Physiological Pharmaceutics

Buccal drug delivery 41Functions of the oral mucosaThe oral mucosa has similarities to both skin and intestinal mucosa. It has a protective roleduring the process of mastication, which exposes the mucosa to compression and shearforces. Areas such as the hard palate and attached gingiva have a horny surface to resistabrasion and are tightly bound to the underlying bone to resist shear forces. The cheekmucosae, on the other hand, are elastic to allow for distension.The oral cavity contains the greatest variety of micro-organisms present within thehuman body. The entry into the body of these organisms and any potential toxic wasteproduct is limited by the oral epithelium, which is not, as is often suggested, a highlypermeable membrane.The oral mucosa responds to the senses of pain, touch, and temperature in additionto its unique sense of taste. Some physiological processes are triggered by sensory input fromthe mouth, such as the initiation of swallowing, gagging and retching.In some animals the oral mucosa is used to aid thermoregulation, for example,panting in the dog. The human skin possesses sweat glands and a more highly controlledperipheral vasculature, so this role is thought to be minimal, although in sleep, dehydrationcan result from prolonged breathing through the mouth.Salivary secretionSalivary glandsThe major salivary glands are the parotid, submandibular (submaxillary) and sublingualglands (Figure 3.3). Minor salivary glands are situated in or immediately below the oralmucosa in the tongue, palate, lips, and cheeks. The major glands are situated some way fromthe oral cavity, but open into it by a long duct. The parotid salivary glands, the largest ofthe three, are located between the ear and ascending branch of the lower jaw. Each glandis enclosed in a tissue capsule and is composed of fat tissue and secretory cells and the majorduct (Stensen’s duct) opens near the second upper molar. The second pair, the submaxillaryFigure 3.3 Position of the salivary glands