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71.
Summary Epithelium of amphibian embryos (Cynops orientalis, Xenopus laevis) was found in preceding experiments to generate and conduct impulses during a limited stage (26–37) of development. In order to elucidate the structural basis of impulse propagation, epithelial cells of four stages were examined by the freeze-etching method: (I) before and (II) during acquisition of conductivity; (III) when propagation was fully established, and (IV) when it was no longer present. Only few gap junctions (GJ) of small size were found in groups I and IV. GJ in epithelia of group III were increased in number and size, and appeared morphologically coupled, i.e., with more loosely arranged connexons. The size of gap-junctional particles did not differ significantly between coupled and uncoupled stages. Zonulae occludentes seemed leaky in stage I, and tight in stages II–IV. Thus, the morphological characteristics of specialized junctions between non excitable cells correlated with the opening and closing of low resistance intercellular current pathways during embryonic development.Gap junctions in particular seem to form an essential link in the non-neural stimulus-response system, which may facilitate the mobility of the embryo during early phases of aquatic life before the reflex pathways have been established. Coupling and uncoupling of gap junctions may also play an important role in the regulation of cell differentiation and morphogenetic movement. The experimental model used in this study provides a useful tool for further investigations of structural correlates of gap junctional permeability under physiological conditions. 相似文献
72.
Summary The ovarian surface and associated germ cells have been studied in human fetuses from 12 weeks of age until near term, using light, TEM and SEM techniques. The surface epithelium and related cords proliferate extensively, especially at midterm. The cords in the ovarian cortex appear to be linked with ingrowths from the surface epithelium, and both structures have a common basal lamina. Germ cells are always interspersed among the somatic cells of the surface epithelium and associated cords. These results indicate that both the proliferating cords and surface epithelium may contribute to the formation of early follicles. Furthermore, the occurrence, of elements having some of the features of primitive steroidogenic cells in the regions of cordsurface epithelium continuity, suggests that both structures (surface epithelium and cords) contribute somatic cells, which in addition to becoming granulosa cells, might also contribute to the provision of primitive interstitial cells.Gonocytes tend to migrate through the developing ovarian tissue towards the surface where they become extruded into the peritoneal cavity. This phenomenon might contribute to the reduction in the number of germ cells at birth and parallels the atretic processes within the ovary. 相似文献
73.
Morphology and lactose synthesis in tissue culture of mammary alveoli isolated from lactating mice 总被引:1,自引:0,他引:1
Polly R. Cline Paul O. Zamora Howard L. Hosick 《In vitro cellular & developmental biology. Plant》1982,18(8):694-702
Summary Mammary epithelial cells from lactating mice synthesize and secrete lactose in culture and retain many features of their in
vivo morphology if mammary glands are only partially dissociated to alveoli, rather than completely dissociated to single
cells. After 5 d in culture lactose synthesis by alveoli cultured on floating collagen gels is 10 to 20 times higher than
in cultures of single cells on floating collagen gels. Moreover, mammary alveoli in culture retain sensitivity to lactogenic
hormones; the synthesis of lactose by alveoli depends on the continued presence of insulin and either hydrocortisone or prolactin.
In addition, within alveoli the original juxtaposition of constituent epithelial cells is retained, and cells are cuboidal
and have many microvilli and fat droplets. In contrast, alveoli on attached gels flatten and lose their secretory morphology.
These results indicate that the shape of the cells, presence of lactogenic hormones, and maintenance of epithelial:epithelial
cell contacts are required for maintenance of mammary epithelial cell differentiation in culture.
This research was supported by Grants CA-16392 and AG-02909 from the National Institutes of Health and Institutional Grant
IN 119 from the American Cancer Society. 相似文献
74.
Lev Fishelson 《Environmental Biology of Fishes》1980,5(2):161-165
Synopsis The architecture of the gill structure of variousTilapia species was studied in relation to their adaptability to hypersaline media. Using SEM and EM, it was shown that the squamose
epithelial cells of the gills have species-typical patterns of ridges on their outer surfaces. These have previously been
misinterpreted by other authors as microvilli or stereocillia. The ridges are more dense and better developed in euryhaline
species, likeT. zillii, and less so in stenohaline species likeSarotherodon niloticus. Comparing freshwater and seawater-adapted individuals ofT. zillii, S. niloticus, S. galflaeus, andTristramella sacra, it was shown that in fresh water the surface cells are slightly swollen, extending over the openings of the chloride cells.
During adaptation to sea water, these ridges become higher and denser and the cell surface shrinks, exposing the underlying
orifices of the apical crypts of the chloride cells. The more euryhaline the species, the less change there is in the ridge
pattern of the cells during passage from fresh to sea water. This evidence implicates the gill epithelium, together with the
chloride cells, in the process of osmoregulation. 相似文献
75.
The ingestion of Bacillus thuringiensis crystal endotoxin by Manduca sexta causes the destruction of both goblet and columnar cells of the midgut. One hour after ingestion, the microvilli show pathological effects. Nearly complete destruction of the goblet and columnar cells has taken place after 4 hr exposure to the toxin. 相似文献
76.
77.
J. D. Sobel R. Tchao J. Bozzola M. E. Levison D. Kaye 《In vitro cellular & developmental biology. Plant》1979,15(12):993-1000
Summary Fragments of normal human adult vagina, when explanted onto glass slides gave rise to outgrowing sheets of pure epithelium,
which had microscopic morphological features in common with normal vaginal epithelium. Infrequent fibroblast contamination
was observed. Proliferating epithelial cells formedmultilayers of stratified squamous epithelium and demonstrated a progressive decrease in proliferative activity after 14 days. Continuous
lines of epithelial cells were not obtained. Even in the absence of estrogens, transmission electron microscopy revealed evidence
of keratinization of the superficial cells of the multilayer. Scanning electron microscopy of the surface of mature epithelial
cells in culture revealed ultrastructural features that closely resembled those present on the surface of exfoliated cells
obtained by scraping the vagina in vivo. This in vitro tissue culture model of human vaginal epithelium may provide a simple
method of studying factors that influence vaginal epithelium growth, maturation and function. 相似文献
78.
Summary The nine-banded armadillo possesses a salivary bladder which is a dilated portion of the main duct of the submandibular gland at its origin. The wall of the bladder is composed of an epithelium, a submucosa and a thick coat of skeletal muscle. The ultrastructure of the epithelium reveals that it is complex and consists of three cell types: 1) principal cells, 2) light cells, and 3) basal cells. The general organization of the epithelium suggests that it is a transporting type of epithelium such as that found in the amphibian and reptilian urinary bladders and the mammalian gall bladder. The submucosa is composed primarily of densely-packed collagen fibers. The skeletal muscle is very vascular and richly innervated.This study was supported in part by a research grant from U.S.P.H.S. (GRS 5-S01-RR-05705)The authors wish to acknowledge the technical assistance of Elizabeth Underwood 相似文献
79.
Dr. H. A. R. Fritsch 《Cell and tissue research》1976,175(1):131-135
Summary Argyrophilic and argentaffin cells occur in the stomach and intestinal epithelium of the sea-squirt, Ciona intestinalis L.. These cells are characterized by their basal swelling which contains the nucleus surrounded by small secretory granules and by a filamentous cell-apex which reaches the gut lumen. The cells are scattered unevenly within the epithelium. Their number decreases rapidly towards the lower part of the intestine. The localization, size of granules and their shape are features which differentiate these cells from other secretory cells in the gut epithelium such as mucous cells. These cells are thought to possess an endocrine function.The excellent technical assistance of Mrs. R. Sprang is gratefully acknowledged 相似文献
80.
The caecal epithelium of Calicotyle kröyeri consists of a single cell type which functions in the uptake and intracellular digestion of host epidermis and associated mucus. Each cell is columnar with a small basal nucleus and prominent nucleolus. Perinuclear cytoplasm contains narrow profiles of GER and mitochondria with numerous cristae. Golgi complexes are small and indistinct. Most of the cell is filled with vacuoles of heterogeneous content, the largest occupying the cell apex. There is in each cell an apical endocytotic complex comprising cell surface lamellae, apical vesicles and numerous tubular invaginations of the plasmalemma. The limiting membrane of all these components is structurally modified and bears a highly organized array of peg-like structures on its luminal surface. The complex is capable of ingesting particulate food material from the gut lumen for transfer, via vesicles, to the vacuoles for digestion. Most of the vacuoles represent the digestive elements of the cell and, histochemically, are reactive for protein, mucus and carboxylic esterases. Indigestible residues and lipid droplets accumulate in the large apical vacuole and are periodically released to the lumen by exocytosis. Small, undifferentiated caecal cells were occasionally observed in the epithelium, but their development has not been recorded. 相似文献