Healthy large intestine, coloured double contrast barium enema X-ray. The large intestine (colon, yellow) is the end part of the digestive system. It is divided into four sections: the ascending (left of centre), transverse (centre), descending (right of centre) and sigmoid colon (at lower centre). It receives digested food from the small intestine (not seen), which joins it at lower left. The colon absorbs water from the digested food which arrives in a liquid form. The product of this is faeces, which are passed to the rectum (bottom centre) and stored for excretion. A double contrast barium enema is a diagnostic technique in which a solution of radio-opaque barium salts are introduced through the anus, and then air is used to inflate the colon.