ABSTRACT
The Oropharynx.........................................................................................................6 The Esophagus...........................................................................................................6 The Stomach ..............................................................................................................6 The Small Intestine....................................................................................................7 The Colon ..................................................................................................................9 The GALT System...................................................................................................10 Nutrient Absorption .................................................................................................11 Carbohydrate............................................................................................................15 Fiber .........................................................................................................................16 Fat ............................................................................................................................17 Protein ......................................................................................................................19 Malabsorption ..........................................................................................................20 Summary ..................................................................................................................22 References................................................................................................................22
The gastrointestinal tract performs three primary functions in human metabolism: digestion, absorption, and protection. Digestion is a process by which large molecules in the diet are broken down into smaller ones that are acceptable to the enterocytes for absorption. Absorption is a process by which luminal contents enter the mucosal epithelial cells, are transported to the basement membrane, and eventually delivered to the portal vein or lymphatics. In its protective function, the gut serves as a barrier to the entry of luminal pathogens and toxins into the body. To perform these tasks the gastrointestinal tract consumes a considerable amount of energy, accounting for approximately 25% of whole body energy expenditure.
