Silvia Correr

Histology of the exocrine pancreas.

The morphology of the exocrine secretory unit of the pancreas, i.e. the pancreatic acinus, is reviewed. The histological features of the acini and their relation with the duct system are described. The acinar three‐dimensional architecture was studied by means of different ultrastructural techniques, some of which are complementary. The fine structure and morphodynamics of the acinar cells are also described. In addition, the location of the organelles in specific cytoplasmic domains and their close morphofunctional relationship with the sequential stages of secretion of the digestive enzymes are specially emphasized. Finally, morphological approaches are suggested to achieve a better comprehension of the physiological and pathological pancreatic activities whose morphodynamics need to be further elucidated or are almost totally unknown. Microsc. Res. Tech. 37:384–398, 1997.

The Rat Pituitary Cleft: A Correlated Study by Scanning and Transmission Electron Microscopy

SummarySEM reveals that the inner surface of the pituitary cleft is lined by a continuous layer of marginal cells possessing microvillous and ciliated apical surfaces. The ciliated cells are more numerous on the posterior side (toward the pars intermedia) than on the anterior side of the cleft (toward the pars distalis). In contrast small infoldings (crypts) were occasionally noted only on the marginal layer covering the distal part of the hypophysis. In some areas of the cleft the surface features of the marginal cells are rather similar to the epithelial cells populating the upper parts of the respiratory tract in their topography and distribution. In other regions they also show striking similarities with the ependymal cells (tanycytes) lining the lateral recesses of the 3rd ventricle and the infundibular process with which the pituitary cleft has a very close topographical relationship.The parenchymal cells of the pars distalis are closely related to the flattened marginal cells of the cleft. The intercellular spaces of the pars distalis form a three-dimensional labyrinthic series of cavities continuous with the submarginal spaces of the cleft. Further SEM and TEM results demonstrate that the majority of the microvillous marginal cells lining both sides of the cleft possess surface features such as bulbous protrusions, laminar evaginations and large cytoplasmatic vacuoles, which are very likely the expression of an active transport of fluids.On the basis of these results it is concluded that the fluid-like material (colloid) present in the pituitary cleft is mainly derived from the fluids contained in the lacunar spaces of the pars distalis. Thus, marginal cells by absorbing fluids from the cleft by active endocytosis, may transport to the pars intermedia material (or hormones) produced in the distal part of the gland and vice versa.The cilia present on many marginal cells, based on their 9+2 tubular pattern, possess a kynetic role. This is very similar to that shown by the ciliated cells of the ependyma lining the brain ventricles. The occurrence of ciliated cells within the pituitary parenchyma (mainly in the follicles) suggests that they probably arise from the ciliated cells populating the marginal layer of the cleft and with which the parenchyma cells are closely related.

STRUCTURE AND FUNCTION OF THE HUMAN OOCYTE-CUMULUS-CORONA CELL COMPLEX BEFORE AND AFTER OVULATION

SummaryThe fine structure of the human cumulus oophorus has been reviewed on the basis of scanning and transmission electron microscopic observations as well as of immunofluorescence data. Tissues sampled from preovulatory ovarian follicles and cumulus-enclosed oocytes and fertilized eggs (collected from the oviduct or obtained during in vitro fertilization procedures) have been evaluated from a microtopographic and morphodynamic point of view in order to better clarify the possible role of this population of cells. In particular, the following aspects have been studied and discussed: the presence of multiple close contacts (modulated by the interposition of the zona pellucida) between the oocyte surface and the long microvillous evaginations projecting from the inner aspect of corona cells surface (through these structures the intraovarian cumulus oophorus may control oocyte growth and metabolism up until the time of ovulation); the occurrence of different subpopulations of cells (steroid-synthetic cells, cells producing adhesive proteins, leukocytes, macrophages) in the postovulatory, extraovarian cumulus oophorus surrounding oocytes, zygotes and early developing embryos. All these elements found in the cumulus mass may positively act, through their paracrine activities, on the chemical composition of the microenvironment in which fertilization occurs.

A scanning electron-microscopic study of “supramarginal cells” in the pituitary cleft of the rat

SummaryUnusual cells lying above the marginal cellular layer of the rat pituitary cleft were studied by SEM and TEM. These cells — from their location termed supramarginal cells — have a characteristically irregular cell body from which arise a number of long and thin branched processes ending among the microvilli and cilia of the marginal cells delimiting the anterior and posterior walls of the cleft. Some supramarginal cells are star-shaped elements with thin extensions, others have a triangular or spindle-shaped body from which emerge long ameboid processes with fibril-like projections. Miniblebs, miniruffles, occasional veils and short microvilli extend over the surface of these elements.Supramarginal cells are very similar to the “Kolmer epiplexus cells” originally found on the choroid plexus or other areas of the third ventricular wall where they are known as “supraependymal cells”.Present evidence suggests that supramarginal cells of pituitary cleft might have phagocytic properties and an hematogenous origin as monocytes and, as such, closely resemble Kolmer epiplexus cells of brain ventricles. Others might arise from “folliculo-stellate cells” or closely related marginal cells once they become free into the pituitary cleft.Supramarginal cells are recognized as motile phagocytes acting as scavengers and possibly regulating the extracellular environment of the cleft and associated adenohypophy-sial tissues. In considering the area where they are located supramarginal cells might assume a specific role in relation to the integrated neuroendocrine function of the hypothalamus-ventricle-hypophysial complex. To this complex the pituitary cleft is closely associated embryologically and anatomically.

Microperoxisomes in steroidogenic cells of the rat ovary: interstitial, thecal and luteal cells.

Microperoxisomes are present in luteal, interstitial and thecal cells. They are in close relation with smooth endoplasmic reticulum and lipids. Their probable role in steroid biosynthesis is discussed.

Morphological expression of angiogenesis in the mammalian ovary as seen by SEM of corrosion casts

In the mammalian ovary, follicular and corpus luteum cycle is associated with intensive microvascular remodelling. The complex angiogenic dynamics are finely tuned by numerous regulatory factors acting as activators (up-regulators) or inhibitors (down-regulators) of angiogenesis. Alterations of such a tight modulation are involved in several pathologies, including infertility, polycystic ovarian syndrome, ovarian hyperstimulation syndrome and ovarian cancer. We have demonstrated in several experimental models that ovarian function is critically and specifically dependent on angiogenesis for follicular development, ovulation, and corpus luteum growth. The aim of this review is to summarize the results we have obtained on the morphodynamic remodelling of ovarian microvascularization, in polyovulatory (rat, rabbit and pig) and monovulatory species (cow), using scanning electron microscopy of vascular corrosion casts. The knowledge of the morphological expression of the up- and down-regulation of angiogenesis occurring in mono and polyovulatory animals might provide useful information to preserve fertility and to increase of the effectiveness of reproductive management in species of domestic interest.

An Ultrastructural Study of Epithelium Differentiation in the Human Fetal Fallopian Tube

The epithelial structure of the developing human fetal Fallopian tube has been studied systematically by parallel light, transmission and scanning electron microscopy. The specimens for this study were collected from spontaneous abortions at the 14th, 18th, 20th and 22nd weeks and from cases of intrauterine fetal death at the 24th and 31st weeks (hydrocephalus). The epithelium lining the wall of the female genital ducts was pseudostratified in a columnar fashion. It consisted of differentiating ciliated and microvillous cells and some degenerating elements. Microvillous cells-by far the most abundant in the early phases of tubal development-often showed a solitary cilium. Ciliated elements, though always less numerous than microvillous cells, were more densely concentrated on the developing fimbriae and at the uterotubal junction than in the ampulla. On the mucosal surface of the same regions, rounded intercellular holes delimited many crypts, from which ciliated elements sometimes sprouted. Notable aspects of cell proliferation and ciliogenesis were commonly observed and are likely to be related to circulating estrogens. These ultrastructural data indicate that the typical pattern of the adult oviduct is already sketched in fetal life. Furthermore, a strategic gathering of cilia was noted primarily at the sites of the developing oviduct, which will serve to mediate the passage of sperm and/or ova and promote fertilization in adult life.

Architecture of the Myosalpinx of the Isthmus in the Guinea Pig by Means of Scanning Electron Microscopy

The three-dimensional architecture of the isthmic myosalpinx in the guinea pig was investigated by means of a technique that involves stretching the myosalpinx under a dissecting microscope, followed by selective digestion of the interstitial connective tissue with KOH and, finally, observation under a scanning electron microscope. The images obtained in this way prove that the myosalpinx is arranged in single bundles of smooth muscle cells which essentially do not show any specific geometrical course. Furthermore, smooth muscle cell bundles following an oblique course, not referred in the literature prior to this report, were demonstrated. These new three-dimensional microanatomical results call for a reevaluation of the functional role of oviduct motility.

Scanning electron microscopy of dissociated pancreatic acinar cell surfaces.

SummaryThe pancreatic acinar cell surfaces have been studied by SEM with a dissection technique and correlated with results obtained by TEM. The SEM results demonstrate characteristic arrangement of microplicae which in some areas are densely packed.In many areas, the microplicae are distributed in such a manner that they create zones with typical geometrical shapes and show a relatively smooth surface.These smooth areas may coincide, as indicated by correlated TEM results, with the limits of intimate contact between adjacent acinar cells which, in turn, represent part of the junctional complex. Another aspect revealed by these SEM preparations concerns the presence of groups of densely packed microplicae, arranged in regular rows and distributed along some grooves and/or infoldings of the cellular surface. On the basis of SEM and TEM information, it is likely that these structures correspond to intercellular (and possibly, in some cases, intracellular) canaliculi which topographically form a kind of extensive microlabyrinthine arrangement running along all the cell sides.One final point revealed by fractured samples concerns the finding of spherical zymogen droplets within the vesicles of the Golgi complex. Because in many scanning images these vesicles appear connected by small openings, it is suggested that they may represent a system of intercommunicating chambers (vacuoles) through which the zymogen droplets can be continuously accumulated and discharged into the acinar lumen.

Ultrastructure of Rathke’s pituitary cleft

Rathke’s pituitary cleft represents the original recess of so-called Rathke’s pouch derived in the embryo from the ectodermal evagination of the stomodeum (1,2). In several mammals, for example the rat, dog and cat, this recess persists during postnatal life as a wide fissure separating the pars distalis from the pars intermedia. It is lined by a continuous layer of cells termed ‘marginal cells’, and contains a fluid-like material (colloid) of uncertain function, origin and chemical composition (3).