Intestinal lining. Coloured scanning electron micrograph (SEM) of a fractured intestinal surface. The fracture plane (lower frame) has cut down through the surface, revealing the deep folds called villi. The intestinal surface (pink, background) is where food is digested. It consists of a layer of surface (epithelial) cells (seen in cross section, pink, foreground), containing goblet cells (small circular cells) that secrete mucus to lubricate food and prevent self-digestion. This outer surface is supported by connective tissue (brown), seen at the core of each fold (villus). The folds increase the area for the absorption of food. Magnification: x200 when printed 10 centimetres wide.