In the small intestine, which section is primarily responsible for chemical digestion?

• A. Jejunum
• B. Ileum
• C. Duodenum
• D. Cecum

Answer: (C)

The duodenum is where chemical digestion primarily occurs in the small intestine. As chyme from the stomach enters this first segment, it mixes with pancreatic juice rich in enzymes and bicarbonate and with bile. This combination neutralizes stomach acid and provides the conditions and enzymes needed to break down foods: carbohydrates are split into simple sugars, proteins into amino acids, and fats into fatty acids and monoglycerides. The lining of the duodenum also has brush-border enzymes that complete digestion at the cell surface. After this initial chemicall processing, most absorption takes place further along in the jejunum and ileum. The cecum, by contrast, is part of the large intestine and not involved in small-intestine chemical digestion.