The epithelium varies significantly along different parts of the GIT. In the esophagus, it is stratified squamous epithelium, which protects against mechanical abrasion. In the stomach, it changes to simple columnar epithelium, which secretes mucus and gastric juices. The small intestine also has simple columnar epithelium with microvilli to increase surface area for nutrient absorption. The large intestine returns to a simple columnar epithelium but with more goblet cells for mucus secretion.
