excretion


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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 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.

Excretion

 

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.

REFERENCES

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

IU. V. NATOCHIN

excretion

[ek′skrē·shən]
(physiology)
The removal of unusable or excess material from a cell or a living organism.
References in periodicals archive ?
Urinary sodium and potassium excretion, mortality, and cardiovascular events.
The investigators found, after multivariate adjustment, that for each 1-g increment in sodium excretion, there was an increment of 2.
Overall, low urinary magnesium excretion was associated with a 60% increased risk of IHD compared with the remainder of the cohort.
For a test with a high within-person imprecision of [greater than or equal to]30% (2, 3), repeat testing is important to confirm a persistent increase in the urinary excretion of albumin.
N excretion was determined from N analysis of urine and faeces and N retention determined using actual N intake values (termed "as determined through BALANCE").
Although average excretion of U-Cd and urinary proteins may be relatively stable over time within individuals--and may therefore accurately reflect long-term effects of Cd on kidney function--excretion of both biomarkers may vary over the day because of physiological factors such as diuresis, body position, and exercise.
In a way the taboo on excretion psychologically reinforces the sanitation system.
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:
It has been shown that chronically denervated kidney in the presence of ganglionically blocked contralateral kidney shows greater decreases in RBF, GFR and sodium excretion in response to NE infusion (12).
Studies were performed in rats to define the tissue distribution and excretion of resveratrol in urine and bile, and to characterize (if possible) any metabolites of resveratrol observed in tissues after ig 20 mg/kg Polygonum cuspidatum extract.
In particular, workers have written little about excretion in spiders (Curtis & Carrel 2000) or other arachnids (Sato et al.