The maturation of cortisone-treated embryonic duodenumin vitro. I. The villus

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Abstract
Mitotic expansion of the mucosa coupled with contraction of intrinsic longitudinal and circular muscle fibers produces previllous ridges on the luminal surface of the embryonic chick duodenum by the thirteenth day of incubation. Subsequently, remodelling by periodic indentation of the mucosal surface yields primitive villi which expand and elongate to form the tall, finger-like projections characterizing the absorptive surface of the mature duodenum (Hilton, 1902; Pap, 1933; Coulombre & Coulombre, 1958). Coincident with the morphogenesis of the villus is the acquisition of enzymatic activity in its epithelium. As early as the 14th day of incubation of the chick embryo, alkaline phosphatase is detectable in the epithelial free border of the duodenum (Hancox & Hyslop, 1954), although other investigators report later appearances for this enzyme (Moog, 1950; Hébert, 1950). The onset of this physiological activity in the duodenal epithelium may be accelerated by exposure to adrenocorticoids as originally postulated by Hébert (1950).