What features make the small intestine an efficient absorption site?

What features make the small intestine an efficient absorption site?

• A. Luminal folds, villi, microvilli
• B. Thick mucus barrier of the colon
• C. A flat surface with no folds
• D. Absorption occurs primarily in the stomach

Answer: (A)

Efficient absorption in the small intestine comes from massively increasing the surface area exposed to chyme. The luminal folds (plicae circulares) slow and mix contents, the villi extend into the lumen to provide numerous finger-like projections, and the microvilli on each enterocyte dramatically multiply the contact area at the brush border. This expanded surface, combined with a rich network of capillaries and lacteals inside each villus, plus brush-border enzymes on the enterocytes, enables nutrients to be efficiently digested, transported, and taken up into the blood or lymph. The thick mucus barrier of the colon and the idea that absorption occurs mainly in the stomach don’t apply to the small intestine’s architecture; a flat surface with no folds would greatly reduce contact with the contents and slow absorption.

Efficient absorption in the small intestine comes from massively increasing the surface area exposed to chyme. The luminal folds (plicae circulares) slow and mix contents, the villi extend into the lumen to provide numerous finger-like projections, and the microvilli on each enterocyte dramatically multiply the contact area at the brush border. This expanded surface, combined with a rich network of capillaries and lacteals inside each villus, plus brush-border enzymes on the enterocytes, enables nutrients to be efficiently digested, transported, and taken up into the blood or lymph. The thick mucus barrier of the colon and the idea that absorption occurs mainly in the stomach don’t apply to the small intestine’s architecture; a flat surface with no folds would greatly reduce contact with the contents and slow absorption.