ULTRASTRUCTURE OF SKIN OF HUMAN EMBRYOS .4. EPIDERMIS

[摘要] In the 12-week-old embryo the epidermis did not show any sign of keratinization. The stratum germinativum contained an abundant amount of glycogen in the intercellular spaces. Melanocytes were often detected both in the dermis and in the epidermis, and they showed active melanin formation. The periderm retained its nucleus and showed thickened microvillous borders which were coated with a fuzzy filamentous substance. Desmospmes and tonofilaments were present, but only in small numbers. Instead of becoming thick, they arranged themselves along the amniotic border in the periderm to form a peripheral band. In the 13-week-old embryo the intercellular glycogen in the stratum germinativum had either diminished or disappeared, while the intracellular glycogen in the upper layers remained the same as in the 12-week-old embryo. In embryos 14[long dash]16 weeks old the intracellular glycogen disappeared from the stratum germinativum, and diminished in the upper layers. The cells in the upper layers began a keratinization process just around the hair canal through a formation of the keratohyaline granules. Keratinization took place in these cells individually, so that a mixture of all degrees of keratinization was observed. The human posterior buccal mucosa was found to be very similar to the epidermis of the 12-week-old embryo in the following features: the nucleus was retained in the cells of the uppermost layer; keratohyaline granules were not formed and no keratinization took place; glycogen was present in abundance in the upper layers; the outer border of the uppermost cells was thickened and bore microvillous projections which were covered with fuzzy filaments. The microvillous borders of the periderm and the lack of keratinization are the manifestations of cellular adaptation of an immature epidermis to the environment and of a rapid rate of turnover of the embryonic epidermis.