Epithelium lining

Other cell lines used in permeability studies include the T84 human colonic adenocarcinoma colonic crypt cell model. This line has a reduced carrier expression, secrets mucus, and has very high resistance [31, 32], The IEC cell line is a rat fetal intestinal epithelium cell with higher permeabilities than Caco-2 cells [33], LLC PKi is a pig kidney epithelial cell line with low expression of efflux systems, but expression systems for transport proteins [32], 2/4/A1 cells are a conditionally immortalized rat fetal intestinal epithelium line with crypt cell-like morphology and temperature-sensitive differentiation [34], They form differentiated monolayers with tight junctions, increased brush border enzymes when grown on extracellular matrices with laminin. Transport of drugs with LP in 2/4/A1 monolayers was comparable to that in the human jejunum and up to 300 times faster than that in Caco-2 monolayers. In contrast, the permeability of HP drugs was comparable in both cell lines [34],... 

The major limitation to developing therapeutic proteins in nonparenteral dosage forms is the poor permeability of these water-soluble and hygroscopic macromolecules across the tissue layers at the site of drug administration. These tissue layers include the epithelium of the gastrointestinal tract, the stratum corneum of the skin, and the epithelium lining of the alveoli and nasal cavity. 

The oral mucosa provides a protective covering for underlying tissues while acting as a barrier to the entry of microorganisms and toxins. Histologically, the stratified squamous epithelium lining the oral cavity exhibits a diverse structure as well as important inter-species differences. This... 

In contrast to epidermis, the epithelium lining the small intestine is a single cell thick (Figure 6-4). This thin layer keeps toxins and pathogens from entering our bodies and also transports nutrients essential for survival from the intestinal lumen into the body (Chapter 7). The cells of the intestinal epithelium... 

Diamine Oxidase Diamine oxidase (DAO, his-taminase) is a degradative enzyme of the polyamine metabolic pathway that is expressed in mature epithelium lining the rodent intestinal villi (Luk et al., 1980). Diminished blood concentrations, measurable by tritiated water assay, have been shown to correlate well with tissue expression... 

The epithelium lining the intestines can be regarded as both secretory and absorptive since most of the small molecules that constitute the ultimate food supply of the animal enter through its cells. Contact with the external biochemical environment is more nearly approached at this point than anywhere else in the body, since the composition of air which bathes skin and lungs is relatively constant, while the food and fluid intake is constantly changing. 

Absorption of acetic, propionic, and butyric acids is known to occur across the stratified squamous epithelium lining the rumen, and this absorption of short-chain fatty acids—or, to be more precise, steam-volatile fatty acids, according to the actual method of determination— also takes place from the reticulum, the omasum, the caecum, and the colon of the sheep, and from the large intestine of the horse, the pig, the rabbit, and the dog. In this way some of the products of the metabolism of the microbial population are continually removed from the milieu, thus satisfying one of the essential requirements for the continuing activity of a mixed culture of organisms. 

CF is an aufosomal recessive disease affecting more than 50,000 individuals worldwide, primarily, although not exclusively, white individuals. The disease affects epithelium-lined organs, such as the respiratory and intestinal tracts, of which the former are the site of major morbidity and mortality. Recurrent chest infections and colonization of the lower airways with organisms such as Staphylococcus aureus and Pseudomonas aeruginosa progress to subsequent bronchiectasis and finally respiratory ilure, the most common cause of death. 

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