Expansion
Hypotonic fluid with amylase, mucins, lysozyme and bicarbonate
Expansion
Volume: about 1 to 1.5 litres a day, from parotid (serous), submandibular (mixed, the largest contributor at rest) and sublingual (mucous) glands.
Composition: hypotonic, because ducts reabsorb sodium and chloride while secreting potassium and bicarbonate. The slower the flow, the more hypotonic.
Functions
- Digestion: salivary amylase and lingual lipase, both minor
- Lubrication by mucins, aiding speech and swallowing
- Protection: lysozyme, lactoferrin, secretory IgA, and bicarbonate buffering
- Taste: dissolving substances so they reach taste receptors
- Dental: calcium and phosphate maintaining enamel
Control is entirely neural, not hormonal:
- Parasympathetic (facial and glossopharyngeal nerves) gives copious watery saliva
- Sympathetic gives a small volume of thick, protein-rich saliva
Xerostomia from drugs (antimuscarinics, tricyclics), Sjogren syndrome, radiotherapy or dehydration causes dental caries, candidiasis and difficulty swallowing, illustrating how much protective work saliva does.