Urine is liquid waste excreted by the kidneys and eventually expelled from the body in a process known as urination. Most commonly the excretion of urine serves for flushing waste molecules collected from the blood by the kidneys, and for the homeostasis of the body liquids; however, many species also use it for olfactory communication.
Urine is made up of a watery solution of metabolic wastes and other substances. The fluid collects generally from the blood or interstitial fluid. The composition of urine is adjusted by returning the necessary substances to the body fluid and the excretory product that contains excess or potentially toxic substances is released from the body. Urine flows through the following structures: the kidney, ureter, bladder, and finally the urethra. Urine is produced by a process of filtration, reabsorption, and tubular secretion.
Urine contains large amounts of urea, an excellent source of nitrogen for plants. As such it is a useful accelerator for compost. Other components include various inorganic salts such as sodium chloride.
Urine is the primary method for excreting chemicals and drugs from the body. These chemicals can be detected and analysed by urinalysis.
Although urine is commonly believed to be 'dirty' this is not actually the case. In cases of kidney or urinary tract infection (UTI) the urine will contain bacteria, but otherwise urine is virtually sterile and nearly odorless when it leaves the body. However, after that, bacteria that contaminate the urine will convert chemicals in the urine into smelling chemicals that are responsible for the distinctive odor of stale urine; in particular, ammonia is produced from urea.
Some diseases alter the quantity and consistency of the urine, (e.g. sugar in the urine is a sign of diabetes). Urine therapy is the use of urine topically or consumed, especially as recommended by the traditional Indian medicine, Ayurveda, under the name Amaroli .
Urine can give an indication of how well hydrated a person is. A hydrated person will commonly urinate a clear, water-like urine, whereas a dehydrated person may pass a darker yellow or brown urine as is often observed the morning after a night's drinking of large quantities of alcohol.
Aztec physicians used urine to clean external wounds to prevent infection, and administered it as a drink to relieve stomach and intestine problems.
The ancient Romans used urine as a bleaching agent for cleaning clothes.
In Siberia, to communicate with the spirits, the Koryak people drank the urine of another who has consumed fly agaric (a hallucinogenic, and occasionally fatally poisonous, mushroom), or of one who has in turn drunk urine of like source. The potency of the mushroom does not decrease significantly until around the seventh drinker, because the muscimol from fly agaric is essentially unaltered after being secreted from the kidneys. Not only does this conserve the mushrooms, but it also eliminates unpleasant side-effects caused by muscarine, which does not pass on through urine. Likewise, reindeer licked the ground where there is urine containing fly agaric from the religious ritual.
In Japan, urine used to be sold to farmers who would process it into fertilizers.
During World War I, Canadian soldiers without gas masks urinated on cloth and wore the cloth during a gas attack.
The golden color of urine was previously thought to come from gold. Alchemists spent much time trying to extract gold from urine, this led to some interesting discoveries such as white phosphorus which was discovered by the German alchemist Hennig Brand in 1669 when he was distilling fermented urine. In 1773 the French chemist Hilaire Rouelle, discovered the organic compound urea by boiling urine dry.