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doi: 10.1002/aja.1001450102pmid: 1246963
It has recently been discovered that the stratum corneum and superficial living epidermis of mammalian skin are organized into neat vertical columns of interdigitating cells. The mechanism for this organization has not yet been determined. This study shows that the stacked organization is not unique to the epidermis but also occurs in cork cambium and the pith of woody plant stems. The structural and spatial organization of the stacked cells in these tissues were compared and found to approximate closely the shape of Kelvin's minimum‐surface polygon, the tetrakaidecahedron. Paper models of flattened tetrakaidecahedra were constructed and found to stack in columns of interdigitating units which are consistent with all of the structural details seen in stacked cells observed under the light and the scanning electron microscopes. Indeed, only polygons of this type are capable of aggregating without interstices in the manner of the stacked cells. A study of stacked arrays of these models has revealed a mechanism by which the epidermis might become organized in columns of stacked and interdigitating cells. The proposed mechanism assumes that cells within an array seek the smallest possible surface‐to‐volume ratio and, under appropriate conditions, form stacked tetrakaidecahedra.
Kormano, Martti; Reijonen, Kalevi
doi: 10.1002/aja.1001450103pmid: 942809
The microvascular anatomy of the human epididymal duct system from rete testis to vas deferens was studied using microangiography and histology. Various segments of the duct system show significant differences in the density and arrangement of the small blood vessels. The rete testis is poorly vascularized while the first lobulated segment of the epididymis, which is formed by the efferent ducts is provided with a dense subepithelial capillary bed. The more distal segments of the epididymis have less dense capillarization surrounding the epididymal duct. In the vas deferens the blood vessels form a double capillary network. The outer capillary network surrounds the smooth muscle layers and the inner is located immediately beneath the duct epithelium. The organization of blood capillaries in the human epididymis and the differences seen in different portions of the excurrent duct system follow basically the general pattern seen in some experimental animals.
King, Barry F.; Tibbitts, F. Donald
doi: 10.1002/aja.1001450104pmid: 1246967
The structure of the placental labyrinth, interlobular or “coarse” syncytium, visceral (splanchnopleuric) yolk sac, giant cells and subplacenta of the chinchilla was studied with the electron microscope. The fine structure of the interhemal membrane of the placental labyrinth was found to be hemomonochorial, consisting of a single layer of syncytial trophoblast. In this respect, the placental labyrinth was similar to that of another caviomorph rodent, the guinea pig. The labyrinthine trophoblast had pinocytotic vesicles as well as larger vacuoles and multivesicular bodies. The interlobular syncytium contained granular endoplasmic reticulum, and in one case from early in gestation there were intracisternal granules in the ER. The visceral endodermal cells of the inverted yolk sac placenta had a well‐developed system of apical vesicles and tubules as well as larger cytoplasmic vacuoles. Their appearance was similar to that of endodermal cells found in other rodents which are known to absorb proteins and other substances from the uterine lumen. Towards term the giant cells were often vacuolated and contained large deposits of glycogen as well as lipid droplets. The syncytial trophoblast of the subplacenta contained numerous moderately electron‐dense granules which may be secretory in function; cytotrophoblastic cells lacked these granules. The subplacental syncytium often surrounded spaces or lacunae which contained an electron‐dense granular material.
Russo, Jose; Furmanski, Philip; Bradley, Ronald; Wells, Peter; Rich, Marvin A.
doi: 10.1002/aja.1001450105pmid: 129001
An ultrastructural and cytochemical study of normal human mammary epithelial cells cultured from post‐weaning breast fluids is described. Cells were examined at the time of plating and at intervals up to 28 days in culture. Three different stages in the morphological differentiation of these cells in vitro were observed: (1) the first stage was the formation of a monolayer of single cells, which occurred between days 1 and 10 in culture. The cells in this stage were not interconnected by junctional complexes and lacked Mg++‐ dependent ATPase activity in the plasma membranes, but did contain a large quantity of lipid and exhibited some secretory characteristics. (2) The second stage, occurring at 10 to 16 days in culture, was characterized by the formation of junctional complexes, the appearance of Mg++‐dependent ATPase in the plasma membrane and a decrease in the number of dense bodies with peroxidase activity. (3) The third stage, occurring at 16 to 28 days in culture, was characterized by the formation of stratified layers of epithelial cells, which were inter‐connected by a large number of desmosomes with numerous pleomorphic microfilaments. The Mg++‐dependent ATPase activity in the plasma membrane was retained and the dense bodies with peroxidase activity were rarely observed at this stage. During the last seven days in culture, secondary lysosomes, autophagosomes and residual bodies were prominent in the cells of the stratified layer. After 28 days in culture, the cells began to round up and slough off the culture plate.
doi: 10.1002/aja.1001450106pmid: 1246968
Degeneration and early regeneration of olfactory epithelium from two strains of mice was studied at the light and electron microscopic levels from 12 hours to 3 days following nasal irrigation with 1% aqueous solution of zinc sulfate (ZnSO4) (a compound known to selectively damage olfactory epithelium). Distinct patterns of degeneration and stages of regeneration were evident following treatment. During the first 24 hours after treatment three progressive manifestations of the degenerative process were seen: (1) a relatively mild condition which was characterized by surface irregularities produced by cell protrusions, highly vacuolated cytoplasm, presence of large lysosome‐like bodies and prominent intercellular spaces, (2) a more severe condition in which large areas of the epithelium were detached from the basement membrane and cellular debris was present in the nasal chamber, and (3) a condition of total or near‐total denudation of the epithelium of olfactory mucosa. The basal lamina was continuous and intact in most regions and the integrity of the subjacent connective tissue was mostly well‐preserved. Nerve bundles of the fila olfactoria were noted in varying degrees of degeneration during the course of the experiment. The most advanced neural degeneration was seen 24 to 72 hours after treatment. Onset of regeneration was suggested by the appearance of a simple squamous layer of cells above the basement membrane 48 to 72 hours after treatment. In addition to the simple epithelium a stratified epithelium consisting of two to four cell layers was also observed at this time. Glandular cells, containing secretory granules identical to those in Bowman's glandular cells, were noted in an apparent process of migration from the lamina propria into the stratified epithelial layer. The last mentioned observation supports the proposition that new supportive epithelial cells originate from cells of Bowman's gland.
doi: 10.1002/aja.1001450107pmid: 1246964
Rabbit spleens have been examined after perfusion fixation with and without prior washing with various fluids. The platelets were stored in the splenic sinuses and in the cord spaces as single platelets, or in loosley packed aggregates which appeared to be anchored to the endothelium by one or a few platelets. After washing prior to fixation most of the platelets disaggregated and regained their normal shape. Some platelets adhered to morphologically normal endothelium even after prolonged perfusion. Occasionally, platelets were observed inside splenic endothelial cells. Others were closely associated with macrophages, many of which also contained engulfed platelets.
doi: 10.1002/aja.1001450108pmid: 1246965
Cycling rats were hysterectomized and/or unilaterally ovariectomized (ULO) on day 2 (metestrus). Collateral blood supply to the remaining ovary via the uterine artery was left intact or disrupted. Animals were killed in metestrus after one complete estrous cycle. Control rats were also killed at this time.
doi: 10.1002/aja.1001450109pmid: 813511
In the monkey lung (Macacus nemestrina) canalization of all bronchopulmonary segments begins simultaneously at the peripheral future‐alveolar‐duct portions of each segment and then continues progressively centralwards. Its simultaneous appearance in all segments of a human lung of the 17th postovulatory week (19th postmenstrual week) has now been confirmed (cf. Boyden, '74). The mode of canalization, as seen under the light microscope, is here demonstrated.
Bondareff, William; Geinisman, Yuri
doi: 10.1002/aja.1001450110pmid: 1246966
Synapses were counted in electron micrographs of the middle third of the molecular layer of the dentate gyrus of Fischer 344 rats, 3 months and 25 months of age. A 27% decrease in the number of synapses was found in senescent animals compared with young adults. This loss of synapses could not be correlated with changes in synaptic size, tissue volume or number of postsynaptic granule cells.
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