Introduction

  • The nervous system controls salivary secretion. The smell or taste of food, and masticatory stimuli affect the amount of salivary secretion. Secretion of saliva can be divided into two phases – the primary phase which involves secretory acini, and the secondary phase which occurs in excretory ducts.

You can read more about the classification and composition of saliva here.

Saliva – Neural Control

  • The autonomic nervous system affects the composition and flow of saliva from glands.
  • Parasympathetic Nerves:
    • Primary control of salivary glands is through parasympathetic nerves. These nerves are responsible for secretion of watery, electrolyte-rich and low protein saliva.
    • The parotid gland is primarily stimulated and partly the submandibular gland. Hence, while eating, serous salivary secretion is stimulated.
    • The most effective stimulus for an increase in salivary secretion is a sour taste followed by a salty taste.
  • Sympathetic Nerves:
    • In situations of fear, anger, stress, or vigorous exercise where sympathetic nerves are stimulated, the salivary glands produce thicker, protein-rich saliva. This occurs due to a modification in vascular supply of gland by the sympathetic nerves.
    • The sublingual gland and partly the submandibular gland are responsible for an increase in mucous content of salivary secretion.

Salivary Reflex

  • Unconditioned reflex: It is an inborn reflex, which induces secretion of saliva when any substance is placed in oral cavity.
  • Conditioned reflex: It is a reflex acquired by experience. Even a thought of your favourite food initiates salivary secretion. 

Physiological Process of Formation:

  • Primary secretory phase:
    • Formation of protein component:
Formation of Protein Component in Saliva- Flow Diagram
Formation of Protein Component – Flow Diagram
    • Formation of electrolyte component:
Formation of electrolyte component in saliva - flow diagram
Formation of electrolyte component – flow diagram
  • Secondary/Modification phase of secretion
    • Saliva produced by secretory acini contain electrolytes such as sodium and chloride. Prevention the loss of sodium and chloride ions from the body is necessary. The excretory ducts play a key role in reabsorbing sodium and chloride secreted in saliva from acini. Thus, the end product is hypotonic to plasma.
    • The striated duct modifies secreted saliva from acini by reabsorbing sodium and chloride ions and simultaneously excreting potassium and bicarbonate ions.
    • The autonomic nervous system and mineralocorticoids control the modification step.

Summary

  • Salivary secretion is controlled by both the parasympathetic and sympathetic nervous systems.
  • The parasympathetic system is typically responsible in normal day-to-day function.
  • The sympathetic system usually works when our ‘fight or flight’ response is triggered.
  • Saliva can be divided in to a protein component and an electrolyte component. These vary in composition based on the nervous system controlling production.
  • Further modification of the saliva occurs in the ducts.

Recommended Reading

References
  1. Kumar GS (2015) Orban’s Oral histology and embryology. 14th edn: Elsevier India.
  2. Sembulingum K and Sembulingum P (2012) Essentials of medical physiology 6th edn: Jaypee publications.

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