Excretion of chemicals

Absorption, distribution, biotransformation, and excretion of chemical compounds have been discussed as separate phenomena. In reality all these processes occur simultaneously, and are integrated processes, i.e., they all affect each other. In order to understand the movements of chemicals in the body, and for the delineation of the duration of action of a chemical m the organism, it is important to be able to quantify these toxicokinetic phases. For this purpose various models are used, of which the most widely utilized are the one-compartment, two-compartment, and various physiologically based pharmacokinetic models. These models resemble models used in ventilation engineering to characterize air exchange. 

Pharmacokinetics—The science of quantitatively predicting the fate (disposition) of an exogenous substance in an organism. Utilizing computational techniques, it provides the means of studying the absorption, distribution, metabolism and excretion of chemicals by the body. 

Stott, W.T. and McKenna, M.J. (1984). The comparative absorption and excretion of chemical vapors by the upper, lower and intact respiratory tract of rats. Fund. Appl. Toxicol. 4 594-602. 

Studies in experimental animals suggest that biliary excretion of chemicals from the liver may be impaired by mirex or chlordecone (Berman et al. 1986 Curtis and Hoyt 1984 Curtis and Mehendale 1979 Curtis et al. 1979b, 1981 Davison et al. 1976 Mehendale 1976, 1977b, 1977c, 1981b Teo and Vore 1991). Measurement of serum bile acid levels may provide information regarding biliary excretory function. 

Some minor routes of excretion exist sweat, hair, saliva, semen, milk. While these routes out of the body do not count for much as excretory processes, excretion of some chemicals into milk can be important because it constitutes an exposure pathway for infants, if the milk is from their mothers, and for many people if it is from dairy cattle. Many fat-soluble chemicals follow this pathway out of the body, dissolved in the fatty portion of the milk. Excretion of chemicals through milk is common enough to prompt considerable attention from toxicologists. 

There are, however, some particular conditions which point to a drug or chemical causation. Hepatitis is one such condition, and it can easily be seen that the liver can be a target because of its part in the metabolism, conjugation and excretion of chemicals. The kidney seems to be at much less risk as an excretory organ alone, nevertheless renal damage by drugs is more common than heart or lungs, for example. 

There are almost no data available concerning the pharmacokinetics (i.e., the uptake, distribution, metabolisms, and excretion) of chemical carcinogens in humans. Nevertheless, it is possible to make limited assumptions about the pharmacokinetics of carcinogens, based on the results of animal studies conducted with various chemicals, notably polycyclic hydrocarbons such as benzo[a]p3nene. 

What physicochemical characteristics determine the absorption, distribution, and excretion of chemicals in biological systems ... 

What factors influence the biliary excretion of chemicals ... 

The biliary excretion of chemicals and their metabolites is influenced by (a) the molecular weight of the chemical, (b) the polarity of the molecule, and (c) the species of animal. 

Research the factors governing human excretion of chemicals in urine and breast milk and how it can affect biomarker results ... 

Pharmacokinetic The quantitative study of factors that control the time course for absorption, distribution, metabolism, and excretion of chemicals within the body. 

The process of excretion of chemicals into the urine (and bile) has developed so as to rid the body of noxious substances. Some of these are products of normal bodily activity such as the breakdown of proteins and removal of the ammonia produced by this process, which is converted into the substance urea in the liver and excreted into the urine. 

Zitko V (1981) Uptake and excretion of chemicals by aquatic fauna. In Stokes PM (ed) Ecotoxicology and the Aquatic Environment. Pergamon Press, New York, pp 67-78... 

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