ABSTRACT
The gastrointestinal (GI) tract can be thought of as a long tube subdivided into a series of compartments with unique pH and enzymatic environments, each being separated from the next by a sphincter. Food residue is pumped through a valve into a receptacle, where chemical changes occur, before it is pumped into a more distal compartment. The most proximal is the mouth, where the tongue and pharyngeal muscles pump food through the upper esophageal sphincter (UES) into the proximal esophagus. Food is then pumped through another valve, the lower esophageal sphincter (LES), into the reservoir portion of the stomach, where the pH is strongly acidic, and subsequently pumped by the antrum through the pylorus into another receptacle, the duodenum. In the duodenum the pH is again alkaline, facilitating the action of trypsin and carboxypeptidases, and the residue is further influenced by enzymes from the small bowel itself, before being pumped through another valve, the ileocecal valve, into the cecum, a reservoir portion of the colon. In the colon, fluids and electrolytes are adjusted and the residue is pumped by the descending colon through the anal sphincter to the exterior.
