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excretion, process of eliminating from an organism waste products of metabolism and other materials that are of no use. It is an essential process in all forms of life. In one-celled organisms wastes are discharged through the surface of the cell. The higher plants eliminate gases through the stomata, or pores, on the leaf surface. Multicellular animals have special excretory organs. In humans the main organs of excretion are the kidneys and accessory urinary organs, through which urine is eliminated (see urinary system), and the large intestines, from which solid wastes are expelled. The skin and lungs also have excretory functions: The skin eliminates water and salt in sweat, and the lungs expel water vapor and carbon dioxide.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



the freeing of the organism from the end products of metabolism as well as from the foreign substances and excess water, salts, and organic compounds that have entered with food or were formed in the organism. As a result of metabolism, carbon dioxide, certain amino acids, urea, and other substances leave the cell and enter the inter-cellular fluid and then the blood. When excess salts or food substances are consumed or when metabolism is impaired, there is increased concentration of inorganic or organic substances in the blood (for example, glucose and amino acids). The organs of excretion have an important role in keeping constant the composition of the fluids of the internal environment (homeostasis). The process of excretion in vertebrates involves the kidneys, lungs or gills, glands of the gastrointestinal tract, skin, and sweat and salt glands (nasal, rectal). In invertebrates the process involves protonephridia, meta-nephridia, gills, and other organs; in protozoans the excretory organs are the contractile vacuoles. In some animals the products of metabolism and salts are deposited in accumulatory organs or integumentary tissues, which are discarded during molting. Excretion of carbon dioxide and other volatile substances occurs through the lungs or gills. Water, salts, and products of nitrogen metabolism (ammonia, urea, and uric acid) are mainly excreted by the kidneys. Sodium salts are excreted by seabirds and reptiles through the nasal glands and by fish through gills or the rectal gland. A human being weighing 70 kg and eating a normal diet discharges from 10,000 to 20,000 millimoles of carbon dioxide in a 24-hour period through the lungs, while nonvolatile mineral and organic acids and just 1-2 millimoles of bicarbonates are re-moved in the urine. The excretion of water is 1.2 liters in urine, 0.5 liter in sweat, and 0.1 liter in feces. The total quantity of nitrogen excreted in urine is 11 grams, in feces 1.7 grams, and in sweat 1 gram. In a 24-hour period the kidneys discharge 21 grams of urea, 0.63 grams of uric acid, 0.56 grams of hippuric acid, 1.05 grams of creatinine, and 0.78 grams of ammonia.


Prosser, L., and F. Brown. Sravnitel’naia fiziologiia zhivotnykh. Moscow, 1967. (Translation from English.)


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The removal of unusable or excess material from a cell or a living organism.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
In laboratory observations, 29 (67.4%) individuals excreted during the five-minute period after release from the vial, and 14 failed to excrete at this time.
At a pH of 7, 400 mg/L of cystine is soluble, so cystine will be completely soluble in those heterozygotes who excrete less than 300 mg a day.
This process explains how the human body can generate 45 gallons of dilute urinary fluid daily and yet excrete only about one quart of urine.
Vertebrates excrete estrogens in the form of water-soluble polar conjugates.
The animals excrete up to 95 percent of a tetracycline administered, Kuhne says.
The most probable explanation, say the researchers, is that the fluid in the blood slips out of the circulatory system into tissues--causing puffiness and swelling but less blood volume--or that the excess fluid in the astronauts' upper body signals the kidneys to excrete fluid as urine.
When bacteria excrete some of their dehydrated gel into the nozzles, they may trigger what Oster calls "snot guns." The gel particles swell dramatically upon encountering water from outside the cell and then erupt out the nozzles' open ends.
These infants, however, did not excrete unusual amounts of urinary porphyrins.
Moreover, because Soto has not yet identified the particular steroids in down-stream waters, Guillette notes, "we can't rule out that these effects are due to natural androgens and estrogens in manure." Even untreated cattle, horses, and chickens excrete natural estrogens, testosterone, and other steroids (SN: 11/3/01, p.
Livestock naturally excrete large amounts of estrogen and testosterone, hormones that can harm crops and wildlife when farmers use manure as fertilizer (SN: 7/15/95, p.
After the scavenger insect digests the prey, it excretes waste onto the plant's leaves or near its roots.
Females then lay eggs, some of which the infected person excretes in feces, potentially spreading the parasite.