Bronchioles epithelium

It is seen that the diameters of bronchioles (averaged over generations 11 - 15) vary little with age. The increase in bronchial size is greater, but still less than might be expected if airways are simply scaled for overall body dimensions (illustrated by the dashed curves in Figure 9, which are functions of body weight W). Since bronchiolar diameter does not change much with age it is likely that the thickness of bronchiolar epithelium is also relatively constant. However, in the case of the bronchi, it is reasonable to assume that epithelial thickness is proportional to bronchial diameter. Thus, it is necessary to use age dependent conversion factors between the surface density of alpha-decays and dose to cells. 

The volume of the conducting airways that does not contain any respiratory epithelium. This stretches from the nasal cavity to the generation 16 terminal bronchioles (ml). 

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. 

The clinicians noted that although the first patient responded well to steroid therapy, steroids may be less useful in more severe cases of bronchiolitis obliterans. Specifically, steroid treatment should be stopped if no improvement is seen during the first days because this treatment may increase the risk of lung infection in the presence of a denuded lung epithelium. 

Male and female Fischer 344 rats and B6C3Fj mice were exposed to 3, 15 or 75 ppm [23, 115 or 577 mg/m J ethylene dibromide for 6 h per day on five days per week for 13 weeks. Rats and mice examined after 13 weeks of exposure showed severe necrosis and atrophy of the olfactory epithelium in the nasal cavity after inhalation of 75 ppm ethylene dibromide. Lower concentrations induced squamous-cell metaplasia, hyperplasia and cytomegaly of the epithelium of the respiratory nasal turbinates. Metaplasia, hyperplasia and epithelial cytomegaly were also seen in other respiratory tissues (larynx, trachea, bronchi, bronchioles) at this dose (Reznik et al., 1980). 

Bronchioles (in vitro) Epithelium-dependent relaxation Burgaud and Oudart, 1993b... 

Burgaud J.L., Oudart, N., 1993a. Bronchodilatation of guinea-pig perfused bronchioles induced by the H3-receptor for histamine role of epithelium. Br. J. Pharmacol. 109, 960-966. 

Stratified squamous to mucociliated epithelium with olfactory cells Mucociliated epithelium (ciliated, mucous cells, basal cells) smooth muscle cells fibroblasts neuroendocrine cells immune cells Mucociliated epithelium with Clara cells in distal bronchioles and alveolar ducts... 

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]. 

At concentrations greater >40 ppm lacrimauon, reddening of conjunctivae, and increased respiration noted. Mortality at 50 ppm after 24 h with gasping and lung edema. Histologic signs included bronchiolitis, desquamated bronchial epithelium, infiltration by polymorphonuclear cells, edema. 

The overall density of the principal la" DC population in young adult animals varies from 500-800 mm tracheal epithelium to <100 mm in the small airways (Schon-Hegrad et ol., 1991 Gong et al., 1992) however, in older animals (> 1 year old) these differences narrow markedly, presumably reflecting net inflammatory history (unpublished). The density of DCs within the epithelium of small bronchioles in humans (sectioned as shown in Holt et al., 1990a) is in the order of 500-600 mm . In parenchymal lung tissue, DCs are typically found in interstitial tissues at the junction of adjoining alveoli ( interseptal junctional zones Holt et... 

Autoradiographic studies of human and guinea-pig airways have demonstrated the presence of tachykinin receptors on vascular smooth muscle, airway epithelium and submucosal glands, with a particularly hi density on airway smooth muscle from the trachea to small bronchioles (Castairs and Barnes, 1986 Hoover and Hancock, 1987). In contrast, in rat airways, there is no labelling of airway smooth muscle (Sertl et al., 1988). 

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