Examine a longitudinal section of the esophago-gastric junction (slide 142). Note the abrupt, major change in the lining epithelium and the effect this has on the underlying mucosa (Fig. 15-17).

What do the different epithelial linings in the esophagus and stomach indicate about the functions of these two organs?

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.