Answer :
Final answer:
Bicarbonate that protects the duodenum from peptic ulcers comes from pancreatic juice, intestinal juice, and saliva but not from gastric juice, which is responsible for adding acidity to the stomach contents.
Explanation:
The bicarbonate that protects the duodenum from peptic ulcers is secreted by several components of the digestive system, with the exception of gastric juice. The pancreatic juice, which the pancreas produces over a liter each day, contains not only several digestive enzymes but also bicarbonate that helps neutralize the acidic chyme entering the duodenum from the stomach. This bicarbonate is crucial as it inactivates pepsin and provides an optimal environment for other digestive enzymes. Additionally, the intestinal juice secreted by the lining of the duodenum, as well as bile from the liver, aid in this neutralization process. However, gastric juice secreted by the stomach mainly contains hydrochloric acid and pepsinogen, and thus does not contribute to the bicarbonate supply; in fact, it adds to the acidity that needs to be neutralized.
Another source of bicarbonate is the alkaline mucus produced by Brunner's glands in the duodenum's submucosa. Saliva, produced by salivary glands such as the parotid gland, also contains small amounts of bicarbonate. However, as stated, the correct answer to which does not contribute bicarbonate for the protection of the duodenum is option 3: gastric juice.
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