Urine (vulgar piss) is 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

Main: 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.Fact: date=August 2008

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

Main: Urinalysis

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.