Urine is the by product or fluid secreted by the kidneys, transported by the ureters to the urinary bladder where it is stored until it is voided through the urethra. It is a transparent solution that is clear to amber in color, and usually is light yellow. 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, come 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 these 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 formed by the combination of the byproducts of deamination (2 NH3 molecules) and cellular respiration (1 CO2 molecule). Other components include various inorganic salts such as sodium chloride (the discharge of sodium through human urine is known as natriuresis).
The typical clear yellow or yellow-orange (usually a sign of dehydration) color of urine is caused by the pigment urochrome, but also from the degradation products of bilirubin and urobilin. Unusual coloration may be the result of certain food products such as betacyanin as found in red beets. Also, removal of excess B vitamins from the bloodstream may cause a yellowing. A common prank is to trick someone into drinking methylene blue, resulting in blue urine. Abnormal coloration from bleeding within the urinary system is termed hematuria (blood in the urine), a symptom that needs medical attention. Dark orange to brown urine can be a symptom of jaundice or Gilbert's syndrome. "Melanuria" refers to black or dark-colored urine and may be caused by a melanoma. Porphyria may also change the color of urine to a reddish or brown.
Turbid urine may be a symptom of a bacterial infection, but can also be due to crystallisation of salts in the urine (e.g. calcium phosphate), which will dissolve if acetic acid (vinegar) is added. If turbidity occurs together with pain in the bladder region or during urinating, it is most probably due to an infection.
The amount of urine produced depends on numerous factors including state of hydration, activities, environmental factors, size, and health. In adult humans the average production is about 1 - 2 L per day. Producing too much or too little urine needs medical attention: Polyuria is a condition of excessive production of urine (> 2.5 L/day), in contrast to oliguria where < 400 mL are produced per day, or anuria with a production of < 100 mL per day.
Urination is the primary method for excreting toxins, chemicals and drugs from the body. These chemicals can be detected and analysed by urinalysis. Cellular metabolism results in a buildup of toxic nitrogen compounds, or nitrogenous waste. Since this waste is toxic, most animals have excretory systems (in humans this is known as the Urinary system, which consists of the Kidneys, Urinary Bladder, Ureter, and Urethra) to rid themselves of this waste. The kidneys extract the nitrogenous wastes from the bloodstream, as well as excess water, sugars, and a variety of other chemicals.
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 smelly chemicals that are responsible for the distinctive odor of stale urine; in particular, ammonia is produced from urea.
Physicians in all ages have resorted to the inspection and examination of the urine of their patients. Hippocrates described urine examination. Hermogenes wrote about the color and other attributes of urine as indicators of certain diseases. Diabetes mellitus got its name because the urine is plentiful and sweet. A urinalysis is a medical examination of the urine and part of routine examinations. A culture of the urine is performed when a urinary tract infection is suspected. A microscopic examination of the urine may be helpful to identify organic or inorganic substrates and help in the diagnosis.
The color and volume of urine can be reliable indicators of hydration level. Clear and copious urine is generally a sign of adequate hydration, dark urine is a sign of dehydration. The exception is when alcohol, caffeine, or other diuretics are consumed, in which case urine can be clear and copious and the person still be dehydrated.
The use of urine therapy as a medical treatment or daily health regimen is uncommon. Aztec physicians used urine to clean external wounds to prevent infection, and administered it as a drink to relieve stomach and intestine problems. Purported beneficiaries of the 'urine cure' include Mohandas Gandhi, Jim Morrison, and Steve McQueen. Its medicinal properties have also been used in China as a part of holistic medicine, and in India, especially as part of the traditional Indian medicine, Ayurveda, under the name Amaroli.
Urine may contain proteins or other substances that are useful for medical therapy. Urine from postmenopausal women is rich in gonadotropins that can yield follicle stimulating hormone for fertility therapy. The first such commercial product was Pergonal. Urine from pregnant women contains enough human chorionic gonadotropins for commercial extraction and purification to produce hCG medication. Pregnant mare urine is the source of estrogens, namely Premarin.
In Siberia, to communicate with the spirits, the Koryak people drank the urine of another who has consumed fly agaric (an entheogenic mushroom that is occasionally fatally poisonous), or of one who has in turn drunk urine of like source. According to Koryak tradition, sometimes the urine of reindeer that had eaten fly agaric would be ingested -- although there are skeptics who claim that an animal would naturally avoid this mushroom because of its deep red color -- and reindeers are reported to lick the ground where users of fly agaric had urinated. 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, as this does not pass through urine and only the initial ingestor must experience the unpleasant effects.
Urine has applications in gardening and agriculture as a fertilizer. Gardeners often recommend a dilution of 10-15 parts water to one of urine for application to pot plants and flower beds during the growing season; pure urine can chemically burn the roots of some species. Urine typically contains more than 50% of the nitrogen and phosphorus and potassium content of whole sewage, and is widely considered as good as or better than commercially-available chemical fertilisers or stabilised sludge from sewage plants. Urine is also used in composting to increase the nitrogen content of the mulch, accelerating the composting process and increasing its final nutrient values.
Urine is also being actively considered as a fertilizer for use in food-crop agriculture in developed countries. Studies into its feasibility and safety usually indicate that it is an acceptable alternative to chemical fertilisers and stabilised sludge. However, the technology to implement its use on a large scale has not been developed, and is considered too expensive. There are also concerns over its safety regarding the potential for transmitting infectious disease and refluxing xenobiotic compounds (associated with toilet-cleaning products and prescribed drugs expelled in urine) in the human food chain. Proponents of adopting urine for this use usually claim the risks to be negligible or acceptable, and point out that sewage causes more environmental problems when it is treated and disposed of compared with when it is used as a resource. Critics generally agree that more research is needed into how the resource is to be collected, processed and handled.
A few people use urine as a crop fertilizer. These include organic farming cooperatives and eco-villages where special urine-diverting toilets with collecting tanks are installed. Many of these also employ concepts such as greywater irrigation and the composting of fecal matter. Many are the subject on ongoing feasibility studies sanctioned by governments and private organisations. These people generally reject safety concerns over its use on food crops provided that it is used with common sense. For example, application to fruit trees is considered safer than to bushes and especially root crops. It is also considered sensible to cease application at a safe interval before harvesting. However, the use of urine for this purpose is even rarer than its use on ornamental gardens.
In developing countries, the application of pure urine to crops is also rare. However, whole, untreated sewage, termed night soil, is often applied to crops and is considered essential. It is worth noting that this practice is not new and has been applied, along with crop rotation schemes, for thousands of years.
In Japan, urine used to be sold to farmers who would process it into fertilizers.
Shipwrecked or people otherwise adrift at sea for long periods often resort to drinking their urine when no rainwater is available, seawater being unsuitable. People stranded in deserts often also drank urine to prevent life-threatening dehydration from setting in. However, this desperate measure achieves little to delay death from thirst as urine dehydrates one in the same manner saltwater does.
During World War I, the Germans experimented with numerous poisonous gases for use during war. After the first German chlorine gas attacks, Allied troops were supplied with masks of cotton pads that had been soaked in urine. It was believed that the ammonia in the pad neutralized the chlorine. These pads were held over the face until the soldiers could escape from the poisonous fumes, although it is now known that chlorine gas reacts with urine to produce toxic fumes (see chlorine and Use of poison gas in World War I).
Urine has also been historically used as an antiseptic. In times of war, when other antiseptics were unavailable, urine, the darker the better, was utilized on open wounds to kill bacteria.
Urban myth states that urine works well against jellyfish stings.
Some people incorporate urine into their sexual activity. A person with urolagnia may urinate on his or her partner or enjoy being urinated upon.
The consumption of urine can be seen in the films CKY and Jackass in the form of a frozen confectionery. After scooping ice into a cone he then urinates into it forming a slush drink which he then consumes. However, shortly afterwards he became sick.
The yellow color 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. In 1773 the French chemist Hilaire Rouelle, discovered the organic compound urea by boiling urine dry.