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Mittal RK. Motor Function of the Pharynx, Esophagus, and its Sphincters. San Rafael (CA): Morgan & Claypool Life Sciences; 2011.

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Motor Function of the Pharynx, Esophagus, and its Sphincters.

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Motor Patterns of the Esophagus—Aboral and Oral Transport

Motor patterns of the esophagus can be divided in two main types: (1) one that carries the bolus toward the stomach, i.e., primary and secondary peristalsis, and (2) another that carries stomach contents toward the esophagus and mouth (oral transport). The latter is seen with belching, regurgitation, rumination, and vomiting. Transient LES relaxation is a key component of the second motor pattern. Swallowing (deglutition) or primary peristalsis begins with a voluntarily phase (oral phase) but once the bolus hits the tonsilar region and pharynx, it becomes autonomous or involuntary. Contraction of the mylohyoid muscle is the first recordable event of involuntary phase of a swallow. Sensory receptors for the involuntary phase are located on the base of tongue, tonsils, anterior and posterior pillars of the fauces, soft palate, uvula, and posterior pharyngeal wall [14]. In man, the tonsilar pillars and posterior pharyngeal wall are the optimal sites for initiation of deglutition reflex.

CIRCULAR MUSCLE CONTRACTION

Each swallow induces a wave of inhibition that spreads along the entire length of the esophagus rapidly followed by a sequential contraction. Since esophagus does not have resting tone, inhibition and relaxation of the esophagus cannot be demonstrate with routine intraluminal pressure recordings. However, using the barostat technique, investigators have found tone in the circular muscle [104,105]. To demonstrate inhibition, one can create an artificial high-pressure zone in the esophagus by distending a small balloon, which shows a fall in the pressure with each swallow, as a marker of esophageal inhibition [106]. If one uses two high-pressure zones using two separate balloons at two different levels in the esophagus, there is simultaneous relaxation of both high-pressure zones with the swallow. Duration of relaxation is longer in the distal as compared to proximal esophagus. LES shows onset of relaxation soon after the onset of swallow (2 seconds before to 4 seconds after the onset of mylohyoid EMG activity). The LES remains relaxed for approximately 6 seconds, the entire time as the peristaltic wave traverses the esophagus. Once peristaltic wave passes the LES, it closes with a 5- to 10-second period of postrelaxation hypercontraction during which the LES pressures are significantly greater than the LES pressure prior to the onset of swallow. LES relaxation may occur without pharyngeal or esophageal phase of swallow reflex. In the awake-state, normal subjects swallow once every minute, and the sequence of events of deglutition reflex repeats itself in a monotonous fashion. Peristalsis may not involve the entire swallowing apparatus as seen in the pharyngeal peristalsis and secondary peristalsis. If one infuses small amounts of water (rapidly or slowly) directly into the pharynx, contraction wave starts in the pharynx without the oral component and marches through the esophagus as in primary peristalsis. Secondary peristalsis under physiological conditions is seen with either retained bolus in the esophagus or distension associated with gastroesophageal reflux. In each of these conditions, wave of contraction starts above the bolus and proceeds distally propelling the bolus into the stomach without involving part of the esophagus above the bolus, pharynx or oral cavity. Under experimental condition one can study secondary peristalsis by distending a balloon in the esophagus. Contraction starts above the site of distension to propel the balloon toward the stomach. If one holds the balloon physically by a string attached to the balloon, the contraction above the balloon (esophageal propulsive force) may last several seconds. Contraction wave usually does not pass over the balloon, as long as the balloon remains distended. Distal to distended balloon, esophagus and LES remain inhibited or relaxed during the entire period of distension. Tertiary contractions of the esophagus are described by radiologists as the irregular contraction or indentations of the distal esophageal wall. Corkscrew esophagus, seen in diffuse esophageal spasm and achalasia esophagus, is also referred to as tertiary contraction. The counterpart of these contractions on manometry is not known but spontaneous simultaneous contractions seen on manometry have also been called as tertiary contractions.

Copyright © 2011 by Morgan & Claypool Life Sciences.
Bookshelf ID: NBK54271

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