• Describe the functional anatomy of the esophagus
and related structures, and their innervation
• Understand the roles played by the oral cavity, pharyngeal structures,and
esophagus in transferring food from the mouth to the stomach during
• Describe the roles played by the upper and lower esophageal sphincters
in esophageal motility
• Understand how the relaxation of these structures is coordinated
with the swallow
• Describe how the lower esophageal sphincter protects against
reflux of gastric contents
• Understand how belching occurs
• Discuss disease states in which esophageal motility and/or swallowing
The esophagus is a muscular tube that serves
to transfer food from the mouth to the stomach. Under normal circumstances,
food resides in the esophagus for only a few seconds and thus there is
no time for it to be acted upon by any esophageal secretions. Thus,
an understanding of the physiology of the esophagus relates primarily
to its motility functions. In addition to moving the food along
its length in the process of swallowing, the movements of the esophagus
and related oral and pharyngeal structures must be carefully regulated
to avoid misdirection of the food into the respiratory tract, or
respired air into the digestive system. At rest, the esophagus is
a relaxed structure that is closed off at both ends by sphincters—
the upper and lower esophageal sphincters, respectively. These sphincters
not only cooperate in the act of swallowing, or deglutition,
but also prevent backflow of gastric contents into the esophageal
lumen or oral cavity. However, under specific circumstances, the
esophagus does allow for retrograde movement. This occurs normally
for air swallowed with the meal, in the process of belching, or
abnormally during vomiting. During retrograde movement in humans
and most mammals, the esophagus itself is a passive conduit; i.e.,
there are no specific motility functions that propel vomitus or
air along the length of the tube. Note that the process of vomiting
will be discussed in detail in Chapter 8.
The process of swallowing, as well as other
esophageal motility functions, is under close regulatory control.
Swallowing can be initiated voluntarily, but thereafter reflects
an automatic reflex that involves, sequentially, impulses from the
brainstem, processing of this information through vagal centers
in the central nervous system, direct effects of parasympathetic
vagal efferents on esophageal muscle layers, and relay of information
via the enteric nervous system (Figure 7–1). Movement of materials
along the length of the esophagus is aided by gravity, but predominantly depends
on a coordinated series of muscle contractions and relaxations that
make up the propulsive motility pattern known as peristalsis.
Functional anatomy and innervation of the esophagus. ...
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