Esophagogastric
Junction
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| Esophagogastric junction |
A gradual but moderate thickening
of both the socalled circular and longitudinal muscles takes
place in the lower end of the esophagus, commencing about 1 or 2 cm above the esophageal
hiatus through the diaphragm and extending to the cardia. This region of
thickened musculature has been termed the “esophagogastric vestibule” and this
region contracts and relaxes as a unit. It is believed that the bolus is
transiently arrested just above the esophageal hiatus by the tonicity of the
distal esophagus and, contrariwise, that its passage into the stomach is made
possible by the relaxation of the muscles working as an integrated or coordinated
unit. It is likewise believed that the contraction of the distal esophagus is one
of the important factors in the prevention of regurgitation from the stomach.
Other factors in the prevention of regurgitation are believed to be the
angulation of the esophagus as it passes through the diaphragm while passing
over into the stomach and a rosettelike formation of loose gastric mucosa at
the cardia. The possibility of sphincteric action of the diaphragm is debated,
although it is recognized that in deep inspiration, when the diaphragm is in
strong contraction, passage into the stomach may be impeded.
The mucosa of the esophagus is
smooth and rather pale in color. When the esophagus is contracted, the mucosa
is gathered up into irregular longitudinal folds. The gastric mucosa, on the
other hand, is a much deeper red in color, with welldefined folds, rugae, in
the lumen of the organ. The transition from esophageal to
gastric mucosa occurs rather sharply and is easily recognizable by a change in
epithelial color. This transition takes place along an irregular dentate or
zigzag line, sometimes called the Z line. The Z line marks the
transition from stratified squamous of the esophagus to simple columnar epithelium
of the stomach; it usually does not coincide with the anatomic border of the
cardia but is slightly superior to it, between the level of the cardia and the
esophageal hiatus. In some instances the gastric mucosa may extend for a
considerable distance into the esophagus.
In its passage through the
esophageal hiatus of the diaphragm, the esophagus is surrounded by the phrenicoesophageal
ligament, also known as the phrenoesophageal ligament or
diaphragmaticoesophageal ligament. The phrenicoesophageal ligament arises from
the circumference of the esophageal hiatus as an extension of the infradiaphragmatic
fascia, which is continuous with the transversalis fascia. At the margin
of the hiatus, it divides into an ascending limb and a descending
limb. The ascending limb passes superiorly through the esophageal hiatus
and surrounds the esophagus in a tentlike fashion. It extends for several
centimeters above the hiatus and inserts circumferentially into the adventitia
of the esophagus. The descending limb passes inferiorly and inserts around the
cardia deep to the peritoneum. The two limbs of the phrenicoesophageal ligament
form a space superficial to the esophagus, in which lies a ring of rather dense
fat. The function of the phrenicoesophageal ligament has been the subject of
much speculation. From its structure it certainly would seem to play, fixing
the distal esophagus in place while per mitting the limited excursion required
for respiration, deglutition, and postural changes. It also serves as an
additional means of preventing pressure transmission through the esophageal
hiatus. It may also in some manner take part in the closure or sphincteric
mechanism of the esophagus in connection with diaphragmatic action.
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Diaphragmatic crura and orifices
The configuration of the esophageal
hiatus of the diaphragm is interesting in that the distal esophagus is directed
toward the left yet the hiatus is formed almost entirely by the right crus
of the diaphragm; the left crus of the diaphragm plays no part in
the formation of the esophageal hiatus. One band of muscle fibers, originating
from the right crus, ascends and passes to the right of the esophagus. Another
band of muscle fibers, originating also from the right crus but more deeply,
ascends and passes to the left of the esophagus. These muscle bands overlap
scissorwise and are inserted into the central tendon of the diaphragm. Thus,
all the muscle fibers about the esophageal hiatus arise from the right crus of
the diaphragm. It is interesting to note that those fibers of the right crus
which pass to the right of the esophagus are innervated by the right phrenic
nerve, whereas those which pass to the left of the esophageal hiatus appear
to be innervated by a branch of the left phrenic nerve, as is also the
left crus itself. The right crus of the diaphragm is usually
considerably larger than is the left crus.
Occasionally, one may find what has
come to be known as the “muscle of Low.” This is a small band of muscle fibers
that originates from the left crus and crosses over to the right, passing
between the muscle fibers of the right crus to reach the central tendon in the
region of the foramen of the inferior vena cava. Somewhat more
frequently, a similar muscle bundle appears on the superior surface of the
diaphragm. More significant is the fact that, in a considerable number of
individuals, a variation may be found that has been described
as a “shift to the left.” In such cases fibers from the left crus of the
diaphragm enter into formation of the right side of the esophageal hiatus. In
some instances the muscles to the right of the esophageal hiatus may take
origin entirely from the left crus and those to the left of the hiatus entirely
from the right crus. The suspensory muscle of the duodenum (suspensory
ligament of the duodenum, ligament of Treitz) typically originates from the
fibers of the right crus of the diaphragm that pass to the right of the
esophagus.
Keyword : collar of helvetius
