[Scanning electron microscope study of the lung epithelium of the rabbit during ontogenesis]. / Rasterelektronenmikroskopische Untersuchungen der Lungenepithelien des Kaninchens während der Ontogenese.

The development of the bronchial and alveolar epithelium was observed in rabbits from the 15th day post conception until the time of birth with the scanning electron microscope. In the pseudoglandular phase, primitive bronchi proliferate in the mesenchyme. The epithelial cells are not differentiated and have single cilia. After retraction of these single cilia cell differentiation begins. Flat cells densely populated with cytopodia can be recognized on the 22nd day, ciliated cells on the 23rd day post conception. Both are located in the bronchi near the hilus. In the canalicular phase of development, the differentiation of the mucoid cells and the Clara-cells begins. The interstitial connective tissue develops more and more capillaries. The alveolar phase begins around the 26th day p. c. The lung capillaries reach the alveolar epithelial cells and arrange themselves directly beneath the epithelial basement membrane. This "alveolarization" of the lung tissue starts in the centre of the lung lobules and proceeds to the periphery. After the 26th day post conception the alveolar epithelial cells retract their single cilium and at the same time become type I or type II pneumocytes. The undifferentiated entodermal stem cell of the alveolar epithelium is the pneumoblast.

[The inside surface of the rat esophagus during ontogenesis]. / Die lumenseitige Oberfläche des Rattenoesophagus während der Ontogenese

The surface architecture of rat esophagus during the ontogeny is studied. Single cilia on the cells of the apical surface can be observed with the scanning electron microscope till the day 17 of the fetal period. Ciliogenesis and function of the single cilia are discussed by literature. Based upon results of our investigations we give the following interpretation: The single cilia are responsible for differentiation of the transitional columnar epithelium. The stop of mitosis, which is connected to constitution of single cilia, allows the formation of cell organelles. About the day 21 after conception ciliary cells are found. Their function is still unknown. They are observed on the esophageal surface at the same time, when primary ciliary cells arise on the trachea of the rat. The columnar epithelial cells transform into a squamous epithelium within 48 hours. The keratinisation and exfoliation of the surface cells occur definitely post-partum.

[The luminal surface of the rat trachea during ontogenesis]. / Die lumenseitige Oberfläche der Rattentrachea während der Ontogenese

To complete the hitherto existing results about the trachea epithelium, the scanning electron microscope was used to get representative statements about the apical surface of the epithelium: First of all the epithelium consists of undifferentiated round cells with cytopodia. The cells rarely carry single cilia at the same time. At the 18. day of pregnancy nearly all of the cells have a single cilium. Until the end of the intrauterine phase the single cilia are retracted again. At the 20. day ciliated cells and cells with protrusions are formed. Mucus granula are secreted into the lumen already before birth. Immediately post partum much mucus appears. Its distribution, viscosity and optical behaviour is different. For ciliated cells and goblet cells no special characteristical distribution was noticed. The building of the cells surface was detailed discussed. The question about function of the single cilia cannot yet be answered.

[The ultrastructure of the rat esophageal epithelium during ontogenesis]. / Uber die Ultrastruktur des Rattenoesophagusepithels während der Ontogenese

The development of the epithelium of the rat esophagus was examined continuously from the 13th day post-conception until one day post-partum. Besides the single-results at different phases of development the knowledge, that the esophageal ontogeny of different mammalians may be considerably different, is of special importance. To this matter of fact was not paid attention in present literature, but the authors accentuate common things. The significant results during development are the following: 1. The completely undifferentiated epithelium of the 13th day at the same time develops basement-membrane and basic membrane of the cytoplasm. The organelles are under construction. Centriols in cells near to the lumen are seen in connection to the single-cilia, which occur till the 17th day of ontogeny. These essentially differ from cilia of the ciliated epithelium. 2. The cylindrical epithelium constitutes until the 16th day. Afterwards the first synthetic productivity like organisation of filaments are observed. By that superficial cells loose their capacity to divide. 3. On the 17th day intercellular spaces between neighbouring cells at the lumen abruptly rip up. In loco cylindrical cells change to squamous cells. There are no essential differences in time between cranial and caudal parts of the esophagus which proofs an entodermal genesis of the epithelium. 4. Changes in the ultrastructure at about 19 days p.c. cause the epithelium's keratinization. 5. 21 days p.c. few cilia-bearing cells scattered between the cells in keratinization are to be seen. 6. Before birth superficial cells become separated and are shed from the surface completely post-partum.