Light and Electron Microscopy of the European Beaver (Castor fiber) Stomach Reveal Unique Morphological Features with Possible General Biological Significance

Anatomical, histological, and ultrastructural studies of the European beaver stomach revealed several unique morphological features. The prominent attribute of its gross morphology was the cardiogastric gland (CGG), located near the oesophageal entrance. Light microscopy showed that the CGG was formed by invaginations of the mucosa into the submucosa, which contained densely packed proper gastric glands comprised primarily of parietal and chief cells. Mucous neck cells represented <0.1% of cells in the CGG gastric glands and 22–32% of cells in the proper gastric glands of the mucosa lining the stomach lumen. These data suggest that chief cells in the CGG develop from undifferentiated cells that migrate through the gastric gland neck rather than from mucous neck cells. Classical chief cell formation (i.e., arising from mucous neck cells) occurred in the mucosa lining the stomach lumen, however. The muscularis around the CGG consisted primarily of skeletal muscle tissue. The cardiac region was rudimentary while the fundus/corpus and pyloric regions were equally developed. Another unusual feature of the beaver stomach was the presence of specific mucus with a thickness up to 950 µm (in frozen, unfixed sections) that coated the mucosa. Our observations suggest that the formation of this mucus is complex and includes the secretory granule accumulation in the cytoplasm of pit cells, the granule aggregation inside cells, and the incorporation of degenerating cells into the mucus.     

Ultrastructure of the cardiac and pyloric glands of the gastric mucosa of the South African hedgehog,Atelerix frontalis

The cardiac and pyloric glands in the gastric mucosa of the South African hedgehog, Atelerix frontalis, are described. The cardiac area of the stomach contains proper cardiac glands and lacks undifferentiated fundic glands. The cardiac glands are simple tubular, coiled, and lined with columnar cells ultrastructurally similar to those of the gastric surface epithelium. Secretory granules with varying electron densities fill the apical cytoplasm of these cells. In contrast to other mammals, these glands lack mucous neck cells. The neck of the pyloric glands contains only a single cell type, whereas the basal regions of these glands contain “light” and “dark” cells. The secretory granules in the “dark” cells and the pyloric neck cells have a moderate electron density and often contain an electron dense core. An electron-lucent cytoplasm with numerous polysomes is characteristic of the “light” cells. Some “light” cells contain electron-dense granules in the apical cytoplasm. The presence of only neutral mucins in the cardiac gland cells denotes the absence of mucous neck cells. The acidic mucins within the pyloric neck cells seem to indicate that these cells are mucous neck cells, whereas the neutral mucins within the basally located pyloric gland cells show at least a partial functional difference from the pyloric neck cells. © 1993 Wiley-Liss, Inc.     

The fine structure of the gastric epithelium of the rainbow trout, Salmo gairdneri, Richardson

Fine structural characteristics of the columnar mucus cells lining the surface and pits of the gastric mucosa, oxyntic cells lining the glands and the gastric endocrine cells were studied. The surface mucus cells, in addition to their primary involvement in production of mucus, showed structural adaptations. Release of the mucus vesicles was achieved by exocytosis. Transition from pit gland cells was abrupt since no mucus neck cells were observed. The oxyntic cells possessed apical and basal microvillous processes, a well developed tubulovesicular system, zymogen granules and extensive RER associated with many large mitochondria. When stimulated by distension of the stomach, the apical cytoplasm was converted into a labyrinth of cytoplasmic processes, while annular lamellae, each of which showed a short peripheral linear density appeared in the basal cytoplasm. The endocrine cells showed apical modifications as microvilli, cilia and reduced glycocalyx covering. Three types were distinguished on the basis of their granular morphology.     

Bromodeoxyuridine-immunohistochemistry on cellular differentiation and migration in the fundic gland of Xenopus laevis during development

Summary Cellular differentiation and migration in the fundic glands of adult and larval Xenopus laevis have been examined using bromodeoxyuridine-immunohistochemistry. In the adult fundic gland, cumulative labeling with bromodeoxyuridine revealed a proliferative cell zone between the surface mucous cells and mucous neck cells, in what is referred to as the neck portion of the gland. The labeling-index of mucous neck cells had rapidly increased by week-5. The labeling-index of oxynticopeptic cells showed a more delayed increase until week-7, coincident with the decrease in the labeling of mucous neck cells. In the immature fundic glands of larvae, the labeled proliferating cells were randomly distributed throughout the developing gastric mucosa. During metamorphosis, the labeling-index of immature epithelial cells was highest at stage 63. Following administration of bromodeoxyurdine at this, stage, there was no significant loss of labeled epithelial cells during the metamorphosing period. Furthermore, there was no significant difference in the labeling-indices among the epithelial cells, such as surface mucous cells/generative cells, mucous neck cells, and oxynticopeptic cells, 7 days after administration. Cellular differentiation and migration pathways of epithelial cells in the fundic gland of adult X. laevis and its larvae are discussed.     

Ultrastructure of intestinal and gall-bladder epithelium in the teleost Gasterosteus aculeatus L., as related to their osmoregulatory function

Summary Intestinal and gall-bladder epithelial cells in sticklebacks have been examined in ultrathin sections and freeze-etch replicas. Enterocytes throughout the intestine appear to have a well-developed basal labyrinth similar to that of renal tubular cells, consisting of baso-lateral infoldings closely associated with numerous mitochondria. The lumen inside these intracellular membranes is continuous with the intercellular space via pores. Such a membrane system is also present in the epithelial cells lining the gall bladder, distinguishing them from gall-bladder cells of higher vertebrates. Morphometric analysis indicates that the basal labyrinth of enterocytes in the posterior part of the intestine increases markedly in both sexually mature males and androgen-treated females. This does not occur in the anterior part or gall bladder. In sticklebacks, androgens cause reduced urine excretion and enhanced fluid release via the anus. We conclude that the cells lining the intestine and gall bladder possess an extensive basal labyrinth that may function as a backward channel system, enabling fluid to be produced in the intestine of fish. The androgen-induced increase in the extent of the basal labyrinth in the posterior part of the intestine may be related to the enhanced rate of intestinal fluid excretion observed in sexually mature male sticklebacks.     

Gastric lipase and pepsinogen during the ontogenesis of rabbit gastric glands

In rabbit stomach, gastric lipase activity level was found to increase from birth to 30 days old (weaning), and then decreased. In contrast, pepsin activity only appeared between 30 to 45 days old, and increased till to the adult level. It was observed that maturation of gastric glands in cardial mucosa was a downward elongation process from the mitotic cell pool. These mitotic cells were always found in the neck of the gastric glands, corresponding to the bottom of the gland at 6 days old and to the mid-zone of the gland in adult. Location of rabbit gastric lipase (RGL) cells in cardial glands varied with age and was found along the pit of the gastric glands at 6 days old. The extent of this cellular location decreased with age, whereas a second RGL cell zone appeared below the mitotic cell area at 18 and 30 days old. At 45 days old, the pepsinogen cells appeared in the bottom of the gland, and consequently the RGL cells were located in the mid-zone of the gastric glands, between mitotic cells (neck of the gland) and pepsinogen cells (lower part of the gland). Ultrastructural study of cardial gastric glands revealed different morphologies of the secretion granules in the cells along the gastric glands. In 6-day-old rabbits, secretory granules were found uniformly electron dense in the bottom of the glands and were RGL-labeled by the immunogold technique. In the medium part of the glands, granules appeared biphasic, with a clear and a dense part, and RGL labeling was confined to the electron-dense part.(ABSTRACT TRUNCATED AT 250 WORDS)     

Glycoconjugate histochemistry of the rat fundic gland using Griffonia simplicifolia agglutinin-II during the development

The development and maturation of fundic glands of Wistar rats were studied using Griffonia simplicifolia agglutinin-II (GSA-II) histochemistry at the light microscopic and electron microscopic levels. In adult rats, mucous neck cells and cells intermediate between mucous neck cells and chief cells were specifically labeled with GSA-II, whereas other fundic gland cells were virtually negative. Ontogenetic studies revealed that GSA-II positive cells appeared at the bottom of the gland by 21 days of gestation. With differentiation and aging, the elongation of the fundic gland continued, and the labeling intensity of the mucous neck cells increased by 3 weeks after birth. Cells intermediate between mucous neck cells and chief cells were discernible from 3 days after birth. Typical mucous neck cells appeared at 3 weeks after birth, when their labeling intensity with colloidal gold (CG) particles approximated that of adults. On the other hand, the reactive cell population gradually moved from the bottom toward the middle portion of the gland. Finally, the reactive cells were localized at the neck portion of the fundic gland. These results suggest that GSA-II is a valuable marker for studying mucous neck cells and both their precursor cells and their derivatives.     

Comparative morphology of the stomach of some laboratory mammals

Histomorphology of the stomach of mouse, rat, hamster, guineapig, gerbil, and rabbit was studied. Although a common structural basis existed in the stomach between these species, the occurrence and distribution of various cells in gastric glands differed considerably between them. In mice, rats, hamsters and gerbils, the lower one-third of the glandular lamina propria was seemingly occupied by a varying proportion of parietal and chief cells. In rabbits, the predominantly occurring chief cells were distributed in the lower three-quarters of the glands intermingling with parietal cells, but in guinea-pigs the chief cells were not discernible. In hamsters, there was, however, a gradual increase of chief cells from the junction between nonglandular-glandular stomach toward the pyloric region. In all these species, parietal cells were the predominant cell type in the upper half to upper one-third of the gastric glands, often extending up to the neck of the glands interspersing between mucus neck cells and occasionally between chief cells.     

Distribution of the glio-interstitial system in molluscs

Summary Ten hamsters received repeated injections of ³H-thymidine for 4 days and were allowed to survive for 7, 28, 42 and 100 days. Changes in spatial distribution of the labelled cells and in labelling indices of each cell line in the gastric glands were studied at various days after ³H-thymidine injections, and the fate of the mucous neck cell, the replacement of the chief cell and the mode of cell migration were discussed.After 4 days of repeated injections of ³H-thymidine, the labelled parietal cells and the mucous neck cells were concentrated at the neck area. Starting from the neck area, they migrated an average of 3 micra downwards per day. By 42 days, they reached the middle level of the glands, where the labelled mucous neck cells decreased but the labelled chief cells increased in number. The differentiation of the chief cell then appears to take place at the middle level of the glands through transformation of the migratory mucous neck cells. After 4 days of the labelling, about 1.8% of the chief cells located in the lower part of the glands was found to undergo in situ replication. This indicates that the renewal of this cell type is partly assured by its own mitotic activity.The foveolar cell — the future surface epithelium — seems to migrate upwards along the long axis of the glandular tubule in the pipe line system, which means first produced, first migrates. After migrating out from the neck area, the parietal cell and the mucous neck cell (the future chief cell) take an average of 200 days to reach the lower end of the glands. In the process of migration, however, the cells produced contemporaneously at the neck area became scatteringly spread from the neck towards the bottom of the gland. The time required for the newly-formed cells to reach the lower end of the gland varied between 100 and 300 days. In the gastric glands the cells first produced at the neck area do not first reach the lower end of the glands. This mode of random migration is referred to as the stochastic flow system. As one of the probable factors which disturb the pipe line flow of downward cell migration, cellular movements perpendicular to the long axis of the glandular tubule were suggested to occur at random at an any level of the gastric glands.Supported by a Grant-in-Aid for Cancer Research from the Ministry of Education, Science and Culture, Japan     

Ultrastructure of the reproductive system of the black swamp snake (Seminatrix pygaea). II. Annual oviducal cycle

This article is the first ultrastructural study on the annual oviducal cycle in a snake. The ultrastructure of the oviduct was studied in 21 females of the viviparous natricine snake Seminatrix pygaea. Specimens were collected and sacrificed in March, May, June, July, and October from one locale in South Carolina during 1998-1999. The sample included individuals: 1) in an inactive reproductive condition, 2) mated but prior to ovulation, and 3) from early and late periods of gravidity. The oviduct possesses four distinct regions from cranial to caudal: the anterior infundibulum, the posterior infundibulum containing sperm storage tubules (SSTs), the uterus, and the vagina. The epithelium is simple throughout the oviduct and invaginations of the lining form tubular glands in all regions except the anterior infundibulum and the posterior vagina. The tubular glands are not alveolar, as reported in some other snakes, and simply represent a continuation of the oviducal lining with no additional specializations. The anterior infundibulum and vagina show the least amount of variation in relation to season or reproductive condition. In these regions, the epithelium is irregular, varying from squamous to columnar, and cells with elongate cilia alternate with secretory cells. The secretory product of the infundibulum consists largely of lipids, whereas a glycoprotein predominates in the vagina; however, both products are found in these regions and elsewhere in the oviduct. In the SST area and the anterior vagina, tubular glands are compound as well as simple. The epithelium of the SST is most active after mating, and glycoprotein vacuoles and lipid droplets are equally abundant. When present, sperm form tangled masses in the oviducal lumen and glands of the SST area. The glands of the uterus are always simple. During sperm migration, a carrier matrix composed of sloughed epithelial cells, a glycoprotein colloid, lipids, and membranous structures surround sperm in the posterior uterus. During gravidity, tubular glands, cilia, and secretory products diminish with increasing development of the fetus, and numerous capillaries abut the basal lamina of the attenuated epithelial lining of the uterus.     

Lectin binding sites in the human gallbladder and cystic duct

A battery of 18 fluorescein isothiocyanate (FITC) labeled lectins was used to histochemically define the features of epithelial cells in the body, neck and the cystic duct of the human gallbladder. Surface epithelium in all three anatomic locations reacted with all lectins, either diffusely or focally, except for lectin type I from Griffonia simplicifolia and type II from Ulex europaeus. No quantitative differences were noted except for the tendency of some lectins to bind more often to the neck and cystic duct epithelium rather than the body and vice versa. In the body the surface epithelium did not differ from cells lining the crypts. On the other hand, glands of the neck and the cystic duct were essentially indistinguishable one from another but differed from the overlying surface epithelium in so far as they reacted with some lectins which were unreactive with surface epithelium and vice versa. Considerable case to case variation in the expression of lectin binding sites in each of three anatomic areas was noted. No consistent differences were noticed between gallbladders removed for cholecystitis--cholelithiasis and those removed for other incidental reasons. We conclude that all epithelial cells in the cholecysto-biliary tract are rich on glyconjugates but the pattern of expression varies depending on the anatomical location and the influence of poorly understood individual determinants.     

Ultrastructure of the larval salivary glands of Megaselia scalaris Loew (Diptera,Phoridae)

Each of the paired salivary glands of third instar larvae of the humpbacked fly Megaselia scalaris is a bag-like structure with a short neck region from which a single duct emerges. The two ducts form a common duct that empties into the ventral region of the pharynx near the mouthparts. The wall of the glands and ducts consists of a simple squamous epithelium that rests upon a connective tissue layer. Cells in the neck are less flattened than those found elsewhere. The basal surfaces of the cells are infolded most deeply in the neck and the least in the duct. The apical surfaces of the cells possess microvilli except in the duct where the apices of the cells are covered by a complex extracellular layer. This layer displays circularly arranged folds that accommodate a thread-like supportive structure resembling taenidial threads of tracheae. Elaborate junctional complexes are associated with the lateral surfaces of the cells. Elements of these complexes include a zonula adherens, a series of pleated septate desmosomes, and conventional desmosomes. The cytoplasm of the glandular cells is filled with RER and other organelles normally seen in cells that export proteins and mucosubstances. Secretory material found in the lumens of the glands reacts only moderately with the PAS procedure but more strongly with alcian blue and methods that demonstrate proteins. The nuclei of the glandular cells contain single large nucleoli and polytene chromosomes whose banding is rather indistinct. Treatment with EDTA produces detrimental effects on all of the foregoing ultrastructural features of the glands and ducts.     

Secretion and activation of the rennin by the rabbit's stomach

The mucosa of the rabbit's stomach has been studied histochemically, electron microscopically and fluorescence immunologically. The main purpose was to find out whether or not this mucosa secrets the enzyme rennin. During the first two weeks after birth, the gastric glands are composed of only undifferentiated cells. The differentiation of these glands into cardiac, fundic and pyloric glands coincides with the final stage of this period. In the course of the period mentioned the P.A.S.-positive material and the fluorescence induced by rennin exhibit a similar location in the apical cytoplasm of the epithelial cells lining the mucosal surface, the gastric pits and the necks of gastric glands. In the light of these findings, the elaboration and activation of the enzyme rennin is being discussed.     

Fine structure of the genital system in the females of Pergamasus mites (Acari: Gamasida: Pergamasidae)

The female reproductive system in Pergamasus mites consists of an unpaired vagina, vaginal duct, uterus, and ovary. Additionally, there are paired vaginal glands, as well as unpaired ventral and paired lateromedial glandular complexes. The vagina and vaginal duct are cuticle‐lined. In the dorsal wall of the vagina, this lining forms the endogynium which possesses a “sac” and two conspicuous “spherules” and is armed with “stipula” and other cuticular protrusions. The endogynium functions as a spermatheca, being a storing site for the spermatophore. The spherule procuticle is perforated by microvilli of underlying cells that are structurally very unusual. The lining of the vaginal duct forms numerous cuticular fibers directed toward the vagina. There is an external layer of muscles, supposedly functioning as a sphincter. The uterus is an organ in which the fertilized egg is stored for some time and starts embryonic development. Its wall is composed of glandular epithelial cells. The ovary consists of inner and outer parts. The former part is formed by a nutritive syncytium, whereas the latter contains growing oocytes. Two groups of glands connect with the genital tract. Paired vaginal glands are composed of glandular and secretion‐storing parts and open into the vagina. Paired lateromedial and unpaired ventral glandular complexes empty into the genital tract between the vaginal duct and uterus. The structure of the female genital system is discussed in terms of its function and phylogeny. J. Morphol. 240:195–223, 1999. © 1999 Wiley‐Liss, Inc.     

Lectin binding sites in the human gallbladder and cystic duct

Summary A battery of 18 fluorescein isothiocyanate (FITC) labeled lectins was used to histochemically define the features of epithelial cells in the body, neck and the cystic duct of the human gallbladder. Surface epithelium in all three anatomic locations reacted with all lectins, either diffusely or focally, except for lectin type I from Griffonia simplicifolia and type II from Ulex europaeus. No quantitative differences were noted except for the tendency of some lectins to bind more often to the neck and cystic duct epithelium rather than the body and vice versa. In the body the surface epithelium did not differe from cells lining the crypts. On the other hand, glands of the neck and the cystic duct were essentially indistinguishable one from another but differed from the overlying surface epithelium in so far as they reacted with some lectins which were unreactive with surface epithelium and vice versa. Considerable case to case variation in the expression of lectin binding sites in each of three anatomic areas was noted. No consistent differences were noticed between gallbladders removed for cholecystitis — cholelithiasis and those removed for other incidental reasons. We conclude that all epithelial cells in the cholecysto-biliary tract are rich on glyconjugates but the pattern of expression varies depending on the anatomical location and the influence of poorly understood individual determinants.     

Immunohistochemical localization of Na+,K+-ATPase in rodent and human salivary and lacrimal glands

The enzyme Na+,K+-ATPase was localized immunohistochemically in major salivary glands of mouse, rat, and human and in exorbital lacrimal glands of the rodents. Immunoreactive Na+,K+-ATPase was abundant in the basolateral membranes of all epithelial cells lining striated and intra- and interlobular ducts of all glands. Reactivity of intercalated ducts varied among gland type and species. Cells lining granular ducts in rodent submandibular gland showed a heterogeneous staining pattern in rat but stained homogeneously in mouse. Secretory cells varied greatly in their content of immunoreactive Na+,K+-ATPase. As with all duct cells, staining was present only at the basolateral surface and was never observed at the luminal surface of reactive secretory cells. Mucous cells failed to show any reactivity in any gland examined. Serous cells showed a gradient of immunostaining intensity ranging from strongly positive in demilunes of human sublingual gland to negative in rat submandibular gland and lacrimal glands of rats and mice. The presence of basolaterally localized Na+,K+-ATPase in most serous cells but not in mucous cells suggests that the enzyme contributes to the ion and water content of copious, low-protein serous secretions. The intense immunostaining of cells in most if not all segments of the duct system supports the idea that the ducts are involved with modification of the primary saliva, and extends this concept to include all segments of the duct system.     

Immunolocalization of surfactant protein-D (SP-D) in human fetal, newborn, and adult tissues.

Immunoreactive surfactant protein-D (SP-D) was assessed in human fetal, newborn, and adult tissues. In the fetal lung, SP-D was detected on airway surfaces by 10 weeks' gestation, staining increasing in the distal airways, decreasing in the proximal conducting airways with advancing gestation. In lungs from near-term infants and adults, SP-D was detected in Type II cells, serous cells of tracheobronchial glands, and subsets of cells lining peripheral airways. Immunostaining was decreased or absent in areas of lungs of neonates after injury to Type II cells, infection, or hemorrhage and was decreased in collapsed or unseptated airways from older infants with bronchopulmonary dysplasia. SP-D was also detected in many organs at all ages. SP-D was readily detected in epithelial cells and luminal material in lacrimal glands, salivary glands, pancreas, bile ducts, renal tubules, esophageal muscle and glands, parietal cells of the stomach, crypts of Lieberkuhn, sebaceous and eccrine sweat glands, Von Ebner's glands, endocervical glands, seminal vesicles, adrenal cortex, myocardium, and anterior pituitary gland. SP-D is a widely distributed member of the "collectin" family of polypeptides secreted onto luminal surfaces by epithelial cells lining ducts of many organs, where it likely plays a role in innate host defense.     

Correlative light and scanning electron-microscopic study of feline gastric mucosa: the cardiac region (pars cardiaca)

The cardiac region (pars cardiaca) of the cat's stomach was examined with light and scanning electron microscopy. The glands are simple, coiled tubular, and contain mucus-secreting cells. Their surfaces are covered with microvilli which are concentrated on the boundaries of the mucus-secreting cells. A few cells interposed between the glandular cells are probably G cells. They are identified by apical projections of long microvilli into the lumen of the gland. The surface epithelial cells lining the cardiac region are covered by minute microvilli. The muscularis mucosae is not distinctly divided into two layers. However, a group of smooth muscle cells which are directed in a circular manner around the gastroesophageal junction is considered to be the distal esophageal sphincter.