Life cycle of the duodenal enterocyte.

Stem cells present in the crypts of the duodenum proliferate and give rise to precursor cells that further differentiate into absorptive cells or enterocytes. These enterocytes are highly specialized for absorption of micronutrients from the intestinal lumen. Their apical membrane is structured with microvilli and contains enzymes that facilitate transport of nutrients through the epithelial cell layer. The majority of iron absorption is facilitated by these specialized cells. The process of differentiation occurs simultaneously with migration out of the crypt and onto the villus. Zones of cells in similar stages are evident when the crypt/villus junction is viewed in cross section. After the cells have migrated to the villar tip, they are exfoliated and excreted.