Why does the small intestine absorb many ingested poisons?

The small intestine is the primary site for the absorption of ingested poisons due to its specialized anatomical and physiological characteristics. While the stomach can absorb certain substances, the small intestine is significantly more efficient for several reasons:

• Enormous Surface Area: The small intestine features a massive absorptive surface area, estimated at up to 2,000,000 cm², facilitated by mucosal folds known as plicae circulares and tiny projections called villi, which are further covered by microvilli.12
• Blood Supply: The intestine possesses a much greater blood supply than the stomach, which facilitates the rapid uptake and systemic distribution of absorbed chemicals.2
• pH and Ionization: Most chemicals diffuse across cell membranes in their nonionized, lipid-soluble form. Because the mucosal surface of the small intestine is alkaline, organic bases are more likely to exist in this nonionized state, allowing them to readily diffuse across the intestinal membrane.2
• Transit Dynamics: Often, stomach contents—including ingested poisons—are passed into the small intestine before significant absorption can occur in the stomach, making the intestine the dominant site for toxic exposure.2