Dissection scheme for the gastrointestinal tract. Different segments of the gastrointestinal tract were dissected from mice fed a low iron diet or fed a normal diet. The first part of the small intestine was divided into two pieces, I1 and I2, corresponding to the proximal and distal parts of the duodenum, respectively. The distal part of the small intestine, the ileum (I3), as well as the colon (C) were also dissected.