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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.
Composition
Urine is a transparent solution that is clear to amber in color, and usually is light yellow. It is the byproduct or waste fluid secreted by the kidneys, transported by the ureters to the urinary bladder where it is stored until it is voided through the urethra. Urine is made up of a watery solution of metabolic wastes (such as urea), dissolved salts and organic materials. Fluid and materials being filtered by the kidneys, destined to become urine, comes from the blood or interstitial fluid. The composition of urine is adjusted in the process of reabsorption when essential molecules needed by the body, such as glucose, are reabsorbed back into the blood stream via carrier molecules. The remaining fluid contains high concentrations of urea and other excess or potentially toxic substances that will be released from the body via urination. 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. Urea is 10,000 times less toxic than ammonia and is a byproduct of deamination (2 NH3 molecules) and cellular respiration's (1 CO2 molecule) products combining together. Other components include various inorganic salts such as sodium chloride (the discharge of sodium through urine is known as natriuresis.)
Function
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.
Other uses
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 and even isolated reports as a teeth whittener.
In Siberia, to communicate with the spirits, the Koryak people drank the urine of another who has consumed fly agaric (an entheogenic, and occasionally fatally poisonous, mushroom), or of one who has in turn drunk urine of like source. Sometimes, the urine of reindeer that had eaten fly agaric would even be drunk. 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. Urine should be diluted with 15 parts of water before it is safe to use on potted plants. Undiluted urine can burn the roots of most common plants. In Japan, urine used to be sold to farmers who would process it into fertilizers.
The use of urine as a medical treatment or daily health regimen is not uncommon. Purported beneficiaries of the 'urine cure' include Mohandas Gandhi, Jim Morrison, and Steve McQueen.
During World War I, Canadian soldiers without gas masks urinated on cloth and wore the cloth during a gas attack.
In recent times, the Port-a-John corporation of Utica, Michigan, USA has developed a filter to collect medically significant proteins from users of their chemical toilets.
History
The golden colour of urine was previously thought to come from gold. Alchemists spent much time trying to extract gold from urine, and 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. During his study of female human anatomy in 1702, famous Scot, Dr L Maddox, erroneously proposed that ingested urine would cure asthma. In 1773 the French chemist Hilaire Rouelle, discovered the organic compound urea by boiling urine dry.
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