mucus, and surrounded by muscles that push food to
the stomach by sequential waves of contraction (peri-
stalsis). The lower esophageal sphincter (LES) is a
thick band of muscles that encircles the esophagus
just above the uppermost part of the stomach. This
sphincter is usually tightly closed and normally opens
only when food passes from the esophagus into the
stomach. Thus, the contents of the stomach are nor-
mally kept from moving back into the esophagus.
The stomach has a thick mucous coating that
protects it from the strong acid it secretes into its
interior when food is present, but the much thinner
esophageal coating doesn’t provide protection against
acid. Thus, if the LES opens inappropriately or fails to
close completely, and stomach contents leak into the
esophagus, the esophagus can be burned by acid. The
resulting burning sensation is called heartburn.
Occasional heartburn has no serious long-lasting
effects, but repeated episodes of gastroesophageal
reflux can ultimately lead to esophageal inflammation
(esophagitis) and other damage. If episodes occur
more frequently than twice a week, and the esophagus
is repeatedly subjected to acid and digestive enzymes
from the stomach, ulcerations, scarring, and thicken-
ing of the esophagus walls can result. This thickening
of the esophagus wall causes a narrowing of the inte-
rior of the esophagus. Such narrowing affects swal-
lowing and peristaltic movements. Repeated irritation
can also result in changes in the types of cells that line
the esophagus. The condition associated with these
changes is termed Barrett’s syndrome and can lead to
esophageal cancer.
Causes and symptomsCauses
A number of different factors may contribute to
LES malfunction with its consequent gastroesopha-
geal acid reflux:
The eating of large meals that distend the stomach
can cause the LES to open inappropriately.
Lying down within two to three hours of eating can
cause the LES to open.An illustration of foaming antacid on top of the contents of
a human stomach. Heartburn is caused by a backflow of
the stomach’s acidic contents into the esophagus, causing
inflammation and a sense of pain that can rise to the
throat.(Illustration by John Bavosi, Custom Medical Stock Photo,
Inc. Reproduced by permission.)
KEY TERMS
Barrett’s syndrome—Also called Barrett’s esopha-
gus or Barrett’s epithelia, this is a condition where
the squamous epithelial cells that normally line the
esophagus are replaced by thicker columnar epi-
thelial cells.
Digestive enzymes—Molecules that catalyze the
breakdown of large molecules (usually food) into
smaller molecules.
Esophagitis—Inflammation of the esophagus.
Fundoplication—A surgical procedure that
increases pressure on the LES by stretching and
wrapping the upper part of the stomach around
the sphincter.
Gastroesophageal reflux—The flow of stomach
contents into the esophagus.
Hiatus hernia—A protrusion of part of the stomach
through the diaphragm to a position next to the
esophagus.
Metabolic—Refers to the chemical reactions in liv-
ing things.
Mucus—Thick, viscous, gel-like material that func-
tions to moisten and protect inner body surfaces.
Peristalsis—A sequence of muscle contractions
that progressively squeeze one small section of
the digestive tract and then the next to push food
along the tract, something like pushing toothpaste
out of its tube.
Scleroderma—An autoimmune disease with many
consequences,including esophagealwallthickening.
Squamous epithelial cells—Thin, flat cells found in
layers or sheets covering surfaces such as skin and
the linings of blood vessels and esophagus.
Ulceration—An open break in surface tissue.Heartburn