In the area of the cardia, the two-layer muscles of the esophagus turns to three-layer muscles. By their contractions, the spirally continuing muscle loops ("Musculus sphincter cardiae") in this area prevent a reflux of the stomach contents into the esophagus.
In histology, one can see the transition from multilayer uncornified squamous epithelium of the esophagus to unilayer columnar epithelium of the stomach. The mucous glands in the area of the cardia are called cardia glands.
Source: Endoskopie-Atlas
