ヒト胎児卵巣における卵胞形成と卵胞閉鎖に関する電子顕微鏡的研究
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概要
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Ovaries of 37 human fetuses from 6 to 40 weeks of gestational age were examined with the electron microscope to know the reason why germ cells decrease in number and to know the process how the follicular epithelial cells are formed. In the fetal ovary before 10 weeks of gestational age, there existed mainly primordial germ cells, and between 10 and 14 weeks, there existed mainly oogonia, and after 17 weeks of gestatinal age there existed mainly oocytes. Between 10 and 14 weeks, germ cells increased remarkably in number, but on the other hand extensive necrosis and degeneration of germ cells occurred during this period. After 17 weeks, groups of dividing oocytes were observed in the same stages of meiotic prophase, and intercellular bridges were often present among them. Between 20 and 40 weeks, oocytes grew slowly. In their cytoplasm, stratiform membranous structures were constructed among the large number of mitochondria. Annulate lamellae were often observed in large mature oocytes. At 40 weeks, primordial germ cells were very few, and existed in the ovarian medulla. Most of them were not encapsulated by epithelial cells. On the contrary, oogonia were covered with epithelial cells. Therefore it is suggested that encapsulation of epithelial cells are required for primordial germ cells to differentiate into oogonia. Between the oocytes and granulosa cells, zona pellucida was found, which indicates zona pellucida is already formed in the fetal stage in humans. Surface epithelial cells divided intensively and increased in number, penetrating into the ovarian medulla, and covered the groups of oogonia. After 17 weeks, a number of primary follicles were formed, and follicle cells changed their shape and developped gradually into granulosa cells. From such observation on human ovaries of whole fetal stage, it is suggested that surface epithelial cells are the origin of granulosa cells. As described above, necrosis and degeneration occurred in germ cells after 10 weeks of gestation. These degenerating germ cells concentrated and became smaller, and were often seen in the cytoplasm of pre-granulosa cells. Since electron dense lipid granules and lysosomes were observed in the cytoplasm of these pre-granulosa cells, it was supposed that they were residual bodies as the result of phagocytosis and digestion.
- 札幌医科大学の論文
- 1990-12-01
札幌医科大学 | 論文
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