Urine is liquid waste excreted by the kidneys and is produced by the process of filtration. This waste is eventually expelled from the body in a process known as urination. Most commonly the excretion of urine serves for flushing waste molecules collected from the blood by the kidneys, and for the homeostasis of the body liquids.

Composition

Urine is a transparent solution that is clear to amber in color, and usually is light yellow. It is the byproduct or waste fluid secreted by the kidneys, transported by the ureters to the urinary bladder where it is stored until it is voided through the urethra. Urine is made up of a watery solution of metabolic wastes (such as urea), dissolved salts and organic materials. Fluid and materials being filtered by the kidneys, destined to become urine, comes from the blood or interstitial fluid. The composition of urine is adjusted in the process of reabsorption when essential molecules needed by the body, such as glucose, are reabsorbed back into the blood stream via carrier molecules. The remaining fluid contains high concentrations of urea and other excess or potentially toxic substances that will be released from the body via urination. 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 contains large amounts of urea, an excellent source of nitrogen for plants. As such it is a useful accelerator for compost. Urea is 10,000 times less toxic than ammonia and is a byproduct of deamination (2 NH3 molecules) and cellular respiration's (1 CO2 molecule) products combining together. Other components include various inorganic salts such as sodium chloride (the discharge of sodium through urine is known as "natriuresis".)

Function

Urination is the primary method for excreting chemicals and drugs from the body. These chemicals can be detected and analyzed by urinalysis.

In cases of kidney or urinary tract infection (UTI) the urine will contain bacteria, but otherwise urine is virtually sterile and nearly odorless when it leaves the body. However, after that, bacteria that contaminate the urine will convert chemicals in the urine into smelling chemicals that are responsible for the distinctive odor of stale urine; in particular, ammonia is produced from urea.

Some Terms:

Urine therapy-Urine therapy is a specialized branch of alternative medicine. Any sort of oral or external application of human urine for medicinal purposes falls into this category. Promoters of urine therapy believe urine to have many curative powers. Some cultures, especially Indian, have traditionally used urine as a medicine.

Urolagnia (also known as urophilia) is a paraphilia involving sexual attraction to urine. People with urolagnia often like to urinate in public, or urinate on, or be urinated on by other people, and may drink the urine. The consumption of urine is urophagia. Some like to watch others doing these things. These activities are often described by the euphemisms "golden showers" or "watersports" (which should not be confused with water sports). Urolagnia is sometimes associated with, or confused with, a sexual attraction to someone experiencing the discomfort or pain of a full bladder, a sadomasochistic inclination.

Drinking urine-A healthy individual's urine is sterile. However, if an individual has a bacterial infection of the urethra, there can be some transmittance of the infection to a person who drinks the urine. It has been suggested that when a person is in desert survival or surrounded by water and devoid of drinking water that the person must resort to drinking his own urine if it is the only liquid available. This technique has been said to extend life from one to two extra days but evidence remains sparse.

Contrary to that notion is that drinking urine may actually increase the speed of dehydration because of certain bodily toxins and salinity in the urine.

Chapter III - Urinary System