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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 systemurinary system,
group of organs of the body concerned with excretion of urine, that is, water and the waste products of metabolism. In humans, the kidneys are two small organs situated near the vertebral column at the small of the back, the left lying somewhat higher than the
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), and the large intestinesintestine,
muscular hoselike portion of the gastrointestinal tract extending from the lower end of the stomach (pylorus) to the anal opening. In humans this fairly narrow (about 1 in./2.
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, from which solid wastes are expelled. The skin and lungs also have excretory functions: The skin eliminates water and salt in sweatsweat
or perspiration,
fluid secreted by the sweat glands of mammalian skin and containing water, salts, and waste products of body metabolism such as urea. The dissolved solid content of sweat is only one eighth that of an equal volume of urine, the body's main
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, and the lungs expel water vapor and carbon dioxide.



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 removal of unusable or excess material from a cell or a living organism.
References in periodicals archive ?
To estimate total fecal excretion of each animal, feeds, orts and feces samples were incubated for 288 h in the rumen of two cannulated Nellore steers to determination of the concentration of indigestible acid detergent fiber (iADF) used as internal marker (Casali et al.
Furthermore, the utilization of ractopamine in diets for pigs can increase the nitrogen retention and reduce the phosphorus excretion (BARK et al.
Several possible physiological mechanisms have been suggested; for example, LMW proteins and Cd-bound metallothionein may have similar affinity for renal tubular binding sites, and excretion of both proteins and U-Cd may be influenced by normal variation in diuresis (i.
Our goal in this study was to analyze urine iodine excretion kinetics before and after a 50 mg iodine/iodide loading dose and to investigate the arbitrary iodine loading test cutoff of 90% excretion used to determine whole-body iodine sufficiency.
Total purine derivatives excretion (mmol/day) or microbial protein synthesized in rumen (gr/day).
Twenty-four-hour BJP excretion was calculated in 3 different ways:
In this context, P/D and P/N plots showed that the significant changes in salt and water excretions appeared to take place within a relatively small range of pressure values.
Therefore, the amount of excreta from pigs fed rations with high contents of low-fermentable fiber is almost twice the amount from pigs fed standard rations containing normal levels of low-fermentable fiber The intention of this study was, therefore, to provide experimental data on the excretion of nitrogen (N) and phosphorus (P) from grower-finisher pigs under prevalent Vietnamese feeding and manure management practices.
In the laboratory, excretions made from the tips of flower petals fell onto the substrate below; in the field they most often completely cleared the plant in question, landing on the grass in the substrate.
In the TOPH follow-up analysis, there was a significant, linear relationship with cardiovascular risk from lowest to highest quartile of the sodium to potassium excretion ratio.
Benthic species release nutrients that are dissolved by their feeding activities, excretion and burrowing into sediments (Covich et al.
They apply to (1) blood; (2) all body fluids, secretions, and excretions except sweat, regardless of whether they contain visible blood; (3) nonintact skin; and (4) mucous membranes.