Amniotic fluid: Source of trophic factors for the developing intestine

Table 1 Phases of mammalian gastrointestinal development (adapted from reference 1)

Phase	Development
Phase 1	Embryonic phase of organogenesis
	Forms primitive GIT
Phase 2	Entrance and exit sites of GIT form
	Formation of rudimentary primitive GIT
	Formation of mouth and anus
	Fetal swallowing of amniotic fluid begins
Phase 3	Active differentiation
	Increase in cell number in crypts
	Cells from crypts start migrating up to the villi
	GIT growth is more rapid than the fetal body as a whole
	Growth accompanied by selective apoptosis
Phase 4	After birth, exposure to enteral nutrition
	Breast milk feeding – rapid mucosal differentiation and development
	Infancy – mucosal growth continues with deepening crypts, increasing villi (increasing width and number) and appearance of sub-mucosal folds
	Development of GIT mucosal immunity due to exposure to dietary antigens
	Mucosal immune system can distinguish between foreign pathogens and safe nutrient proteins and commensal organisms
Phase 5 (Weaning)	Late infancy – early childhood. Transition from milk feeding to solid foods. This is second phase of mucosal immunity with epithelial hyperplasia with maturation of gut functions similar to older children.

GIT: Gastrointestinal tract.