Intestinal Development

Abstract

ABSTRACT A description of chick duodenal morphogenesis is given. It is based on (a) quantitative measures of the change in size and shape of the duodenum, (b) a histogenetic study of the duodenal musculature, and (c) a quantitative description of changes in size, shape, and number of the duodenal villi throughout their development. Correlation of these data on a developmental time-scale has led to the following hypotheses: Mesenchymal cells are oriented by mechanical forces acting to distort a tissue. The orientation of smooth muscle is determined by the orientation of the premuscle mesenchyme in which it differentiates. In the wall of a hollow viscus such as the duodenum the contraction of the first layer of muscle to form will orient the remaining mesenchymal cells at right angles to itself, thus determining the orientation of the muscle-layers which subsequently differentiate. The duodenal villi are shaped by mechanical forces which act on the mucosa and which arise from epithelial expansion, on the one hand, and muscular contraction, on the other.