Which condition is characterized by the backflow of stomach contents into the esophagus?

The condition characterized by the backflow of stomach contents into the esophagus is gastro-esophageal reflux disease (GERD). This occurs when the lower esophageal sphincter, which normally prevents the backflow of stomach contents, becomes weakened or relaxes inappropriately. As a result, digestive acids and food can travel back up into the esophagus, leading to symptoms such as heartburn, regurgitation, and discomfort.

The other conditions listed do not primarily involve the backflow of stomach contents. Peptic ulcer disease involves sores on the lining of the stomach or duodenum and is associated with pain and digestive issues but does not typically cause the reverse flow characteristic of GERD. Diverticulitis is inflammation of diverticula in the colon and is more related to bowel function and pain rather than esophageal reflux. Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder that affects bowel habits and pain but does not directly involve the return of stomach contents to the esophagus. Therefore, GERD is distinctly identified by this specific flow reversal, making it the correct choice.