Physiology of the salivary glands

Salivary gland products are essential for oral health. Saliva is produced by three pairs of major salivary glands, the parotid, the submandibular and sublingual glands and by numerous minor salivary glands scattered around the oral cavity. Salivary water and electrolyte secretion is an energy consuming active two-stage process. First the acini secrete isotonic primary saliva into the luminal terminal end pieces of the gland parenchyma. This saliva is then modified by electrolyte reabsorption to form a hypotonic secretion in the ductal systems. Salivary proteins are continuously synthesized, and stored in secretory granules within the cell. Both electrolyte and protein secretion are highly regulated processes. Electrolyte secretion is primarily stimulated by parasympathetic stimulation while protein secretion is preferentially activated by sympathetic stimulation, but there is a considerable cross-talk and synergism between the two regulatory pathways. Approximately 1.0–1.5 litres of saliva is secreted by healthy persons each day, consisting of water, electrolytes, lubricants, antimicrobial compounds, enzymes and growth factors. These components of saliva facilitate speech, mastication and swallowing, and initiate food digestion. In addition, it protects the oral mucosa and the teeth. Thus, saliva secreted into the oral cavity is essential to maintain physiological conditions in the mouth.