Salivary secretion !
- Mechanism
- For completeness
The salivary glands make 1 to 1.5 L of saliva a day to moisten food, start starch digestion and protect the mouth and teeth.
Updated 2026-11-01
Also called: Saliva, Salivary glands
See it in 3D: Parotid gland · Submandibular gland · Sublingual gland · Tongue
What it is
Saliva is made in two steps. Acini secrete a plasma-like fluid, and the ducts modify it: they reabsorb Na⁺ and Cl⁻ and secrete K⁺ and HCO₃⁻ while letting little water through, so the final saliva is hypotonic. Unlike almost all of the gut, both parasympathetic and sympathetic nerves stimulate it, although the parasympathetic dominates.
How it works, step by step
- Smell, taste, chewing or thinking of food activates the salivatory nuclei of the brainstem.
- Acetylcholine (M3) raises Ca²⁺ in acinar cells and opens apical Cl⁻ channels.
- Cl⁻ moves into the lumen, Na⁺ and water follow: an isotonic, plasma-like fluid forms.
- In the ducts, the water-tight epithelium reabsorbs Na⁺ and Cl⁻ and secretes K⁺ and HCO₃⁻.
- The final saliva leaves hypotonic and slightly alkaline, with a pH near 7 at high flow.
- Local vasodilation (bradykinin, VIP) sustains high flow during stimulation.
Clinical notes
- Anticholinergic drugs and head and neck radiotherapy cause dry mouth (xerostomia) and more caries.
- Sialolithiasis: ≈80% in the submandibular gland (thicker, more alkaline saliva and a long uphill duct); pain and swelling at meals.
- Mumps: painful parotid swelling and raised serum amylase of salivary origin.
- A high serum amylase is not always pancreatic: the salivary glands contribute too.
Test yourself
Think of the answer, then tap the question to see it.
Why is saliva hypotonic even though the acini secrete an isotonic fluid?
The ducts reabsorb more Na⁺ and Cl⁻ than the K⁺ and HCO₃⁻ they secrete, and their epithelium is poorly permeable to water; water does not follow the salt, so saliva ends up hypotonic.
Why is saliva closer to plasma when flow is very high?
Fluid moves through the ducts faster, leaving less time to reabsorb Na⁺ and Cl⁻; even so, saliva stays hypotonic.
Why do most salivary stones form in the submandibular gland?
Its saliva is more mucous and alkaline, with more calcium, and its duct is long and runs uphill; slow flow favours salt precipitation.
See it in 3D
The structures of Durgical's 3D anatomy where it happens.
Related topics
- Carbohydrate digestion and absorption
- Sympathetic and parasympathetic effects on each organ
- Adrenergic and cholinergic receptors
- Taste and smell
- Swallowing and esophageal motility
Related conditions
In Biochemistry
Educational physiology content; not a diagnostic or treatment guide and no substitute for a health professional's advice. Values are approximate references. No doses are given.
Sources: 23.3 The Mouth, Pharynx, and Esophagus (OpenStax (Rice University), 2022); Anatomy, Head and Neck, Salivary Glands (StatPearls (NCBI Bookshelf), 2024); Sialolithiasis (StatPearls (NCBI Bookshelf), 2024); Hall JE. Guyton and Hall Textbook of Medical Physiology, 13th ed. (ch. 65). Reference book used to check facts; its text and figures are not reproduced (Elsevier, 2016).
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Representative model, for educational purposes only.