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 ?
Ammonia excretion was calculated according to ALTINOK & GRIZZLE (2004) based on the following formula: excretion rate = {[(NHF NHI / g total] / L}, where NHF corresponds to final ammonia concentration, and NHI corresponds to the initial ammonia concentration, which was divided by the biomass and the amount of water in each tank.
Before leaving this issue of ammonium excretion, please note the following quote in which Adeva and Souto point out that protein source has an impact:
Hypercalciuria is defined as calcium excretion above 4 mg/kg/day in urine in children (4).
The present study was aimed to (i) ascertain the incidence of delayed excretion of MTX among osteosarcoma patients treated with HD-MTX; (ii) evaluate the correlation between the gender, age, number of chemotherapy cycles, and serum concentrations of MTX at different times and delayed excretion of MTX; (iii) provide a basis for risk prevention of delayed excretion of MTX; (iv) provide a basis for an individualized rescue strategy.
In this study the urinary excretion of Zn was higher than Italian (0.
We excluded patients (1) with primary hyperparathyroidism (HPT); (2) without pre- and post-VDCS metabolic stone workup; (3) with hypercalciuria (urinary calcium excretion >300 mg/d for men, >275 mg/d for women) prior to VDCS; (4) on thiazide diuretic prior to VDCS; and (5) pregnant women (Fig.
Total excretion of purine derivatives (PD) expressed in mmol/d was calculated by the sum of the excretions of allantoin and uric acid in the urine, and by the amount of allantoin excreted in the milk.
Urinary sodium and potassium excretion, mortality, and cardiovascular events.
The largest segment of the study population, 46%, had a sodium excretion of 3-5 g/day, and the next largest segment, 44%, had a sodium excretion of more than 5 g/day.
The accuracy of sodium intake was calculated as the ratio of reported dietary intake to that estimated from the urinary sodium excretion.
Results indicated that urinary magnesium excretion was inversely correlated with age, systolic BP and triglyceride and CRP concentrations whilst being positively correlated with HDL cholesterol and urinary excretion of calcium, sodium, potassium, albumin and creatinine.