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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 analyzed by urinalysis. In pregnant women, amniotic fluid is closely related to urine, and can be analyzed by amniocentesis.


Sample of human urine


Main article: Renal 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.[How to reference and link to summary or text] 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.


Urine is a transparent solution that can range from colorless 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 color of urine is caused by the pigment urochrome as well as the degradation products of bilirubin and urobilin.[How to reference and link to summary or text] It can range from clear to a dark amber, depending mostly upon the level of hydration of the body, among other factors.

Chemical analysis[]

Main article: Urinalysis

Urea structure

Urine contains a range of substances that vary with what is introduced into the body. Aside from water, urine contains an assortment of inorganic salts and organic compounds, including proteins, hormones, and a wide range of metabolites. Other substances found of interest to psychologists include:

Unusual coloration[]

  • Clear- indicates over-hydration, which is usually considered much healthier than dehydration. In the context of a drug test, it could indicate a potential attempt to avoid detection of illicit drugs in the bloodstream thru over-hyrdration[1].
  • 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. It’s red.
  • 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/brownish 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 odor is not universally detectable.[2]


Turbid urine may be a symptom of a bacterial infection, but can also be due to crystallization of salts such as calcium phosphate.


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.[3]


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 Liters per day. Producing too much or too little urine needs medical attention: Polyuria is a condition of excessive production of urine (> 2.5 Liters/day), in contrast to oliguria where < 400 milliliters (4 deciliters) are produced per day, or anuria with a production of < 100 milliliters (1 deciliter) per day.A deciliter is 1/10 liter.

Density or specific gravity[]

Normal urine density or specific gravity values vary between 1.003-1.035 ( , 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. 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.[4] 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.[How to reference and link to summary or text]


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.[How to reference and link to summary or text]

Other uses[]

Survival uses[]

See also: Urophagia

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.

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.[How to reference and link to summary or text]

Urban myth states that urine works well against jellyfish stings, and this scenario was demonstrated on an early episode of the unscripted CBS-TV show Survivor. At best, it is ineffective and in some cases this treatment may make the injury worse.[5][6][7]



See also[]

External links[]


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