Non-keratinized

Alfano MC, Chasens AI, Masi CW (1977) Autoradiographic study of the penetration of radiolabelled dextrans and inulin through non-keratinized oral mucosa in vitro. J Periodontal Res 12 368-377... 

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... 

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... 

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... 

Human oral mucosa consists of different cell types including keratinized and non-keratinized striated epithelial, but the buccal mucosa is composed predominately of the latter. In selecting an appropriate animal model care was taken to ensure that the mucosal structure in the selected species matched that in man as closely as possible. Based on histological examinations all the rodent species (rat, guinea pig, hamster and rabbit) would constitute poor models because of extensive keratinization of their buccal mucosa. Of the other possibilities, the dog appeared to be the best choice. 

The epithelium of the mouth consists of stratified, squamous epithelium, which can be keratinized, or non-keratinized. 

Keratinized epithelium is dehydrated, mechanically tough and chemically resistant. It is found in areas of the oral cavity subject to mechanical stress such as the mucosa of the gingiva (gums) and hard palate (roof of mouth). Non-keratinized epithelium is relatively flexible and is found in areas such as the soft palate, the floor of the mouth, the lips and the cheeks. Thus the regions of the oral cavity pertinent to drag delivery (i.e. the sublingual and buccal regions) have a non-keratinized epithelium. 

Figure 7.1 Structure of non-keratinized oral epithelium, as found in the sublingual and buccal regions of the oral cavity. (Note keratinized epithelium has a broadly similar structure however, the epithelial cell layers comprise basal layer, prickle cell layer, granular layer and keratinized layer)...

Permeation studies using a number of tracers, including horseradish peroxidase and lanthanum nitrate, have confirmed that the outer third of the epithelium is the rate-limiting barrier for mucosal penetration. When applied to the outer surface of the epithelium, these tracers are seen to penetrate only through the outermost layers of cells. Thus the compacted, flattened cells of the lower superficial layer and intermediate layer present a major physical barrier to transport. The intercellular lipids also play an important role, since extraction of these lipids results in more permeable tissue. Generally, keratinized epithelium appears to be more impermeable than non-keratinized epithelium. 

The ocular membranes comprise the cornea (not vascularized) and the conjuctiva (vascularized). The corneal epithelium consists of five or six layers of non-keratinized squamous cells, and it is considered to be the major pathway for ocular drug penetration. ... 

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

Membrane Coating Granules (MCG). MCGs are spherical or oval organelles (100-300 nm in diameter) found both in keratinized as well as in non-keratinized epithelia but are different with regard to composition in both epithelia. MCGs discharge their contents into... 

The oral mucosa can be divided into a non-keratinized area consisting of the floor of the mouth (sublingual), the buccal mucosa (cheeks), and a keratinized area com-... 

Koch et al. [9] report that repeated shampooing removes 70 to 90% of the ether-extactable hpid and that enzymatic hydrolysis of hair after ether extraction, followed by extraction of the residual membranes, yields internal lipid. Koch found the composition of this internal lipid to be somewhat similar to that of surface hair hpid. Koch, therefore, concludes that internal lipid of hair must in part originate from the sebaceous glands (see the section entitled Intercellular Matter and the Non-Keratin Regions of Hair of Chapter 1). 

C. Scale Edge Lifts nr Penetrant either dissolves non keratin matter or forms indepeadeni layer and causes lifting or shape distortion... 

Cytokeratin 13 (CK13) Squamous cell carcinoma Mature non-keratinizing squamous epithelium, basal and intermediate cells of transitional epithelium... 

Cytokeratin 14 (CK14) Squamous cell carcinoma, basal cell carcinoma, Hiiithel cell tumors Detection of myoepithelial cells in prostatic carcinoma Keratinizing and non-keratinizing squamous epithelium, basal and myoepithelial cells in salivary glands, breast prostate and uterus, Hiiilhel thyroid cells... 

The way in which water softens the stratum corneum appears to be performed at a rather macroscopic level, i.e. by its filling inter- and intracellular spaces of the dead corneocj es, and to some extent perhaps at the molecular level by binding to cell protein macromolecules, both keratinous and non-keratinous. The aggregate result, however, is to provide an aqueous lubricating system for the cellular lattice structure of the stratum corneum, a lubrication that accounts for unusual pliability of the stratum corneum. 

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