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Urine (from Latin Urina, ae, f.) is a typically sterile liquid by-product of the body secreted by the kidneys through a process called urination and excreted through the urethra. Cellular metabolism generates numerous by-products, many rich in nitrogen, that require elimination from the bloodstream. These by-products are eventually expelled from the body in a process known as micturition, the primary method for excreting water-soluble chemicals from the body. These chemicals can be detected and analyzed by urinalysis. Certain disease conditions can result in pathogen-contaminated urine.
Most animals have excretory systems for elimination of soluble toxic wastes. In humans, soluble wastes are excreted primarily by the urinary system and, to a lesser extent in terms of urea removed, by perspiration. The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. The system produces urine by a process of filtration, reabsorption, and tubular secretion. The kidneys extract the soluble wastes from the bloodstream, as well as excess water, sugars, and a variety of other compounds. The resulting urine contains high concentrations of urea and other substances, including toxins. Urine flows from the kidney through the ureter, bladder, and finally the urethra before passing from the body.
Exhaustive detailed description of the composition of human urine can be found in NASA Contractor Report No. NASA CR-1802, D. F. Putnam, July 1971. That report provided detailed chemical analyses for inorganic and organic constituents, methods of analysis, chemical and physical properties and its behavior during concentrative processes such as evaporation, distillation and other physiochemical operations. Urine is an aqueous solution of greater than 95% water, with the remaining constituents, in order of decreasing concentration urea 9.3 g/L, chloride 1.87 g/L, sodium 1.17 g/L, potassium 0.750 g/L, creatinine 0.670 g/L and other dissolved ions, inorganic and organic compounds.
Urine is sterile until it reaches the urethra, where epithelial cells lining the urethra are colonized by facultatively anaerobic Gram negative rods and cocci. Subsequent to elimination from the body, urine can acquire strong odors due to bacterial action, and in particular the release of ammonia from the breakdown of urea.
Some diseases alter the quantity and consistency of urine, such as diabetes introducing sugar. Consuming beets can result in beeturia (pink/red urine containing betanin) for some 10–14% of the population.
Healthy urine is not toxic. However, it contains compounds eliminated by the body as undesirable, and can be irritating to skin and eyes. After suitable processing it is possible to extract potable water from urine.
Urine is principally water. It also contains an assortment of inorganic salts and organic compounds, including proteins, hormones, and a wide range of metabolites, varying by what is introduced into the body.
Urine varies in appearance, depending principally upon a body's level of hydration, as well as other factors. Normal urine is a transparent solution ranging from colorless to amber but is usually a pale yellow. In the urine of a healthy individual the color comes primarily from the presence of urobilin. Urobilin in turn is a final waste product resulting from the breakdown of heme from hemoglobin during the destruction of aging blood cells.
Colorless urine indicates over-hydration, generally preferable to dehydration (though it can remove essential salts from the body). Colorless urine in drug tests can suggest an attempt to avoid detection of illicit drugs in the bloodstream through over-hydration.
The odor of normal human urine can reflect what has been consumed.
Eating asparagus can cause a strong odor reminiscent of the vegetable caused by the body's breakdown of asparagusic acid. Likewise consumption of saffron, alcohol, coffee, tuna fish, and onion can result in telltale scents. Particularly spicy foods can have a similar effect, as their compounds pass through the kidneys without being fully broken down before exiting the body.
The pH of urine can vary between 4.6 and 8, with neutral (7) being norm. In persons with hyperuricosuria, acidic urine can contribute to the formation of stones of uric acid in the kidneys, ureters, or bladder. Urine pH can be monitored by a physician or at home.
A diet high in citrus, vegetables, or dairy can increase urine pH (more basic)[dubious ]. Some drugs also can increase urine pH, including acetazolamide, potassium citrate, and sodium bicarbonate.
A diet high in meat can decrease urine pH (more acidic). Cranberries, popularly thought to decrease the pH of urine, have actually been shown not to acidify urine. Drugs that can decrease urine pH include ammonium chloride, chlorothiazide diuretics, and methenamine mandelate.
Average urine production in adult humans is about 1 – 2 L per day, depending on state of hydration, activity level, environmental factors, weight, and the individual's health. Producing too much or too little urine needs medical attention. Polyuria is a condition of excessive production of urine (> 2.5 L/day), oliguria when < 400 mL are produced, and anuria one of < 100 mL per day.
Normal urine density or specific gravity values vary between 1.003–1.035 (g·cm−3), and any deviations may be associated with urinary disorders.
Many physicians in history have resorted to the inspection and examination of the urine of their patients. Hermogenes wrote about the color and other attributes of urine as indicators of certain diseases. Abdul Malik Ibn Habib of Andalusia d.862 AD, mentions numerous reports of urine examination throughout the Umayyad empire. 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 occurs when alcohol, caffeine, or other diuretics are consumed, in which case urine can be clear and copious and the person still be dehydrated.
Urine contains proteins and other substances that are useful for medical therapy and are ingredients in many prescription drugs (e.g., Ureacin, Urecholine, Urowave). Urine from postmenopausal women is rich in gonadotropins that can yield follicle stimulating hormone and luteinizing 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. Urine also contains antibodies, which can be used in diagnostic antibody tests for a range of pathogens, including HIV-1.
Urine contains large quantities of nitrogen (mostly as urea), as well as significant quantities of dissolved phosphates and potassium, the main macronutrients required by plants, with urine having plant macronutrient percentages (i.e. NPK) of approximately 11-1-2 by one study or 15-1-2 by another report, illustrating that exact composition varies with diet. Undiluted, it can chemically burn the roots of some plants, but it can be used safely as a source of complementary nitrogen in carbon-rich compost.
When diluted with water (at a 1:5 ratio for container-grown annual crops with fresh growing medium each season, or a 1:8 ratio for more general use), it can be applied directly to soil as a fertilizer. The fertilization effect of urine has been found to be comparable to that of commercial fertilizers with an equivalent NPK rating. Urine contains most (94% according to Wolgast) of the NPK nutrients excreted by the human body. Conversely, concentrations of heavy metals such as lead, mercury, and cadmium, commonly found in solid human waste, are much lower in urine (though not low enough to qualify for use in organic agriculture under current EU rules). The more general limitations to using urine as fertilizer then depend mainly on the potential for buildup of excess nitrogen (due to the high ratio of that macronutrient), and inorganic salts such as sodium chloride, which are also part of the wastes excreted by the renal system. The degree to which these factors impact the effectiveness depends on the term of use, salinity tolerance of the plant, soil composition, addition of other fertilizing compounds, and quantity of rainfall or other irrigation.
Urine typically contains 70% of the nitrogen and more than half the phosphorus and potassium found in urban waste water flows, while making up less than 1% of the overall volume. Thus far, source separation, or urine diversion and on-site treatment has been implemented in South Africa, China, and Sweden among other countries with the Bill and Melinda Gates Foundation provided some of the funding implemenations. China reportedly had 685,000 operating source separation toilets spread out among 17 provinces in 2003.
"Urine management" is a relatively new way to view closing the cycle of agricultural nutrient flows and reducing sewage treatment costs and ecological consequences such as eutrophication resulting from the influx of nutrient rich effluent into aquatic or marine ecosystems. Proponents of urine as a natural source of agricultural fertilizer claim the risks to be negligible or acceptable. Their views seem to be backed by research showing there are more environmental problems when it is treated and disposed of compared with when it is used as a resource.
It is unclear whether source separation, urine diversion, and on-site urine treatment can be made cost effective; nor whether required behavioral changes would be regarded as socially acceptable, as the largely successful trials performed in Sweden may not readily generalize to other industrialized societies. In developing countries the use of whole raw sewage (night soil) has been common throughout history, yet the application of pure urine to crops is rare. Increasingly there are calls for urine's use as a fertilizer, such as a Scientific American article "Human urine is an effective fertilizer".
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In pre-industrial times urine, being rich in ammonia, was used – in the form of lant – as a cleaning fluid.
Urine was used before the development of a chemical industry in the manufacture of gunpowder. Urine, a nitrogen source, was used to moisten straw or other organic material, which was kept moist and allowed to rot for several months to over a year. The resulting salts were washed from the heap with water, which was evaporated to allow collection of crude saltpeter crystals, that were usually refined before being used in making gunpowder.
Numerous survival instructors and guides, including the US Army Field Manual, advise against drinking urine for survival. These guides explain that drinking urine tends to worsen, rather than relieve dehydration due to the salts in it, and that urine should not be consumed in a survival situation, even when there is no other fluid available. In hot weather survival situations where other sources of water are not available, soaking cloth (a shirt for example) in urine and putting it on the head can help cool the body.
During World War 1 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). The Vickers machine gun, used by the British Army during World War 1, required water for cooling when fired so soldiers would resort to urine if water was unavailable.
Urban myth states that urine works well against jellyfish stings, and this scenario was demonstrated on a Season 4 episode of the NBC-TV show Friends, "The One With the Jellyfish", an early episode of the CBS-TV show Survivor and the documentary film The Real Cancun. At best, it is ineffective and in some cases this treatment may make the injury worse.
Tanners soaked animal skins in urine to remove hair fibers—a necessary step in the preparation of leather.
Urine can be used as a base material for the production of hydrogen. Unlike water, urea has four hydrogen atoms per molecule and these are atoms less tightly bonded than the hydrogen atoms found in water molecules.
Prior to the acquisition of soap from the Germanic peoples during the first century AD, Ancient Romans used fermented human urine (in the form of lant) to cleanse grease stains from clothing. The emperor Nero instituted a tax (Latin: vectigal urinae) on the urine industry, continued by his successor, Vespasian. It is Vespasian to whom the Latin saying Pecunia non olet (money doesn't smell) is attributed – said to have been the emperor's reply to a complaint from his son about the unpleasant nature of the tax. Vespasian's name is still attached to public urinals in France (vespasiennes), Italy (vespasiani), and Romania (vespasiene).
Alchemists spent much time trying to extract gold from urine, which led to discoveries such as white phosphorus by German alchemist Hennig Brand when distilling fermented urine in 1669. In 1773 the French chemist Hilaire Rouelle discovered the organic compound urea by boiling urine dry.
The onomatopoetic term "piss" was the usual word for urination prior to the 14th century. "Urinate" was at first used mostly in medical contexts. "Piss" continues to be used, but is considered vulgar; it is also used in such colloquialisms as "to piss off" and "piss poor". Euphemisms and expressions used between parents and children such as "wee", "pee", and many others, arose.