Which substance neutralizes stomach acid in the duodenum?

The substance that neutralizes stomach acid in the duodenum is pancreatic juice. When chyme leaves the stomach and enters the duodenum, it is highly acidic due to the presence of hydrochloric acid from gastric secretions. This acidity can be harmful to the intestinal lining and needs to be neutralized for proper digestion and enzymatic activity.

Pancreatic juice contains bicarbonate ions, which are alkaline, and these bicarbonates effectively raise the pH of the chyme in the duodenum, neutralizing the stomach acid. Additionally, pancreatic juice also contains various digestive enzymes that play crucial roles in carbohydrate, protein, and fat digestion.

Bile, while important for emulsifying fats, does not play a direct role in neutralizing stomach acid. Hydrochloric acid is found in the stomach and contributes to acidity, but it does not neutralize anything in the duodenum. Lipase is an enzyme responsible for fat digestion and is present in pancreatic juice, but it also does not neutralize acid; its primary function is to break down fats. Therefore, pancreatic juice is the key substance that neutralizes stomach acid in the duodenum, enabling a suitable environment for further digestion.