- 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.
- 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 electrolyte component:
- 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.
- 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.