Nervous Regulation of Salivary Secretion

Figure 64-3 shows the parasympathetic nervous pathways for regulating salivation, demonstrating that the salivary glands are controlled mainly by parasympa-thetic nervous signals all the way from the superior and inferior salivatory nuclei in the brain stem.

The salivatory nuclei are located approximately at the juncture of the medulla and pons and are excited by both taste and tactile stimuli from the tongue and other areas of the mouth and pharynx. Many taste stimuli, especially the sour taste (caused by acids), elicit copious secretion of saliva—often 8 to 20 times the basal rate of secretion. Also, certain tactile stimuli, such as the presence of smooth objects in the mouth (e.g., a pebble), cause marked salivation, whereas rough objects cause less salivation and occasionally even inhibit salivation.

Salivation can also be stimulated or inhibited by nervous signals arriving in the salivatory nuclei from

Tractus solitarius

Superior and inferior salivatory nuclei

Submandibular gland

Submandibular

Superior and inferior salivatory nuclei

Submandibular gland

Tractus solitarius

The Central Nervous System

Glossopharyngeal nerve

Figure 64-3

Chorda tympani Sublingual gland É

Parotid gland

Otic ganglion ^Taste and tactile stimuli

Figure 64-4

Oxyntic gland from the body of the stomach.

Glossopharyngeal nerve

Figure 64-3

Parasympathetic nervous regulation of salivary secretion.

higher centers of the central nervous system. For instance, when a person smells or eats favorite foods, salivation is greater than when disliked food is smelled or eaten. The appetite area of the brain, which partially regulates these effects, is located in proximity to the parasympathetic centers of the anterior hypothalamus, and it functions to a great extent in response to signals from the taste and smell areas of the cerebral cortex or amygdala.

Salivation also occurs in response to reflexes originating in the stomach and upper small intestines—par-ticularly when irritating foods are swallowed or when a person is nauseated because of some gastrointestinal abnormality. The saliva, when swallowed, helps to remove the irritating factor in the gastrointestinal tract by diluting or neutralizing the irritant substances.

Sympathetic stimulation can also increase salivation a slight amount, much less so than does parasympa-thetic stimulation. The sympathetic nerves originate from the superior cervical ganglia and travel along the surfaces of the blood vessel walls to the salivary glands.

A secondary factor that also affects salivary secretion is the blood supply to the glands because secretion always requires adequate nutrients from the blood. The parasympathetic nerve signals that induce copious salivation also moderately dilate the blood vessels. In addition, salivation itself directly dilates the blood vessels, thus providing increased salivatory gland nutrition as needed by the secreting cells. Part of this additional vasodilator effect is caused by kallikrein secreted by the activated salivary cells, which in turn acts as an enzyme to split one of the blood proteins, an alpha2-globulin, to form bradykinin, a strong vasodilator.

Figure 64-4

Oxyntic gland from the body of the stomach.

Esophageal Secretion

The esophageal secretions are entirely mucous in character and principally provide lubrication for swallowing. The main body of the esophagus is lined with many simple mucous glands. At the gastric end and to a lesser extent in the initial portion of the esophagus, there are also many compound mucous glands. The mucus secreted by the compound glands in the upper esophagus prevents mucosal excoriation by newly entering food, whereas the compound glands located near the esophagogastric junction protect the esophageal wall from digestion by acidic gastric juices that often reflux from the stomach back into the lower esophagus. Despite this protection, a peptic ulcer at times can still occur at the gastric end of the esophagus.

Was this article helpful?

0 0
Brain Blaster

Brain Blaster

Have you ever been envious of people who seem to have no end of clever ideas, who are able to think quickly in any situation, or who seem to have flawless memories? Could it be that they're just born smarter or quicker than the rest of us? Or are there some secrets that they might know that we don't?

Get My Free Ebook


Responses

  • Richard Davey
    Does a smooth pebble placed on the tongue cause more salivation than the rough one?
    3 years ago
  • Marie
    Why saliva secret when smooth object is taken in mouth not rough?
    3 years ago
  • bellisima
    How fear affects saliva production medical physiology?
    3 years ago
  • jensen alexander
    Which nervous system causes salivary gland secretion?
    1 year ago
  • Editta
    How does salivary secretions get inhibited pathway?
    1 year ago
  • luke
    How is the secretion of saliva regulated?
    9 months ago
  • dora goold
    Is salivary secretion parasympathetic?
    8 months ago
  • caramella
    How does human salivary gland cells get nutrients?
    3 months ago

Post a comment