Salivation

Salivation is the process by which saliva is produced and secreted into the oral cavity by the major (parotid, submandibular, sublingual) and minor salivary glands. Saliva is primarily water but also contains electrolytes, mucus, and proteins such as enzymes (salivary amylase and lingual lipase) and defense factors (lysozyme, lactoferrin, secretory IgA). Its functions include lubrication of the mouth and food bolus formation, initiation of starch digestion, enhancement of taste, and protection of teeth and mucosa through buffering, remineralization, cleansing, and antimicrobial action.

Secretion is regulated by the autonomic nervous system. Parasympathetic stimulation markedly increases saliva flow, while sympathetic input modulates the composition and can modestly affect volume. A parasympathetic pathway begins in the brainstem and travels via the facial nerve to the submandibular and sublingual glands, and a separate pathway travels via the glossopharyngeal nerve to the parotid gland. Both pathways end in connected ganglia before reaching the glands. Salivary secretion is stimulated by the cephalic phase of digestion through sight, smell, anticipation, and taste, and continues through reflex pathways during eating.

Major glands produce largely serous saliva (parotid) or mixed saliva (submandibular, sublingual). Unstimulated baseline flow in adults is about 0.3–0.5 mL/min; stimulated flow can reach roughly 1–3 mL/min depending on factors such as hydration and arousal. Flow rate influences composition: higher flow contains more bicarbonate and fewer mucins.

Clinical aspects include xerostomia (dry mouth) and hypersalivation (ptyalism). Causes of dry mouth include dehydration, medications, radiation therapy, and autoimmune diseases such as Sjögren syndrome. Evaluation uses sialometry and, when needed, imaging. Treatments aim to manage underlying causes and may include saliva substitutes or mAChR agonists (pilocarpine, cevimeline) to increase production.