Examine a longitudinal section of the esophago-gastric junction. Note the abrupt, major change in the lining epithelium and the effect this has on the underlying mucosa.

WWhat does the histology of the esophagus tell you about the protective functions of this organ?

Clinical note: If the muscularis of the lower esophagus fails to maintain the state of partial contraction that normally prevents reflux of the gastric contents upward, heartburn results. Since the esophageal mucosa lacks a thick blanket of protective mucus, acidic gastric juices irritate it, causing painful esophagitis. If chronic, this is called gastro-esophageal reflux disorder (GERD) and can lead to metaplasia of stratified squamous epithelium into a simple columnar, mucous epithelium. (Image courtesy of WebMD)

Now to the stomach.