Gastrointestinal tract important features

Figure 3.12 The mammalian gastrointestinal tract showing important features of the small intestine, the major site of absorption for orally administered compounds (A) liver (B) stomach (C) duodenum (D) ileum (E) colon (F) longitudinal section of the ileum showing folding, which increases surface area (G) detail of fold showing villi with circular and longitudinal muscles, (H) and (I) respectively, bounded by (J) the serosal membrane (K) detail of villi showing network of (L) epithelial cells, (M) capillaries, and (N) lacteals (O) detail of epithelial cells showing brush border or (P) microvilli. The folding, vascularization, and microvilli all facilitate absorption of substances from the lumen. Source From Ref. 1.

The primary function of the liver is to receive and process chemicals absorbed from the gastrointestinal tract before they are stored, secreted into bile or released into the general circulation. The microsomal enzyme system (hepatic enzymes) is located mainly in the smooth endoplasmatic reticulum and performs this biotransformation (Olinescu and Greabu, 1990). The most important enzymes involved in biotransformation are the microsomal oxidases, especially cytochrome P-450 monooxygenases. The pollutants act as a substrate for the microsomal enzyme system and the most important feature is that it is easy to induce the biosynthesis of the enzyme (the number of these enzymes can be increased by exposure to pollutants). 

The following are some of the important features of the human gastrointestinal tract. 

The main function of mucin from secretions of submaxi 11 ary glands, along with similar mucoproteins found in the respiratory, gastrointestinal, reproductive tracts and also in the tear liquid, is to lubricate epithelial cells and protect them from the external environment. The role of the mucous glycoproteins as a macromole-cular surfactant is therefore of great importance in the science and technology of biomaterials. Such different biosurfaces as dentures, contact lenses or intrauterine contraceptive devices, in spite of different functions, have one coimnon feature, namely that all are placed on a mucosal surface. 

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