Subepithelial cells

Virus infections such as influenza and the common cold (in reality 300-400 different strains ofrhinovirus) infect epithelial cells ofthe respiratory tract and nasopharynx, respectively. Release ofthe virus, after lysis ofthe host cells, is to the void rather than to subepithelial tissues. The epithelia is further infected resulting in general degeneration ofthe tracts. Such damage predisposes the respiratory tract to infection with opportunistic pathogens such as Neisseria meningitidis and Haemophilus influenzae. 

Particular strains of salmonellae (section 4.2) such as Sal. typhi, Sal. paratyphi and Sal. typhimurium are able not only to penetrate into intestinal epithelial cells and produce exotoxins but also to penetrate beyond into subepithelial tissues. These organisms therefore produce, in addition to the usual symptoms of salmonellosis, a characteristic systemic disease (typhoid and enteric fever). Following recovery frxm such infection the organism is commonly found associated with the gall bladder, hi this state, the recovered person will excrete the organism and form a reservoir for the infection of others. 

After acute mild insult the nonciliated cells proliferate and the epithelium regenerates to normal. In the airways, nonciliated basal cells are the main proliferating population. In the bronchioles, the Clara cell is the main precursor cell for regeneration. Because of the delicate nature of the respiratory tract epithelium and the close proximity of subepithelial blood vessels, an inflammatory response occurs to all but the mildest form of injury. Many lesions are therefore diagnosed as rhinitis, tracheitis, and bronchiolitis and qualified as acute, subacute, and chronic depending on the stage of the response. 

Bronchial biopsies of subjects with occupational asthma induced by TDI revealed pathologic features such as increased number of inflammatory cells in the airway mucosa and thickening of subepithelial collagen. ... 

Mitotic effect. STE, administered to the buccal mucosa of 15 female HMT rats, 6 months of age, weekly for 1 year, produced hyperorthokeratosis, acanthosis, numerous binucleate spinous cells, and subepithelial connective tissue hyalinization. Verrucous carcinoma and squamous cell carcinoma were not seen. Karyotyping revealed that lymphocytes of tobacco-treated, as well as control rats, had normal chromosome number and morphology. However, approx 25% of buccal epithelial cells of the tobacco-treated rats were tetraploid and 5% octa-ploid, compared with only 11% tetraploid and no octaploid in the controls. Results indicated that the mitotic process could be disturbed by tobacco treatment b Molluscicidal activity. Water extract of the dried leaf, at a concentration of 168 ppm, produced equivocal effect on Lymnaea luteola . 

The pharynx, larynx, trachea and bronchi are lined with pseudostratified, ciliated columnar epithelium that contain at least eight cell types, including mucous secretory goblet and Clara cells, which produce a protective mucus layer of 5-10 jum thickness (see Table 9.2). Subepithelial secretory glands, present in the bronchial submucosa, also contribute to the mucus blanket [9]. Through coordinated ciliary movement a propulsive wave is created, which continuously moves the mucus layer up towards the larynx. Consequently, the mucosal surface of trachea and bronchi is constantly swept to remove inhaled materials. As the bronchi divide into bronchioli, the ciliated columnar respiratory epithelium is much thinner and changes to a simpler non-ciliated cuboidal epithelium. The epithelium in the terminal and respiratory bronchioles consists of ciliated, cuboidal cells and a small number of Clara cells. However, Clara cells become the most predominant type in the most distal part of the respiratory bronchioles [10]. 

Epithelial cells are interconnected at the apical (mucosal) side by a complex network of proteins, called the tight junctions (TJ). First thought to have merely a static role in restricting access of compounds present in the luminal fluid to the underlying subepithelial tissue and systemic circulation by the paracellular pathway, TJ are known today to be dynamic structures involved in cellular differentiation, cell signaling (Harder and Margolis 2008), polarized vesicle trafficking, and protein synthesis. 

McCormick, B., Colgan, S., Delp-Archer, C., Miller, S., Madara, J. Salmonella typhimurium attachment to human intestinal epithelial monolayers transcellular signalling to subepithelial neutrophils. J Cell Biol 123 (1993) 895-907. 

Couser et al. (1978) studied the development of immune deposits on the subepithelial surface of the glomerular capillary wall in isolated rat kidneys perfused at controlled perfusion pressure, pH, temperature, and flow rates with recirculating oxygenated perfusate containing bovine serum albumin in buffer and sheep antibody to rat proximal tubular epithelial cell brush border antigen. 

As a class of tissue, epithelia demarcate body entry points, predisposing a general barrier function with respect to solute entry and translocation. The intestine is lined with enterocytes, which are polarized cells with their apical membrane facing the intestinal lumen that is separated by tight junctions from the basolateral membrane that faces the subepithelial tissues. In addition to their barrier function, the epithelia that line the GI tract serve specialized functions that promote efficient nutrient digestion and absorption and support other organs of the body in water, electrolyte, and bile salt homeostasis. The homeostatic demand on GI tissue that results from this dual function may pose special transport consideration compared with solute translocation across biologically inert barriers. 

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