What substance does the pancreas secrete to neutralize the pH of the chyme from the stomach?

The pancreas secretes bicarbonate ions to neutralize the acidic chyme that enters the small intestine from the stomach. Chyme, which is a mixture of partially digested food and stomach acids, is highly acidic due to the presence of hydrochloric acid secreted in the stomach. This acidity is harsh for the digestive enzymes active in the small intestine, which function optimally at a neutral to slightly alkaline pH.

Bicarbonate ions act as a buffering agent, raising the pH of the chyme and creating a more suitable environment for these enzymes to work effectively. The proper pH is crucial for the functionality of enzymes that facilitate digestion in the small intestine, including pancreatic enzymes that further break down carbohydrates, proteins, and fats.

The other substances listed do not serve this neutralizing function. Hydrochloric acid is produced in the stomach and contributes to acidity rather than neutralizing it. Insulin is a hormone produced by the pancreas that regulates blood sugar levels and does not play a role in neutralizing stomach acid. Pepsin is an enzyme activated in the acidic environment of the stomach for protein digestion, but it is not involved in neutralizing pH in the small intestine.