Mucosal cell layer

Kimura T, Yarnano H, Tanaka A, Matsumura T, Ueda M, Ogawara K, Higaki K (2002) Transport of D-glucose across cultured stratified cell layer of human oral mucosal cells. J Pharm Pharmacol 54 213-219... 

The barriers of the eye differ from that of skin in dimensions and mucosal organization there are epithelial cel-Inlar barriers made of lipid layers on the eye and dry snrfaces made of proteins in the stratihed snrfaces of the skin. Skin is protected by a superficial outer fatty hhn, the stratum comeum, and covered by a thick layer of cells, the basal cellnlar layer. Thanks to these thick layers, skin has a high resistance to initial diffusion of aqueous fluids and less resistance to lipophilic solvents and to acids. The initial chemical cracking of the lipid layer allows fluids to invade deeper layers of the skin. The basal cell layer and the hair follicles contain stem cells capable of epithelial regeneration. 

The products of lipid digestion—free fatty acids, 2-monoacylglycerol, and cholesterol—plus bile salts, form mixed micelles that are able to cross the unstirred water layer on the surface of the brush border membrane. Individual lipids enter the intestinal mucosal cell cytosol. 

In comparison to the skin, the buccal mucosa offers higher permeability and faster onset of drug delivery, whereas the key features which help it score over the other mucosal route, the nasal delivery system, include robustness, ease of use, and avoidance of drug metabolism and degradation. The buccal mucosa and the skin have similar structures with multiple cell layers at different degrees of maturation. The buccal mucosa, however, lacks the intercellular lamellar bilayer structure found in the stratum corneum, and hence is more permeable. An additional factor contributing to the enhanced permeability is the rich blood supply in the... 

The main resistance to drug permeation is caused by the variant patterns of differentiation exhibited by the keratinized and nonkeratinized epithelia. As mucosal cells leave the basal layer, they differentiate and become flattened. Accumulation of lipids and proteins also occurs. This further culminates in a portion of the lipid that concentrates into small organelles called membrane-coating granules (MCGs). 

In the submucosal layer of the gastrointestinal tract, there are numerous MCX mucosal cells. They are equipped with granules and contain biogenic amines, chemotactic factors, and as far as proteases are concerned, tryptase. 

Although rodent buccal mucosa is reported to consist of both keratinized and non-keratinized striated epithelia, no evidence for the latter was obtained in the present study. In all rodents examined, heavily keratinized striated epithelia were observed on the inner central cheek (see Figure 1 for rat). Mucosal sections exhibited characteristic epithelial cell differentiation with cells becoming progressively flatter and forming a granular layer with increasing distance from the basal cell layer. The outer... 

A number of ciliotoxicity studies have pointed out a low correlation between the results obtained using different in vitro and in vivo methods [121], The effects of nasal formulations on the ciliary beat frequency in vitro are usually more expressed than in vivo, since in vivo, cilia are partially protected by the mucous layer and investigated formulation is eventually cleared from the nasal cavity due to the mucociliary clearance mechanism. Also, toxic effects of the formulations on the cilia in vivo may be reversible due to the constant nasal mucosal cell turnover [121]. 

The toxicity of formaldehyde is route-dependent. Irritation at the point of contact is seen by inhalation, oral, and dermal routes. High doses are cytotoxic and result in degeneration and necrosis of mucosal and epithelial cell layers. These observations are consistent with the hypothesis that toxic effects are mediated by formaldehyde itself and not by metabolites. No specific target molecule has been identified, although DNA-protein cross links have been identified (Casanova and Heck 1987). As discussed in... 

Adherence of a drug delivery system directly to any mucosal membrane can occur if the mucus layer is disturbed or the bioadhesive penetrates the mucin. Disruption of the mucus layer can be by abrasion, cell sloughing, chemical alterations by mucolytic agents, or disease state of the tissue [15]. If such an interruption occurs, bioadhesives can serve (1) to maintain continuity of the mucus layer and minimize the exposed area, (2) replace the mucus layer and provide a protective covering for the underlying cell layers from physical and chemical injury, and (3) act as a platform for drug delivery to local tissues and facilitate recovery of the damaged or diseased cell layers. 

Experiment I. In a time-course experiment, mucosal PGE production and phospholipid fatty acid profile were assessed at d 0,4,8,12, and 16 of dietary treatment in formula-fed and naturally reared piglets (n = 5 piglets per time per dietary treatment). Mucosal cells were scraped from proximal ends of the small intestine and frozen at -80°C for later lipid analysis. Lipids were extracted by a modified Folch procedure (15). Phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were separated by thin-layer chromatography (16), and fatty acids in each phospholipid fraction were analyzed by gas chromatography. For eicosanoid measures, fresh mucosal tissue was incubated in Kreb s Ringer bicarbonate buffer as described previously (17). PGE2 was extracted from the incubation media with ethyl acetate and quantified using a competitive enzyme-linked immunosorbent assay (Cayman Chemical, Ann Arbor, MI). 

The infant immune system is not fnlly mature at birth it has deficits in the ability to prevent invasion of pathogens and to respond to antigens. Of particular concern in the context of ingredients new to infant formulas is the increased permeability of the gut mucosal barrier in the presence of inflammation or infection or if the integrity of the epithelial cell layer is disrupted. The increased permeability allows macromolecules to be absorbed, which stimulates allergic responses to food proteins. 

Micellar solubilization of lipids within the intestinal lumen permits the lipids to diffuse to the surface of the intestinal epithelium and make contact with the microvillus membrane. This is important because there is a major physiological diffusion barrier called the unstirred water layer, that covers the surface of the epithelial cell membranes. The unstirred layer of water is a feature common to all biological membranes. Micelles penetrate this relatively immobile aqueous layer more readily, thus increasing the efficiency of lipid uptake into the intestinal mucosal cell. 

The oligopeptides formed by the action of the endopeptidases are broken down into their constituent amino acids by the action of the exopeptidases. The carboxypeptidase of the pancreas splits amino acids one by one from the C-terminus so that, by the time they reach the absorbing cells of the small intestine, the dietary proteins have been converted into a mixture of amino acids and small peptides. The mucosal cells which contain both aminopeptidases and dipeptidase take up the small peptides which are then hydrolysed either within the brush border or in the layer immediately beneath it. Thus the final stages of protein digestion, like those of carbohydrates, are intracellular. Under normal circumstances no peptides pass across the mucosa to enter the bloodstream. 

The morphologic substrate for gallbladder dysfunction is cytoplasmic meta-chromasia of the mucosal cells. The villi are distended by accumulation of pha-gocytizing histiocytes, which are also filled with metachromatic lipid. This material may also be seen in small medullated nerves of deeper layers of the gallbladder wall. In addition, phagocytes contain cholesterol and other lipid which stains with Scarlet-red. 

Oral mucosal cell sheets are also cfinically applied to the treatment of esophageal ulcerations using an endoscopic transplantation method (Kanai, Yamato, Ohki, Yamamoto, Okano, 2012 Ohki et al., 2006, 2012). Removal of large esophageal cancer tissue section by endoscopic submucosal dissection causes postoperative inflammation and stenosis from a lack of an epithelial layer. After the transplantation... 

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