摘要:

AbstractThe yolk sac of the little brown bat is unusual in that during the course of gestation both the inner endodermal cells (bordering the yolk sac cavity) and outer mesothelium (facing the exocelom) form simple columnar epithelia which persist throughout gestation. These endodermal cells develop an extensive system of agranular endoplasmic reticulum, numerous lipid droplets and unusual “giant” mitochondria. During development the Golgi apparatus changes position from the apical to the basal side of the nucleus, reversing the polarity of the cells. In general, the endodermal cells have cytological features suggestive of synthetic or secretory activity. The mesothelial cells develop an extensive “absorptive apparatus” in their apices, while large crystalloid‐containing granules become numerous in their basal cytoplasm. The mesothelial cells have large deposits of glycogen, especially during mid‐gestation, but few mitochondria and little granular endoplasmic reticulum. Endodermal cells do not absorb exogenous protein (peroxidase) even if it is injected directly into the yolk sac cavity. However, placement of peroxidase either in the exocelom or in the maternal vascular system results in the appearance of this protein in the “absorptive apparatus” of mesothelial cells as well as in macrophages in the stroma of the yolk sac. While evidence of absorption was clear, no direct evidence of transport of tracer to fetal blood vascular system was obtained. It is postulated that a major function of the hypertrophied mesothelial cells during gestation is the absorption of proteins and possibly other substances from the exocelomic fluid. The major function of the hypertrophied endodermal cells may be synthesis and secretion of substances into the fe

ISSN:0002-9106    

DOI:10.1002/aja.1001460102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe development of the elastic cartilage in the mouse pinna was studied with the electron microscope. For descriptive purposes, the developmental process was divided into five stages. These begin with the onset of cartilage matrix production by chondroblasts. The second stage is the major mitotic stage although the cells now resemble chondrocytes and cartilage matrix production evidently continues. This is followed by a period during which cartilage matrix production appears to be the major activity of the chondrocytes. In Stage IV, the cells continue to produce cartilage matrix but at the same time they also produce lipid which comes to occupy most of the cell as a large lipid droplet. In the adult, Stage V, matrix production appears to be at an end and each cell contains a lipid droplet which is so large that the cells bear some resemblance to white fat cells and might be designated as lipochondrocytes.The adult cartilage matrix contains elastic plates in a three‐dimensional honeycomb pattern. Between the elastic plates and the cells, the matrix contains elements similar to those seen in hyaline cartilage but it does not contain matrix vesicles such as those which have been associated with the calcification of cartilage.Two types of filaments differing in appearance, size, and location are seen within the chondrocytes. They have been designated cytofilaments and cortical filaments. Cytofilaments are dispersed throughout the cell and also contact the substance of the lipid droplet, cortical filaments (sub‐plasmalemmal microfilaments) are located directly under the plasma membrane. They are thought to be involved in movement of the plasma membrane as a concomitant to extracellular fibrogene

ISSN:0002-9106    

DOI:10.1002/aja.1001460103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractTo study the structural features of fetal rat duodenal mucosa associated with histogenesis of villi, duodena from 15‐ to 19‐day fetuses were examined by light and electron microscopy. The duodenal epithelium of 15‐to 18‐day fetuses was stratified. Distinctive junctional complexes associated with membrane‐bounded vesicles and cilia‐like structures were seen in the deeper epithelial layers at 15 and 16 days. Small lumina, designated “secondary lumina,” lined with a variable number of microvilli developed between epithelial cells at these junctional complexes during the sixteenth through eighteenth days. Degenerative changes and exfoliation of superficial epithelial cells were obvious in 17‐ and 18‐day fetuses. In 18‐day fetuses, aggregates of mesenchyme had invaginated the basal aspect of the stratified epithelium. Concomitantly, the number of epithelial layers overlying these mesenchymal projections was decreased. In 19‐day fetuses, well formed, short duodenal villi lined by a simple columnar epithelium which included goblet and endocrine cells were evident. Injection of ferritin into the main duodenal lumen of 17‐day fetuses failed to reveal continuity between the main lumen and the secondary lumina. However, continuity between many secondary lumina and the main lumen was demonstrated in 18‐day fetuses. Thus, major morphological features associated with villus formation in fetal rat duodenum include: (1) formation of many secondary lumina in primitive stratified epithelium, (2) eventual fusion of these lumina with the main duodenal lumen, by their continued growth coupled with exfoliation of degenerating superficial layers and (3) upward growth of mesenchyme towards the lumen as cell exfoliation and expansion of

ISSN:0002-9106    

DOI:10.1002/aja.1001460104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

摘要:

AbstractThe diameter of lymphocytes, isolated from a sample of peripheral blood by Ficoll‐Hypaque sedimentation, was determined after eight different steps in the preparative procedure for scanning electron microscopy (SEM). There was a 43% total reduction in mean cellular diameter of the lymphocytes studied, the diameter dropping from 8.4 μm prior to fixation, to a final diameter of 4.8 μm in the cells examined under the scanning electron microscope. The bulk of this shrinkage occurred during critical‐point drying. In view of this finding, caution should be exercised in describing detailed cell surface morphology by SEM when similar preparative procedures are emp

ISSN:0002-9106    

DOI:10.1002/aja.1001460105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001460106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001460101

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1976

数据来源: WILEY