Everything about Urine totally explained
Urine is an aqueous solution of waste electrolytes and metabolites excreted by
mammals,
birds,
reptiles,
fish and
amphibians. Although urine is excreted as a paste (uric acid) by most birds, it's commonly excreted as a fluid varying in color from clear, when dilute, to a dark amber, when concentrated. Urine is produced by the
kidneys, and plays a vital role in maintaining
homeostasis by removing excess water, electrolytes such as
sodium,
chloride,
potassium, and
calcium ions,
urea and other metabolites from the blood. Urine excreted by healthy kidneys is
sterile. The production of urine is called
diuresis.
Composition
Water
The main constituent of urine is water. All vertebrates must carefully maintain the volume of fluid in their
extra-cellular space in order to prevent fluid
overload or
dehydration. Some water is inevitably lost during solute excretion, and represents an unavoidable fluid loss. However, the majority of water excreted in the urine is lost to prevent fluid overload. Different animals have different renal physiologies depending on their need to retain water.
Freshwater fish, for example, produce very large amounts of very dilute urine, whereas desert-dwelling animals such as the
meerkat have evolved very effective renal systems, allowing them to conserve water by producing small amounts of extremely concentrated urine. By comparison, even the most concentrated
human urine is relatively dilute. The excretion of water is called
aquaresis.
Electrolytes
Along with volume regulation, urine regulates the
osmolarity of an animal's internal space. The concentration of ions in the blood and extra-cellular fluid must stay within a fairly tight range to maintain health and avoid dehydration. Although some ions are lost to normal bodily function (such as sweating), most animals have a large surplus of ions in their diets and must excrete them. Most humans, for example, ingest many more
sodium and
chloride ions than they need in the form of [salt] - it's secretion of these surplus ions which makes urine taste salty.
Nitrogen
Urine production and excretion is a vertebrate's primary method for removal of
nitrogen. This is a waste product, produced in the form of ammonia by the liver. Excess nitrogen is found in the diet, and released into the blood during the
deamination of
amino acids in protein metabolism. In fish, where water conservation isn't an issue, ammonia is excreted in dilute urine. However, at higher concentrations it's toxic, and so in mammals' urine, this mainly is in the form of
urea, produced from ammonia in the
liver. Birds generally excrete
uric acid as a paste, to further conserve water.
Acid
The kidneys play a vital role in regulating body pH, preventing
acidosis or
alkalosis by excreting excess
hydrogen ions or
bicarbonate ions as required. 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 + H
2O →
CO2 + 2
NH3
Metabolites
Animals ingest a wide variety of compounds daily. Not least are humans, who consume an incredible array of natural and artificial chemicals in the form of food, drink and pharmaceutical products. With the exception of
vitamins,
minerals and other micro-nutrients such as
essential fatty acids, none of these are needed or desirable within the body. All are either metabolised by the liver, excreted in bile or filtered from the blood by the kidneys, and excreted in urine.
Dissolved heavy metals
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):
Glucose
Glucose is constantly lost from the blood into the filtrate at the kidneys - however, active reuptake in the
proximal tubule usually prevents any being excreted. This is desirable, as glucose is a valuable source of energy, not a waste product. However, in
hyperglycaemia - most commonly arising from
diabetes mellitus in humans - the tubular limit on glucose reabsorbtion may be breached, in which case some glucose will be lost in the urine.
Bacteria
Urine excreted by healthy kidneys is
sterile. When it leaves the body, however, the urine can pick up bacteria from the surrounding skin, which would contaminate it.
Characteristics
Color
Urine is normally yellow because it contains
urobilin. It can also be a clear color if an excessive amount of water is drunk.
Uses
Diagnostic tests
Testing urine for its constituents is a cost-effective and non-invasive means of assessing the internal situation of an animal. It is commonly used to test for pregnancy, by measuring levels of hormones excreted. Urinalysis can also be used to test for the metabolites of illegal drugs, if substance abuse is suspected. It is also an invaluable first-line investigation in clinical medicine, where pH, glucose, protein,
white blood cell, bacteria and blood content can all be tested to aid in making a diagnosis.
Fertilizer
Urine has been and is used extensively as
fertilizer. Its high nitrogen content allows increased amino acid synthesis by plants. During WWII, Japanese farmers used urine collected in so-called "honeypots" as cheap fertilizer for their crops.
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 repel those animals by essentially "marking their territory". 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
sulfur and
charcoal to create
black powder.
(External Link
)(External Link)
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 (a
neologism derrived from 'pregnant mare urine'). The drug, manufactured and sold by
Wyeth, is an estrogen replacement therapy used in the treatment of
menopause symptoms.
Further Information
Get more info on 'Urine'.
|
External Link Exchanges
Do you know how hard it is to get a link from a large encyclopaedia? Well we're different and will prove it. To get a link from us just add the following HTML to your site on a relevant page:
<a href="http://urine.totallyexplained.com">Urine Totally Explained</a>
Then simply click through this link from your web page. Our crawlers will verify your link, extract the title of your web page and instantly add a link back to it. If you like you can remove the words Totally Explained and embed the link in article text.
As long as your link remains in place, we'll keep our link to you right here. Please play fair - our crawlers are watching. Your site must be closely related to this one's topic. Any kind of spamming, dubious practises or removing the link will result in your link from us being dropped and, potentially, your whole site being banned. |
