ABSTRACT
The alimentary tract contains single cells in the mucosal layer and collections of cells organized as acinar glands dedicated to ion and water secretion or absorption. The balance between secretion and absorption produces local environments that differ widely in ion composition, osmolarity, and acidity. The material composition of the oral cavity environment varies in ways that reflect ongoing physiological activity in a manner analogous to stimulated activity in lower regions of the gastrointestinal tract. The salivary glands (parotid, submaxillary, and sublingual) provide the major part of the aqueous milieu of the oral cavity. These are acinar glands with end pieces that form a primary secretion that is conducted through a system of convergent ducts that modify the secretion before emptying into the oral cavity. Typically, salivary composition varies considerably with flow rate, which depends on the extent of parasympathetic and sympathetic neural stimulation. At basal flow rates ( <0.5 ml/min) saliva, relative to plasma, is hypotonic (ca. 90 mosmol), rather low in sodium (3 to 25 mM), chloride (ca. 25 mM), and bicarbonate (<25 mM), but notably high in potassium (25 to 30 mM). 1 In the stimulated state salivary tonicity more closely approaches that of plasma; sodium, chloride, and bicarbonate are at higher than basal levels, and, while potassium levels may fall somewhat, they still exceed plasma levels by a wide margin (ca. 20 mM).
