Urea is made up of carbon, nitrogen and oxygen. It is found in urine, sweat, blood and milk in mammals. But the most concentrated form is in urine. It is a crystalline compound, and the nitrogen content is always at least 46 percent when dry. Urea is used in fertilizer because it is very high in nitrogen. It is also used in food given to animals, and has other applications, such as being an ingredient in certain plastics and glues, and as a stabilizer in explosive components.
Ammonia is formed in the body, but the body does not "like" it (it's extremely toxic), and in turn, works to remove it. The ammonia is pulled into the blood cells and is carried along to the liver. At this point, it is connected to carbon dioxide particles, which changes it into the combination of urea and water. The process continues as the blood moves through the kidney, where the urea is filtered out of the bloodstream and mixed with more water. This is called urine. It moves through the bladder next and out of the body.
Urea can also be manufactured synthetically. This was first done in 1828, and by complete accident, as the scientist involved was trying to make ammonium cyanate. In the process of adding ammonium chloride to silver cyanate, a crystal type substance formed. When analyzed, it was the chemical compound urea. In today's processing, urea is made through a process of heating ammonium carbamate. The compound is placed in a sealed container and heated. The ammonium carbamate is a combination of ammonia and carbon dioxide. This heating dehydrates the compound, and the crystals that form are urea.