How do nutrients cross from your intestine into your body?

The inside of the small intestine is folded rather than smooth. Its lining has many tiny fingerlike projections called villi. Each villus is covered with cells, and each cell has much smaller projections called microvilli. Folding and projecting add surface inside the same tube, giving nutrients more lining across which they can enter the body.

Digestion first breaks food into smaller substances. These do not fall through open holes. They cross the lining cells using particular transport routes. Simple sugars and amino acids, the small building parts obtained from proteins, can then enter tiny blood vessels inside a villus. That blood carries them toward the liver and onward through the circulation.

Many fats take another route. After entering a lining cell, their components are rebuilt and packaged into particles. These enter a small lymph vessel inside the villus called a lacteal. Lymph is fluid carried in a separate vessel network that eventually joins the bloodstream. The two paths are different first stages of transport, rather than one useful route and one dead end.

A villus is large enough to contain blood and lymph vessels; a microvillus is only an extension of one cell and contains neither. Both help explain absorption at different scales. The food tube's enlarged lining brings small digested substances close to transport systems, connecting a meal inside the intestine to materials the rest of the body can use.