How is the pH of chyme adjusted as it enters the duodenum?

• A. By acid secretion from the stomach to reduce pH.
• B. Pancreatic bicarbonate neutralizes acidic chyme, increasing pH toward neutrality.
• C. Bile salts actively raise pH.
• D. Saliva neutralizes chyme before entering the duodenum.

Answer: (B)

Chyme entering the duodenum is very acidic, so it needs buffering to protect the lining and to let digestive enzymes work. The main way this pH rise happens is the release of pancreatic juice rich in bicarbonate into the duodenum. The bicarbonate neutralizes the stomach acid, pushing the pH toward neutral, which is the range in which pancreatic enzymes and other intestinal enzymes operate best. This buffering is a coordinated response to the acidic chyme, with secretin signaling the pancreas to release bicarbonate. While other factors like alkaline mucus from Brunner’s glands or bile salts play supportive roles, they don’t primarily raise the pH to the same extent. Saliva helps buffer in the mouth, not in the duodenum.