Histochemical changes in the midgut of two ixodid tick speciesBoophilus microplus andRhipicephalus appendiculatus during digestion of the blood meal

The changes in the midgut epithelia of two ixodid tick species,Boophilus microplus andRhipicephalus appendiculatus, have been studied using several histochemical techniques. It was revealed that there is an accumulation of RNA at the time of tick attachment to the host and prior to the arrival of the blood meal, indicating that the midgut digest cell is furnished with the machinery characteristic of a synthetic cell. There appears to be a synchrony in the appearance of granules with peroxidase activity and the uptake of haemoglobin into the midgut digest cells. Alkaline phosphatase activity was observed in the midgut epithelia of all ticks except in a few of the long-starved ticks, and was concentrated in the apical plasma membrane regions of those digest cells involved in absorption and the intracellular digestion of haemoglobin. The presence of these enzymes suggests that the midgut digest cell is a multifunctional cell capable of both secretory and digestive activities. The colloidal material in the midgut lumen was found to result from the accretion of several products both secreted and excreted by the midgut epithelial cells and exhibited different staining reactions depending on which component dominated. The nature of the material suggests that in addition to its digestive function it may serve as a sink to bind all the by-products of digestion and thereby facilitate their excretion.     

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.     

The ultrastructure of the midgut and the formation of peritrophic membranes in a harvestman,Phalangium opilio (Chelicerata Phalangida)

Summary The ultrastructure of the midgut epithelium of Phalangium opilio was examined. In the anterior part of the midgut the epithelium consists of three different types of cells, called resorption, digestion, and excretion cells according to their presumed functions. Excretion cells may represent old digestion cells. The relation between resorption and digestion cells needs further investigation. The epithelium of the posterior part of the midgut consists of two types, transport and secretion cells, which seem to serve mainly for the resorption of water and the secretion of peritrophic membranes, respectively.Peritrophic membranes are secreted by the anterior midgut epithelium mainly in a period between 2 and 4 h after feeding. Chitin or chitin precursors could be localized in vesicles and in the brush border of midgut cells, and in the peritrophic membranes, using colloidal gold labelled with wheat germ agglutinin. Two different textures of chitin-containing microfibrils were found in the peritrophic membranes, either a random or a hexagonal texture. The latter results if the microfibrils polymerize between the basal parts of the microvilli. Irregularities of the hexagonal texture can be correlated with an irregular pattern of the microvilli. In the posterior midgut peritrophic membranes with a random texture, chitin-containing microfibrils are continuously secreted in the form of patches.     

Ultrastructural studies on the midgut epithelium and digestion in the female tickArgas (Persicargas) arboreus (Ixodoidea: Argasidae)

The ultrastructure of the midgut epithelium and digestion in the female tickArgas (Persicargas) arboreus are described before and after feeding, up to oviposition. The epithelium consists of secretory cells, digestive cells (DI and DII), and regenerative cells which may differentiate into any of the other cell types. In unfed ticks, the midgut wall consists mainly of type DII digestive cells retained from a previous feeding, and a few regenerative cells. Within 3 days after the tick feeding, haemolysis of the host blood components occurs in the midgut lumen. Secretory cells, the first differentiation of the regenerative cells, are presumed to produce a haemolysin and an anticoagulant which are released by merocrine and holocrine secretions. The DII cells seen in unfed ticks, and secretory cells which have completed their secretory cycle, start to have a specialized surface for endocytosis characteristic of type DI digestive cells. From 5 to 7 days after feeding up to the female oviposition, type DI cells which have completed their endocytosis are transformed into type DII digestive cells specialized for intracellular digestion and the storage of reserve nutrients required by the tick for long starvation. The various phases of the digestive cycle are considered according to ultrastructural changes of the midgut epithelium.     

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.     

Cellular localisation of aminopeptidase in the midgut of Rhodnius prolixus Stål (Hemiptera:Reduviidae) during blood digestion

Summary By use of the artificial substrate leucyl--naphthylamide, aminopeptidase was localised in the midgut cells of the haematophagous insect Rhodnius prolixus before and at various times up to 25 days after a meal of rabbit blood. The enzyme was primarily associated with the membranes of the microvilli, with extracellular membrane layers and with the lysosomes of the midgut cells. Aminopeptidase activity was also detected on the rough endoplasmic reticulum and at the periphery of intracellular storage vesicles. The absence of aminopeptidase on the microvilli of the crop supports the conclusion that the crop is not involved in the digestion of blood-meal proteins and that protein digestion is restricted to the intestine. The sites of localisation are in accordance with models for the spatial separation of digestive enzymes in the midgut of several non-haematophagous insects, and this suggests that aminopeptidase plays a major role in the terminal digestion of the blood meal. The changes in enzyme localisation during the digestive period correlate with previously described cycles of digestive-enzyme activity and changes in midgut ultrastructure. A model for blood protein digestion in R. prolixus is described.     

Changes in the digestive gland of the loliginid squid Sepioteuthis lessoniana (Lesson 1830) associated with feeding

Changes associated with feeding in the histological and cytological structure of the digestive gland of the loliginid squid Sepioteuthis lessoniana were examined, along with the nature of both the intracellular and extracellular enzymes produced by the gland. The timing of the release of the extracellular enzymes during the digestive cycle was also determined using a quantitative experimental program. Like that of all coleoid cephalopods, the digestive gland was characterised by one type of cell with several functional stages. As is the case for other loliginid squids, however, the digestive cells did not contain the large enzyme-carrying boules that characterise the digestive glands of most cephalopods. Instead, smaller secretory granules were found in the digestive cells and these may be the enzyme carriers. The prominent rough endoplasmic reticulum, large mitochondria and active Golgi complexes present in the digestive cells are characteristic of cephalopods and indicate a high metabolic activity. Like that of other cephalopods, endocytotic absorption of nutrients and intracellular digestion occurs in the digestive gland of this squid. From quantitative and qualitative examinations of structural changes in the digestive gland of S. lessoniana after feeding, a schedule of its function during the course of digestion was proposed. This indicated that digestion was very rapid, being completed in as little as 4 h in S. lessoniana. Extracellular digestive enzymes were only released after the first hour following feeding, which implies that they are stored in the stomach between meals to increase digestive efficiency.     

黑水虻消化道形态及组织结构的观察

本文比较了不同发育阶段黑水虻Hermetia illucens消化道的形态学差异,掌握了幼虫消化系统的组织学特征。利用体视镜观察黑水虻5龄幼虫、预蛹及成虫的消化道形态,利用光学显微镜和扫描电镜观察幼虫消化道各段(前肠、中肠、后肠)的显微及超微结构。结果表明：黑水虻幼虫及预蛹的消化道均由前肠(食道和前胃)、中肠及后肠组成,从幼虫到成虫,消化道的长度不断缩短。与幼虫和预蛹相比,成虫消化道形态变化明显,前胃消失,出现了嗉囊及胃盲囊,中肠进一步缩短,后肠分化为回肠、结肠和直肠。组织学观察结果显示,幼虫的唾液腺开口于口腔,由膨大的管状腺体和腺管组成。食道由特化为角质刺突的内膜层及发达的肌层组成,其末端延伸至前胃。前胃膨大为球状,包括三层组织结构。根据上皮细胞形态的差异,中肠可分为四个区段。后肠薄,肠腔内褶丰富,肠壁可见数量较多的杆状细菌。马氏管开口于中、后肠交界处,包括4支盲管,管内壁密布微绒毛。黑水虻消化道形态随发育阶段的变化,反映了各阶段摄食及消化生理的差异。幼虫消化道各段具有各自典型的组织学特征,其前、中、后肠可能分别承担了食物接纳与初步消化、消化与吸收以及重吸收功能。本研究结果为进一步了...     

银盾革蜱的中肠上皮变化与血餐消化

用光学显微镜及电子显微镜对不同生理状况下银盾革蜱Dermacentor niveus Neumann雌虫中肠上皮及血餐消化进行了研究.饿蜱的中肠只由一种干细胞组成,脂滴作为饿蜱营养的贮藏形式.非滞育蜱消化分三个阶段,即第一连续消化阶段,减慢消化阶段及第二连续消化阶段.吸血后中肠上皮共观察到四种细胞类型,即替代细胞、分泌细胞、消化细胞及卵赞原细胞.滞育蜱第一连续消化阶段延长.饱血后60天到120天,消化作用几近停止,为停滞消化阶段.卵黄原细胞的超微结构有明显改变.滞育解除后,开始进行减慢消化阶段及第二连续消化阶段.     

Ultrastructure and functional features of midgut of an adult water mite Teutonia cometes (Koch, 1837) (Hydrachnidia: Teutoniidae)

Shatrov, A. B. 2010. Ultrastructure and functional features of midgut of an adult water mite Teutonia cometes (Koch 1837) (Hydrachnidia: Teutoniidae). —Acta Zoologica (Stockholm) 91 : 222–232 The midgut of the adult water mite Teutonia cometes (Koch 1837) (Hydrachnidia: Teutoniidae) was investigated by means of transmission electron microscopy and on semi‐thin sections. The midgut is represented by a blind sac composed of the narrow ventriculus, two proventricular lateral diverticula and three pairs of postventricular caeca. A single‐layered epithelium consists of one type of endodermal digestive cells of quite different shape and size, which may form protrusions into the midgut lumen. The large nuclei are frequently lobed and contain one to three nucleoli. The apical cell membrane forms short scarce microvilli, between their bases the pinocytotic vesicles of unspecific macropinocytosis as well as the narrow pinocytotic canals are formed and immersed into the cell. The intracellular digestion of the food ingested into the midgut after extraintestinal digestion is predominant. The pinocytotic vesicles fuse with small clear vesicles of proposed Golgi origin to form secondary lysosomes. The digestive cells also contain small amounts of rough endoplasmic reticulum, variously structured heterolysosomes, residual materials in the form of both the small electron‐dense bodies and the large variously granulated substances, reserve nutritive materials such as lipid and glycogen, as well as clear vacuoles. Residual materials are obviously extruded from the cells into the gut lumen.     

Morphofunctional changes in the midgut of tick females of the genus Ixodes (Acari: Ixodidae) during and after feeding

Cyclic changes of the midgut epithelium were observed in females of 5 ticks species of the genus Ixodes during 7-10 days of feeding. The midgut epithelium of unfed females is represented by the digestive cells of nymphal phase and stem cells. The digestive cells of nymphal phase are functional during 1.5-2 days after attachment of the tick, and then, after the tearing away they go into the gut lumen. The secretory cells substitute the digestive cells of nymphal phase and finish their growth during the 4-4.5 days. Secretion of digestive enzymes is performed by the holocrine type with tearing away a whole cell. Intracellular digestion takes place in the digestive cells of four consequent generations. The secretory and digestive cells form a peritrophic matrix on their surface. The presence of peritrophic matrix gives an evidence the maturity and functional activity of the secretory and digestive cells. We suggest, that the peritrophic matrix takes part in intracellular digestion, namely in the process of micropinocytosis. The phagocytosis was not found in the ticks investigated. Digestion in the midgut lumen is performed by enzymes of the ruptured secretory and digestive cells, that is proved by the haemolysis of erythrocytes in the zone of their contact with these cells. The digestive cells of each generation functioned almost synchronously, with largest difference in starting about 12 hours.     

Ultrastructure of the midgut and blood meal digestion in the adult tickDermacentor variabilis

Digestive cells in the midgut of male and femaleDermacentor variabilis (Say) took up the blood meal in coated vesicles and smooth flask-shaped vesicles, and deposited it in endosomes which were digested via heterophagy. Iron was concentrated in residual bodies.Digestion occurred in three distinct phases in mated females: (1) continuous digestion (initiated by feeding) occurred during slow engorgement; (2) reduced digestion (initiated by mating) occurred in mated females during the period of rapid engorgement; (3) a second continuous digestion phase (initiated by detachment from the host) occurred throughout the post-feeding periods of preoviposition and oviposition.It is proposed that the stem cells in the midguts of unfed females were progenitors of digestive, replacement, and presumed vitellogenic cells in midguts of mated feeding females. Digestive cells were present in all three digestion phases. Only during the first continuous digestion phase did digestive cells fill up with residual bodies, rupture and slough into the lumen, or did whole cells slough into the lumen. During the other two digestion phases no sloughing of digestive cells was observed. At the end of oviposition the digestive cells were filled with residual bodies. Replacement cells were present only during the first continuous-digestion phase. Presumed vitellogenic cells were present only during the reduced-digestion phase and during the second continuous-digestion phase. Stem cells in unfed males developed only into digestive cells in feeding males. Fed males and fed unmated females had only the first continuous-digestion phase. After being hand-detached from the host, unmated 13-day-fed females went through cellular changes associated with the reduced-digestion phase and second continuous-digestion phase of fed mated females, then began ovipositing. Maximum development of the basal labyrinth system and lateral spaces matched the known time of maximum water and ion movement across the midgut epithelia.Spectrophotometric analyses of lumen contents and midgut cells, sampled after detachment from the host, showed that concentrations of protein and hemoglobin at day 1 post-detachment decreased by one-half at the beginning of oviposition, while hematin increased about twofold by the end of oviposition. This supported the idea of the presence of a second continuous-digestion phase.     

The digestion of cellulose and other dietary components, and pH of the gut in the amphipod Gammarus pulex (L.)

SUMMARY. Gut extracts from Gammarus pulex hydrolysed native and other cellulose substrates in vitro. Digestive fluid cellulase is probably endogenous as cell-free fluid mediated cellulose hydrolysis, but no bacteria were isolated from the fluid which produced a detectable extra-cellular cellulase. There was no apparent digestion of plant cell walls during their passage along the digestive tract, which took about 5–7 h at 10°C. The pH sensitivities of the digestive enzymes and the pH of the various regions of the gut suggest that carbohydrate digestion occurs in the proventriculus, midgut glands and anterior midgut, but protein digestion may be largely limited to the posterior midgut. The pH of the digestive fluid was altered slightly, but significantly, by the consumption of different natural and artificial test diets and by starvation. The most probable reason for the non-digestion of plant cell-walls is the lack of necessary enzymes other than cellulase. The role of cellulase may be confined to digesting the many small, non-cellular particles which are present in the gut.     

Morphological aspects of blood digestion in a parasitic mite Bakericheyla chanayi

All life stages of B. chanayi (Acariformes: Cheyletidae) are characterized by occasional bloodsucking and a long period of digestion. No newly engorged mites were found during the period of their host birds' migration. The fine structure of the digestive tract of a blood-feeding acariform mite is described for the first time. The anterior midgut (AMG) is a place of blood digestion, while the posterior midgut (PMG) is involved in nitrogen metabolism forming guanine crystals as the main end-product. The AMG epithelium consists of digestive cells that probably arise from mitotically active basal cells with high synthesizing activity.As observed in ticks, blood digestion is accompanied by the formation of huge endosomes that serve as places of storage and sorting of ingested material. Digestive cells show different types of endocytotic activity as well as various late endosomes, which implies different subcellular pathways for different blood components. In both midgut regions, elimination of the excretory material occurs by apocrine secretion or by discharging of apical cell fragments (loaded with lysosomes) into the gut lumen. The formation of guanine granules occurs inside the lysosomes of PMG epithelial cells thus having much in common with intracellular digestion. Peculiarities of intracellular blood digestion were analyzed according to the modern hypothesis of endocytosis and compared to what is known in ticks.     

The labial gland system of larvae of the imported fire ant,Solenopsis invicta Buren

Summary The authors describe the ultrastructure of the labial gland system in imported fire ant larvae, Solenopsis invicta Buren and present an enzyme analysis of enzymes in labial-gland secretions and midgut contents. The tubes of the labial gland produce and secrete a proteinaceous substance rich in digestive enzymes. The narrow cells of the reservoir of the gland have little or no secretory function but the lumen stores the proteinaceous secretion. The labial-gland enzymes include proteases and amylases, which function in extraintestinal digestion of solid food placed on the anteroventral body region of 4th-instar larvae by adult workers. The midgut contains proteases, amylases, and upases. Lipids appear to be predigested by the workers before being fed to the larvae.Approved as TA 15262 by the Director of the Texas Agricultural Experiment Station in cooperation with ARS/USDA. Supported by the Texas Department of Agriculure interagency agreement IAC-0487 (78-79)We would like to thank Rosemary Kamas, Dr. John Mirenda, and Mike Strand for their help in dissections of larvae and Dr. Howard Williams for his advice and suggestions     

The fine structure of the midgut of mite Myobia murismusculi

The pattern of digestion in females of Myobia murismusculi was studied with light and electron microscopy. The midgut consists of a stomach and two pairs of blind caeca. The stomach is connected dorsoposteriorly with the excretory organ, that leads externally to an anal opening via the cuticle-lined rectum. No differences were found between the stomach and its caeca. The midgut epithelial cells are of a single type. Their fine structure and gut contents greatly vary depending on different physiological conditions of the mite. Four stages of digestion can be shown with electron microscope. Pino- and phagocytose takes place in the same cells. At an active stage of digestion numerous pinocytic canals were observed in the midgut cells. At each stage of the digestive cycle groups of flat cells are present in the midgut epithelium. They do not take part in the intracellular digestion of food material. Cytoplasmic processes from the underlying cells of coxal glands project into the midgut cells through the orifices in the gut basal lamina.     

CARBOHYDRASES IN THE DIGESTIVE SYSTEM OF THE SPINED SOLDIER BUG,Podisus maculiventris (SAY) (HEMIPTERA: PENTATOMIDAE)

The spined soldier bug, Podisus maculiventris, is a generalist predator of insects and has been used in biological control. However, information on the digestion of food in this insect is lacking. Therefore, we have studied the digestive system in P. maculiventris, and further characterized carbohydrases in the digestive tract. The midgut of all developmental stages was composed of anterior, median, and posterior regions. The volumes of the anterior midgut decreased and the median midgut increased in older instars and adults, suggesting a more important role of the median midgut in food digestion. However, carbohydrase activities were predominant in the anterior midgut. In comparing the specific activity of carbohydrases, α‐amylase activity was more in the salivary glands (with two distinct activity bands in zymograms), and glucosidase and galactosidase activities were more in the midgut. Salivary α‐amylases were detected in the prey hemolymph, demonstrating the role of these enzymes in extra‐oral digestion. However, the catalytic efficiency of midgut α‐amylase activity was approximately twofold more than that of the salivary gland enzymes, and was more efficient in digesting soluble starch than glycogen. Midgut α‐amylases were developmentally regulated, as one isoform was found in first instar compared to three isoforms in fifth instar nymphs. Starvation significantly affected carbohydrase activities in the midgut, and acarbose inhibited α‐amylases from both the salivary glands and midgut in vitro and in vivo. The structural diversity and developmental regulation of carbohydrases in the digestive system of P. maculiventris demonstrate the importance of these enzymes in extra‐oral and intra‐tract digestion, and may explain the capability of the hemipteran to utilize diverse food sources.     

Ultrastructure and Immunofluorescence of the midgut of Bombus morio (Hymenoptera: Apidae: Bombini)

Bumblebees are widely distributed across the world and have great economic and ecological importance as pollinators in the forest as well as in agriculture. The insect midgut consists of three cell types, which play various important roles in digestion, absorption, and hormone production. The present study characterized the anterior and posterior midgut regions of the bumblebee, Bombus morio. The digestive, regenerative and endocrine cells in the midgut showed regional differences in their number, nuclear size, as well as the size of the striated border. Ultrastructurally, the digestive cells contained many mitochondria and long microvilli; however, in the anterior midgut region, these cells showed dilated basal labyrinths with a few openings for the hemocoel, whereas the labyrinths of the basal posterior region remained inverse characteristics. Thus, the characterization of the midgut of B. morio supported an ecto-endoperitrophic circulation, contributing to a better understanding of the digestive process in this bee.