Final answer:
The pancreas secretes a bicarbonate-ion-rich fluid in response to secretin to neutralize the acidity of chyme.
Step-by-step explanation:
In response to the hormone secretin, the pancreas secretes a fluid that is rich in bicarbonate ion. This bicarbonate is an alkali that neutralizes the highly acidic chyme coming from the stomach. The pancreatic juices play a critical role in digestion, not only by neutralizing acids but also by containing enzymes necessary for breaking down proteins and carbohydrates.