家兎顎下腺の発生に関する電子顕微鏡学的観察

抄録

The development of the rabbit submandibular gland was investigated by electron microscopy.
Adult, 1st-5th day's postnatal, and 18th-29th day's prenatal rabbit submandibular glands were used. The results obtained are as follows;
1) Approximately on the 20th embryonic day, the rabbit submandibular gland tissues were occupied by coarse bush-like structures, consisted of primary ducts and terminal bulbs. A few days later, the lumen formation was observed in the terminal bulb. By the 24th day, the terminal tubular cells and proacinar cells were apparently distinguishable from undifferentiated cells in the terminal tubules. On the 26th day, the differentiation of the terminal tubular cells into the granular segmental cells, and the proacinar cells into the acinar cells were evident.
2) On the 23rd day, the primary intercalated ducts, originated from undifferentiated cells in the terminal bulbs, were seen between the terminal tubule and the primary duct. Intercalated ducts were clearly found on the 26th day. Some of the intercalated ductal cells contained the same granules as found in the terminal tubular cells. This fact indicated that some of the terminal tubular cells were differentiated into the intercalated ductal cells in the late embryonic days.
3) Approximately on the 28th or 29th day, the primary striated ducts were originated from the primary ducts in close proximity to the intercalated ducts. However, the striated ducts were unremarkable even on the 5th postnatal day. It was considered that the primary ducts at the distal portion of the primary striated ducts were differentiated into the excretory ducts.
4) Myoepithelial precursor cells, originated from the undifferentiated cells of the terminal bulb, were found at the basal portion of the terminal tubules on the 23rd day. On the 24th day, myofilaments were obviously observed in the cytoplasm of some of the precursor cells. Therefore, myoepithelial cells were considered to be epithelial origin.