What structure prevents food from backing up into the esophagus?

• A. Pyloric sphincter
• B. Cardiac sphincter
• C. Epiglottis
• D. Sphincter of Oddi

Answer: (B)

The lower esophageal sphincter, often called the cardiac sphincter, prevents materials from the stomach from moving back up into the esophagus. It’s a ring of smooth muscle at the junction of the esophagus and stomach that stays contracted to form a seal. When you swallow, it relaxes just long enough for the food to enter the stomach, then tightens again to maintain the barrier. If this sphincter is weak or relaxes too often, stomach contents can reflux into the esophagus, causing heartburn. The other options have different roles: the pyloric sphincter sits between the stomach and the duodenum and regulates gastric emptying; the epiglottis protects the airway, not the esophagus; and the Sphincter of Oddi controls bile and pancreatic juice entry into the small intestine.