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U N I T 8
Gastrointestinal and Hepatobiliary Function
Hiatal Hernia
Hiatal hernia is characterized by a protrusion or hernia-
tion of the stomach through the esophageal hiatus of the
diaphragm. There are two anatomic patterns of hiatal
herniation: sliding (axial) and paraesophageal (nonax-
ial).
6
The sliding hiatal hernia is characterized by a bell-
shaped protrusion of the stomach above the diaphragm
(Fig. 29-1A). Small sliding hiatal hernias are common
and considered to be of no significance in asymptom-
atic people. In paraesophageal hiatal hernias a separate
portion of the stomach, usually along the fundus of the
stomach, enters the thorax through a widened open-
ing (Fig. 29-1B). The hernia progressively enlarges and
increases in size. In extreme cases, most of the stomach
herniates into the thorax. Large paraesophageal hernias
may require surgical treatment.
Gastroesophageal Reflux
The term
reflux
refers to backward or return move-
ment. In the context of gastroesophageal reflux, it refers
to the backward movement of gastric contents into the
esophagus, a condition that causes heartburn or pyro-
sis. Most people experience heartburn occasionally as a
result of reflux. Such symptoms usually occur soon after
eating, are short lived, and seldom cause more serious
problems.
The lower esophageal sphincter regulates the flow of
food from the esophagus into the stomach. Both inter-
nal and external mechanisms function in maintaining
the antireflux function of the lower esophageal sphinc-
ter. The circular muscles of the distal esophagus con-
stitute the internal mechanisms, and the portion of the
diaphragm that surrounds the esophagus constitutes the
external mechanism (Fig. 29-2). The oblique muscles
of the stomach, located below the lower esophageal
sphincter, form a flap that contributes to the antireflux
function of the internal sphincter. Relaxation of the
lower esophageal sphincter is a brain stem reflex that
is mediated by the vagus nerve in response to a number
of afferent stimuli. Transient relaxation with reflux is
common after meals. Gastric distention and meals high
in fat increase the frequency of relaxation. Normally,
refluxed material is returned to the stomach by second-
ary peristaltic waves in the esophagus, with swallowed
saliva neutralizing and washing away the refluxed acid.
Gastroesophageal Reflux Disease
The persistent reflux of gastric contents into the esoph-
agus is referred to as
gastroesophageal reflux disease
(GERD).
8–10
It is thought to be associated with a weak
or incompetent lower esophageal sphincter that allows
reflux to occur, the irritant effects of the refluxate, and
decreased clearance of the refluxed acid from the esopha-
gus after it has occurred. In most cases, reflux occurs dur-
ing transient relaxation of the esophagus. Delayed gastric
emptying also may contribute to reflux by increasing gas-
tric volume and pressure. Esophageal mucosal injury may
occur and is related to the destructive nature of the reflux-
ate and the amount of time it is in contact with mucosa.
The mucosa is partially protected by mucin and alkaline
secretions from the submucosal glands. Injury occurs
when the reflux episodes are frequent and prolonged.
Agents that decrease the tone of the lower esophageal
Body of
stomach
Diaphragm
Stomach
Esophagus
Thorax
A
Abdomen
Body of
stomach
Diaphragm
Stomach
Esophagus
Thorax
B
Abdomen
FIGURE 29-1.
Hiatal hernia.
(A)
Sliding hiatal hernia.
(B)
Paraesophageal hiatal hernia.
Diaphragm
Esophagitis
Erosive
esophagitis
Esophageal
stricture
Incomplete
closure of
lower
esophageal
sphincter
Acid reflux
Stomach
FIGURE 29-2.
Gastroesophageal junction and site of
gastroesophageal reflux. (From Anatomical Chart Company.
Atlas of Pathophysiology. Springhouse, PA: Springhouse;
2004:171.)
