environment. Ammonia is readily soluble in water and the large bodies of water they live in help to dissipate the toxic chemical. If an organism excreats urea, it is grouped as urea-tellic. Amphibians and mammals are classified as urea-tellic. They convert ammonia into urea via the urea cycle that occurs in the liver and kidney. The urea is less toxic compound than ammonia. Two nitrogen atoms are eliminated through it and less water is needed for excretion. It requires 0.05 liter of water to excrete 1 gram of nitrogen. Approximately only 10% of that required in an ammonia or telly organism. Finally, organisms that excrete uric acid are grouped as urea-tellic animals. These include insects, birds and most reptiles. Though requiring more metabolic energy to make than urea, uric acid is low in toxicity and low in solubility in water. This allows it to be concentrated into small volumes of pasty white suspension compared to the liquid urine of mammals. Uric acid is a heterocyclic compound of carbon, nitrogen, oxygen and hydrogen, with the formula C5, H4, N4, O3. It forms ions and salts known as urates and acid urates, such as ammonium acid urate. Uric acid is a product of the metabolic breakdown of purine nucleotides and it is a normal component of urine. My blood concentrations of uric acid can lead to a disease called gout and are associated with other medical conditions including diabetes and the formation of ammonium acid urate, kidney stones. Uric acid displays lactam-lactium tautomerisms, also defined as a keto-enol tautomerism. Although the lactium form is expected to possess some degree of aromacity, uric acid crystallizes in the lactam form. The tautomer is indicated to be much more stable. Zanthine oxidase is an enzyme which catalyzes the formation of uric acid from Zanthine and Hypo-Zanthine, which in turn are produced from other purines. Zanthine oxidase is a large enzyme whose activity consists of of the metal, molybdeninum, bound to sulfur and oxygen. In the cells, Zanthine oxidase can exist as Zanthine dehydrogenase and Zanthine oxy reductase. Uric acid is released in the hypoxic condition or low oxygen saturation condition. In birds and reptiles and some desert living mammals like the kangaroo rat, uric acid is also the end product of purine metabolism and is excreted in the feces as a dry mass. This involves a complex metabolic pathway that is energetically costly in comparison to production of other nitrogenous waste such as urea from the urea cycle or ammonia, but has the advantage of reducing water loss and preventing dehydration. In humans, the normal concentration of uric acid or hydrogen-urate ion in the blood is 25 to 80 mg per liter for men and 15 to 60 mg per liter for women. And individuals can have serum values as high as 96 ml per liter and not have gout. In humans, about 70% of daily uric acid dispersal occurs via the kidneys and 5 to 25% of humans have impaired renal kidney excretion leading to hyper-uricemia. In other higher primates, uric acid in the form of hydrogen-urate ion is the final oxidation or breakdown product of purine metabolism and is excreted via the urine. In most mammals, the enzyme uricase further oxidizes uric acid to alantonin.