Light micrograph of a section through a duodenum, the beginning of the small intestine, which runs from the stomach to the large intestine. It is where digestion begins and nutrients are absorbed into the blood. The interior (lumen) is lined with villi, which are folds in the intestinal surface that greatly increase the surface area for absorption. Within the villi are goblet cells, which secrete mucus (blue). Also within the surface are crypts of Lieberkuhn (red-lined ovoids), which secrete enzymes into the lumen that help to digest the food. Magnification: x400 when printed at 15 centimetres wide.