Buccal cavity epithelia

Oesophageal tissue resembles that seen in the buccal cavity stratified squamous epithelium. Due to the contad with the food, the cells near to the lumen are dead. Liquid is only provided by swallowed saliva - note the absence of secretory cells. Oesophageal retention of a formulation containing an irritant drug can lead to damage to the mucosa, ulceration and even stricture or perforation. Damage is produced by a prolonged contact of the dmg... 

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)...

The process of maturation from basal cell through to desquamation (shedding) has been estimated at 13 days for the buccal epithelium and this process is probably representative of the oral mucosa as a whole. Thus the rate of cell turnover in the oral cavity is considerably faster than that of skin, which takes approximately 30 days (see Section 8.2.1). 

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. 

A rich blood supply and lymphatic network in the lamina propria serve the oral cavity, thus drag moieties which traverse the oral epithelium are readily absorbed into the systemic circulation. The blood flow in the buccal mucosa is 2.4 mL min 1 cm 2 whereas that to the sublingual mucosa is 0.97 mL min-1 cm 2. 

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