Peristalsis is a radially symmetrical contraction and relaxation of muscles which propagates
in a wave down a muscular tube, in an anterograde fashion. Peristalsis is often found in the
contraction of smooth muscle tissue to propel food/chyme through a digestive tract, such
as the human gastrointestinal tract. It is wave contraction of longitudinal and circular
muscles preceded by wave relaxation of these muscles. Earthworms use a similar mechanism
to drive their locomotion. The word comes from New Latin and is derived from the Greek
peristallein, "to wrap around," from peri-, "around" + stallein, "to place".
In much of the gastrointestinal tract, smooth muscle contracts in sequence to produce a
peristaltic wave, which forces a ball of food along the gastrointestinal tract. Peristaltic
movement is initiated by circular smooth muscles contracting behind the chewed material to
prevent it from moving back into the mouth, followed by a contraction of longitudinal
smooth muscles which pushes the digested food forward. Catastalsis is a related intestinal
muscle process.
Esophagus After food is chewed into a bolus, it is 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 will
work to rapidly force the food into the stomach. The migrating motor complex helps trigger
peristaltic waves. This process works in one direction only and its sole purpose is to
move food from the mouth into the stomach. In the esophagus, two types of peristalsis
occur.
First, there is a primary peristaltic wave, which occurs when the bolus enters the esophagus
during swallowing. The primary peristaltic wave forces the bolus down the esophagus and
into the stomach in a wave lasting about 8–9 seconds. The wave travels down to the stomach
even if the bolus of food descends at a greater rate than the wave itself, and will continue
even if for some reason the bolus gets stuck further up the esophagus.
In the event that the bolus gets stuck or moves slower than the primary peristaltic
wave, stretch receptors in the esophageal lining are stimulated and a local reflex response
causes a secondary peristaltic wave around the bolus, forcing it further down the esophagus,
and these secondary waves will continue indefinitely until the bolus enters the stomach. The process
of peristalsis is controlled by medulla oblongata. Esophageal peristalsis is typically assessed
by performing an esophageal motility study. Small intestine
Once processed and digested by the stomach, the milky chyme is squeezed through the pyloric
sphincter into the small intestine. Once past the stomach a typical peristaltic wave will
only last for a few seconds, travelling at only a few centimeters per second. Its primary
purpose is to mix the chyme in the intestine rather than to move it forward in the intestine.
Through this process of mixing and continued digestion and absorption of nutrients, the
chyme gradually works its way through the small intestine to the large intestine.
In contrast to peristalsis, segmentation contractions result in that churning and mixing without
pushing materials further down the digestive tract.
During vomiting the propulsion of food up the esophagus and out the mouth comes from
contraction of the abdominal muscles; peristalsis does not reverse in the esophagus.
Mermane is a controlled villa for the small intestine. It loops around the large intestine's
cell wall. Large Intestine
As opposed to the more continuous peristalsis of the small intestines, faecal contents are
propelled into the large intestine by periodic mass movements. These mass movements occur
one to three times per day in the large intestines and colon, and help propel the contents from
the large intestine through the colon to the rectum.
Earthworms
The earthworm is a limbless annelid worm with a hydrostatic skeleton that moves by means
of peristalsis. This 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, resulting in an increase in 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
backwards slipping. Earthworms increase in size by four orders of magnitude during their
lifetime and during this period the dimensions increase according to geometric similarity,
or 'isometry'. Unlike rigid skeletons which cannot exhibit both geometric and stress similarity,
the hydrostatic skeleton can maintain both forms which may be due to decoupling of weight
and skeletal function. Robotics
Peristalsis is also being used for robot locomotion. See also
Peristaltic pump - Mechanical device that uses peristaltic action to drive fluids
Catastalsis - Downward wave of contraction occurring in the gastrointestinal tract during
digestion Basal electrical rhythm - Slow wave of electrical
activity that can initiate contraction Aboral
References ^ "Earthworm - Muscular System".
^ a b c Marieb, Elaine N. & Hoehn, Katja "Human Anatomy & Physiology" 8th Ed., Benjamin Cummings/Pearson,
2010 ^ a b Quillin KJ. "Ontogenetic scaling of
hydrostatic skeletons: geometric, static stress and dynamic stress scaling of the earthworm
lumbricus terrestris". The Journal of Experimental Biology 201: 1871–83. PMID 9600869.
^ https:www.youtube.com/watch?v=Sb1V_OKqRfc See also Peristaltic Linear Motion. A flexible
tube constricted with rollers which produces linear motion when pressurised with air or
liquids. External links
Interactive 3D display of swallow waves at menne-biomed.de
Peristalsis at the US National Library of Medicine Medical Subject Headings
Physiology at MCG 6s6ch3_9 Overview at colostate.edu