Neurogastroenterology encompasses the study of the brain, the gut, and their interactions with relevance to the understanding and management of gastrointestinal motility and functional gastrointestinal disorders. Specifically, Neurogastroenterology focuses on the functions, malfunctions, and the malformations of the sympathetic, parasympathetic, and enteric divisions of the digestive tract[1].
The Function of Neurons in the Gastrointestinal Tract
editControl of Motility
editThe Peristaltic Reflex
editPeristalsis is a series of radially symmetrical contractions and relaxations of muscles which propagate down a muscular tube. In humans and other mammals, peristalsis is found in the smooth muscles of the digestive tract to propel contents through the digestive system. The word is derived from New Latin and comes from the Greek peristallein, "to wrap around," from peri-, "around" + stallein, "to place". Peristalsis was discovered in 1899 by the work of physiologists William Bayliss and Ernest Starling. Working on the small intestines of dogs, they found that the response of increasing the pressure in the intestine caused the contraction of the muscle wall above the point of stimulation and the relaxation of the muscle wall below the point of stimulation. [2] [3]
Segmentation
editSegmentation contractions are the contractions in intestines carried out by the smooth muscle walls. Unlike peristalsis, which involves the contraction and relaxation of muscles in one direction, segmentation occurs simultaneously in both directions as the circular muscles alternatively contract. This allows for thorough mixing of intestinal contents, known as chyme, to allow greater absorption.
Secretion
editThe secretion of gastrointestinal enzymes, such as gastrin and secretin, is regulated through cholinergic neurons residing in the walls of the digestive tract. Hormone secretion is controlled by the vagovagal reflex, where the neurons in the digestive tract communicate through both afferent and efferent pathways with the vagus nerve.[4]
Anatomy
editEnteric Nervous System
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Auerbach's Plexus
editAuerbach's plexus, also known as the myenteric plexus, is a collection of unmyelinated fibers and postganglionic autonomic cell bodies that lie between the circular and longitudinal layers of the muscularis externa in the gastrointestinal tract. [5]. It was discovered and named by German neuropathologist Leopold Auerbach. These neurons provide motor inputs to both layers of the muscularis externa, and provide both parasympathetic and sympathetic input. The anatomy of the plexus is similar to the anatomy of the central nervous system. The plexus includes sensory receptors, such as chemoreceptors and mechanoreceptors, that are used to provide sensory input to the interneurons in the enteric nervous system. The plexus is the parasympathetic nucleus of origin for the vagus nerve, and communicate with the medulla oblongata through both the anterior and posterior vagal nerves.
Meissner's Plexus
editMeissner's plexus is a collection of the plexuses of parasympathetic nerves that run from Auerbach's plexus to the muscularis mucosae of the gastrointestinal wall. It was discovered and named by German physiologist Georg Meissner. It functions as a pathway for the innervation in the mucosa layer of the gastrointestinal wall.
Disorders
editFunctional Gastrointestinal Disorders
editFunctional gastrointestinal (GI) disorders are a class of gastrointestinal disorders where there is a malfunction in the normal activities of the gastrointestinal tract, but there are no structural abnormalities that can explain the cause. There are rarely any tests that can detect the presence of these disorders. Clinical research in neurogastroenterology focuses mainly on the study of common functional gastrointestinal disorders such as Irritable bowel syndrome, the most common functional GI disorder.[6]
Motility Disorders
editMotility disorders are the second classification of gastrointestinal disorder studied by neurogastroenterologists. Motility disorders are divided by what they affect, with four regions: The esophagus, the stomach, the small intestines, and the large intestines. Clinical research in neurogastroenterology focuses mainly on the study of common motility disorders such as Gastroesophageal reflux disease, the damage of the mucosa of the esophagus caused by rising stomach acid through the lower esophageal sphincter. [7]
Neurogastroenterology Societies
editSee also
editReferences
edit- ^ Wood, JD (1999). "Fundamentals of Neurogastroenterology". Gut. 45: 6–16. doi:10.1136/gut.45.2008.ii6. PMID 10457039.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Keet, A. D. "The Pyloric Sphincteric Cylinder in health and disease". Retrieved 18 November 2013.
- ^ Gershon, Michael (1998). The Second Brain. New York: HarperCollins. pp. 2–7. ISBN 0-06-018252.
{{cite book}}: Check|isbn=value: length (help) - ^ Herman MA, Cruz MT, Sahibzada N, Verbalis J, Gillis RA (January 2009). "GABA signaling in the nucleus tractus solitarius sets the level of activity in dorsal motor nucleus of the vagus cholinergic neurons in the vagovagal circuit". Am. J. Physiol. Gastrointest. Liver Physiol. 296 (1): G101–11. doi:10.1152/ajpgi.90504.2008. PMC 2636929. PMID 19008339.
{{cite journal}}: CS1 maint: date and year (link) CS1 maint: multiple names: authors list (link) - ^ myenteric+plexus at eMedicine Dictionary
- ^ Kumar, A. (2012). "Irritable Bowel Syndrome: A Review". J Phys Pharm Adv. 2 (2): 97–108.
{{cite journal}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ DeVault KR, Castell DO (1999). "Updated guidelines for the diagnosis and treatment of gastroesophageal reflux disease. The Practice Parameters Committee of the American College of Gastroenterology". Am J Gastroenterol. 94 (6): 1434–42. doi:10.1111/j.1572-0241.1999.1123_a.x. PMID 10364004.
