Fine structure of the basal-granulated cells in human fetal duodenum

Fine structure of the duodenal mucosa in ten human fetuses 4 to 7 months old was studied by light and electron microscopy using Epon-embedded specimens. Cells containing membrane-bound granules were found both in the connective tissue and in the epithelia and identified to be basal-granulated cells, since they essentially corresponded in their cytoplasmic fine structures to the named cells in the adult. However, their relation to nerves and epithelial elements revealed some primitive features. In the 4 month fetus, the basal-granulated cells were seen in the lamina propria forming clusters which were often in contact with the basal part of the epithelium. In the 5 month fetus, occurrence of clustered basal-granulated cells in the connective tissue was among other epithelial cells, gaining an apical process which reached the lumen. The basal-granulated cells in the lamina propria were frequently surrounded by a Schwann-like cell. Profiles of unmyelinated nerve fibers were ample in the space between the Schwann-like cell and the basal-granulated cell. An phi-shaped invagination of the basal plasma membrane encompassing granular material was often found in the D type basal-granulated cells in the 7 month fetus. This suggests that the secretion of at least some of the basal-granulated cells starts in the prenatal period by emiocytosis.