C h a p t e r 2 9
Disorders of Gastrointestinal Function
701
Disorders of the Stomach
The stomach is a reservoir for contents entering the
digestive tract. It lies in the upper abdomen, anterior to
the pancreas, splenic vessels, and left kidney. Anteriorly,
the stomach is bounded by the anterior abdominal wall
and the left inferior lobe of the liver. While in the stom-
ach, food is churned and mixed with hydrochloric acid
(HCl) and pepsin before being released into the small
intestine. Normally, the mucosal surface of the stom-
ach provides a barrier that protects it from the hydro-
chloric acid and pepsin contained in gastric secretions.
Disorders of the stomach include gastritis, peptic ulcer,
and gastric carcinoma.
Gastric Mucosal Barrier
The stomach lining usually is impermeable to the acid
it secretes, a property that allows the stomach to con-
tain acid and pepsin without having its walls digested.
Several factors contribute to the protection of the gastric
mucosa, including an impermeable epithelial cell surface
covering, coupled secretion of hydrogen (H
+
) and bicar-
bonate (HCO
3
–
) ions, and the characteristics of gastric
mucus.
16
These mechanisms are collectively referred to
as the
gastric mucosal barrier.
The cells of the epithelial layer of the stomach are
connected by tight junctions that prevent acid pen-
etration, and they are covered with an impermeable
hydrophobic lipid layer that prevents diffusion of ion-
ized water-soluble molecules. Aspirin, which is nonion-
ized and lipid soluble in acid solutions, rapidly diffuses
across this lipid layer, increasing mucosal permeability
and damaging epithelial cells.
16,17
Gastric irritation and
occult bleeding occur in a significant number of persons
who take aspirin on a regular basis. Alcohol, which
is lipid soluble, can also disrupt the mucosal barrier.
When there is reflux of duodenal contents in the stom-
ach, bile acids also can attack the lipid components of
the mucosal barrier and produce gastric irritation.
Normally, the secretion of HCl by the parietal cells of
the stomach is accompanied by secretion of HCO
3
–
(see
Chapter 28, Fig. 28-9). For every H
+
that is secreted, a
HCO
3
–
is produced, and as long as HCO
3
–
production
is equal to H
+
secretion, mucosal injury does not occur.
Changes in gastric blood flow, as in shock, tend to
decrease HCO
3
–
production. This is particularly true in
situations in which decreased blood flow is accompanied
by acidosis.
16
Prostaglandins, chemical mediators derived
from cell membrane lipids, play an important role in
protecting the gastric mucosa from injury.
6
The prosta-
glandins exert their effects through several mechanisms,
including improved mucosal blood flow, decreased acid
secretion, increased bicarbonate secretion, and enhanced
mucus production. The fact that drugs such as aspirin
and the nonsteroidal anti-inflammatory drugs (NSAIDs)
inhibit prostaglandin synthesis contributes to their abil-
ity to produce gastric mucosal irritation and injury.
Gastritis
Gastritis refers to inflammation of the gastric mucosa.
There are many causes of gastritis, most of which can be
associated with either acute or chronic gastritis.
Acute Gastritis
Acute gastritis is characterized by an acute mucosal
inflammatory process, usually transient in nature. The
inflammation may be accompanied by hemorrhage
into the mucosa of the stomach and, in severe cases, by
sloughing of the superficial mucosa and acute gastric
bleeding. The condition is most commonly associated
with local irritants such as aspirin or other NSAIDs,
alcohol, or bacterial toxins.
6,17
Oral administration of
corticosteroid drugs, which inhibit prostaglandin syn-
thesis, may also cause acute hemorrhagic gastritis. Any
serious illness or trauma that is accompanied by pro-
found physiologic stress renders the gastric mucosa
more vulnerable to acute hemorrhagic gastritis (dis-
cussed under stress ulcers).
7
Uremia, treatment with can-
cer chemotherapy drugs, and gastric radiation are other
causes of acute gastritis.
The complaints of persons with acute gastritis vary.
Persons with aspirin-related gastritis can be totally
unaware of the condition or may complain only of heart-
burn or sour stomach. Gastritis associated with exces-
sive alcohol consumption is often a different situation;
it often causes transient gastric distress, which may lead
to vomiting and, in more severe situations, to bleeding
and hematemesis. Gastritis caused by the toxins of infec-
tious organisms, such as the staphylococcal enterotox-
ins, usually has an abrupt and violent onset, with gastric
distress and vomiting ensuing approximately 5 hours
after the ingestion of a contaminated food source. Acute
gastritis usually is a self-limiting disorder, with complete
regeneration and healing of the gastric mucosa occur-
ring within several days of removal of the inciting agent.
Chronic Gastritis
Chronic gastritis is characterized by the absence of
grossly visible erosions and the presence of chronic
inflammatory changes, eventually leading to atrophy of
■■
Gastroesophageal reflux is a common problem
in infants and children. Symptoms are typically
mild and abate in most children by 2 years of
age. However, some infants and small children
have significant reflux that interferes with
feeding, causes esophagitis, and results in
respiratory symptoms and other complications.
■■
Cancer of the esophagus is a relatively
uncommon form of cancer that is commonly
linked to gastroesophageal reflux and Barrett
esophagus (adenocarcinoma) or alcohol and
tobacco use (squamous cell carcinoma).
