What is the effect of segmental contractions on chyme exposure?

• A. Propel chyme rapidly toward the rectum
• B. Generate long-distance peristaltic waves
• C. Enhance the amount of time the chyme is exposed to the villi for absorption
• D. Increase gastric emptying

Answer: (C)

Segmental contractions mix chyme by causing circular muscle segments to contract in a back-and-forth pattern. This churning increases the contact time between the chyme and the absorptive villi, allowing more nutrients to be exposed to the mucosa for absorption. They’re not about rapid forward propulsion or long-distance waves—that’s the job of peristalsis—and they don’t affect gastric emptying, which is controlled by the stomach. So the key effect is enhancing the time chyme spends exposed to the villi for absorption.