How is the the small intestine adapted for absorption?

The Ileum is long (up to 7m!) and has a very high surface area due to the presence of many villi and microvilli. A single villus is made up of many cells, each with lots of microvilli, and have many blood vessels close to the surface. The walls of each villus are thin (one cell thick) to ensure a short diffusion distance, and their rich blood supply helps to maintain a high concentration gradient for diffusion across the small intestine, as the absorbed food is carried away by the blood. Many enzymes, such as amylase, protease and lipase, act in the ileum to digest food into smaller products which can then diffuse across the wall of the small intestine more easily due to their small size.