Clinical meaning
Barrett esophagus is a premalignant condition in which the normal stratified squamous epithelium lining the distal esophagus undergoes metaplastic transformation to specialized intestinal-type columnar epithelium containing goblet cells. This process, known as intestinal metaplasia, is the body's adaptive response to chronic injury from gastroesophageal reflux disease (GERD). Understanding the cellular progression from normal esophageal tissue to Barrett esophagus and potentially to esophageal adenocarcinoma requires knowledge of the underlying mechanisms at each stage. The normal esophagus is lined by nonkeratinized stratified squamous epithelium, which is designed to withstand mechanical abrasion from food bolus transit but is poorly equipped to resist chemical injury from gastric acid and bile salts. The gastroesophageal junction (GEJ), also called the Z-line or squamocolumnar junction, marks the transition point between the squamous epithelium of the esophagus and the columnar epithelium of the stomach. In GERD, the lower esophageal sphincter (LES) fails to maintain adequate pressure, allowing gastric contents (hydrochloric acid with pH 1-2, pepsin, and bile acids) to reflux into the distal esophagus. The LES is a physiologic sphincter rather than a true anatomic sphincter; its tone...