How is chyme released into the duodenum?

• A. Through the ileocecal valve
• B. Only during sleep
• C. Intermittently via the pyloric sphincter
• D. Continuously via the pyloric sphincter

Answer: (C)

The key idea is that stomach contents move into the first part of the small intestine in small, controlled bursts rather than all at once or continuously. The pyloric sphincter at the stomach’s outlet opens briefly with each wave of stomach contractions, letting a small amount of chyme pass into the duodenum. It then closes again, so the next portion is held back until the next contraction. This intermittent release gives the duodenum time to mix the chyme with pancreatic juice and bile and to start neutralizing the stomach acid.

Signals from the duodenum help regulate this process. If the chyme is very acidic or rich in fat, hormones like secretin and CCK rise and slow gastric emptying, keeping the pyloric sphincter closed longer to avoid overwhelming the duodenum.

Why the other ideas don’t fit: the ileocecal valve controls movement from the ileum to the large intestine, not the release of chyme into the duodenum; chyme release is not tied to sleep—it's part of active digestion; and it is not continuous—it's released in small bursts as the stomach contracts.