is a liquid waste product of the body secreted by the kidneys
by a process of filtration from blood
through the urethra
. Cellular metabolism generates numerous waste compounds, many rich in nitrogen, that require elimination from the bloodstream. This waste is eventually expelled from the body in a process known as urination
, the primary method for excreting water-soluble chemicals from the body. These chemicals can be detected and analysed by urinalysis
. In pregnant women, amniotic fluid
is closely related to urine, and can be analysed by amniocentesis
To eliminate soluble wastes, which are toxic, most animals have excretory systems. In humans soluble wastes are excreted via the urinary system
, which consists of the kidneys
, urinary bladder
, and urethra
. The kidneys extract the soluble wastes from the bloodstream, as well as excess water, sugars, and a variety of other compounds. The composition of urine is adjusted in the process of reabsorption whereby certain solutes
, such as glucose
, are reabsorbed back into the blood stream via carrier molecules. The remaining fluid contains high concentrations of urea
and other substances, including toxins. Urine flows through these structures: the kidney
, and finally the urethra
. Urine is produced by a process of filtration
, and tubular secretion.
Urine is a transparent solution that can range from colourless to amber but is usually a pale yellow. Urine is an aqueous solution of metabolic wastes such as urea
, dissolved salts, and organic compounds. Fluid and materials being filtered by the kidneys, destined to become urine, come from the blood or interstitial fluid
Except in cases of kidney or urinary tract infection (UTI), urine is virtually sterile and nearly odorless. Subsequent to elimination from the body, urine can acquire strong odors due to bacterial action. Most noticeably, ammonia is produced by breakdown of urea, a major component of urine. Some diseases alter the quantity and consistency of the urine, such as sugar as a consequence of diabetes.
Urea is toxic and can be irritating to skin and eyes. High concentrations in the blood can cause damage to organs of the body. Low concentrations of urea such as in urine are not dangerous.
The typical bright yellow colour of urine is caused by the pigment urochrome
as well as the degradation products of bilirubin
. Clear colors are a sign of hydration and are the preferred colors of urine.
Urine contains a range of substances that vary with what is introduced into the body. Aside from water, urine contains an asortment of inorganic salts and organic compounds, including proteins, hormones, and a wide range of metabolites.
- Yellowing/light Orange may be caused by removal of excess B vitamins from the bloodstream.
- Certain medications such as rifampin and pyridium can cause orange urine.
- Bloody urine is termed hematuria, potentially a sign of a bladder infection.
- Consumption of beets can cause urine to have a pinkish tint; the condition is harmless and temporary.
- Dark orange to brown urine can be a symptom of jaundice or Gilbert's syndrome.
- Black or dark-colored urine is referred to as melanuria and may be caused by a melanoma.
- Reddish or brown urine may be caused by porphyria. Again, the consumption of beets can cause the urine to have a harmless, temporary pink or reddish tint.
- Fluorescent Yellow / Greenish urine may be caused by dietary supplemental vitamins, especially the B vitamins.
- Dark yellow urine is usually indicative of dehydration.
Usually odorless, urine can be pungent after the consumption of certain foods. Eating asparagus is known to produce a strong odor in human urine. This is due to the body's break down of asparagusic acid
. Although odorous urine is a universal consequence of eating asparagus, the odour is not universally detectable.
urine may be a symptom of a bacterial infection, but can also be due to crystallisation of salts such as calcium phosphate
of urine is close to neutral (7) but can normally vary between 4.5 and 8. Strongly acidic or alkaline urine may be symptomatic of disease.
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.
Density or specific gravity
Normal urine density or specific gravity
values vary between 1.003-1.035 (g.cm-3
) , and any deviations may or may not be associated with urinary disorders.
Urine in medicine
Many physicians in history 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. Abdul Malik Ibn Habib
d.862CE, 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 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 intestinal problems. Purported beneficiaries of the 'urine cure' include 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
In historical times, urine was collected and used in the manufacture of gunpowder
. Stale urine was filtered through a barrel full of dry straw and allowed to continue to sour for a year or more. After this period of time, water was used to wash the resulting chemical salts
from the straw. This slurry was filtered through wood ashes and allowed to dry in the sun. Saltpeter
crystals were then collected and added to sulfur
to create black powder
Urine has often been used as a mordant
to help prepare textiles, especially wool, for dyeing. Urine was used for dyes such as indigo
where the urea in the urine reacted with the insoluble dye to form a soluble solution.
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
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
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.
- The ancient Romans used urine as a bleaching agent for cleaning clothes and teeth.
- In Scotland, it was used to wash wool to prevent shrinking.
Urine contains large amounts of urea
, an excellent source of nitrogen
for plants. As such it is a useful accelerator for compost
. Urea is much less toxic than ammonia
and is formed by the indirect 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
discharge is called natriuresis
Urine has applications in gardening and agriculture as a fertilizer
. Gardeners often recommend a dilution of 10-20 parts water to one of urine for application to plants and flower beds during the growing season; undiluted urine can chemically burn the roots of some species. Urine typically contains more than 50% of the nitrogen
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 of 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. This practice has been applied, along with crop rotation schemes, for thousands of years.
In Japan and Nepal, urine can be used in small scale aquaculture.
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 drink urine to prevent life-threatening dehydration. This desperate measure, however achieves little as urine is as dehydrating as saltwater.
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 as an antibacterial.
Urban myth states that urine works well against jellyfish stings, although it is at best ineffective and in some cases may make the injury worse.
The yellow color of urine was previously thought to come from gold. Alchemists
spent much time trying to extract gold from urine, and this effort led to discoveries such as white phosphorus
, which was discovered by the German alchemist Victor Wernanowicz
in 1669 when he was distilling fermented
urine. In 1773 the French chemist Hilaire Rouelle
discovered the organic compound urea
by boiling urine dry.