Urine is a liquid waste product of the body secreted by the
kidneys by a process of filtration from
blood and
excreted 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.
Physiology
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,
ureters,
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,
ureter,
bladder, and finally the
urethra. Urine is produced by a process of
filtration,
reabsorption, and tubular secretion.
Composition
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.
Hazards
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.
Characteristics
The typical bright yellow colour of urine is caused by the pigment
urochrome as well as the degradation products of
bilirubin and
urobilin. Clear colors are a sign of hydration and are the preferred colors of urine.
Chemical analysis
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.
Unusual colouration
- 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.
Odor
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.
Turbidity
Turbid urine may be a symptom of a bacterial infection, but can also be due to crystallisation of salts such as
calcium phosphate.
pH
The
pH 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.
Volume
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
Examination
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 of
Andalusia 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.
Application
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.
Munitions
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 and
charcoal to create
black powder.
Textiles
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.
Resource
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.
Other uses
Ancient uses
- 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.
Fertilizers
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 NH
3 molecules) and cellular respiration (1 CO
2 molecule). Other components include various inorganic
salts such as
sodium chloride (
sodium discharge is called
natriuresis).
Gardening
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 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.
Food-crop agriculture
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.
Survival uses
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.
History
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.
Notes
References
See also
External links
