Search

The degenerative process of the rough surfaced elements of endoplasmic reticulum in hepatic cells after DL-ethionine administration is examined with the electron microscope. The findings in ethionine-treated rats, in comparison with the normal findings, are described. [ABSTRACT FROM PUBLISHER]

Copyright of Zeitschrift Für Zellforschung und Mikroskopische Anatomie is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The mesangium of the glomerulus of dogs and mice was examined. Basement membranes and their branches in the mesangial region were described. Stress was laid upon the intercapillary location of mesangial cells which are always separated by endothelial cells from capillary lumina and upon their cytoarchitectural features: irregularly-shaped nuclei, a dense and homogeneously, finely granular cytoplasm with centrally distributed organelles and peripherally placed filaments, a well developed endoplasmic reticulum with abundant numbers of RNP granules, peripherally placed cytoplasmic densities comparable to attachment bodies of smooth muscle cells, as well as cytoplasmic protrusions into endothelial cells (Intrakapillarhöckerchen). Based upon the above findings and upon a comparison of smoth muscle cells of arteries with mesangial cells located close to and distant from the 'vascular pole' (Gefäßpol), the conclusion was reached that mesangial cells differ essentially from endothelial cells and from fibroblasts and that they bear a marked resemblance to smooth muscle cells. An attempt was made to relate the structure of mesangial cells to their function. [ABSTRACT FROM AUTHOR]

The fine structure of fibroblasts in mouse embryo skin was studied with the electron microscope. The fibroblasts with highly functional activity are characterized by a well-developed endoplasmic reticulum, enlargement of the Golgi complex and swelling of the mitochondria. Some filamentous dense materials, presumably collagen precursors, are found within the cisternae of the endoplasmic reticulum, in the peripheral region of the cytoplasm and on the cell surface. Possible modes of the egress of the materials out of the cell are discussed. The available electron micrographs suggest that the Golgi complex are probably responsible for the secretion of the extracellular substance. [ABSTRACT FROM PUBLISHER]

The ultrastructural characterization of the prothoracic glands derives interest from the fact that they are the only known source of a steroid hormone (ecdysone) among invertebrates. The present material includes nymphal glands of two blattarian species studied at graded intervals over a period of several intermolt cycles. Among the prominent cytological features of this organ are long and intricately interwoven cellular processes that may be separated from each other by extracellular channels with an average width of 0.5 μ. The plasma membranes of the cells facing these spaces are coated by an external lamina (boundary membrane) representing extensions of the same extracellular material that provides the connective tissue sheath of this and other insect organs. Micropinocytotic caveolae and vesicles present along this large cellular surface area may facilitate the transport of material between glandular cells and hemolymph, or vice versa. The cytoplasm contains a fairly moderate amount of membranous structures. Golgi units are distinctive but never spectacular; ergastoplasmic elements are sparse in most cells. This sparsity as well as the absence of membrane-bounded secretory granules is in line with the known steroidal nature of the secretory product involved. Some cells show a striking array of microtubules. Certain structural attributes of nucleoli, mitochondria, and lysosome-like bodies seem to vary in conjunction with distinct phases of the intermolt cycle. [ABSTRACT FROM AUTHOR]

Thin methacrylate sections of developing tails of Amblystoma opacum larvae were examined in the electron microscope and a series of stages in the differentiation of the myotome musculature was reconstructed from electron micrographs and earlier light microscopic studies of living muscle. The earliest muscle cell precursor that can be clearly identified is a round or oval cell with abundant cytoplasm containing scattered myofilaments and free ribonucleoprotein granules, but little endoplasmic reticulum. These cells sometimes form a syncytium and they may also be fused with adjacent formed muscle fibers by lateral processes. Nuclei are large and nucleoli are prominent. This cell, called a 'myoblast' here, is distinctly different in its appearance from the adjacent mesenchymal cells which have abundant granular endoplasmic reticulum. The earliest myofilaments are of both the thick and thin varieties and are distributed in a disorganized fashion in the cytoplasm. These filaments are similar to the actin and myosin filaments described by Huxley and they are present in the cytoplasm at an earlier stage of differentiation than heretofore suspected from light microscopy studies. The first myofibrils are a heterogeneous combination of thick and thin filaments and dense Z bands and are not homogeneous as so many light microscopists have contended. As development progresses, cross striations become more orderly and definitive sarcomeres are formed. Thereafter, new myofilaments and Z bands seem to be added to the lateral surfaces and distal ends of existing myofibrils. Free ribonucleoprotein granules are a prominent part of the myoblast cytoplasm and are found in close association with the differentiating myofilaments in all stages of development. In early muscle fibers and some of the formed fibers, similar granules are often concentrated in the I bands. A theory of myofilament differentiation based on current concepts of the role of ribonucleoprotein in protein synthesis is presented in the discussion. Stages in myofibril formation and possible relationships of the filaments in developing muscle cells to other types of cytoplasmic filaments are also discussed. [ABSTRACT FROM AUTHOR]

The submandibular organ (a sort of apocrine sweat glands) of the rabbit was observed with the electron microscope. The cell structure of glandular tubules varies depending upon the secretory activity; there are three functional stages. The secretory cells at the resting stage are characterized by low height, absence of secretory substance, and presence of small and slender mitochondria. In the synthesizing stage, enlargement and peculiar deformation of mitochondria are observed. Secretory substance always occurs near the deformed mitochondria. The part of a mitochondrion closely abutting on the secretion mass is extremely thin, and contains longitudinally oriented cristae. Sometimes a direct continuity is observed between the thinned portion of the deformed mitochondria and the mass of secretory substance. It is presumed that the secretion is initially produced in the mitochondria and then discharged from them. The Golgi apparatus and the rough surfaced endoplasmic reticulum may be involved indirectly. Smooth surfaced vesicles, probably related to the transport of raw material, are extremely abundant in the cells of this stage. The development of a generally homogeneous projection into the gland lumen is characteristic of the stage of secretion discharge. The mitochondria are again small and slender, and the secretion is liquefied. At the base of the full-grown projection, cytoplasm is condensed to form a demarcation zone from which the projection may become detached. This mechanism of release of secretory product is quite the same as the so-called apocrine secretory process long postulated by light microscopists. [ABSTRACT FROM AUTHOR]