Changes in the gastrointestinal tract during enteral or parenteral feeding.

Intestinal adaptation, in terms of increasing intestinal length and weight, usually occurs rapidly after small-bowel resection. However, this response depends on provision of enteral nutrients. If total parenteral nutrition without enteral feeding is prolonged, hypoplasia of the intestinal mucosa results. Adaptation is probably mediated through the presence of luminal nutrients, particularly glutamine, which is preferentially used by the intestine. However, systemic hormonal factors, possibly gastrin, cholecystokinin, and glucagon, also influence intestinal adaptation. Thus, in the management of short-bowel syndromes, enteral nutrition should be added to total parenteral nutrition as soon as possible.