The duodenum of a person was surgically removed. Which of the following substances would have their digestion affected?

Analyze the question: The duodenum is the first part of the small intestine. We need to know which food substances depend on it for digestion.

Concept: The duodenum is where food from the stomach (chyme) meets the major digestive secretions:

• Pancreatic juice (enters through the pancreatic duct) contains: • Pancreatic amylase, which digests starch to maltose • Trypsin, which digests proteins and peptones to peptides • Lipase, which digests lipids (fats) to fatty acids and glycerol
• Bile (from the liver, stored in the gall bladder) emulsifies fats, which helps lipase work.
• The duodenum also releases hormones, such as secretin and CCK, that control these secretions.

Solution:

• Starch: pancreatic amylase acts in the duodenum, so it is affected.
• Protein: trypsin and other pancreatic proteases act in the duodenum, and the stomach's pepsin only partly digests protein, so it is affected.
• Lipids: bile and pancreatic lipase act in the duodenum, so they are affected.

Options A and B each leave out a substance that is affected. Option C includes maltose, but maltose is digested by maltase in the ileum, which comes after the duodenum, so it is not primarily affected. Option C also leaves out lipids.

Option D, starch, protein and lipids, covers all three major food classes whose digestion depends on duodenal secretions.

Tip: Remember that the duodenum is the "meeting point" where bile and pancreatic juice join the food. Bile and pancreatic juice together handle carbohydrates, proteins and fats. Final sugar digestion (maltose, sucrose, lactose) happens at the intestinal wall, in the ileum.