| Abstract: | The ultrastructure of the colon of normal human embryos and fetuses was examined continuously from the 8th to 23rd week of pregnancy. The development of the colonic mucosa could therefore be presented at the moment, where the cellular differentiation nearly resembles those of adults. During the 8th week of pregnancy in the embryonic epithelium endocrine cells begin to differentiate. In the tunica submucosa unmyelinated axon bundles can already be found. The first goblet cells occur on 9 week old fetuses. The superficial epithelium carries a brush border covered by glycocalix. Osmiophile granules and enterochromaffin cells type 4 after Cristina are situated near the basal membrane. Underneath the tunica submucosa a thin layer of circular musculature has developed. From the 13th week onwards a stripe of longitudinal musculature joins the circular muscle layer in direction of the serosa. Between the muscle layers lie nerve bundles of the myenteric plexus. 14 or 15 week old fetuses show crypts. The endocrine cells can be classified into type 1, 2 and 4 after Cristina. In the 22nd week additionally to the lipid granules at the basal membrane, osmiophile bodies appear in the apical cytoplasm. At this stage a certain variety of intermediate forms between goblet- and endocrine cells occurs. Enterochromaffin cells type 3 after Cristina can be defined as well. A lamina muscularis mucosae has not yet arisen. |
