Which structure is the muscular ring that regulates emptying of the stomach into the small intestine?

• A. Pyloric sphincter
• B. Cardioesophageal sphincter
• C. Esophageal sphincter
• D. Anal sphincter

Answer: (A)

Gate between the stomach and the small intestine: the pyloric sphincter is a ring of smooth muscle at the distal end of the stomach that regulates the passage of chyme into the duodenum. It stays mostly closed to slow emptying and opens briefly in response to coordinated gastric peristalsis, allowing small amounts of chyme to enter the small intestine. This controlled release protects the duodenum from being overwhelmed and helps coordinate digestion with hormone signals that modulate motility. Other sphincters listed have different roles: the lower esophageal (cardioesophageal) sphincter prevents reflux from the stomach into the esophagus; the esophageal sphincter is another name for that region; the anal sphincter controls defecation. The pyloric sphincter is the one that directly regulates gastric emptying into the small intestine.