Blood vessels. Coloured scanning electron micrograph (SEM) of blood vessels from villi in the duodenum, part of the small intestine. Villi are finger-like projections on the inner wall of the intestines, which serve to increase the surface area available for absorption of nutrients. Each villus is richly supplied with blood vessels into which the nutrients are absorbed. This is a cast: the vessels were filled with a resin, which then set. The surrounding tissues were then eaten away chemically, leaving the cast of the vessels. Magnification: x285 when printed 10cm wide.