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GASTROINTESTINAL PHYSIOLOGY

Lowrr Esophageal Sphincter

mm Mr

Normal LES tonę is physiologic bamer to reflux

from nostril

I F$, a complcx ot myogenic, neural, and hormonal factors. acts to maintain pressure of 12-20 mm Hg in distal 3-5 cm of esophagus

Decreased LES tonę or shorlened LES segment allows acid reiki*

Myogenic

Figurę 7.3 Lower Esophageal Sphinctfr_

Perislalsis is initiated by the voluntary action ot swallowing, which is controlled by efferent fibers in the vagus. Vagal fibers synapsę on nei> rons within the mycnteric. plexus (enteric nervou$ system) of the esophagus. The myenteric plexus directly Controls the peristaltic wave by altematively relaxing then contracting the musdes of the esophagus. The smooth musde im reases in thickness at the junction with the stornach and lomis tlie lower esophageal sphincter (LES). NormalK, the resting tonę of the LES is high, which prevenłs the reflux of gastru contents into ihe esophagus. As the peristaltic wave carries a bolus < tood to the stornach, release of nitnc oxide (NO) and vasoac.tivc intestinal peptide tVIP) from neurons of the myenteric plexus cause-relaxation of the LES, and food enters the stornach.

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