Villi (singular: villus) are tiny, finger-like structures that protrude from the wall of the intestine and have additional extensions called microvilli (singular: microvillus) which protrude from epithelial cells lining villi. In all humans, the villi and microvilli together increase intestinal absorptive surface area 30-fold and 600-fold, respectively, providing exceptionally efficient absorption of nutrients in the lumen. This increases the surface area of the intestine to around the area of a small parking lot or a tennis court. There are also enzymes on the surface for digestion. Villus capillaries collect amino acids and simple sugars taken up by the villi into the blood stream. Villus lacteals collect absorbed fatty acids.
Crypts (of Lieberkuhn) are moat-like invaginations of the epithelium around the villi, and are lined largely with younger epithelial cells which are involved primarily in secretion. Toward the base of the crypts are stem cells, which continually divide and provide the source of all the epithelial cells in the crypts and on the villi.