What type of epithelium lines the esophagus, and what is the functional significance of the lower esophageal sphincter (LES)?

• A. Keratinized stratified squamous epithelium; LES contracts to prevent reflux.
• B. Non-keratinized stratified squamous epithelium; LES prevents reflux of gastric contents and relaxes during swallowing.
• C. Simple columnar epithelium; LES has no significance.
• D. Pseudostratified ciliated columnar; LES opens during swallowing.

Answer: (B)

The esophagus is lined with non-keratinized stratified squamous epithelium, which provides durable protection against the rough, abrasive passage of food while staying moist. At the junction with the stomach lies the lower esophageal sphincter, a thickened ring of smooth muscle that maintains a high resting tone to act as a barrier against reflux of gastric contents. When swallowing begins, the LES relaxes briefly to allow the bolus to enter the stomach, then it tightens again to prevent backward flow. This coordination is crucial: a properly functioning LES stops reflux between swallows, while its relaxation during swallowing enables smooth passage of food. The other options don’t fit because they describe epithelium that isn’t present in the esophagus (keratinized, simple columnar, or pseudostratified ciliated types) and misstate the LES role.