Peristalsis: Difference between revisions

'''Peristalsis''' ({{IPAc-en|ˌ|p|ɛr|ɪ|ˈ|s|t|æ|l|s|ɪ|s}} {{respell|PERR|ih|STAL|siss}}, {{IPAc-en|usalso|-|ˈ|s|t|ɔː|l|-}} {{respell|-|STAWL|-}})<ref>{{cite LPD|3}}</ref> is a type of [[intestinal motility]], characterized by [[symmetry in biology#Radial symmetry|radially symmetrical]] contraction and relaxation of [[muscle]]s that propagatespropagate in a [[wave]] down a tube, in an [[wikt:anterograde|anterograde]] direction. Peristalsis is progression of coordinated contraction of involuntary circular muscles, which is preceded by a simultaneous contraction of the longitudinal muscle and relaxation of the circular muscle in the lining of the gut.<ref>{{Cite book|last=Mittal|first=Ravinder K.|url=https://www.ncbi.nlm.nih.gov/books/NBK54265/|title=Peristalsis in the Circular and Longitudinal Muscles of the Esophagus|date=2011|publisher=Morgan & Claypool Life Sciences|language=en}}</ref>

In much of a [[digestive tract]], such as the [[human gastrointestinal tract]], [[smooth muscle tissue]] contracts in sequence to produce a peristaltic wave, which propels a ball of [[food]] (called a [[bolus (digestion)|bolus]] before being transformed into [[chyme]] in the stomach) along the tract. The peristaltic movement comprises relaxation of circular smooth muscles, then their contraction behind the chewed material to keep it from moving backward, then longitudinal contraction to push it forward.

[[Earthworm]]s use a similar mechanism to drive their locomotion,<ref>{{Cite web|url=https://www.angelfire.com/de2/atoy/mus.htm|title=Earthworm - Muscular System|website=www.angelfire.com[[Angelfire]]}}</ref>{{self-published inline|date=September 2014}} and some modern machinery imitate this design.<ref>{{Cite journal|url=https://iopscience.iop.org/article/10.1088/0964-1726/13/3/016/meta|title=Development of a peristaltic crawling robot using magnetic fluid on the basis of the locomotion mechanism of the earthworm|publisher=IOP Publishing|journal=Smart Materials and Structures|date=2004 |doi=10.1088/0964-1726/13/3/016 |access-date=2024-04-06 |last1=Saga |first1=Norihiko |last2=Nakamura |first2=Taro |volume=13 |issue=3 |pages=566–569 |bibcode=2004SMaS...13..566S }}</ref>

The word comes from [[New Neo-Latin]] and is derived from the [[Greek language|Greek]] ''peristellein'', "to wrap around," from ''peri''-, "around" + ''stellein'', "draw in, bring together; set in order".<ref>{{Cite web|url=http://etymonline.com/index.php?allowed_in_frame=0&search=peristaltic|title=Online Etymology Dictionary|website=etymonline.com|access-date=2016-06-30}}</ref>

Peristalsis is generally directed caudal, that is, towards the [[Human anus|anus]]. This sense of direction might be attributable to the polarisation of the [[myenteric plexus]]. Because of the reliance of the peristaltic reflex on the myenteric plexus, it is also referred to as the myenteric reflex.<ref>{{cite book|last1=Hall|first2=John E.|last2=Hall|first1=Michael E.|title=Guyton and Hall textbook of medical physiology|year=2021|publisher=Saunders/Elsevier|location=Philadelphia, Pa.|isbn=978-0-323-59712-8|edition=14th}}</ref>

The food bolus causes a stretch of the gut [[smooth muscle]] that causes [[serotonin]] to be secreted to sensory neurons, which then get activated. These sensory neurons, in turn, activate neurons of the [[myenteric plexus]], which then proceed to split into two [[cholinergic]] pathways: a retrograde and an anterograde. Activated neurons of the retrograde pathway release [[substance P]] and [[acetylcholine]] to contract the smooth muscle behind the bolus. The activated neurons of the anterograde pathway instead release [[nitric oxide]] and [[vasoactive intestinal polypeptide]] to relax the smooth muscle caudal to the bolus. This allows the food bolus to effectively be pushed forward along the digestive tract.<ref>{{cite book|title=Ganong's Review of Medical Physiology|year=2019|isbn=978-1-26-012240-4|last1=Yuan|first1=Jason|last2=Brooks|first2=Heddwen L.|last3=Barman|first3=Susan M.|last4=Barrett|first4=Kim E.|publisher=McGraw-Hill Education }}</ref>

After food is chewed into a bolus, it is [[swallowing|swallowed]] and moved through the esophagus. Smooth muscles contract behind the bolus to prevent it from being squeezed back into the mouth. Then rhythmic, unidirectional waves of contractions work to rapidly force the food into the stomach. The [[migrating motor complex]] (MMC) helps trigger peristaltic waves. This process works in one direction only, and its sole esophageal function is to move food from the mouth into the stomach (the MMC also functions to clear out remaining food in the stomach to the small bowel, and remaining particles in the small bowel into the colon).<ref name="ReferenceA"/>

During [[vomiting]], the propulsion of food up the esophagus and out the mouth comes from the contraction of the [[abdominal muscles]]; peristalsis does not reverse in the esophagus.{{cn|date=July 2022}}

When a peristaltic wave reaches at the end of the [[esophagus]], the [[cardiac sphincter]] (gastroesophageal sphincter) opens, allowing the passage of bolus into the stomach. The gastroesophageal sphincter normally remains closed and does not allow the stomach's food contents to move back. The churning movements of the stomach's thick muscular wall blend the food thoroughly with the acidic [[gastric juice]], producing a mixture called the [[chyme]]. The [[Muscular layer|muscularis layer]] of the stomach is thickest and maximum peristalsis occurs here. After short intervals, the [[pyloric sphincter]] keeps on opening and closing so the chyme is fed into the intestine in installments.

The human [[lymphatic system]] has no central pump. Instead, [[lymph]] [[lymph#Circulation|circulates]] through peristalsis in the lymph capillaries, as well as valves in the capillaries, compression during contraction of adjacent skeletal muscle, and arterial pulsation.

During [[ejaculation]], the smooth muscle in the walls of the [[vasvasa deferensdeferentia]] contractscontract reflexively in peristalsis, propelling [[sperm]] from the [[testicle]]s to the [[urethra]].<ref name="Reece2013">{{cite book|author=William O. Reece|title=Functional Anatomy and Physiology of Domestic Animals|url=https://books.google.com/books?id=C_q3Q-IpkNMC&pg=PA451|date=21 March 2013|publisher=John Wiley & Sons|isbn=978-1-118-68589-1|pages=451–}}</ref>

The [[earthworm]] is a limbless [[annelid]] worm with a [[hydrostatic skeleton]] that moves by peristalsis. Its hydrostatic skeleton consists of a fluid-filled body cavity surrounded by an extensible body wall. The worm moves by radially constricting the anterior portion of its body, increasing length via hydrostatic pressure. This constricted region propagates posteriorly along the worm's body. As a result, each segment is extended forward, then relaxes and re-contacts the substrate, with hair-like [[setae]] preventing backward slipping.<ref name=Quillin>{{cite journal |author=Quillin KJ |title=Ontogenetic scaling of hydrostatic skeletons: geometric, static stress and dynamic stress scaling of the earthworm lumbricus terrestris |journal=The Journal of Experimental Biology |volume=201 |issue=12 |pages=1871–83 |date=May 1998 |doi=10.1242/jeb.201.12.1871 |pmid=9600869 |url=https://jeb.biologists.org/content/201/12/1871.long|doi-access=free }}</ref> Various other invertebrates, such as [[caterpillar]]s and [[millipede]]s, also move by peristalsis.

* [http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html Overview at colostate.edu] {{Webarchive|url=https://web.archive.org/web/20200128004815/http://www.vivo.colostate.edu/hbooks/pathphys/digestion/basics/peristalsis.html |date=2020-01-28 }}