Physiology of Salivary Glands

Oral Stimuli and Salivary Glands

• Oral stimuli include gustatory, masticatory, olfactory, thermoreceptive, and nociceptive stimuli.
• Afferent pathway involves transmission of stimuli to the nucleus of the solitary tract (NST), thoracic spinal cord, and finally to salivary nuclei, medulla, and brainstem.

Mechanisms of Salivary Secretion

• Parasympathetic nerves evoke most fluid secretion, some protein secretion, cause vasodilation, and contract myoepithelial cells.
• Sympathetic nerves act collaboratively with parasympathetic nerves, seldom cause fluid secretion, cause protein secretion, and contract myoepithelial cells.
• Denervation of parasympathetic nerves causes gland atrophy, while denervation of sympathetic nerves causes some gland atrophy.

Formation and Secretion of Saliva

• Saliva is formed by acinar cells in the salivary gland epithelial cells.
• Acinar cells synthesize and secrete different mixtures of proteins in different glands:
  • Parotid gland: serous
  • Submandibular gland: seromucous
  • Sublingual gland: mucous
• Salivary protein secretion includes blood proteins (albumin, IgA) and acinar proteins (amylase, mucins, PRPs, statherins).

Ductal Cell Modification of Saliva

• Striated ductal cells modify saliva by reabsorbing sodium and secreting potassium.
• Resting/unstimulated saliva is isotonic, while stimulated saliva is hypotonic.
• Ductal cell modification of saliva involves changes in sodium, potassium, and chloride concentrations.

Salivary Glands

• Salivary glands are exocrine glands that secrete onto the surfaces of the mouth.
• There are major salivary glands (parotid, submandibular, sublingual) and minor salivary glands (present in most oral mucosal surfaces).
• Minor salivary glands are present in the oral mucosa, including labial and palatine minor glands.

Newly Discovered Paired Salivary Glands

• Newly discovered paired salivary glands are present in the oral cavity.
• Salivary secretion is a nerve-mediated reflex involving collaboration between parasympathetic and sympathetic nerves.