ISSN:0002-9106    

DOI:10.1002/aja.1001360402

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe fine structure of developing connective tissue components of the chick embryo aorta of eight and nine days incubation ages was studied after treatment with one of seven enzymes (α‐amylase, α‐chymotrypsin, collagenase, elastase, β‐glucuronidase, hyaluronidase, and trypsin). Both tissue pieces and thin sections of aldehyde‐fixed aorta and great vessels were utilized. All preparations were mounted on stainless steel grids and stained with silver metalloporphyrin, uranyl acetate, and lead citrate.The homogeneous component of elastic fibers (elastin) responded only to elastase, indicating that it was well characterized early in its development. Eight‐day elastin was less susceptible to digestion than nine‐day elastin. Microfibrils were only slightly responsive to the actions of α‐amylase and trypsin, while α‐chymotrypsin completely eliminated them. Of the three connective tissue components, unit collagenous fibrils showed the greatest response. Complete or nearly complete digestions were effected by α‐amylase, α‐chymotrypsin, collagenase, and trypsin. Less extensive effects were produced by β‐gl

ISSN:0002-9106    

DOI:10.1002/aja.1001360403

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

年代:1973

数据来源: WILEY

摘要:

AbstractSpermatogenesis begins in the rabbit at seven to eight weeks of age. During the preceding postnatal period, seminiferous tubules contain round to oval prespermatogonia arranged in pairs at the tubular periphery and elongated Sertoli cells lying perpendicular to the basal lamina. Prespermatogonia are distinguished from fetal gonocytes by their abundant cytoplasm and the presence of intercellular bridges. Preceding the onset of spermatogenesis, prespermatogonia undergo diminution in cell size and cytoplasmic condensation. At the same time there is marked nucleolar enlargement, with elaborate proliferation of the nucleolonema. By the end of the seventh week, characteristic type A and B spermatogonia are present. Spermatocytes are seen at the end of the eighth week. Spermatids appear in the twelfth week, coincident with tubular lumen formation. The duration of the initial spermatogenic cycle is similar to that in the adult. Sertoli cells are closely associated with adjacent germinal elements throughout the postnatal period. The Sertoli cell cytoplasm includes elongated mitochondria, abundant smooth endoplasmic reticulum and prominent Golgi complexes. Many of the cells contain phagocytized material, presumably derived from degenerating germ cells. The observations suggest possible mechanisms by which Sertoli cells support early germ cell maturation.

ISSN:0002-9106    

DOI:10.1002/aja.1001360404

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe gross and microscopic anatomy of the vasculature of the monitor lizard liver was studied. The portal vein has a peculiar arrangement of smooth muscle. The tunical media of the entering portal vein has bundles of smooth muscle cells separated by large numbers of collagenous fibers. The amount of smooth muscle decreases as the vessel decreases in diameter and soon one finds intermittent broad, thin bands of smooth muscle. As the caliber of the vessels continues to decrease, the smooth muscle bands become narrower and thicker so that they appear as doughnut‐shaped sphincters. The sphincters are usually found at the beginning of each branch of the portal vein as well as along the course of veins between areas of branching. Some sphincters are found in direct contact with the outer capsule of the liver. Sphincters occur in the terminal branches of the portal vein just proximal to the sinusoids.Small numbers of scattered smooth muscle cells were seen arranged longitudinally, obliquely, or circularly in the smaller hepatic veins. Even the large hepatic veins had only small amounts of smooth muscle. At no place along the course of hepatic veins could smooth muscle sphincters equivalent to those seen around portal veins be found.The monitor lizard should be an excellent subject for physiological and pharmacological studies of regulation of intrahepatic portal vein blood flo

ISSN:0002-9106    

DOI:10.1002/aja.1001360405

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe fine structure and micropinocytotic capabilities of epithelial cells closely associated with lymphoid follicles in the chicken bursa of Fabricius, rabbit appendix, and mouse Peyer's patch were compared. Epithelial cells capable of transporting ferritin and India ink tracers from the lumen were demonstrated in all three locations. Epithelial cells not associated with lymphoid follicles in the bursa and appendix did not express pinocytotic activity. Lymphoid cells were identified in bursal epithelium of chick embryos as early as the twelfth day of incubation. These lymphoid cells were smaller than typical bursal lymphocytes, had dense cytoplasm, numerous cytoplasmic projections, and prominent nucleoli. The small lymphoid cells were first demonstrable at a time in incubation during which lymphoid stem cells have been shown to migrate into the bursal epithelium. Lymphoid cells were seen earlier than the specialized follicle‐associated epithelium. It is concluded that specialized pinocytotic follicle‐associated epithelium does not induce initial migration of stem cells into areas along the intestinal tract, but that this transepithelial pinocytotic flow of intestinal contents after birth may provide a significant stimulus for attraction, proliferation and egression of lymphocy

ISSN:0002-9106    

DOI:10.1002/aja.1001360406

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

年代:1973

数据来源: WILEY

摘要:

AbstractThe inherent growth potential of synchondrosal cartilage has been studied as follows. Sixty CD‐1 mice were injected with3H‐thymidine on their first day of life. Thirty of these were sacrificed one hour after injection, and their cranial bases were removed and placed in an organ culture system. The explants were removed from culture at six‐hour intervals for one day and then every 24 hours for five more days. The remaining animals, which comprise the in vivo series, were sacrificed by decapitation at corresponding times. In order to detect cell movements, the spheno‐occipital synchondroses were divided into five zones, and labeled cell counts were done for each zone. The labeled cartilage cells spread apart with growth as new cells were formed in the central zone and moved toward the outer zones The labeled cells moving from the central resting zone to the outer hypertrophic zones were comparable in absolute number and in rate of movement in both the in vivo and in vitro cartilages. The fact that synchondroses grown in culture retained their capacity for growth without benefit of neighboring tissues seems to indicate that the spheno‐occipital synchondrosis possesses an inherent potential for growth and is not merely reactive or adaptive

ISSN:0002-9106    

DOI:10.1002/aja.1001360407

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

年代:1973

数据来源: WILEY

摘要:

AbstractHeart development in the Mexican axolotl,Ambystoma mexicanum, from early embryonic stages to the adult was studied by electron microscopy. During early development, myocardial cells exhibit scanty cytoplasmic matrixes which contain numerous large yolk platelets and lipid droplets. As development progresses the yolk and lipid materials become reduced; the cytoplasmic matrixes increase in glycogen content and membranous organelles. Degradation of yolk platelets appears to take place by an “unraveling” process. The Golgi complex becomes well‐developed just prior to the first heart beats and its many associated vesicles are suggestive of secretory activity. Degeneration and death of certain myocardial cells are evident at the onset of trabeculation. Several mechanisms for myofibrillogenesis appear to operate both simultaneously and at different developmental stages. Pre‐heart‐beat myocardial cells display ribosome‐containing amorphous masses and unorganized 60 Å and 140 Å filaments in their cytoplasm. They also have electron‐opaque plaques on their plasma membranes. Sarcomeric myofibrils first appear parallel to and immediately beneath the sarcolemma. This occurs at stage 34, the heart‐beat initiation stage (6 days). During later development “isolated” Z band‐myofilament complexes, numerous loosely‐organized 60 Å filaments and a few 140 Å filaments are observable in the cell matrixes. This suggests that Z bands may form centers for myofibril organization at these stages. Also at later stages, polysomes are parallel to the already‐formed myofibrils. These polysomes are possibly synthesizing contractile proteins “in situ” and may represent a mechanism for myofibril diameter growth. In late embryonic and juvenile stages 100 Å—110 Å filaments appear to be continuous between Z bands of adjacent myofibrils. It is possible that such filaments of intermediate size are involved in aligning myofibrils into register

ISSN:0002-9106    

DOI:10.1002/aja.1001360408

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

年代:1973

数据来源: WILEY

摘要:

AbstractAlpha cells can be demonstrated in embryonic rat pancreas by a modification of the Grimelius silver nitrate technique. At the start of culture at 18 days of gestation, alpha cells are closely associated with exocrine tubules and beta cells. After ten days of culture they are arranged peripherally around a mass of beta cells, in islets that are characteristic of adult rat pancreas.

ISSN:0002-9106    

DOI:10.1002/aja.1001360409

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

年代:1973

数据来源: WILEY

摘要:

AbstractScanning electron microscopy reveals unique supraependymal cells in preoptic and infundibular recesses of 3‐ to 21 ‐week‐old monkeys. Most supraependymal cells are located on nonciliated areas, and characteristically have round bodies from which multiple branched processes extend. Surface spherules occur on cell bodies and processes. Processes exhibit local enlargements, interweave with processes from other cells, and penetrate underlying epe

ISSN:0002-9106    

DOI:10.1002/aja.1001360410

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

年代:1973

数据来源: WILEY

摘要:

AbstractMucosa of the rat stomach was (fast) frozen rapidly by immersion in liquid nitrogen or Freon 22 before chemical fixation in glutaraldehyde and/or osmium tetroxide. In parietal cells, continuity between membranes of the canalicular system and tubulovesicles was seen. This confirms the hypothesis that membrane flow between the two elements occurs in the secretory cycle. Such continuity is difficult to demonstrate in material fixed directly and presumably, therefore, the rapid freezing was effective in preventing changes in membranes and membrane flow during the period of fixation.

ISSN:0002-9106    

DOI:10.1002/aja.1001360411

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

年代:1973

数据来源: WILEY