Saliva and the control of its secretion

Abstract

The various functions of saliva—among them digestive, protective, and trophic ones—not just limited to the mouth and the relative contribution of the different types of gland to the total volume secreted as well as to various secretory rhythms over time are discussed. Salivary reflexes, afferent and efferent pathways, as well as the action of classical and non-classical transmission mechanisms regulating the activity of the secretory elements and blood vessels are in focus. Sensory nerves of glandular origin and an involvement in gland inflammation are discussed. Although the glandular activities are principally regulated by nerves, recent findings of an “acute” influence of gastrointestinal hormones on saliva composition and metabolism are paid attention to, suggesting, in addition to the cephalic nervous phase both a regulatory gastric and intestinal phase. The influence of nerves and hormones in the long-term perspective as well as old age, diseases and consumption of pharmaceutical drugs on the glands and their secretion are discussed with focus on xerostomia and salivary gland hypofunction. Treatment options of dry mouth are presented as well as an explanation to the troublesome clozapine-induced sialorrhea. Final sections of this chapter describe the families of secretory salivary proteins and highlight the most recent results obtained in the study of the human salivary proteome. Particular emphasis is given to the post-translational modifications occurring to salivary proteins before and after secretion, to the polymorphisms observed in the different protein families and to the physiological variations, with a major concern to those detected in the paediatric age. Functions exerted by the different families of salivary proteins and the potential use of human saliva for prognostic and diagnostic purposes are finally discussed.