The mucosa of the duodenum is simple columnar epithelium
With four major cell types: (1) Absorptive cells, which have microvilli,
produce digestive enzymes and absorb digesred food; (2) goblet cells
produce a proteCtive mucus; (3) granular cells (Paneth cells) help
protect the intestinal epithelium from bacteria; and (4) endocrine
cells produce regulatory hormones. The epithelial cells are produced
within tubular invaginations of the mucosa, called intestinal glands,
at the base of the villi. The absorptive and goblet cells migrate from the
intestinal glands to cover the surface of the villi and eventually are shed
from its tip. The granular and endocrine cells remain in the bottom of
the glands. The submucosa of the duodenum contains coiled, tubular
mucous glands, called duodenal glands, which open into the base of
the intestinal glands.