What is the role of an inadequate control of the lower esophageal sphincter (structure, position, innervation, hormonal control)?
O. Korn, A. Csendes, I. Braghetto (Santiago)
Anatomy of the lower esophageal sphincter
There are few structures in the human anatomy more debated than the existence of an anatomical sphincter at the level of the gastroesophageal junction (GEJ) [1]. However, manometric studies have shown a clear sphincterian mechanism at GEJ [2, 3], which constitutes a mayor barrier against reflux of gastric content into the esophagus [4]. The main problem until recent years was to demonstrate an anatomical structure on distal esophagus that matched to the classical concept of a sphincter, that is, a distinct ring of a thickened circular muscle separated from the adjoining muscles by connective tissue septums [1, 5]. Such a structure has not been demonstrated at GEJ. Winans challenged the classic concept of a circular sphincter in 1977, when he demonstrated a manometric asymmetry of the lower esophageal sphincter (LES) [6]. Anatomical studies from Liebermann et al. [7], have demonstrated a particular disposition and an increment in the amount of the fibers of the internal muscular sheath at the GEJ. This internal muscular coat does not form a ring or circular muscle, instead, it forms a layer of semicircular fibers or clasps oriented transversally, which are open at the anterior and posterior aspect of the esophagus. At the GEJ, these clasps fibers are inserted firmly into the submucous connective tissue at the margin of contact with the oblique fibers. On the opposite side, the oblique fibers replace progressively the short transverse muscle bundles of the esophagus at the greater curvature and they build a muscular sling structure that covers the anterior and posterior wall of the stomach, the so-called "gastric sling fibers" (Figure 1). These oblique fibers are a muscular bundle of 3 cm width and cover an area that starts 1.5 cm above the angle of His and ascends forming part of the distal end of the esophagus. In this way they surround the GEJ at the greater curvature and its two arms run parallel to the lesser curvature in direction to the antrum. The end of the clasp fibers border at almost a right angle at the lateral margin of the sling fibers. The muscular fibers of both clasps and sling fibers increase in number and concentration across the GEJ determining a subtle thickening of the wall at this level. This thickening is asymmetric and is more prominent at the greater curvature side at approximately 1 cm above the angle of His. A recent study has shown that the manometric three-dimensional pressure images of the lower esophageal high-pressure zone correlates with the radial and longitudinal asymmetry of muscular structures at the GEJ [8].
Therefore, the LES is not an annular sphincter, but rather formed by two muscles bundles, which are acting complementary: the "clasp" and the "oblique" muscular fibers (Figure 2).
...
only available for members ()
