Compartmentalization of the digestive process in Abracris flavolineata (Orthoptera: Acrididae) adults

Carbohydrases predominate in the crop and their pH optima agree with pH prevailing in crop contents. Major amounts are also found in caecal contents. Aminopeptidase and trypsin are active mainly in the caeca, where they predominate in cells and contents, respectively. Aminopeptidase is partly membrane-bound. Except for trehalase, salivary glands display negligible amounts of digestive enzymes. The specific activity of digestive enzymes is high in all midgut cells and the enzyme molecules do not differ among gut compartments, as judged by polyacrylamide gel electrophoresis. Thus, it is probable that digestive enzymes are synthesized and secreted by all midgut cells (mainly in caeca) and then passed forward into the crop. Digestive enzymes are found in hindgut in concentrations similar to those in ventricular contents and, since they are stable in gut contents, they are likely excreted at a rate similar to undigested food. The data support the hypothesis that carbohydrate and protein are digested mainly in crop and caecal lumina, respectively, with part of the final digestion of proteins occurring at the surface of caecal cells. The peculiar features of the digestion of A. flavolineata grasshoppers, including the lack of midgut countercurrent fluxes, are thought to be derived from putative Polyneoptera ancestors.     

臭腹腺蝗（直翅目：锥头蝗科）消化道对食物储存、消化和吸收相适应的显微结构

显微观察发现臭腹腺蝗Zonocerus variegatus（直翅目：锥头蝗科）嗉囊、中肠和后肠的肠壁结构有所不同。嗉囊为空时纵向折叠。中肠上皮层的厚度随龄期有明显变化,1龄和2龄时明显大于3龄、4龄和5龄。后肠具有帮助消化和吸收的功能。     

Digestive morphophysiology of Gryllodes sigillatus (Orthoptera: Gryllidae)

The evolution of the digestive system in the Order Orthoptera is disclosed from the study of the morphophysiology of the digestive process in its major taxa. This paper deals with a cricket representing the less known suborder Ensifera. Most amylase and trypsin activities occur in crop and caeca, respectively. Maltase and aminopeptidase are found in soluble and membrane-bound forms in caeca, with aminopeptidase also occurring in ventriculus. Amaranth was orally fed to Gryllodes sigillatus adults or injected into their haemolymph. The experiments were performed with starving and feeding insects with identical results. Following feeding of the dye the luminal side of the most anterior ventriculus (and in lesser amounts the midgut caeca) became heavily stained. In injected insects, the haemal side of the most posterior ventriculus was stained. This suggested that the anterior ventriculus is the main site of water absorption (the caeca is a secondary one), whereas the posterior ventriculus secretes water into the gut. Thus, a putative counter-current flux of fluid from posterior to anterior ventriculus may propel digestive enzyme recycling. This was confirmed by the finding that digestive enzymes are excreted at a low rate. The fine structure of midgut caeca and ventriculus cells revealed that they have morphological features that may be related to their involvement in secretion (movement from cell to lumen) and absorption (movement from lumen to cell) of fluids. Furthermore, morphological data showed that both merocrine and apocrine secretory mechanisms occur in midgut cells. The results showed that cricket digestion differs from that in grasshopper in having: (1) more membrane-bound digestive enzymes; (2) protein digestion slightly displaced toward the ventriculus; (3) midgut fluxes, and hence digestive enzyme recycling, in both starved and fed insects.     

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.     

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.     

Digestive anatomy of Halella azteca (Crustacea,Amphipoda)

The digestive tract of the freshwater amphipod Hyalella azteca is a straight but differentiated tube consisting of foregut, midgut, and hindgut divisions. The foregut is subdivided into a tubular esophagus, a cardiac stomach, and a pyloric stomach. The cuticular lining of the cardiac stomach is elaborated into a set of food-crushing plates and ossicles, the gastric mill, while the pyloric cuticle forms a complex straining and pressing mechanism. Nine caeca arise from the midgut, seven anteriorly and two posteriorly. Four of the anterior caeca, the hepatopancreatic caeca, are believed to be the primary sites of digestion and absorption. The remaining caeca may be absorptive, secretory, or both. The much-folded hindgut wall is capable of great distention by extrinsic muscle action for water intake to aid in flushing fecal material out of the anus; such action also may stimulate antiperistalsis by intrinsic rectal muscles.     

Digestive enzyme compartmentalization and recycling and sites of absorption and secretion along the midgut of Dermestes maculatus (Coleoptera) larvae

Bostrichiformia is the less known major series of Coleoptera regarding digestive physiology. The midgut of Dermestes maculatus has a cylindrical ventriculus with anterior caeca. There is no cell differentiation along the ventriculus, except for the predominance of cells undergoing apocrine secretion in the anterior region. Apocrine secretion affects a larger extension and a greater number of cells in caeca than in ventriculus. Ventricular cells putatively secrete digestive enzymes, whereas caecal cells are supposed to secrete peritrophic gel (PG) glycoproteins. Feeding larvae with dyes showed that caeca are water-absorbing, whereas the posterior ventriculus is water-secreting. Midgut dissection revealed a PG and a peritrophic membrane (PM) covering the contents in anterior and posterior ventriculus, respectively. This was confirmed by in situ chitin detection with FITC-WGA conjugates. Ion-exchange chromatography of midgut homogenates, associated with enzymatic assays with natural and synthetic substrates and specific inhibitors, showed that trypsin and chymotrypsin are the major proteinases, cysteine proteinase is absent, and aspartic proteinase probably is negligible. Amylase and trypsin occur in contents and decrease along the ventriculus; the contrary is true for cell-membrane-bound aminopeptidase. Maltase is cell-membrane-bound and predominates in anterior and middle midgut. Digestive enzyme activities in hindgut are negligible. This, together with dye data, indicates that enzymes are recovered from inside PM by a posterior-anterior flux of fluid outside PM before being excreted. The combined results suggest that protein digestion starts in anterior midgut and ends in the surface of posterior midgut cells. All glycogen digestion takes place in anterior midgut.     

The anatomy and histology of the midgut and hindgut of Charybdis (Goniohellenus) truncata (Fabricius, 1798) (Decapoda: Brachyura)

The midgut of C. (G.) truncata accounts for half of the postgastric intestinal tract. The paired anterior midgut caeca arise just behind the pyloric stomach, on either side of the midgut. The unpaired posterior midgut caecum arises dorsally at the rear end of the midgut, where this joins the hindgut. The midgut and its caeca help in the digestive absorption of food. The hindgut is of ectodermal origin and is lined with chitin of a collagenous nature. The connective tissue of the anterior part of the hindgut is packed with tegumental glands whose secretion contains both sulphated and weakly acidic mucosubstances, which facilitate the passage of faecal matter and help to bind food particles. The digestive gland - the hepatopancreas - opens into the anterior part of the midgut, below the anterior midgut caeca. Histologically, its tubules contain three different types of cells - "F", "R" and "B" cells.     

Functional morphology of the stomach of Corophium volutator Pallas

Corophium volutator Pallas is a small amphipod crustacean which burrows in inter-tidal mud on the British coast, and feeds on organic detritus, mainly vegetable, by selecting particles from the mud.
The alimentary canal consists of foregut, midgut and hindgut. The midgut is produced into a pair of anterior dorsal caeca, a pair of ventral caeca and a pair of posterior dorsal caeca.
The cardiac stomach has a large number of chitinous plates or ridges beset with hooks and spines for the trituration of food.
The pyloric stomach has long fine bristles which form an eifective filter apparatus and allow only fine particles of food to pass into the midgut, where they are digested and absorbed.
The hepato-pancreas secrete digestive enzymes and store reserve food material as oil globules.     

Ultrastructure and immunocytochemistry of endocrine cells in the midgut of the desert locust,Schistocerca gregaria (Forskal)

Summary The endocrine cells of the midgut epithelium of the desert locust are found dispersed among the digestive cells and are similar to those of the vertebrate gut. According to their reactivity to silver impregnation techniques and the ultrastructural features of the secretory granules (shape, electron-density, size, and structure) 10 types of endocrine cell have been identified, of which seven are located in the main segment of the midgut or in the enteric caeca, and the other three seem to be present only in the ampullae through which the Malpighian tubules drain into the gut. The endocrine cells have a slender cytoplasmic process that reaches the gut lumen, a feature that supports the receptosecretory nature postulated for this cellular type in insects as well as vertebrates. Antisera directed against mammalian gastrin, CCK, insulin, pancreatic polypeptide and bombesin reacted with some of the endocrine cells. This is the first time that insulin- and bombesin-like immunoreactive cells have been described in the midgut of an insect.     

Endocrine cells in the gut of the shore crab Carcinus maenas immunoreactive to crustacean hyperglycaemic hormone and its precursor-related peptide

The distribution and morphology of gut endocrine cells, which are immunoreactive to crustacean hyperglycaemic hormone (CHH) and the corresponding precursor-related peptide (CPRP), have been described in the shore crab Carcinus maenas. The cells are uniquely distributed throughout the fore- and hindgut, but were never observed in the midgut or associated caeca. Expression of CHH and CPRP in the gut endocrine cells is generally restricted to premoult, although small numbers of immunoreactive cells were observed in intermoult and postmoult. A notable feature of the distribution of these slender cells was that, whilst they are distributed evenly over much of the fore- and hindgut, all extrinsic and intrinsic muscles of the gastric and pyloric stomach examined were surrounded by a ring(s) of cells, suggesting a mechanoreceptive function. Ultrastructural studies revealed that these cells contain numerous immunopositive, electron-dense granules. This suggests that they are "paraneurones", which secrete CHH and CPRP into the haemolymph during ecdysis, accounting for the ecdysial surge in CHH, which is implicated in water uptake and swelling prior to ecdysis.     

Comparative Morphology and Function of Hepatic Caeca in Four Enteropneusts

A morphological and functional study was made of the hepatic region in four enteropneust hemichordates: Schizocardiumsp., Ptychodera flava, Ptychodera bahamensis, and an undescribed ptychoderid from Maui, Hawaii, using light and electron microscopy. The hepatic region of these enteropneusts, as well as others, is characterized by a brown-green color and the presence of numerous caeca which represent dorsal extensions of the gut. These caeca extend above the dorsal surface of the worm and are organized into bilateral rows. Species-specific differences were noted in the organizational pattern of the sacculations within rows and the morphology and histology of individual sacculations. Numerous brown-green vesicles were discovered in both the epithelial cells and lumen of sacculations. Transmission electron microscopy revealed these bodies to be heterophagic vacuoles and residual bodies. Morphological evidence suggests that hepatic caeca are involved in intracellular digestion. Once endocytosed food particles are packaged as heterophagic vacuoles, and digestion has been completed, the residual bodies are packaged together and exuded from the cell in a spherule of cytoplasm.     

Functional morphology of the midgut of a sandfly as compared to other hematophagous nematocera

The midgut epithelium of female Lutzomyia longipalpis was investigated by means of electron microscopic morphometry before and during blood digestion. Ultrastructure and cytological changes of the stomach cells upon blood feeding were generally similar to the ones described for Phlebotomus longipes (Gemetchu, 1974) and for mosquitoes (Hecker, 1977), In addition, the quantitative composition of the cells resembled the one of mosquitoes in many respects. Despite some morphological differences in the functional gut cytology, it can be admitted that, in general, digestive processes may run similarly in the midguts of sandflies and mosquitoes.     

Countercurrent flows,water movements and nutrient absorption in the locust midgut

Using amaranth dye as a marker solute, the movements of fluids in the gut of Schistocerca gregaria was studied, either by feeding a meal containing the dye or by injecting the dye into the haemolymph, and by comparing the distribution of amaranth with those of naturally-occurring solutes in the alimentary tract.In animals deprived of food for more than 2–4 hr, some of the fluid from the Malpighian tubules moves forward through the solid food matrix in the midgut carrying solutes into the anterior midgut and gastric caeca, where water is absorbed. After a meal the crop empties at a rate which saturates the absorptive capacity of the anterior caeca, producing a net movement of fluid down the midgut and so such a countercurrent system is not observed in animals fed ad lib., where dye introduced into the gut always moves posteriorly.A countercurrent fluid movement confers several advantages on the alimentary system which act to maximise the efficiency of nutrient absorption: the principal disadvantage of the countercurrent system is that noxious solutes, as well as nutrients, will accumulate at high concentrations near the permeable site of nutrient uptake. Thus a countercurrent flow of solutes is observed only when the insect is deprived of food and the need to conserve nutrient resources exceeds that of excretion of noxious substances. Ways in which the site of nutrient absorption may be protected from noxious solutes are discussed.The anterior caeca gradually become bloated with dark fluid as digestion proceeds; this is expelled into the midgut when a fresh meal is ingested.     

Peculiar digestion patterns of sponge-associated zoochlorellae in the caddisfly Ceraclea fulva

The caddisfly Ceraclea fulva feeds exclusively on the freshwater sponge Ephydatia fluviatilis. Sponge spicules are accumulated in the insect midgut and arranged perpendicularly to the longitudinal axis of its gut. The peritrophic membrane of the midgut is so thick that it prevents spicules from damaging the epithelium during their transit. The digestion process of the endocellular zoochlorellae, which are vehiculated by the sponge cells, was examined by transmission electron microscopy (TEM). Zoochlorellae were seen in the midgut lumen, close to the peritrophic membrane and in the underlying space. Discrete algal cells became evident in tight apposition to the brush border of the midgut cells and were enveloped by the microvilli. Digestion progressed to the final transformation of the organism into membrane-delimited vacuoles.     

臭腹腺蝗（直翅目：锥头蝗科）胃盲囊的异速生长和功能特性

通过对臭腹腺蝗Zonocerus variegatus（直翅目：锥头蝗科）6个若虫期及成虫期主消化道和胃盲囊分段进行解剖和测量,对其胃盲囊的异速生长和功能特性进行了研究。结果表明,胃盲囊和主消化道的生长是不同速的。胃盲囊前段较后段生长速率更高,但两者生长速率显著相关。消化道和胃盲囊的平均长度亦显著相关。随年龄增长,消化道的生长速率降低,而胃盲囊的生长速率上升。与胃盲囊前段功能相同,胃盲囊后段亦具有消化和吸收功能,被认为能在营养缺乏的旱季起到增加肠胃吸收面的功能。     

The alimentary canal of <Emphasis Type="Italic">Blomia tropicalis</Emphasis> (Acari: Astigmata: Echymopodidae): the application of three-dimensional reconstruction technology

The domestic mite species Blomia tropicalis is an important indoor allergen source related to asthma and other allergic diseases in tropical and subtropical regions. Here, we describe the alimentary canal of B. tropicalis with the particular application of three-dimensional reconstruction technology. The alimentary canal of B. tropicalis resembles the typical acarid form consisting of the cuticle-lined foregut and hindgut separated by a cuticle-free midgut. The foregut is divided into a muscular pharynx and an esophagus. The midgut is composed of a central ventriculus, two lateral caeca, a globular colon and a postcolon with two tubiform postcolonic diverticula. The most common cells forming the epithelium of ventriculus and caeca are squamous and cuboidal. The globular cells contain a big central vacuole in the posterior region of the caeca. The epithelium of the colon and postcolon has significantly longer microvilli. The anal atrium is a simple tube with flattened epithelial cells. The spatial measurements of the three-dimensional model suggest that the paired caeca and central ventriculus occupy 55.1 and 34.6%, respectively, of the total volume of the alimentary canal and may play the key role in food digestion. J. Wu and F. Yang contributed equally.     

Ultrastructure of the digestive system and the fate of midgut during embryonic development in Porcellio scaber (Crustacea: Isopoda)

Microscopic anatomy of the digestive system in embryos and larvae of the terrestrial isopod crustacean Porcellio scaber was investigated by light bright field, fluorescence and electron microscopy. During marsupial ontogenetic development the event-dependent staging was used to discriminate the various embryonic stages. At the late embryo stage the differentiation of the ectodermal part of the gut into the complex filtering foregut and the hindgut with absorptive and transporting functions is accomplished. The gut of the marsupial manca larva is fully developed and similar to that of the adult. In early embryos the endodermal midgut gland primordia are filled with yolk and lipid globules. In late embryos the epithelium of paired midgut gland tubes is composed of two cell types; one of them exhibits orange autofluorescence. The endodermal cells located between the foregut and the midgut glands of late embryos form the prospective midgut. The cells have electron dense cytoplasm, abundant glycogen fields, endoplasmic reticulum, dictyosomes and numerous vesicles. In the adults the endodermal cells of the midgut remain only in the midgut gland ducts which connect the midgut glands and the foregut. Details of the cellular ultrastructure and morphogenesis of the ectodermal and endodermal parts of the digestive system during embryonic development of Porcellio scaber provide data for further phylogenetic and comparative studies in peracaridan crustaceans and other arthropods.     

Digestion in the cattle-tick Boophilus microplus: light microscope study of the gut cells in nymphs and females

The gut caeca of B. microplus were studied by light microscopy using paraffin and methacrylate embedded material. It has been shown that during feeding of nymphs and adults, the midgut consists of five cell types, stem cell, digest cell, secretory cells (s₁) and (s₂) and basophilic cell. The stem cell differentiates into any of the other cell types. The digest cell matures through a series of stages and has up to three generations during feeding on the host. The final generation has two distinct cell types, the first type is thought to be capable of both phagocytosis and pinocytosis. Cells of the second type are predominant at the end of feeding, and may be specialized to ingest and digest haemoglobin. The final stage of the digest series is the spent digest cell which discharges its content into the gut lumen or is excreted whole. The basophilic cell has structures which suggest that one of its functions is to transport digested materials, water and ions across the gut. Secretory cell (s₁) secretes a glycoprotein which may be a haemolysin and secretory cell (s₂) secretes the gut “colloid” mass, an acid mucopolysaccharide, which may function as an anticoagulant. Intracellular digestion leads to the breakdown of host blood and storage of lipid and glycogen in the digest cells.     

日本沼虾消化道形态和组织学特点

应用石蜡切片和扫描电镜技术对日本沼虾消化道进行了研究。结果表明,食道壁向腔内形成四个纵突,食道上皮由单层柱状细胞构成,上皮下的结缔组织中具有放射肌和皮肤腺,环肌层近于连续。食道和胃连结处的管腔背方具食道瓣,胃内具胃磨、滤器和滤沟等结构,胃的组织学结构中除无皮肤腺分布外与食道相似。中肠较长,约占整个消化道的７１７％,具一对中肠前盲囊。中肠上皮细胞大致有两种类型,基膜着色深,环肌层连续,纵肌成束分散排列。后肠为一短管,管腔呈迷路状,其中部为一球形膨大的直肠。后肠的组织学结构与前肠相似。