Urine

Urine is a liquid by-product of metabolism in the bodies of many animals, including humans. It is expelled from the kidneys and flows through the ureters to the urinary bladder, from which it is soon excreted from the body through the urethra during urination.

Cellular metabolism generates numerous by-products, many nitrogenous (rich in nitrogen), that require clearance from the bloodstream. These by-products are eventually expelled from the body during urination, the primary method for excreting water-soluble chemicals from the body. These chemicals can be detected and analyzed by urinalysis. Of the many such substances that exist, the three main nitrogenous wastes of the mammalian body are urea, uric acid, and creatinine.

Animal urine forms part of the nitrogen cycle. In balanced ecosystems it fertilizes soil and plants, which in turn continue to support the animal population. Some animals use it to mark their territories. Human urine and human feces are collectively referred to as human waste; as sewage, they require sewage treatment in places where population density is high. urine and feces similarly require proper management if the livestock population density is high. Such management is part of ecological sanitation.

...
Wikipedia