Maintenance of the Body
the abdomen. It joins the stomach at the
the abdominal cavity. Te cardial oriﬁce is surrounded by the
which is a
sphincter (see Figure 23.13). Tat is,
it acts as a sphincter, but the only structural evidence of this
sphincter is a slight thickening of the circular smooth muscle
at that point. Te muscular diaphragm, which surrounds this
sphincter, helps keep it closed when food is not being swal-
lowed. Mucous cells on both sides of the sphincter help protect
the esophagus from reﬂux of stomach acid.
, the ﬁrst symptom of
gastroesophageal reﬂux disease
), is the burning, radiating substernal pain that occurs
when stomach acid regurgitates into the esophagus. Symptoms
are so similar to those of a heart attack that many ﬁrst-time suﬀer-
ers of heartburn are rushed to the emergency room. Heartburn
squamous epithelium well supplied with mucus-producing
glands. Te external muscle layer consists of two
layers. Te cells of the inner layer run longitudinally. Tose of
the outer layer, the
muscles, encircle the
wall like three stacked ﬁsts (see Figure 10.9c). Contractions of
these muscles propel food into the esophagus below.
ah-gus; “carry food”) is a muscular tube
about 25 cm (10 inches) long and is collapsed when not involved
in food propulsion
. A±er food moves through
the laryngopharynx, it is routed into the esophagus posteriorly
as the epiglottis closes oﬀ the larynx to incoming food.
As shown in Figure 23.1, the esophagus takes a fairly straight
course through the mediastinum of the thorax. It pierces the
diaphragm at the
tus; “gap”) to enter
epithelium of stomach
• Circular layer
• Longitudinal layer
Microscopic structure of the esophagus.
Cross-sectional view of the
esophagus taken from the region close to the stomach junction (10
). The muscularis is
composed of smooth muscle.
Longitudinal section through the esophagus-stomach junction
). Notice the abrupt transition from the stratiﬁed squamous epithelium of the esophagus
(top) to the simple columnar epithelium of the stomach (bottom).