Toxicology ingestion mechanisms

Mechanisms of Absorption. Ingestion is generally referred to as oral or per oral (PO) exposure and includes direct intragastric exposure in experimental toxicology. The regions for possible agent action and absorption from PO absorption should, however, be considered separately. 

Perhaps the most important toxicological role played by the GI tract is its influence over the absorption of chemicals that enter it. That absorption rates vary widely among chemicals has been explained in Chapter 2, but how the GI tract and its contents contribute to this phenomenon was not explained. Mechanisms of absorption are many and varied, and are influenced by the type and quantity of food present at the time of chemical ingestion, the pH (degree of acidity) of various portions of the GI tract, and even the nature and activity of the microorganisms that normally live in the intestines. In fact, metabolism of certain chemicals brought about by these microorganisms can play a crucial role, not only in their absorption, but also in the nature of the systemic toxicity they ultimately produce. 

In a two-year toxicological study (Culp et al., 2000), the incidences of tumours and DNA adducts in mice fed either coal tar or pure benzo[a] pyrene were examined. Benzo[a]pyrene formed adducts readily with DNA and appeared to be responsible for forestomach tumours, like those induced by ingestion of coal tar, but not for lung tumours. Other mice that were fed coal tar (Koganti et al., 2001) had DNA adducts with benzo[u]pyrene, benzo[c]fluorene and benzo[Z)]fluoranthene in the lungs, but those fed coal tar-contaminated soil had only the adducts with benzo[c]fluorene and benzo[ ]fluoranthene. Although benzo[u]pyrene activation has been studied extensively, little is known about the activation mechanisms of benzofluor-enes and benzofluoranthenes. 

The most important route of exposure is inhalation, occurrs when neon escapes from natural sources (rocks and water) or neon-containing products (see Uses). Skin exposure and ingestion can also occur however, only the inhalation route is considered to be important from a toxicological standpoint, because of the way inhalation of excessive concentrations of this inert gas can still potentially produce harmful effects (see Mechanism of Toxicity). 

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