Large intestine. Coloured X-ray of the human abdomen showing a healthy large intestine (colon), after a barium enema. The colon (yellow) filled with barium has three regions. At left is the caecum and the ascending region of the colon; at centre and top, the transverse colon here forms a U-shaped loop and then runs up to the right; leading to the descending colon (at right). At bottom centre is the rectum. The colon absorbs water and electrolytes from digested food, leaving the dehydrated contents (faeces) to move towards the rectum. A barium enema of barium sulphate (which is opaque to X-rays) is infused into the rectum and shows up the large intestine on X-ray.