Villus surface of the small intestine; columnar epithelial cells, animated coloured scanning electron micrograph (SEM). The smooth portion of image shows the surface of the villus with densely packed columnar epithelia cells. The rough portion shows a longitudinal view of the columnar epithelial cells. The small intestine is the part of the gastrointestinal tract between the stomach and the large intestine. It is where most of the digestion and absorption of food takes place, via the villi, which increase its surface area. The villi have an outer epithelial cell layer (columnar epithelial cells) that possess many tiny microvilli. Microvilli are tiny finger-like projections, which increase the surface area available for absorption of nutrients such as lipids, proteins and fat-soluble vitamins. The microvilli have a rapid turnover of 3-4 days.