Urine

Overview
Urine is a liquid produced by animals through the kidney, and is collected in the bladder and excreted through the urethra.

Urine formation helps to maintain the balance of minerals and other substances in the body. For example, excess of calcium is normally eliminated through the urine. Urine also excretes ammonia, the build-up of which is harmful to the body. In addition, urine is the result of a mechanism that maintains the appropriate amount of water in the body.

A range of substances, including ethanol and artificial sweeteners, are also eliminated from the body through the urine.

Characteristics
The typical bright yellow colour of urine is caused by the pigment urochrome, but also from the degradation products of bilirubin and urobilin. Clear colors are a sign of hydration and are the preferred colors of urine.

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 produce pungent smells 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.

Nitrogen
Urine production and excretion is the body's primary method for removal of nitrogen. In human urine, this is mainly in the form of urea, a protein metabolic byproduct. Aquatic organisms such as fish, alternatively excrete ammonia. Birds and reptiles excrete uric acid, as a protein metabolic byproduct, instead of urea or ammonia. There are some exceptions to these excretion patterns.

pH
When it leaves the body, urine is usually around pH 6, though it may be as low as 4.5 or as high as 8.2. As urea--the compound which accounts for 75-90% of the nitrogen in urine--begins to decay, hydroxide ions form, raising the pH as high as 9-9.3.

The decay of urea into carbon dioxide is catalyzed by urease:

(NH2)2CO + H2O → CO2 + 2NH3

Dissolved heavy metals
Because urine is a liquid collection of metabolic byproducts (whereas feces contains both metabolized and unmetabolized compounds), and because the concentration of heavy metals is low in metabolized compounds, this translates into a low concentration in urine. Studies of urine in organic cattle farms in Sweden in 1999 and 2002 yielded the following concentrations of heavy metals (all in μg/kg wet weight):
 * Copper: 67
 * Zinc: 30
 * Chromium: 5
 * Lead: 1
 * Cadmium: 0

Bacteria
Urine is generally considered to be sterile. When it leaves the body, however, the urine can pick up bacteria from the surrounding skin, which would contaminate it. However, it is not generally advisable to use urine to clean open wounds for it may feed the infecting bacteria.

Demographics of composition
The presence of macronutrients in urine varies significantly from one region of the world to another. However, the amount of nutrients which is lost in the urine, in proportion to the amount of nutrients one consumes, remains relatively constant.

Urinalysis
Many drug tests and other clinical chemical analyses are done on urine. These tests are used to find whether individuals are pregnant, drug users, or other hormone and substance usage questions. There are normal levels for things in urine as well.

Animal repellent
Taking advantage of the scents of male animals' urine, some companies sell animal urine, usually coyote or fox, to cities and other organizations to prevent their trees from being stolen for use as Christmas trees. The scents of carnivore urine (bobcat, mountain lion, and wolf, in addition to coyote and fox) are also sold to the public in pelletized form to repel garden browsing by herbivores such as squirrels and rabbits, as well as deterring domestic or feral cats from marking territory, or catching birds, in gardens. When the pellets are sprinkled on a target area, the intruding animal will instinctively recognize the territorial urinary scent of its predators and avoid the area.

Munitions
In historical times, urine was collected and used in the manufacture of gunpowder. Stale urine was filtered through a barrel full of 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 brimstone 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.

Hormone Replacement Therapy
Steroid hormones extracted from the urine of pregnant mares are used in a drug sold under the trade name Premarin. The drug, manufactured and sold by Wyeth Pharmaceuticals, is an estrogen replacement therapy used in the treatment of menopause symptoms.

Jelly Fish Stings
Contrary to popular belief, urine should not be applied to Jellyfish stings. The urine could actually cause the release of more of the poisonous venom from the sting.