The differentiation of intestinal epithelium in fresh human embryo from the 2nd month to the 9th month were investigated systematically, from the points of both their fine cell structures and its histochemistry.
1. At the end of the 2nd month the limits between epithelial cells were indistinct and a pile of 3 to 4 nuclei were found in the middle of the cells, and in the cytoplasm numerous vacuoles were found. In these cells glycogen and fat stainings were unsuccessful. At the beginning of the 3rd month the epithelium thickened, because the epithelial cells piled up together and the intestinal lumen was blocked temporarily. At the end of the 3rd month, the intestinal canal became passable and the limits between cells became detectable again. The epithelial cells were then arranged in one layer, and at the same time the cuticular border appeared.
2. Formation of the villi began at the end of the 3rd month, because the mesenchyme developed into the lumen of the intestinal canal, and simplification of the epithelial layer occurred simultaneously. Epithelial cells changed prior to the simplification of the layer. Nuclei stood side by side and formed a line in the superficial portion of the epithelium and then move to the basal portion, but on the contrary, the vacuoles moved from the subnuclear zone to the supranuclear zone.
3. The villi began to grow rapidly at the end of the 4th month, and then the cuticular borders were formed in all of the epithelial cells. Their development began from the tip of the villus. And their form became similar to those of adults at the end of the 7th month.
4. Granules with ribonucleic acid as their main constituent element appeared in the supranuclear portion of cells of the villus tip at the end of the 3rd month, and they remarkably increased during the 6th month and then disappeared by the end of the 7th month. It is conceivable that the appearance of grains which contain ribonucleic acid has very much to do with the differentiation of epithelium, but its meaning is not yet clear.
5. Mitochondria in epithelial cells were very much rod-like or filament-like. At the end of the 3rd month when the cuticular border appeared the granular mitochondria became crowded in the supranuclear zone. Around the 4th or the 5th month the granular and rod-like mitochondria became densely distributed in the supranuclear zone, and the filamentous and rod-like mitochondria were loosely distributed. According to the above-stated observations we can imagine that the cells perform several different functions in the supranuclear and subnuclear zone. The number of mitochondria decreased when ribonucleic acid was plentifully in the cytoplasm. It is probably significant that mitochondria became numerous at the end of the 7th month and that their form became like those in adults.
6. Goblet cells appeared at the end of the 3rd month, and they suddenly increased from the 5th month, and were still found in the intestinal glands during the 9th month.
7. PANETH cells appeared for the first time at the end of the 6th month, and about this time there were already seen in several forms, such as unriped cells, as a typical granulous cell or as vacuolous cells. PANETH cells increased in number, and in the 9th month vacuolated ones were particularly rich.
8. Basalgranular cells appeared in the mesenchymal layer and penetrate into the epithelium as they developed. They appeared for the first time at the end of the 3rd month, and ripe cells were found with unriped ones at the same time. The apex of the ripe cell reached the surface of the epithelium.
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