The structure and function of the distal esophagus and its junction with the stomach have been the subject of much investigation. This has led to an improved under standing of clinical ailments such as achalasia, hiatal hernia, Barrett esophagus, esophagitis, and peptic ulcer of the esophagus. The longitudinal muscle coat of the esophagus extends inferiorly and continues over the surface of the stomach as the outer longitudinal layer of the smooth muscle of the stomach. The socalled inner circular layer of esophageal musculature, which at this point is spiral in character, also continues over the stomach but divides, in the region of the cardia, into the middle circular layer of the gastric musculature and the inner oblique layer of muscle fibers. The esophagus’s inner oblique muscle fibers pass slinglike across the cardiac notch, whereas the middle circular fibers pass more or less horizontally around the stomach. These two layers of muscle fibers thus cross each other at an angle, forming a muscular ring, which became known as the collar of Helvetius. To the left of the esophagus the oblique fibers form sling fibers that project from the anterior wall of the stomach to the posterior wall, making a tight bend around the cardial notch. On the opposite side of the cardiac region, the circular layer has substantial clasp fibers that pinch and narrow the cardiac region. Acting together, the sling and clasp fibers help prevent gastric reflux and form a functional, but not anatomic, lower esophageal sphincter.
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.
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