Pediatric Nutrition, Gastroenterology and Child Development

Biology of Gastrointestinal Function

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The gastrointestinal tract (GIT) arises initially during the process of gastrulation from the endoderm of the trilaminar embryo (week 3) and extends from the buccopharyngeal membrane to the cloacal membrane. The tract and associated organs later have contributions from all the germ cell layers. Digestion is the breakdown of food into smaller particles or individual nutrients. It is accomplished through six basic processes, with the help of several body fluids—particularly digestive juices that are made up of compounds such as saliva, mucus, enzymes, hydrochloric acid, bicarbonate, and bile.

Enterohepatic circulation refers to the circulation of biliary acids, bilirubin, drugs, or other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocyte and transport back to the liver. The mixture of organisms regularly found at any anatomical site is referred to as the normal flora, except by researchers in the field who prefer the term "indigenous microbiota”. The gastrointestinal mucosal immune system has the daunting task of coexisting with an incredibly complex mix of luminal antigens, including partially digested dietary constituents, host proteins, and commensal bacteria, while maintaining the capacity to recognize and eliminate pathogenic microbial organisms and transformed epithelial cells.