A contribution to the functional morphology of the midgut gland in phalangiid harvestmen Gyas annulatus and Gyas titanus during their life cycle

The structure of the midgut gland and its changes in different seasons have been examined in the harvestmen Gyas annulatus and Gyas titanus (Arachnida: Opiliones: Phalangiidae). In both species, in the epithelium of the midgut gland two different types of cells are present: secretory and digestive ones. The secretory cells are characterized by plentiful rER and secretory granula. The digestive cells are characterized by an apical system of tubules. Both cells are connected by prominent specialized junctions. If a secretory cell is in contact with a digestive cell, rER cisterna are in close vicinity and parallel to these junctions. As found light- and electron microscopically and also histochemically, glycogen and lipids are stored in both cells. In both species, glycogen was seen to be used as energy compound during overwintering. At the end of their life, the digestive cells develop into excretory ones, containing metabolic wastes.     

Autophagic activity in the midgut gland of the overwintering harvestmen Gyas annulatus (Phalangiidae,Opiliones)

Juvenile harvestmen Gyas annulatus overwinter in dormancy in hypogean habitats for 4–5 months. The ultrastructure of the autophagic structures in their midgut epithelium cells was studied by light microscopy, transmission electron microscopy (TEM) and immunofluorescence microscopy (IFM) during this non-feeding period. Before overwintering (November), autophagic structures were scarce. In the middle (January) and at the end of overwintering (March), phagophores, autophagosomes and autolysosomes were present in the cytoplasm of both the secretory and the digestive midgut epithelium cells, gradually increasing their abundance during overwintering. In addition, vacuolization of the cytoplasm intensified. Both processes are induced by starvation. Autophagic structures and cytoplasm vacuolization enable the reuse of the cell's own components required for the maintenance of vital processes during dormancy. While TEM is a much more convenient method for recognition of the autophagic structure types and their ultrastructure, IFM enables exact counting of these structures.     

Cytochemical studies of developmental stages during oogenesis in Culex pipiens molestus (Forsk?l). I. Lipids and carbohydrates

Lipids and carbohydrates were studied in the polytrophic ovaries of Culex pipiens molestus during oogenesis. The cytoplasm of both the oocyte and the nurse cells contains lipid structures at all stages of development--granules in the early stages and spheres in the later stages. Intranuclear lipid bodies can be demonstrated in the oocyte and in the nurse cells. After leaving the nucleus, lipids are deposited in the peripheral cytoplasm. From the third to the seventh adult phase, lipid granules are concentrated in the area of the nurse cell and oocyte junction, indicating that lipids originate in the nurse cells and are transported from these to the oocyte. The follicular epithelial cells provide the oocyte with lipid material for fatty yolk synthesis and formation of the egg envelopes. Lipids are distributed similarly to the Golgi apparatus, indicating that there is a relationship between this organelle and fat formation. In the early stages, the cytoplasm of the oocyte, the nurse cells and the follicular epithelium contains glycogen granules. In the later stages these cells also contain mucopolysaccharides. The mucopolysaccharide yolk spheres are enclosed in vacuoles, while the chorion is composed of acid mucopolysaccharides. The follicular epithelium and vitelline membrane are of a mucopolysaccharide nature. A topographical relationship exists between the Golgi apparatus and the glycogen granules, indicating that this organelle also plays a role in glycogen synthesis.     

The ultrastructural investigation of the midgut in the quill mite Syringophilopsis fringilla (Acari,Trombidiformes: Syringophilidae)

The midgut of the females of Syringophilopsis fringilla (Fritsch) composed of anterior midgut and excretory organ (=posterior midgut) was investigated by means of light and transmission electron microscopy. The anterior midgut includes the ventriculus and two pairs of midgut caeca. These organs are lined by a similar epithelium except for the region adjacent to the coxal glands. Four cell subtypes were distinguished in the epithelium of the anterior midgut. All of them evidently represent physiological states of a single cell type. The digestive cells are most abundant. These cells are rich in rough endoplasmic reticulum and participate both in secretion and intracellular digestion. They form macropinocytotic vesicles in the apical region and a lot of secondary lysosomes in the central cytoplasm. After accumulating various residual bodies and spherites, the digestive cells transform into the excretory cells. The latter can be either extruded into the gut lumen or bud off their apical region and enter a new digestive cycle. The secretory cells were not found in all specimens examined. They are characterized by the presence of dense membrane-bounded granules, 2–4 μm in diameter, as well as by an extensive rough endoplasmic reticulum and Golgi bodies. The ventricular wall adjacent to the coxal glands demonstrates features of transporting epithelia. The cells are characterized by irregularly branched apical processes and a high concentration of mitochondria. The main function of the excretory organ (posterior midgut) is the elimination of nitrogenous waste. Formation of guanine-containing granules in the cytoplasm of the epithelial cells was shown to be associated with Golgi activity. The excretory granules are released into the gut lumen by means of eccrine or apocrine secretion. Evacuation of the fecal masses occurs periodically. Mitotic figures have been observed occasionally in the epithelial cells of the anterior midgut.     

Ultrastructural changes of the midgut epithelium in Isohypsibius granulifer granulifer Thulin, 1928 (Tardigrada: Eutardigrada) during oogenesis

The midgut epithelium of Isohypsibius granulifer granulifer (Eutardigrada) is composed of columnar digestive cells. At its anterior end, a group of cells with cytoplasm which differs from the cytoplasm of digestive cells is present. Probably, those cells respond to crescent-like cells (midgut regenerative cells) described for some tardigrade species. Their mitotic divisions have not been observed. We analyzed the ultrastructure of midgut digestive cells in relation to five different stages of oogenesis (previtellogenesis, beginning of the vitellogenesis, vitellogenesis—early choriogenesis, vitellogenesis—middle choriogenesis, late choriogenesis). In the midgut epithelium cells, the gradual accumulation of glycogen granules, lipid droplets and structures of varying electron density occurs. During vitellogenesis and choriogenesis, in the cytoplasm of midgut cells we observed the increasing number of organelles which are responsible for the intensive synthesis of lipids, proteins and saccharides such as cisterns of endoplasmic reticulum and Golgi complexes. At the end of oogenesis, autophagy also intensifies in midgut epithelial cells, which is probably caused by the great amount of reserve material. Midgut epithelium of analyzed species takes part in the yolk precursor synthesis.     

Effects of Fumidil B on the spore of Nosema apis and on lipids of the host cell as revealed by freeze-etching

The epithelial cells of the midgut of honey bees, Apis mellifera, infected with Nosema apis showed young and mature spores randomly distributed in the cytoplasm. In these cells, only mitochondria and protein granules were observed. After treating infected bees with Fumidil B, an ultrastructural alteration in the spore membrane, especially in the young spore, was observed. At the same time, lipid granules appeared in the cytoplasm, mostly around the spores. The number of protein granules also increased.     

Digestive cells in the midgut of Triatoma vitticeps (Stal, 1859) in different starvation periods

Triatoma vitticeps (Stal, 1859) is a hematophagous Hemiptera that, although being considered wild, can be found in households, being a potential Chagas’ disease vector. This work describes the histology and ultrastructure of the midgut of T. vitticeps under different starvation periods. Fifteen adults of both sexes starved for 3, 7, 20 and 25 days were studied. In general, digestive cells had apical microvilli, basal plasma membrane infoldings and central nucleus. The perimicrovillar membrane was found in all insects examined. Digestive cells of anterior midgut had lipid droplets, glycogen granules, developed basal labyrinth associated with mitochondria suggesting their role in nutrient storage and in fluid and ion transport. The cells of median and posterior regions of the midgut were rich in rough endoplasmic reticulum, lysosomes, vesicles and granules with different electron-densities. Moreover, cells of the posterior portion of the midgut had hemozoyn granules and mitochondria in the apical cytoplasm close to microvilli, suggesting their role in blood digestion and active nutrient absorption. The midgut of T. vitticeps showed differences in digestive cells associated with the time after feeding, and the increase of vesicles amount in long starvation periods, which suggests enzyme storage, which is readily used after a blood meal.     

Topochemistry of blood cells of the Gallus domesticus (Aves, Galliforme).

Blood smears of both male and female chicken Gallus domesticus were analysed by using the following topochemical methods: a) Periodic acid-Schiff (PAS) for glycogen. b) Mercury-bromophenol blue for protein. c) O-Toluidine for myeloperoxidase. d) Sudan black B for lipid. The PAS reaction revealed glycogen in the cytoplasm of all thrombocytes and in a few heterophils. The presence of proteins was evidenced in all types of cells. However variation in the intensity of staining of protein granules was observed in the fusiform structures of the heterophils. A negative reaction for myeloperoxidase was found in all cells. Although some evidence of myeloperoxidase activity was show in the polymorphonuclears it was not enough to ascertain a positive reaction. Lipids were detected in the cytoplasm of few heterophils, eosinophils and monocytes.     

Anatomy and fine structure of the alimentary canal of the spittlebug Lepyronia coleopterata (L.) (Hemiptera: Cercopoidea)

The alimentary canal of the spittlebug Lepyronia coleopterata (L.) differentiates into esophagus, filter chamber, midgut (conical segment, tubular midgut), and hindgut (ileum, rectum). The filter chamber is composed of the anterior extremity of the midgut, posterior extremity of the midgut, proximal Malpighian tubules, and proximal ileum; it is externally enveloped by a thin cellular sheath and thick muscle layers. The sac-like anterior extremity of the midgut is coiled around by the posterior extremity of the midgut and proximal Malpighian tubules. The tubular midgut is subdivided into an anterior tubular midgut, mid-midgut, posterior tubular midgut, and distal tubular midgut. Four Malpighian tubules run alongside the ileum, and each terminates in a rod closely attached to the rectum. Ultrastructurally, the esophagus is lined with a cuticle and enveloped by circular muscles; its cytoplasm contains virus-like fine granules of high electron-density. The anterior extremity of the midgut consists of two cellular types: (1) thin epithelia with well-developed and regularly arranged microvilli, and (2) large cuboidal cells with short and sparse microvilli. Cells of the posterior extremity of the midgut have regularly arranged microvilli and shallow basal infoldings devoid of mitochondria. Cells of the proximal Malpighian tubule possess concentric granules of different electron-density. The internal proximal ileum lined with a cuticle facing the lumen and contains secretory vesicles in its cytoplasm. Dense and long microvilli at the apical border of the conical segment cells are coated with abundant electron-dense fine granules. Cells of the anterior tubular midgut contain spherical secretory granules, oval secretory vesicles of different size, and autophagic vacuoles. Ferritin-like granules exist in the mid-midgut cells. The posterior tubular midgut consists of two cellular types: 1) cells with shallow and bulb-shaped basal infoldings containing numerous mitochondria, homocentric secretory granules, and fine electron-dense granules, and 2) cells with well-developed basal infoldings and regularly-arranged apical microvilli containing vesicles filled with fine granular materials. Cells of the distal tubular midgut are similar to those of the conical segment, but lack electron-dense fine granules coating the microvilli apex. Filamentous materials coat the microvilli of the conical segment, anterior and posterior extremities of the midgut, which are possibly the perimicrovillar membrane closely related to the nutrient absorption. The lumen of the hindgut is lined with a cuticle, beneath which are cells with poorly-developed infoldings possessing numerous mitochondria. Single-membraned or double-membraned microorganisms exist in the anterior and posterior extremities of the midgut, proximal Malpighian tubule and ileum; these are probably symbiotic.     

Electron microscopic study of the anterior midgut in Cenocorixa bifida Hung. (Hemiptera: Corixidae) with reference to its secretory function

The epithelium of anterior midgut of adult Cenocorixa bifida was examined with light and electron microscopy. The folded epithelium is composed of tall columnar cells extending to the lumen, differentiating dark and light cells with interdigitating apices and regenerative basal cells in the nidi surrounded by villiform ridges that penetrate deeply into the epithelium. The columnar cells display microvilli at their luminal surface. Microvilli lined intercellular spaces and basal plasma membrane infoldings are associated with mitochondria. These ultrastructural features suggest their role in absorption of electrolytes and nutrients from the midgut lumen. The columnar cells contain large oval nuclei with prominent nucleoli. Their cytoplasm is rich in rough endoplasmic reticulum, Golgi complexes and electron-dense secretory granules indicating that they are also engaged in synthesis of digestive enzymes. The presence of secretory granules in close proximity of the apical plasma membrane suggests the release of secretion is by exocytosis. The presence of degenerating cells containing secretory granules at the luminal surface and the occurance of empty vesicles and cell fragments in the lumen are consistent with the holocrine secretion of digestive enzymes. Apical extrusions of columnar cells filled with fine granular material are most likely formed in response to the lack of food in the midgut. The presence of laminated concretions in the cytoplasm is indicative of storageexcretion of surplus minerals. The peritrophic membrane is absent from the midgut of C. bifida.     

Cellular details of the midgut of Cryptocellus boneti (Arachnida: Ricinulei)

The midgut of Cryptocellus boneti was studied by light and electron microscopy. The epithelia of the diverticula and of the anterior part of the midgut tube are composed of two cell types: digestive and secretory. In contrast, the epithelia of posterior part of the midgut tube and of the stercoral pocket consist of one type of cells only. In some places, parts of the midgut system are connected by an intermediate tissue. Digestive cells are characterized by an apical system of tubules, nutritional vacuoles, and spherites; characteristic features of secretory cells are secretory granules and a prominent rough endoplasmic reticulum. Cells of the midgut tube appear not to be involved in the absorption of food. © 1994 Wiley-Liss, Inc.     

Glycogen accumulation in the parathyroid gland of the rat after fluoride ingestion

Summary The parathyroid glands of young male rats given 150 ppm fluoride in their drinking water for 10 weeks were examined by transmission electron microscopy. As a result of fluoride ingestion, the parathyroid chief cells of the experimental animals accumulated glycogen in excess of that seen in control animals given distilled drinking water for the same time period. In the majority of active chief cells, glycogen granules were diffusely spread throughout the cytoplasm as single granules or in small deposits. Large aggregations of glycogen granules were also seen within intercellular spaces. Accompanying the increase in glycogen was a rise in the number and development of the organelles associated with protein synthesis and secretion. The accumulation of glycogen is similar to that in hyperparathyroidism caused by chronic stimulation and prolonged secretory activity of the parathyroid gland. The results of this study suggest that increased amounts of glycogen occur in hyperactive chief cells of the parathyroid in response to the ingestion of large doses of fluoride.     

Structural and ultrastructural features of boar bulbourethral glands

The morphological features of boar bulbourethral glands were examined by light and transmission microscopy. Bulbourethral glands are compound tubuloalveolar glands surrounded by a capsule of dense connective tissue and arranged in multiple lobules formed by endpieces and excretory ducts. Endpieces and excretory ducts are both lined by a single epithelium of mucous cells with a basal nucleus. Epithelial cells accumulate secretory granules containing neutral and carboxylated acid mucosubstances and a small amount of sulphated acid mucosubstances. The ultrastructure of epithelial cells varies according to the secretory cycle. In initial stages, the cells show a columnar shape and secretory granules unevenly distributed in the cytoplasm. As the synthesis of mucosubstances progresses, the amount of the secretory granules increases and the cellular shape becomes pyramidal. Secretory granules can contain inclusions and present differences among them according to their different phases of formation. In pyramidal cells, secretory products are released into the lumen by a merocrine mechanism.     

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.     

Microstructural Analysis of the Capture Thread Spinning Apparatus in Orb Web Spiders

The microstructural characteristics of the capture thread production from silk glands in the orb web spiders were analyzed using scanning and transmission electron microscopes. Sticky and gluey capture threads of the web are originated from the silks of two flagelliform glands and four aggregate glands. They supply precursors of the secretory silks to a pair of characteristic “triad” spinning units on the posterior spinnerets. The aggregate gland is composed of large and multi‐lobed secretory region and thick excretory duct surrounded by large irregular nodules. The excretory duct of this gland basically consists of three superposed types of cells which are inner columnar epithelium, nodule forming cells and outer connectives. The nodules contain numerous mitochondria and glycogen particles within their cytoplasm and they are surrounded by the same sheath of thin connective tissues. Secretory region of the aggregate gland which produce water‐soluble components of the capture thread comprises discrete secretory vesicles and extensive rough endoplasmic reticulum. Characteristically, secretory droplets are formed without involvement of the Golgi complexes, suggesting that they do not play an important role in the processing of the capture threads. However the electron densities and internal textures of the granules are observed with diverse according to their maturation level. Finally, the secretory products are released by the mechanism of apocrine secretion losing part of their cytoplasm during this process.     

Histological and ultrastructural characterization of the alimentary system of solifuges (Arachnida,Solifugae)

Solifuges are voracious and fast predators. Once having captured a prey item, mostly small arthropods or even small vertebrates, they start feeding on their prey by constant chewing movements with their huge chelicerae. At the same time, they squeeze out the soft tissue that passes the anterior lattice‐like part of the mouthparts. The digestion of the food takes place in the midgut, which is anatomically highly complex. It consists of the midgut tube from which numerous prosomal and opisthosomal diverticula and tubular lateral branches arise. The dimorphic epithelium of the midgut tube and the diverticula is constituted of digestive and secretory cells. The digestive cells are characterized by an apical tubulus system and contain nutritional vacuoles, lipids, spherites, and glycogen. Secretory cells contain a huge amount of rough endoplasmic reticulum and secretory vacuoles. The lateral branches are ultrastructurally similar to Malpighian tubules and are likely involved in excretion. In contrast to the midgut, the epithelium of the hindgut consists of only one type of cell overlain by a thin cuticle. Digested residuals are stored in the hindgut until defecation. J. Morphol., 2010. © 2009 Wiley‐Liss, Inc.     

Electron microscope studies of Fasciola hepatica. 13. Fine structure of newly excysted juvenile

The gross morphology and fine structure of the newly excysted juvenile fluke are described. The tegument is organized as in the adult, with a spine-containing surface syncytium connected to a perinuclear region lying below the muscle layers. It differs from the adult, however, in having only one type of perinuclear region and one type of secretory body. The digestive system has all the morphological characteristics of a secretory epithelium, rather than an absorptive one. It has numerous dense secretory bodies, ribosomes, and GER, an irregular apical surface due to eccrine secretion, and a lumen filled with a moderately dense material derived from the dispersed secretory granules.The excretory system closely resembles that of the adult, but has, in addition, part of its ascending ducts ciliated and concretions as well as lipid droplets as visible excretory products. The muscle is identical with that of the adult and the parenchyma is also very similar to the adult, although it has more lipid droplets and is associated in a less complex way with cells of other organ systems. Groups of embryonic cells are present and are characterized by a dense, invaginated nucleus surrounded by a very thin layer of cytoplasm.     

Salivary gland of the tick vector of east coast fever. IV. Cell type selectivity and host cell responses to Theileria parva

Responses of cells in the tick salivary gland to parasitism by Theileria parva were studied by electron microscopy. The gland is composed of three distinct types of acini (I, II, III) which together include ten or more different cell types. Of some 30 infected cells observed in the present study, all were E-cells of acinus III. The parasite thus exhibits a high degree of selectivity for acinus and cell type. The glandular cell invaded undergoes massive hypertrophy and accumulates glycogen deposits in its cytoplasm which may serve as an energy source for the growing intracellular parasite. As synthesis of its secretory material declines the product is packaged in progressively smaller secretory granules. The extensive arrays of endoplasmic reticulum are dismantled and eliminated in autophagic vacuoles. Excess secretory granules are also broken down by crinophagy. After 4 days, sporogony is completed and the host cell contains 30,000–50,000 sporozoites in an electron-lucent cytoplasm largely devoid of cytomembranes and secretory granules. Mitochondria are still present and normal in appearance. The loss of basophilia and secretory granules observed heretofore by light microscopy have been attributed to ingestion and destruction of host organelles by the parasite. The pallid appearance of the cytoplasm has been interpreted as a sign of impending degeneration of the host cell. In electron micrographs no ingestion of organelles by the parasite or degenerative changes were found. The host cell clearly remains viable and metabolically active throughout sporogony. The striking changes in its ultrastructure result from active elimination of organelles and inclusions by the host cell itself in response to parasitism.     

The ultrastructure of the midgut epithelium in millipedes (Myriapoda,Diplopoda)

The midgut epithelia of the millipedes Polyxenus lagurus, Archispirostreptus gigas and Julus scandinavius were analyzed under light and transmission electron microscopies. In order to detect the proliferation of regenerative cells, labeling with BrdU and antibodies against phosphohistone H3 were employed. A tube-shaped midgut of three millipedes examined spreads along the entire length of the middle region of the body. The epithelium is composed of digestive, secretory and regenerative cells. The digestive cells are responsible for the accumulation of metals and the reserve material as well as the synthesis of substances, which are then secreted into the midgut lumen. The secretions are of three types – merocrine, apocrine and microapocrine. The oval or pear-like shaped secretory cells do not come into contact with the midgut lumen and represent the closed type of secretory cells. They possess many electron-dense granules (J. scandinavius) or electron-dense granules and electron-lucent vesicles (A. gigas, P. lagurus), which are accompanied by cisterns of the rough endoplasmic reticulum. The regenerative cells are distributed individually among the basal regions of the digestive cells. The proliferation and differentiation of regenerative cells into the digestive cells occurred in J. scandinavius and A. gigas, while these processes were not observed in P. lagurus. As a result of the mitotic division of regenerative cells, one of the newly formed cells fulfills the role of a regenerative cell, while the second one differentiates into a digestive cell. We concluded that regenerative cells play the role of unipotent midgut stem cells.     

Ultrastructure and regeneration of midgut epithelial cells in Lithobius forficatus (Chilopoda,Lithobiidae)

Lithobius forficatus (Myriapoda, Chilopoda, Lithobiidae) is a widespread species of centipede that is common across Europe. Its midgut epithelial cells are an important line of defense against toxic substances that originate in food, such as pathogens and metals. Despite this important role, the biology of the midgut epithelium is not well known. Here we describe the ultrastructure of the midgut epithelium, as well as the replacement of degenerated midgut epithelial cells. The midgut epithelium of L. forficatus is composed of digestive, secretory, and regenerative cells. The cytoplasm of digestive cells shows regionalization in organelle distribution, which is consistent with the role of these cells in secretion of enzymes, absorption of nutrients, and accumulation of lipids and glycogen. Secretory cells, which do not reach the luminal surface of the midgut epithelium, possess numerous electron‐dense and electron‐lucent granules and may have an endocrine function. Hemidesmosomes anchor secretory cells to the basal lamina. Regenerative cells play the role of midgut stem cells, as they are able to proliferate and differentiate. Their proliferation occurs in a continuous manner, and their progeny differentiate only into digestive cells. The regeneration of secretory cells was not observed. Mitotic divisions of regenerative cells were confirmed using immunolabeling against BrdU and phosphohistone H3. Hemocytes associate with the midgut epithelium, accumulating between the visceral muscles and beneath the basal lamina of the midgut epithelium. Hemocytes also occur among the digestive cells of the midgut epithelium in animals infected with Rickettsia‐like microorganisms. These hemocytes presumably have an immunoprotective function in the midgut.