villus

A villus (plural villi) is a finger-like projection of the small intestine's lining, and its whole purpose is surface area. Absorption needs a surface to pass across, and the small intestine folds its lining into millions of villi, each carrying a network of capillaries and a lymph vessel (the lacteal): the sugars and amino acids cross into the blood, and most of the fat crosses into the lacteal and reaches the blood from there. That is why the small intestine, and not the stomach, is where most nutrients are absorbed: the stomach churns and begins protein digestion, and the villi do the collecting. Water travels with the nutrients along the same surface, and the water that is left is reclaimed later in the large intestine, which has no villi and whose job is forming the waste into feces. A villus is a surface, not a movement: peristalsis moves the material onward.