How do the folds and projections of the small intestine increase poison absorption?

The folds and projections of the small intestine significantly increase the surface area available for the absorption of ingested poisons, making it the primary site for such absorption in the gastrointestinal tract.1

This massive surface area—estimated to reach up to 2,000,000 cm²—is achieved through a hierarchical structure:

• Plicae circulares: These are large, concentric mucosal folds that act as transverse ridges, increasing the surface area of the intestinal lining by five to eight times.2
• Villi: These are tiny, slender, vascular projections that cover the mucosa, further multiplying the surface area. They contain a rich network of blood vessels that facilitate the uptake of substances into the bloodstream.23
• Microvilli: Located on the surface of individual epithelial cells, these even finer projections (the brush border) enlarge the absorbing surface by approximately 25 times.2

Because the small intestine possesses this vast surface area and a high blood supply, it is far more efficient at absorbing chemicals than the stomach, even when the chemical properties might otherwise favor gastric absorption.1