Keratinizing epithelium

Gilbert, S., Loranger, A., Daigle, N., and Marceau, N. (2001). Simple epithelium keratins 8 and 18 provide resistance to Fas-mediated apoptosis. The protection occurs through a receptor-targeting modulation./. Cell Biol. 154, 763-774. 

Figure 26.1 Succession of cells in lightly keratinizing stratified squamous epithelium. Keratinized squames are shown in black with the width of intercellular spaces exaggerated...

Human Keratins and Their Expression Patterns in Breast Epithelium... 

The type II keratin K5 and the type I keratin K14 form the primary keratin pair of progenitor cells of the breast epithelium, including cells of the basal... 

Fig. 13.1 Triple immunostaining of a normal duct epithelium for K14 (Ckl4, pink), K5 (Ck5/6, red), and K8/18 8 (Ckl8, green). Note that few progenitor cells are stained only for K5 and/or K14 (1), whereas most are stained both for basal (usually K5) and glandular keratins K8/18. These cells represent intermediary glandular cells. Few cells stained only for K8/18 are differentiated glandu lar cells...

In normal breast epithelium the type I keratin K17, which was identified by Moll et al. (1982b) by early gel electrophoretic studies as a major keratin of basal cell carcinomas of the skin, shows a similar distribution in breast epithelium as K5... 

Hayward AF (1976) Ingestion of colloid in a keratinized epithelium and its localization in membrane-coating granules. J Anat 121 313-321... 

Squier CA (1973) The permeability of keratinized and nonkeratinized oral epithelium to horseradish peroxidase. J Ultrastruct Res 43 160-177... 

Squier CA (1982) Zinc iodide-osmium staining of membrane-coating granules in keratinized and non-keratinized mammalian oral epithelium. Arch Oral Biol 27 377-382... 

Another 3-D cornea model, comprising rabbit primary cultures of epithelial and stromal cells as well as mouse immortalized endothelial cells, was described in 1994 by Zieske and coworkers [70], They showed the influence of endothelial cells on the formation of a tightly packed, multilayered epithelium as well as the expression of laminin, type VII collagen, a6 integrin, keratin K3, and a-enolase. Furthermore, their findings suggested that the formation of an in vivo-like epithelium requires the cultivation of the 3-D corneal construct under AIC conditions. By contrast, LCC methods of cultivating corneal equivalents in the absence of endothelial cells failed to promote the expression of differentiation markers and basement membrane components. 

In another approach, Parnigotto and coworkers reconstructed corneal structures in vitro by using corneal stroma containing keratocytes to which corneal epithelial cells from bovine primary cultures were overlaid [73], However, this particular corneal model did not contain an endothelial layer. This model was histochemically characterized and the toxicity of different surfactants was tested using MTT methods. This stroma-epithelium model has been reported to show a cornea-like morphology, where a multilayered epithelial barrier composed of basal cells (of a cuboidal shape) and superficial cells (of a flattened shape) is noted. Furthermore, the formation of a basement membrane equivalent and expression of the 64-kDa keratin were reported, indicating the presence of differentiated epithelial cells. The toxicity data for various surfactants obtained with this model correlate well with those seen by the Draize test [73], However, this corneal equivalent was not further validated or used as a model for permeation studies. 

Epithelium. The predominant barrier to drug diffusion resides approximately within the outermost one-third of the epithelium. This is true of both keratinized and nonkeratinized epithelia. Therefore, keratinization is unlikely to offer major resistance to bueeal permeation. 

Whole body exposure of rats 6 hours/day, 5 days/week for 13 weeks at levels of 24, 70, and 243mg/m resulted in respiratory effects (keratinization of the metaplastic epithelium in the larynx) at the highest exposure level with complete recovery within 4 weeks after exposure. Treatment-related responses such as labored breathing and nasal discharge were observed during many of the exposures, but these also abated during the recovery period. 

Oronasal exposure of mice to 2.6ppm led to a 50% decrease in respiratory rate. Mice exposed at 0.3, 1.0, and 2.6ppm 6 hour/day for 4, 9, and 14 days had lesions of the respiratory epithelium including squamous metaplasia, focal necrosis, and keratin exudate that were dose dependent at the lower exposure levels. Lesions persisted 2 weeks after exposure but were decreasing 4 weeks after the end of exposure. No exposure-related lesions were observed in the lungs of exposed mice. 

Other effects were keratinized squamous metaplasia of the trachea (4000ppb) dose-related increases in tracheitis and desquamation of the tracheal epithelium, and bronchitis, desquamation, and regeneration of the bronchial epithelium (100, 400, and 4000 ppb) bone marrow erythropoietic hyperplasia (males, 4000ppb) testicular atrophy (males, 4000 ppb) and degenerative changes in the convoluted tubules of the kidneys. ... 

The epithelium, the most superficial cellular layer of the cornea of the eye, is chemically less resistant than the keratinized epidermis of the skin. However, during ocular accidents, we know that it takes a few seconds for the first lesions to appear. This delay is bound to multiple factors, winking reflex, protective and diluting effect of the lachrymal liquid, effect of sweeping of the palpebral movements. After a short period, a kinetic of diffusion will set up in a variable way according to the nature of the corrosive. 

Male and female Fischer 344 rats were exposed to 0, 3, 10 or 40 ppm [0, 23, 77 or 308 mg/m ] ethylene dibroniide for 6 h per day on five days per week for 13 weeks for a total of 67-68 exposures in 95-96 days. Animals were killed after one, six or 13 weeks of exposure and after a recovery period of 88-89 days. At 10 ppm, ethylene dibromide caused slight epithelial hyperplasia of the nasal turbinates in animals killed after one, six or 13 weeks of exposure. However, 88 days after the last exposure, nasal turbinate changes were not obsen ed. Rats exposed to 40 ppm ethylene dibromide had increased liver and kidney weights, hyperplasia and non-keratinizing squamous metaplasia of the respiratoiy- epithelium of the nasal turbinates. After the recovery period of 88 days, the turbinates had reverted to normal histology. The most sensitive response associated with... 

The mean total surface area of the mouth has been calculated to be 214.7 12.9 cm2 [4]. The teeth, keratinized epithelium, and nonkeratinized epithelium occupy about 20%, 50%, and 30% of this surface area, respectively. 

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