Blood vessels from the small intestine, coloured scanning electron micrograph (SEM). At left are the larger vessels of the outer wall of the intestine. At right are the much thinner vessels of the inner wall. The inner wall of the intestine is folded into villi, projections that serve to increase the surface area available for the absorption of nutrients. The villi are packed with dense networks of capillaries, through whose walls nutrients pass into the bloodstream. 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: x60 when printed 10cm high.