Ganong's Review of Medical Physiology, 23rd Edition

472 SECTION V Gastrointestinal Physiology
Tongue
Hard palate
Food
Epiglottis
Soft palate
Glottis
Upper
esophageal
Trachea
Esophagus
sphincter
(a) (b) (c)
FIGURE 28–3 Movement of food through the pharynx and upper esophagus during swallowing. (a) The tongue pushes the food bolus
to the back of the mouth. (b) The soft palate elevates to prevent food from entering the nasal passages. (c) The epiglottis covers the glottis to
prevent food from entering the trachea and the upper esophageal sphincter relaxes. (d) Food descends into the esophagus.
at the junction with the stomach (intrinsic sphincter). Fibers
of the crural portion of the diaphragm, a skeletal muscle, surround
the esophagus at this point (extrinsic sphincter) and exert
a pinchcock-like action on the esophagus. In addition, the
oblique or sling fibers of the stomach wall create a flap valve
that helps close off the esophagogastric junction and prevent
regurgitation when intragastric pressure rises.
The tone of the LES is under neural control. Release of acetylcholine
from vagal endings causes the intrinsic sphincter to
Lower
esophageal
sphincter
Internal
External
Phrenoesophageal
ligament
Pharynx
Squamocolumnar
junction
contract, and release of NO and VIP from interneurons innervated
by other vagal fibers causes it to relax. Contraction of
the crural portion of the diaphragm, which is innervated by
the phrenic nerves, is coordinated with respiration and contractions
of chest and abdominal muscles. Thus, the intrinsic
and extrinsic sphincters operate together to permit orderly
flow of food into the stomach and to prevent reflux of gastric
contents into the esophagus (Clinical Box 28–1).
Stomach
Longitudinal muscle
Circular muscle
Costal part
Crural part
FIGURE 28–4 Esophagogastric junction. Note that the lower esophageal sphincter (intrinsic sphincter) is supplemented by the crural portion
of the diaphragm (extrinsic sphincter), and that the two are anchored to each other by the phrenoesophageal ligament. (Reproduced with
permission, from Mittal RK, Balaban DH: The esophagogastric junction. N Engl J Med 1997;336:924. Copyright © 1997 by the Massachusetts Medical Society. All rights reserved.)
(d)
Diaphragm
Sling fibers