Oral mucosa keratinized layer

With sublingual or buccal application, the drug encounters the nonkeratinized, multilayered squamous epithelium of the oral mucosa. Here, the cells establish punctate contacts with each other in the form of des-mosomes (not shown) however, these do not seal the intercellular clefts. Instead, the cells have the property of sequestering polar lipids that assemble into layers within the extracellular space (semicircular inset, center right). In this manner, a continuous phospholipid barrier arises also inside squamous epithelia, although at an extracellular location, unlike that of intestinal epithelia. A similar barrier principle operates in the multilayered keratinized squamous epithelium of the skin. 

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