Epithelial restitution in the gastrointestinal tract.

Injury to the gastrointestinal mucosa can be divided into two types: (a) deep injury involving extensive hemorrhage and large areas of tissue necrosis, and (b) superficial injury confined to the upper regions of the mucosa and not involving hemorrhagic lesions. Mucosal repair differs according to the severity of the damage. Repair of deep injury takes weeks because large regions of the mucosa must be replaced with new tissue, a process involving mitosis. Superficial injury is initially repaired rapidly over hours by epithelial restitution that does not involve mitosis but proceeds in the following sequence of events: First, the damaged surface epithelial cells are shed and form a layer that protects the restituting mucosa. Then the viable epithelial cells that remain attached to the mucosa at the margin of the wound become flattened and rapidly migrate over the denuded basal lamina. The superficial epithelium is re-established when migrating cells touch, form new tight junctions, and repolarize their organelles. This rapid protective mechanism, called restitution, has recently been documented in the stomach, duodenum, colon, and rectum. The cellular mechanisms, speed of migration, recovery of transmucosal electrical potential difference, and specific peculiarities of rapid epithelial restitution in the various regions of the gastrointestinal tract are reviewed here.