The ultrastructure of the duct system in the rat extraorbital lacrimal gland

Summary The duct system of the rat exorbital lacrimal gland consists of intercalated ducts, interlobular ducts and excretory ducts. The morphological changes from one type of duct to the next are gradual. At the light microscopical level this consists of a change from a bilaminar epithelium in the intercalated ducts to an epithelium, consisting of approximately three layers — which may be pseudostratified — in the excretory ducts. The basal layer of the intercalated ducts consists of myoepithelial cells, whereas the inner epithelial cells may have both a secretory and an electrolyte transporting function. The interlobular duct epithelium contains many cells with deep infoldings of the basolateral plasma membranes and associated mitochondria, suggesting a similar function to the striated duct epithelium in salivary glands. Numerous basal cells in this epithelium have tentatively been interpreted as unusual myoepithelial cells. Nerve terminals have been observed in the ductal epithelium.This work was supported by the National Health and Medical Research Council of Australia. — We wish to thank Mrs. Eva Vasak for her expert technical assistance.     

Anatomical studies of the secretory structures: Glandular trichomes and ducts, in Grindelia pulchella Dunal (Astereae, Asteraceae)

The ultrastructure of the glandular trichomes and secretory ducts of Grindelia pulchella was studied. Plastids, mitochondria and endoplasmic reticulum are involved in the secretory process of both, trichomes and ducts. A special tissue with “transfer cells” is associated with the duct epithelial cells. The secretion is produced in the transfer cells and then is transferred to the duct epithelial cells where it accumulates in the vacuoles. The occurrence of cavities within the cell walls of the trichome cells and duct epithelial cells is described. The secretion is accumulated between the cell wall and the cuticle of these cells. When the cuticle is broken the secretion is released. We conclude that granulocrine secretion operates in this species.     

Immunolocalization of PTHrP in the sublingual glands of three mammals

The present study deals with immunohistochemical localization of PTHrP in sublingual glands of white mouse, bank vole, and common vole. PTHrP immunoreactivity was observed in epithelial cells of striated, interlobular and main excretory ducts of the salivary glands in all the three animal species tested. However, we found no positive reaction for PTHrP in epithelial cells of the intercalated ducts. In striated duct cells, the reaction intensity was species-dependent. In bank vole and common vole, the reaction was very strong, while in white mouse very weak. In the remaining segments of excretory ducts (interlobular and main excretory duct) we found no species-related differences in the reaction intensity or character. Myoepithelial cells surrounding ducts and mucous tubules with serous demilunes in sublingual glands were also PTHrP-negative in all the three animal species tested.     

Distribution of aquaporin 1 in the rat pancreatic duct system examined with light- and electron-microscopic immunohistochemistry

The pancreatic duct is the major site for the secretion of pancreatic fluid, but the pathway of water transport in this system is not known. Recently, intense signal for mRNA of aquaporin 1 (AQP1) water channels was detected in isolated rat interlobular ducts. Therefore, we performed light- and electron-microscopic (EM) immunohistochemistry for AQP1 in the rat pancreatic ducts. AQP1 immunoproducts were not observed in the acinar cells, centroacinar cells or intercalated ducts. In the smaller intralobular ducts less than 10 microm in diameter (the lumen plus duct cells), most cells were immunonegative. AQP1-positive cells appeared in intralobular ducts 10-15 microm in diameter. In small and medium-sized interlobular ducts 15-70 microm in diameter surrounded by periductal connective tissue 2-40 microm thick, most cells were AQP1 positive with various degrees of immunoreactivity. In the larger interlobular ducts, the expression of AQP1 was variable, ranging from immunopositive to negative. In the main pancreatic duct, most cells were negative for AQP1. EM immunohistochemistry of the intralobular and small interlobular ductal epithelial cells showed that the AQP1 immunoproducts were more abundant in the basolateral membrane than in the apical membrane, though they were present in both membranes. In the medium-sized interlobular ducts, AQP1 immunoproducts were distributed densely along the apical, lateral interdigitation and basal membrane of the epithelial cells. In the various sizes of interlobular ducts, immunoproducts were associated not only with the plasma membrane, but also with the caveolae and vesicle-like structures. Secretin did not induce any significant difference in AQP1 expression and cellular and subcellular localization. These results indicate that the expression and subcellular localization of AQP1 vary considerably depending on the duct size, which may reflect water transport characteristics in the different divisions of the pancreatic duct system.     

Cell proliferation kinetics of the bile duct epithelium of the rat

Abstract. Cell proliferation kinetics of the extrahepatic bile duct were studied by flash and cumulative labelling methods and immunohistochemical techniques. We compared the cell kinetics of the epithelium of the intra- and extra-pancreatic bile ducts and of the bile duct of the ampulla in rats administered intraperitoneally with bromodeoxyuridine (BrdUrd). After a single injection of BrdUrd (flash labelling), labelled cells appeared in the lower portion of the downgrowths of the epithelium in the intra-and extra-pancreatic bile ducts. A gradual accumulation of the labelled cells at the surface epithelium was observed during the cumulative labelling. After cumulative labelling the labelled cells gradually decreased in number and were finally confined to the degenerative cell zone of the surface epithelium 30 days later. Similarly, after a single injection of BrdUrd, the labelled cells in the bile duct of the ampulla appeared at the lower half of the crypt from where they migrated to the upper portion during cumulative labelling. These findings indicate that epithelial cells of the bile duct are renewed at the lower portion of the downgrowths of the epithelium, or crypt, and shed from the surface epithelium or upper portion of the fold. The labelling indices reached 23.83 ± 7.47% in the intra-pancreatic bile duct, 14.74 ± 7.99% in the extra-pancreatic bile duct and 43.42 ± 4.40% in the bile duct of the ampulla at the end of 70 h cumulative labelling. The fluctuating values of the labelling index were higher in the bile duct of the ampulla than in the intra- or extra-pancreatic bile ducts. These results indicate that the bile-duct epithelium undergoes a slower renewal rate than the other parts of the gastrointestinal tract, and that the renewal time of the epithelial cells is shorter at the bile duct of the ampulla than at the intra- or extra-pancreatic bile ducts.     

Fine structure of the mandibular gland in volcano rabbit

The mandibular glands of 6 male and 6 female volcano rabbits were examined by means of light and transmission electron microscopy. The acinar cells of the glands were seromucous in nature, and contained faintly basophilic granules. The cells were classified into the light cells containing granules of low or moderate densities and the clear cells having polygonal granules of low density. The preacinar cells were occasionally observed at the site between acinus and intercalated duct. These cells had many weakly basophilic granules which contained fine granular materials of moderate density. The intercalated ducts were composed of light cells containing cored granules. The striated duct cells consisted of light cells and dark cells. Both of them contained a few vacuoles and vesicles, but no secretory granules. No sex-and age-related differences were observed in the mandibular gland of the volcano rabbit. The mandibular gland of the volcano rabbit was similar to the rabbit mandibular gland rather than the pika mandibular gland morphologically.     

A comparative study of the differentiation and involution of the Mullerian duct and Wolffian duct in the male and female fetal mouse

The present investigation has examined the ultrastructural differentiation of the genital ducts of both sexes of fetal mice. The emphasis of observations was placed on the phenomenon of morphogenetic cytolysis, particularly during the critical periods of Wolffian duct stabilization and Mullerian duct involution. Both developing and regressing genital ducts evidence extensive cytolysis. Autophagy appears to be the mechanism of morphogenetic changes in the developing male Wolffian duct. Autophagy, heterophagy, and degeneration in situ are all prominent cytolytic activities in female Wollfian duct involution. The developing female Mullerian duct undergoes extensive morphogenetic remodeling by the mechanisms of autophagy, heterophagy, and degeneration in situ. In the male Mullerian duct, autophagy, heterophagy, and degeneration in situ are also prominent. In addition, whole degenerated epithelial cells are extruded from the duct early in regression which may be realted to the transformation of periductal mesenchymal cells into an "epithelioid cell cuff" which does not form around the regressing Wolffian duct. The formation of this mesenchymal condensation surrounding the duct is also accompanied by the protrusion of Mullerian epithelial cell cytoplasm into the mesenchymal cells. These observations may evidence a complex epithelial-mesenchymal interaction occurring during male Mullerian duct involution.     

An ultrastructural analysis of the salivary system of the terrestrial mollusc, Limax maximus.

The bilateral salivary glands, ducts, and nerves of the giant garden slug Limax maximus control the secretion of saliva and its transport to the buccal mass. Each salivary nerve, which originates at the buccal ganglion, contains over 3000 axon profiles. The axons innervate the musculature of the duct and branch within the gland. The salivary duct is composed of several muscular layers surrounding an epithelial layer which lines the duct lumen. The morphology of the duct epithelium indicates that it may function in ion or water balance. The salivary gland contains four major types of secretory cells. The secretory products are released from vacuoles in the gland cells, and are presumably transported by cilia in the collecting ducts of the gland into the larger muscular ducts.     

An electron microscopic study of the spermathecal complex of virgin Aedes aegypti mosquitoes

Virgin mosquitoes were studied with the electron microscope. Spermathecal duct walls contain cuticle, epithelium, and a richly innervated spiral muscle; myocytes are linked by desmosome-like attachment plaques to the underlying epithelium. Periductal cells along upper portions of the ducts have a large secretory droplet within a highly irregular extracellular lacuna and are attached to a long secretory ductule through which finely granular material is delivered to the duct lumen and this enters the spermathecae. Basal gland cells of spermathecae have short ductules containing secretion in virgins. Secretory material in spermathecae of virgins does not form a complete internal membrane.     

Fine structure of the mandibular gland of the Djungarian hamster (Phodopus sungarus)

The mandibular gland of the Djungarian hamster was examined by light microscopy, and transmission and scanning electron microscopies. Its acinar cells reacted with periodic acid-Schiff (PAS) and were weakly stained with alcian blue (AB). There were intercellular canaliculi between the acinar cells. These cells therefore appeared to be seromucous. The acinar epithelium was composed of light cells containing various spherical secretory granules. The granular cells of the mandibular gland possessed many acidophilic granules exhibiting a positive reaction to PAS stain. They were frequently observed at the junction of the acini and intercalated ducts in all mandibular glands examined. All of these cells were light and contained secretory granules of varying size and density. The intercalated ducts consisted exclusively of light cells possessing a few round granules of high density in the apical region. The striated ducts were comprised of two portions--a secretory portion and a typical striated portion without secretory granules. The secretory portion consisted of light, dark and specifically light epithelial cells containing acidophilic granules, which exhibited a strongly positive PAS reaction. The epithelium of typically striated portions was composed of light and dark cells containing fine vacuoles in the apical region. The mandibular gland of the Djungarian hamster revealed no histological differences between sexes.     

The post-embryonic changes in Melipona quadrifasciata anthidioides Lep. (Hym. Apoidea). II. Development of the salivary glands system

The paper deals with the development of the salivary gland system in Melipona quadrifasciata anthidioides, which begins in the prepupal stage. The silk glands degenerate by autolysis at the end of the larval stage. Degeneration is characterized by cytoplasmic vacuolization and pycnosis of the nuclei of the secretory cells. The glandular secretory portion of degenerated silk glands separates from the excretory ducts. The salivary glands develop from the duct of the larval silk glands. The thoracic salivary glands develop from the ducts of the secretory tubules and the head salivary glands from the terminal excretory duct. The mandibular glands appear in the prepupa as invaginations of mandibular segments, and their differentiation to attain the adult configuration occurs during pupation. The hypopharyngeal glands have their origin from evaginations of the ventral anterior portion of the pharynx. A long tubule first appears with walls formed by more than one cellular layer. Then some cells separate from the lumen of the duct, staying attached to it by a cuticular channel in part intracellular. The initial duct constitutes the axial duct, in which the channel of the secretory cells opens. During the development of salivary and mandibular glands, they recapitulate primitive stages of the phylogeny of the bees. During the development of salivary glands system, mitosis accounts for only part of the growth. Most of the growth occurs by increase in size of cells rather than by cell division. In brown-eyed and pigmented pupae six days before emergence, the salivary gland system is completely developed, although not yet functioning.     

Fine structure of the parotid and mandibular glands of the cotton rat (Sigmodon hispidus).

The parotid and mandibular glands of the cotton rat were examined by light and transmission electron microscopy. Parotid gland: Acinar cells were serous in nature, and contained electron-dense granules. Intercalated duct cells contained electron-dense granules. Striated duct cells had small granules of moderate and high electron densities. Mandibular gland: Acinar cells were seromucous in nature, and contained granules of low and moderate electron densities. Intercalated duct cells contained granules of moderate and high electron densities. Striated ducts were comprised of two portions - a secretory portion and a striated portion without granules. The secretory portion had many electron-dense granules. A sexual dimorphism was obserbed in these granules, which were smaller and fewer in females than in males.     

Distribution, Development and Structure of Resin Ducts in Guayule (Parthenium argentatum Gray)

The distribution, development and structure of resin ducts inguayule (Parthenium argentatum Gray), the second best sourceof natural rubber, have been studied. Resin ducts are widelydistributed in stem, root, leaf, petiole and peduncle. The ductsin the primary tissues are initiated schizogenously and theirfurther development is schizolysigenous. The ducts in the cortexof the root do not have a well-defined epithelium. Ducts developedfrom the vascular cambium are initiated and develop schizogenously.Both resin and rubber are produced in the epithelial cells ofresin ducts. While resin is secreted into the duct lumen, rubberis stored within these cells. Epithelial cells store more thanneighbouring parenchyma cells. Guayule, rubber, resin, ducts, epithelial cells     

Changes in the main submandibular salivary duct of rabbits resulting from ductal ligation

Normal submandibular ducts from rabbits have been examined by mucosubstance histochemistry, transmission and scanning electron microscopy. The results were compared with the appearances of ducts removed 4...6 weeks after ligation. The normal ducts were composed mainly of columnar "light" cells and basal cells but, in addition, some "dark" cells and scattered goblet containing sulphated mucins were always present. The luminal surface of the ductal cells possessed numerous microvilli protruding into the lumen, and a rim of negatively charged mucin was present on this surface of these cells. After ligation the ducts became greatly distended by their fluid contents which remained under pressure until the duct was incised. The epithelial cells were flattened and appeared to contain less cytoplasm per cell; "light" cells, basal cells and "dark" cells were still recognisable. Goblet cells were much more plentiful than in the control ducts and often protruded into the lumen despite the increased intraluminal pressure. The development of a number of ciliated cells had also occurred and they were often situated close to goblet cells. Lymphatic vessels were more prominent around the ligated ducts. Luminal microvilli were less numerous than in the control ducts but the rim of negatively charged mucin on the luminal surface of ductal cells was more conspicuous. Mixed inflammatory cells were present within the lumina of ligated ducts especially in those parts adjacent to the ductal cells. No inflammatory cell has been observed passing through the wall of a main duct and the possibility exists that these cells had entered lumina within the gland and migrated from there to the main duct. The above findings may serve to help our understanding or physiological events in the ducts.     

Evidence that dilation of isolated salivary ducts from the tick Dermacentor variabilis (Say) is mediated by nitric oxide

We used pharmacological methods to test the hypothesis that female Dermacentor variabilis salivary ducts dilated when dopamine-stimulated and that dilation was nitric oxide-mediated. Stimulation with dopamine resulted in an increased diameter (19.7%) compared to unstimulated ducts (P<0.005). Pretreatment with L-NAME, an inhibitor of nitric oxide synthase, or cytochalasin D abolished the dilation. Addition of L-arginine to L-NAME-treated ducts partially restored the ability to dilate. A cuticular coil composed of a series of concentric rings ran the length of the duct adjacent to the epithelial cell layer. In stimulated ducts, the center-to-center periodicity of these rings increased from 0.59 μm in unfed ducts to 1.0 μm from partially fed ducts (P<0.05). When the ducts from partially fed females were stimulated with dopamine, the periodicity increased further to 1.75 μm (P<0.05), suggesting the coils moved further apart in response to stimulation. Prominent folds lining the lumen of unstimulated ducts were less pronounced in stimulated preparations, suggesting that the cuticle stretches, thereby increasing lumen size. Actin was localized in epithelial cells as a honeycomb pattern that we suggest links the epithelial cells to the rings. Together, these data support the following hypothesis: stimulated ducts dilated during fluid production; dilation involved an actin-based system, and was mediated by nitric oxide. Dilation of the duct may enhance its role as a reservoir for saliva produced by the acini during the period between imbibition and salivation.     

Development, Histochemistry and Ultrastructure of Gum-resin Ducts in Commiphora mukul Engl.

Gum-resin ducts are present in the primary and secondary phloemof Commiphora mukul Engl. The important gum-resin, known commerciallyas ‘guggul’, is secreted and collected in ductswhich develop schizogenously. The duct initials have dense cytoplasm,large nuclei, increased cytoplasmic RNA and proteins. The lumenof newly-formed ducts widens accompanied by anticlinal divisionsand subsequent tangential elongation of epithelial cells. Histochemicaltests reveal that the epithelial cells have apparently largeamounts of proteins, cytoplasmic RNA, and DNA in the nucleus.Lipid globules are also present in these cells. Epithelial cellwalls in contact with the duct are thin and of a loose fibrillarmesh. Microtubules, randomly oriented in the epithelial cellsare always parallel and adjacent to the wall. The cytoplasmis rich in ribosomes, endoplasmic reticulum, mitochondria, plastidsand vacuoles containing osmiophilic substances. At the peripheralregion of the duct, electron-transparent bodies containing densely-stainedmaterial are present close to the tangential wall.     

The origin and fate of spermatophores in the viviparous teleost Cymatogaster aggregata (Perciformes: Embiotocidae)

The sperm of the shiner surfperch are packaged into high density aggregations which are introduced into the female genital tract at insemination. Germ cell differentiation occurs within cysts formed by nongerminal Sertoli cells. In late spermiogenesis, spermatozoa within the cysts come to lie parallel to each other and become more densely packed. These sperm packets (spermatophores), containing approximately 600 spermatozoa, then are released into the efferent sperm ducts. The exact nature of the spermatophore binding material is not known, but a major component is proteinaceous and is synthesized in the rough endoplasmic reticulum of the efferent sperm duct epithelial cells. The mechanism by which the spermatophores pass from cysts into ducts is not clear. It appears that whereas many Sertoli cells degenerate causing the cyst wall to break down, many Sertoli cells do not degenerate, but rather assume the configuration of columnar duct cells. The spermatophores remain intact within the testicular ducts, but rapidly dissolve within the female ducts in response to increased pH.     

Fine structure of the excretory system of the deep posterior (Ebner's) salivary glands of the human tongue

Human deep posterior lingual glands (von Ebner's glands) are located beneath the circumvallate papillae. They are formed by tubuloalveolar adenomeres, intercalated ducts and excretory ducts coming together in the main excretory duct. The tubuloalveolar cells, pyramid-shaped, show large and dense secretory granules (clear cored) throughout the cytoplasm, rare basal folds and packed cisternae of rough endoplasmic reticulum (RER) at the basal pole. The columnar cells of the intercalated ducts are arranged in a monolayer. They are characterized by dense, clear-core secretory granules (mostly in the apical cytoplasm), a basal nucleus, well-developed RER and Golgi apparatus, and thin filaments distributed in supra- and perinuclear cytoplasm. Striated ducts are absent. Excretory ducts, coming together in the main duct, are lined by a bistratified epithelium. The inner layer consists of columnar cells showing bundles of tonofilaments with scarce secretory activity. The outer layer is composed of basal cells lying on the basal lamina. The main excretory duct, which opens at the bottom of the vallum, shows a stratified epithelium. The outer side is composed of 2-3 layers of malpighian cells lying on the basal lamina. The inner side consists of a single layer of cuboidal-columnar cells with dense apical granules and well-developed organelles synthesizing and condensing secretions. These cells interpolate with goblet cells, rare mitochondria-rich cells, ciliated cells and numerous small globous cells showing a clear matrix and lacking secretory granules. The cilia show a 9 + 2 microtubular structure with basal bodies provided with striated rootlets. Myoepithelial cells surround with their processes the basal portions of the secretory cells and the intercalated ducts. The conclusions concern some comparative aspects and some hypothesis on the functional role of goblet cells, ciliated cells and epithelial cells lining the different ducts, also in relation to the final secretory product.     

Localization of laminin-5, HD1/plectin, and BP230 in the submandibular glands of developing and adult mice

We studied the distributions of laminin-5 and hemidesmosome components, HD1/plectin and BP230, in the submandibular glands of adult and developing mice. In adult mice, laminin-5 was expressed in the basement membranes of both the myoepithelial cells and excretory ducts. The former expression was predictable because laminin-5 is a ligand for hemidesmosomes, which appear in myoepithelial cells and stratified epithelium. However, the latter expression pattern suggested that the non-stratified epithelium of the excretory duct might also be associated with hemidesmosomes. During fetal development, laminin-5 was found in the basement membrane of developing ducts but not epithelial end buds in which future lobules are formed by epithelial branching. The expression of HD1/plectin but not BP230 was noted in the developing duct at early embryonic stages, indicating the presence of type II hemidesmosomes. Expression of BP230 appeared in the excretory duct epithelium at around the day of birth. At this stage, the typical hemidesmosome was observed in the duct epithelium. Our results suggest that laminin-5 is involved in duct development rather than epithelial branching. The results also suggest that the developing duct epithelium interacts with laminin-5 through the type II hemidesmosome, which later matures into a typical hemidesmosome upon the onset of expression of BP230. Accepted: 12 October 1999     

Light and electron microscope investigations on the salivary glands of the slug,Agriolimax reticulatus (Müller)

Summary Ten cell types have been identified with the light microscope in the salivary glands ofA. reticulatus. Eight of these have also been observed with the electron microscope. A secretory cycle involving several cell types is absent. At least six different secretions are believed to be released from the glands. The pathways by which the secretions pass from the cells to the collecting ducts are outlined.Salivary duct epithelial cells have a characteristic ultrastructure which is similar to that found in ion and water transporting cells. It is proposed that the duct epithelial cells have a similar function.