[Ultrastructural studies of mucosal epithelium in histological internal os of human uterus]

The surface epithelium of the mucosal lining of the histological internal os (HIOs) in the human uterine cervix was examined by scanning (SEM) and transmission electron microscopy (TEM). By SEM, the ultrastructure of the surface epithelium of HIOs was seen to be quite different from that of the usual endocervical and endometrial epithelium: The epithelia of HIOs were flat and found to be composed of various sizes and shapes of epithelial cells. Most of the epithelial cells had poorly developed microvilli, and the following characteristic patterns of cell arrangements: Funicular arrangement of spindle-shaped cells, pavement-like arrangement of small round cells and relatively large flat multiangular cells and island-like accumulation of cells whose surface was elevated like a dome. TEM observations revealed that most of the epithelial cells might be functionally undeveloped. However, some epithelial cells developed into mucus-secreting cells, and others resembled endometrial glandular cells. Some of the cells which resembled the endometrial glandular cells had an accumulation of glycogen granules in the subnuclear region in the early secretory phase. There were no cyclic morphological changes on the surface epithelium of HIOs during the menstrual cycle, except for the accumulation of glycogen granules in a few cells in the early secretory phase.