What does the small intestine do?

What does the small intestine do?

• A. Digestion and nutrient absorption
• B. Water reabsorption
• C. Additional digestion of plant material
• D. Storage of bile

Answer: (A)

The main idea is that the small intestine is where most digestion and nutrient absorption happen. After chyme enters from the stomach, it mixes with bile and pancreatic juices. Enzymes from the pancreas and enzymes on the lining of the small intestine (brush-border and small-intestine enzymes) break down carbohydrates, proteins, and fats. The wall is lined with villi and microvilli, giving a huge surface area so nutrients can be absorbed efficiently into the blood (and lymph). In particular, most carbohydrate and protein digestion and nearly all vitamin and mineral absorption occur here, with the ileum also reabsorbing bile acids and vitamin B12. Water reabsorption does occur in the small intestine, but the primary job of this organ is digestion and absorption, not storage of bile—that happens in the gallbladder—and cellulose digestion from plant material is not a major function of the human small intestine.

The main idea is that the small intestine is where most digestion and nutrient absorption happen. After chyme enters from the stomach, it mixes with bile and pancreatic juices. Enzymes from the pancreas and enzymes on the lining of the small intestine (brush-border and small-intestine enzymes) break down carbohydrates, proteins, and fats. The wall is lined with villi and microvilli, giving a huge surface area so nutrients can be absorbed efficiently into the blood (and lymph). In particular, most carbohydrate and protein digestion and nearly all vitamin and mineral absorption occur here, with the ileum also reabsorbing bile acids and vitamin B12.

Water reabsorption does occur in the small intestine, but the primary job of this organ is digestion and absorption, not storage of bile—that happens in the gallbladder—and cellulose digestion from plant material is not a major function of the human small intestine.