The human intestinal tract is divided into a number of regions: oesophagus, stomach, small intestine, large intestine and anus (Figure 4.1). The intestinal tract is approximately 30 feet long. In the mouth, food is chewed which breaks it into smaller pieces and mixes it with bacteria. Interactions between the cell membranes and the luminal contents are facilitated by the glycocalyx, a complex mucus layer overlaying the enterocytes. Undigested food enters the colon, which has a neutral pH and slow transit time (up to 60 hours). Finally, food residues and intestinal microbes exit the intestinal tract via the anus.