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Related to excretion: kidney, Excretory system


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 It might be outdated or ideologically biased.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 ?
The duration of drug action in the body is dependent on its elimination through metabolism and excretion. Cumulative percentage of dose excreted of cefixime via urine after 12 hours after oral administration in our subjects was 11.6%.
Furthermore, Ca2+ is maintained in the body, especially in bones (KEMME-KROONSBERG, 1993), and has low urinary excretion and blood circulation (GUYTON & HALL, 2011).
On the basis of creatinine excretion, her SM mass was 26 kg (9.2 kg [m.sup.-2]) on the first admission and 10.2 kg (3.6 kg [m.sup.-2]) on the second admission.
We hypothesise the ratio of urinary phosphate excretion (mg/day) to serum FGF23 to serve as an index correlating with the nephron number, which we define as the nephron index [4, 5].
Daily urinary sodium, potassium, urea, and creatinine excretion were calculated as the product of urine metabolite concentration by urine volume.
After voiding the bladder, participants were asked to drink 30 ml water per kg body weight in one hour (corresponding to 2200 ml in average), additionally replacing fluid loss 1:1 if urinary excretion exceeded 100 ml within one hour.
Moreover, lumasiran lowered urinary oxalate excretion below 1.1 mmol/24hrs/1.73m2, a threshold associated with reduced progression to end-stage renal disease in clinical studies in all patients with baseline excretion >= 1.6 mmol/24hrs/1.73m2 (N=3).
In this pilot investigation, we found that urine excretion of AQP2 and AQP5, but not AQP1, was dramatically higher in DN patients compared to DM and NDN patients and positively correlated with the progression of the DN, according to the histologic classification.
We also evaluated the usefulness of fractional excretion (FE) of MCP-1, MCSF, and neopterin as pluripotent markers of inflammation, monocyte-macrophage interplay, and tubular damage in the course of CKD.
We measured Rituximab excretion into the urine and in one case where continuous ambulatory peritoneal dialysis (CAPD) was already initiated in the peritoneal fluid as well, using a flow cytometry based approach.
Urinary ammonium excretion was evaluated after emergence of respiratory and metabolic acidosis, respectively, over the course of time as well.