Physiological Pharmaceutics

42 Physiological Pharmaceuticsglands, is located along the side of the lower jawbone. The major duct of each (Wharton’sduct) opens into the floor of the mouth at the junction where the front of the tongue meetsthe mouth’s floor. A capsule of tissue also surrounds each of these glands. The third pair,the sublingual glands, is situated beneath the mucous membrane of the floor of the mouth,near the chin region. They are not covered by a capsule and are therefore more dispersedthroughout the surrounding tissue. They have many ducts (Rivinus’s ducts) that empty nearthe junction of the tongue and the mouth’s floor; several unite to form Bartholin’s ductwhich empties into or near the submaxillary duct. The parotid and submaxillary glandsproduce watery secretion, while the buccal and sublingual glands produce mainly viscoussaliva.SalivaOne to two litres of fluid are excreted daily into the human mouth and there is a continuous,low basal secretion of 0.5 ml.min -1 which will rapidly increase to more than 7 ml.min -1 bythe thought, smell or taste of food. Control over salivary secretion is exerted primarily viathe parasympathetic system. Small amounts of saliva are continually being secreted into themouth, but the presence of food, or even the smell or thought of it, will rapidly increasesaliva flow. Saliva is viscous, colourless and opalescent, hypotonic compared to plasma(between 110 and 220 milliOsmoles per litre), with a specific gravity of about 1003. ThepH varies between 7.4 to 6.2 (low to high rates of flow), but the action of bacteria on sugarcan reduce the pH to between 3 and 4 around the teeth.Saliva can be detected in the oral cavity soon after birth. Salivary secretion increasesup to the age of 3 to 5 years, but then sharply declines, reaching a steady state by the ageof 8 years. In adult females, the flow rate of saliva is somewhat lower than in males 2 .Figure 3.4 Influence of flow on saliva composition