Oral mucosae specialized mucosa

Oral mucosae are composed of multiple layers of cells, which show various patterns of differentiation dependent on the functions of different regions in the oral cavity. The oral mucosa is covered by a stratified, squamous epithelium, and three different types of mucosa can be distinguished the masticatory, the lining, and the specialized mucosa. Blood supply to the oral cavity tissues is delivered via the external carotid artery, which branches to the maxiliary lingual and facial artery. There are no mucus-secreting goblet cells in the oral mucosa, but mucins are found in human saliva. These mucins are water-soluble and form a gel of 10-200 pm thickness. Saliva, mainly composed of water (99%), is continuously secreted in the oral cavity and exists as a film with a thickness of 0.07-0.1 mm. ... 

Absorption through the oral mucosa can take place in two ways i) inter- or paracellular pathway, which is a passive transport through the lipid matrix between the cells and ii) trans- or intracellular pathway through the cell walls, which can be either passive or active transport. The following dosage forms may be used i) polymer-coated nanoparticles, ii) special tablets, iii) pol)mtier films, and iv) gels (patches) [112-119]. 

The permeability of the oral mucosal epithelium is intermediate between that of the skin epithelium, which is highly specialized for a barrier function (see Section 8.1) and the gut, which is highly specialized for an absorptive function. Within the oral cavity, the buccal mucosa is less permeable than the sublingual mucosa. 

Iscan et al. compared a number of parameters of a specially formulated buccal bioadhesive captopril tablet with that of a conventional tablet. The buccal formulation provided controlled release of captopril with a smooth plasma level profile and a long duration of action however, its bioavailability was 40% via the buccal route as compared to 65% following an oral dose. This was attributed to the intestinal mucosa being more permeable than the buccal mucosa, and it was concluded that further work was required to improve its bioavailability. 

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