The GEJ is normally mostly intra-abdominal and is 3-4 cm in length. To some extent, the esophagus slides in and out of the abdomen during respiration and when there is elevation of intra-abdominal pressure.
It is comprised of two histologically distinct areas:
- stratified squamous epithelium (same as the esophageal folds superiorly)
- columnar epithelium (same as the gastric rugae inferiorly)
Where these two distinct areas join, there is an abrupt but non-linear change in the mucosal layer: this is called the Z-line. The non-linear, zig zagging nature of the Z-line explains that the GEJ can be several centimeters in length, while the histological transition from esophageal folds to gastric rugae is abrupt.