[Luminal surface of human esophagus during ontogeny]

The development of human esophagus epithelium was continuously examined from the 7th to the 23rd week post conception (p.c.) by transmission as well as scanning electron microscopes. Essential steps of the development are: 1. From the 7th to the 9th week p.c. the lumen of the esophagus is open along the whole length. Many superficial cells cease their mitotic activity and produce single cilia. 2. In the 9th week p.c. large low electron dense areas still exist in the cells. Most of the superficial cells are incapable of mitosis. 3. In the 11th week p.c. we found two possibilities for differentiation of the primary cells: ciliated cells and cells with glycogen. 4. In the 14th week p.c. there is the greatest amount of ciliated cells. At the same time, the transformation of ciliated cells to columnar cells begins. The reduction of mitochondria correlates with the migration of the nucleus. 5. After the 17th week p.c. no more glycogen-rich cells exist. The number of ciliated cells decreases discontinuously. 6. Polygonal shaped epithelial cells predominate in the 23rd week p.c. Stratified epithelium develops only after 23 weeks p.c. Thus, through the use of transmission and scanning electron microscopes, we found new aspects which are contrary to the known theories based on light microscopical investigations.