Mucosa components

Epidemiologic studies of the macroenvironment focused on the diet and the long incubation period have led us to postulate that long-lasting disturbances in the normal gastric mucosa may determine the final outcome of the neoplastic transformation W. This explains the present interest in precursor lesions rather than in cancer itself. We, therefore, need to scrutinize the gastric microenvironment and attempt to point out the components that may be relevant to neoplasia. The microenvironment could be considered to be determined by three basic elements ... 

The first of these new, electron transferring components was coenzyme Q (CoQ). Festenstein in R.A. Morton s laboratory in Liverpool had isolated crude preparations from intestinal mucosa in 1955. Purer material was obtained the next year from rat liver by Morton. The material was lipid soluble, widely distributed, and had the properties of a quinone and so was initially called ubiquinone. Its function was unclear. At the same time Crane, Hatefi and Lester in Wisconsin were trying to identify the substances in the electron transport chain acting between NADH and cytochrome b. Using lipid extractants they isolated a new quininoid coenzyme which showed redox changes in respiration. They called it coenzyme Q (CoQ). CoQ was later shown to be identical to ubiquinone. 

Because of the possible effects of active and carrier-mediated processes and metabolic biotransformation, the issue of tissue viability is important for in vitro buccal mucosal experiments. The barrier nature of the buccal mucosa resides in the upper layers of the epithelium, where unlike in the stratum corneum, the cells contain a variety of functional organelles [119, 122, 125, 150], and so tissue viability may be an important component of the barrier function of the tissue. Various methods have been employed to assess the viability of excised buccal mucosa, including measurement of biochemical markers, microscopic methods, and linearity of transport data [42], While biochemical methods, including measurement of adenosine 5 -triphosphate (ATP) levels and utilization of glucose, provide information on the metabolic activity of the tissue, this does not necessarily relate to the barrier function of the tissue. In excised rabbit buccal mucosa, levels of ATP were measured and found to decline by 40% in 6 h, and this correlated well with transmission electron microscopic evaluation of the tissue (intact superficial cells) [32], In addition, the permeability of a model peptide was unaltered up to 6 h postmortem, but at 8 h, a significant change in permeability was observed [32], These investigators therefore claimed that excised rabbit buccal mucosa could be used for diffusion studies for 6 h. 

Richter T, Keipert S (2004) In vitro permeation studies comparing bovine nasal mucosa, porcine cornea and artificial membrane androstenedione in microemulsions and their components. Eur J Pharm Biopharm 58 137-143. 

FIG. 1. Schematic diagram showing the principal components of oral mucosa (from Ref. 8). 

Oral mucosae are covered with mucus which serves as a link between the adhesive and the membrane. Mucus is a glycoprotein consisting of a large peptide backbone with pendant oligosaccharide side chains. The side chains terminate in sialic or sulfonic acids, L-fucose, sulfated galactose, or A -acetylglucosamine. The glycoprotein component imparts the viscous or gel-like (non-Newtonian) nature due to its capacity... 

The joining chain (J in Figs. 1 and 2) is attached to IgA in the submucosa, forming the 10 S dimer which, by the process of pinocytosis, enters the mucosa and there becomes attached to the secretory component (SC), giving rise to the 11 S dimer. Secretory component prevents hydrolysis of S IgA in the lumen of the gut. The 7 S IgA monomer does not become attached to the J chain but enters the circulation via the venous-lymphatic circulation. This physicochemical property of IgA probably accounts for its relatively increased values in the serum of some children with kwashiorkor. 

Untreated localized infections involving the nasal mucosa hypersensitivity to the drug or any component of the product. 

A survey about the dietary habits within the scope of the "National Health and Nutritional Examination Survey" showed that an inverse correlation (Morabia et al., 1989) exists between COPD and vitamin A supply as the only one of 12 examined dietary components. If a diminished supply of vitamin A increases the appearance of obstructive respiratory diseases, a marginal or local vitamin A deficit could be responsible for the observed changes of the respiratory mucosa. Such a deficit results in a loss of cilia, an increase of secreting cells and finally the formation of squamous metaplasia (Biesalski et al., 1985 Chytil, 1985 Shah and Rajalekshmi, 1984). 

Once an agent is topically applied in the oral cavity, the free drug can act at the primary site (i.e., bacteria in the plaque), or it can be partitioned to compartments where the drug binds nonspecifically. These drug reservoirs include the enamel, dentin, and/or cementum of the tooth, the oral mucosa, the organic and inorganic components of plaque, and salivary proteins. 

Chlorhexidtne is a symmetrical cationic molecule that is most stable as a salt the highly water-soluble digluconate is the most commonly used preparation. Because of its cationic properties, it binds strongly to hydroxyapatite (the mineral component of tooth enamel), the organic pellicle on the tooth surface, salivary proteins, and bacteria. Much of the chlorhexidine binding in the mouth occurs on the mucous membranes, such as the alveolar and gingival mucosa, from which sites it is slowly released in active form. 

Mechanism of Action An enzymatic mineral that is an essential component in the formation of Hgb, myoglobin, and enzymes. Promotes effective erythropoiesis and transport and utilization of oxygen (Oj). Therapeutic Effect Prevents iron deficiency. Pharmacokinetics Absorbed in the duodenum and upper jejunum. Ten percent absorbed in patients with normal iron stores increased to 20%-30%in those with inadequate iron stores. Primarily bound to serum transferrin. Excreted in urine, sweat, and sloughing of intestinal mucosa. Half-life 6 hr. 

Sucralfate is a basic aluminium salt of sucrose, a complex of sucrose octasulphate and aluminium hydroxide. At acid pH (<4), it forms a very sticky gel polymer, which adheres to epithelial cells and the base of ulcer craters. It has little or no antacid activity, but more importantly has a major cytoprotective action, both protecting the mucosa from damaging influences and also causing accelerated healing. It appears to work through a number of relatively poorly understood mechanisms, enhancing several gastric and duodenal protective mechanisms—different actions may be related to its chemistry as an aluminium salt, and to the sucrose octasulphate component. 

The vagus nerve is a major connection between central and peripheral components. It contains both afferent (80%) and efferent (20%) pathways from and to the upper GIT. These include both cholinergic and non-cholinergic nerve fibres the non-cholinergic neurones may have serotonin as transmitter. Two types of vagal afferent receptors are involved in the emetic response (1) mechanoreceptors, iocated in the muscular wall of the distal stomach and proximal duodenum, which are activated by distension or contraction of the gut wall and (2) chemoreceptors located in the gut mucosa of the upper small bowel. These monitor the... 

Transport to the liver Retinol esters present in the diet are hydrolyzed in the intestinal mucosa, releasing retinol and free fatty acids (Figure 28.19). Retinol derived from esters and from the cleavage and reduction of carotenes is reesterified to long-chain fatty acids in the intestinal mucosa and secreted as a component of chylomicrons into the lymphatic system (see Figure 28.19). Retinol esters contained in chylomicrons are taken up by, and stored in, the liver. 

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