Gastroenterology is the study of the normal function of the Esophagus, stomach, intestines, colon, rectum, pancreas, gallbladder, bile ducts, and liver, as well as the diseases that affect these systems. Gastroenterologists have an intimate understanding of how nutrients move through the digestive tract, as well as the physical and chemical breakdown of those nutrients and the removal of waste byproducts from the body.