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Small intestine. Coloured barium X-ray of the abdomen showing a healthy coiled small intestine (yellow). The small intestine breaks down and absorbs partially-digested food from the stomach, before passing it on to the large intestine. The banding within the intestine is caused by circular folds called plicae circulares in its mucosal lining. The folds increase the surface area through which nutrients can be absorbed. The radio-opaque barium, introduced through an enema, enables the shape of the soft tissues of the small intestine to be seen. (KEYSTONE/SCIENCE PHOTO LIBRARY/INNERSPACE IMAGING)