Keratinized epithelium

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

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. 

A weakening of the binding forces between the keratinized epithelium and the layer of grease via the reduction of the surface tension between the water and the water-resistant oil/grease. Because of this reduced surface tension, water (and surfactant molecules) can penetrate into the finest wrinkles of the skin. In this way, more and more interface is occupied by surfactant, and the adhesiveness of the soil-containing layer is further weakened, a process facilitated by mechanical rubbing. 

J. G. Rheinwald and H. Green, Formation of a keratinizing epithelium in culture by a cloned cell line derived from a teratoma, Cell 6, 331 -343 (1975). 

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)...

This maturation and differentiation process is broadly similar to the process for keratinized epithelium, although obviously cells of keratinized epithelium also show increasing amounts of the fibrous protein, keratin, in the upper layers. 

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. 

Rodents contain a highly keratinized epithelium and thus are not very suitable as animal models when studying buccal drag delivery. Suitable animal models for studying oral mucosal drag delivery include pigs and... 

The epidermis is a stratified, squamous, keratinizing epithelium. The keratinocytes comprise the major cellular component (>90%) and are responsible for the evolution of barrier function. The epidermis per se can be divided into five distinct strata which correspond to the consecutive steps of keratinocyte differentiation. The ultimate result of this differentiation process is formation of the functional barrier layer, the stratum corneum (-0.01 mm). 

The keratinized epithelium of the eyelids gradually transforms into the moist mucous membrane of the conjunctiva. The palpebral conjunctiva adheres tightly to the tarsus over the entire superior eyelid, as compared with the loosely adherent inferior palpebral conjunctiva. Clinically, this anatomic variation contributes to the different appearance of papillary hypertrophy occurring in the superior versus inferior palpebral conjunctiva. 

Oromucosal 0.02 m easily accessible Mucus, stratified, partly keratinized epithelium (500-600 pm), hydrated -h-h-h 0-5%... 

Cell specializations include keratinized cells and ciliated cells. The keratinized epithelium contains the cytoskeletal protein keratin, and provides a tough impermeable barrier, mainly in the skin. Cihated cells have apical plasma membrane extensions composed of microtubules and are capable of beating rhythmically so as to move mucus or other substances through a duct. CiUa are common in the respiratory system. 

Cytokeratin 10 (CKIO) Squamous cell carcinoma Breast ductal carcinoma Keratinizing epithelium... 

Clinically, infection with HPV7 appears as warts, usually on the hands. The mode of transmission remains unclear (Melchers et al. 1993). Transmission from animals is unlikely as animal papilloma virus is host specific. One possible explanation of the high prevalence of warts among slaughterhouse workers and butchers is that components of meat facilitate replication of HPV7 in keratinized epithelium (Keefe et al. 1994a). 

Fig. 6. Lung of a vitamin A-deficient rat, showing focal replacement of the columnar ciliated epithelium of bronchus by stratified keratinizing epithelium, and infiltration of submucosa.

Fig. 8. Fore-stomach of a normal rat. Note normal squamous keratinizing epithelium, thin and relatively avascular lamina propria, well-developed muscularis mucosae, submucosa with less connective tissue and numerous blood vessels, and circular and longitudinal layers of the muscularis externor.

A second function of vitamin A is the maintenance of normal epithelium, but the precise role that this vitamin plays in the metabolic processes of epithelial cells is unknown. The changes which occur in vitamin A deficiency have been studied extensively by Wolbach and associates and consist essentially of atrophy of the epithelium with reparative proliferation of the basal cells and differentiation into stratified keratinizing epithelium (Chapter 13) regardless of the original type of epithelial cell. This keratinizing metaplasia has been observed in many animal species, including man. 

CR Keratinized epithelium EP multilayer flat epithelial CT Connective tissue ML Muscle layer, Blackened silver particle TL 102 M Mucoadhesive drug Solution Solution of cottonseed oil... 

The superficial layer is used to classify the stratification into simple, which consists of a single layer of cells, and stratified, which consists of more than one layer of cells. Stratified epithelium is usually composed of three layers. Cell division takes place in the basal cell layer (layer 1). Cells migrate and differentiate in the intermediate cell layer (layer 2) until they reach the superficial cell layer (layer 3). Specializations include keratinized and ciliated cells. Keratinized epithelium, which contains the cytoskeletal protein keratin and provides a tough impermeable barrier, occurs mainly in the skin. Ciliated cells have apical plasma membrane extensions composed of microtubules capable of beating rhythmically to move mucus or other substances through a duct. Cfiia are common in the respiratory system. 

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