NUTRITION AND ONTOGENIC DEVELOPMENT OF THE INTESTINE

Fetal, suckling, and postweaning vertebrates have distinct dietary inp uts that impose different functional demands on the developing intesti ne. Differences between species and life-history stages in intestinal structure and functions are set by genetic determinants that reflect e volutionary diets. Dietary inputs interacting with genetic determinant s influence intestinal functions by triggering the production of new e nterocyte populations and (or) by reprogramming existing enterocytes. In addition to nutrients, nonnutritive components of amniotic fluid an d milk, such as growth factors and hormones, are important mediators o f intestinal development and in humans can exert influences at as earl y as 10 weeks of gestation, when fetuses begin swallowing amniotic flu id. Changes in diet composition during suckling elicit limited and app arently nonspecific responses in intestinal structure and activities o f brush-border hydrolases and transporters. The ability to adaptively modulate intestinal brush-border functions develops at weaning, when d iet composition begins to vary unpredictably. Hydrolytic and transport capacities of the developing intestine are matched to age-related inc reases in dietary inputs, are not in great excess, and may be growth l imiting. Although not as extensively studied, postnatal diet also infl uences development of intestinal endocrine and immune functions and ha s a complex, poorly understood interaction with the developing microfl ora.