Small intestine. Coloured scanning electron micrograph (SEM) of a biopsy from the small intestines of a child. The small intestine runs from the stomach to the large intestine. It is where digestion is completed and nutrients and water are absorbed into the blood. The interior (lumen) of the small intestine is lined with a highly folded surface. The folds, known as villi (purple), project into the lumen increasing the surface area for absorption. Magnification: x 50 when printed at 10 centimetres wide.