2017 Elsevier Inc. All rights reserved. The gastrointestinal (GI) tract regulates the digestion and absorption of water and nutrients, including vitamins, proteins, carbohydrates, and fats, allowing for their uptake into circulation and use for energy-requiring functions. The mucosa of the GI tract is the largest organ in the body and is the largest surface area that is exposed to the external environment. This large surface area allows for efficient uptake of nutrients, but also results in vulnerabilities. The epithelium that lines the intestinal tract is constantly being renewed making it susceptible to the development of certain cancers. As well, the intestinal tract is the site of exposure to a multitude of toxins and pathogens, which present challenges for the intestinal immune system. This article reviews the relationships between gastrointestinal physiology and function in health and disease.
