Functional Morphology of the Introvert and Digestive System of Myzostoma cirriferum (Myzostomida)

Myzostoma cirriferum feeds by diverting food particles carried by the ambulacral grooves of its comatulid host Antedon bifida. When searching for food, the myzostome uses its protrusible introvert to fulfil two major functions: sensory perception and the capture of food particles. The digestive system is composed of four parts, viz. a pharynx, that is contained within the introvert, a stomach, a series of paired caeca and an intestine that lie in the myzostome's trunk. The pharynx is supplied with a thick muscle which, thanks to peristaltic movements, carries food particles from the mouth to the stomach. Both stomach and caecal cells are able to absorb dissolved nutriments and to store lipids, whereas intestinal cells are only capable of absorption. Due to the beating of their cilia, stomach cells also carry food particles into the caecal lumen, where they are subjected to endocytosis and intracellular digestion by caecal cells. Undigested food fragments eventually gather in a very large, apical vacuole, and the cell apices containing vacuoles are eliminated into the caecal lumen by an apocrinal process. Detached cell apices reach the stomach, where they are embedded in a matrix, together forming a spindle-shaped faecal mass that is expelled through the postero-ventral anus. The observed digestive process—entailing the regular elimination of the apical part of the caecal digestive cells—appears to be unique among the Spiralia.     

Light and electron microscopic studies on experimental nocardia-toxicosis in mice

An exotoxin (HS-6) produced by Nocardia otitidiscaviarum isolated from certain lesions of cutaneous nocardiosis of a male 82-year-old patient induced severe injuries in the pancreas, liver, stomach, small intestine, heart, thymus and kidney of male ICR mice. Mice given Nocardia-free preparation of HS-6 at a dose of 1 mg/kg of body weight developed several autophagic vacuoles in the pancreas and liver within 20 min after the i.p. injection. Thereafter, the autophagic vacuoles increased in number and size with time. About 24 hr after the administration of HS-6, the liver showed marked accumulation of fat droplets in the cytoplasm of the hepatocytes. Although they contained abundant autophagic vacuoles in the regions of RER, there were no lipomatoses in the acinar cells of the pancreas, those of the chief cells and smooth muscle cells of the stomach, Paneth cells, goblet cells, smooth muscle cells of the small intestine, and plasma cells in the digestive tract. Biochemical examinations revealed that HS-6 had no significant effect on the protein synthesis of reticulocytes. Inoculation of the Nocardia into the mouse peritoneal cavities caused marked granulomatoses in the pancreas, liver and regional lymph nodes, but did not develop autophagic vacuoles in RER regions of these organs.     

Histological structure of the digestive tract,liver, and pancreas of Ambassis nalua (Hamilton, 1822) with ultrastructural details of the gastric gland

The scalloped perchlet Ambassis nalua is one of the dominant fishes in the Estuarine Pranburi River, Thailand. It is suggested that this fish is in the secondary trophic level with a carnivorous nature. Studies on digestive system will help us further identify the niche of this species in the food web/food chain. The present study therefore aimed to report the detailed structure and ultrastructure of A. nalua digestive system. Fish samples (n = 30) with a total length of 5.7 ± 0.5 cm were obtained using beach seines from the Estuarine Pranburi River. Their digestive tract length and intestine coeficient were 3.6 ± 0.07 cm and 0.91, respectively. Light microscopic observation showed that the digestive wall comprised four layers, namely mucosa, submucosa, muscularis, and serosa. The prominent mucous-secreting cells were found in the mucosal oesophagus. The stomach had many gastric folds, with height and width being 649.76 ± 85.15 and 370.30 ± 68.56 μm, respectively. Gastric glands were found in the anterior stomach but not in the posterior stomach. Each gastric gland was made up of a single type of columnar cells. The gastric cells were ultrastructurally characterized by numerous mitochondria and well-developed secretory granules of varying sizes. A few small vacuoles were also identified in the apical area of the gastric cells. The intestine had two regions (anterior and posterior intestines), and pyloric caecum was absent. The density of the goblet cell was significantly higher in the posterior intestine. These results provide basic knowledge of the digestive system of A. nalua, and the low intestine coefficient and the absence of pyloric caecum suggest the carnivorous feeding habit of this species.     

Phagotrophic Ingestion of a Blue-Green Alga by Ochromonas*†

Anacystis nidulans disappeared rapidly from culture in the presence of an unidentified species of Ochromonas. Disappearance was light-independent and could be induced neither by bacteria associated with, nor by soluble products released from the flagellate. Electronmicrographs of mixed cultures revealed numerous A. nidulans cells in various stages of digestion within vacuoles of Ochromonas. Evidently the disappearance of the alga from culture resulted from phagotrophy by the chrysomonad. A 2-stage digestive process is suggested whereby A. nidulans cells are initially sequestered in the posterior “leucosin” vacuole and then undergo the terminal stages of digestion and elimination in smaller, peripheral vacuoles.     

Endocytosis,digestive vacuolar movement and exocytosis on refeeding starvedTetrahymena pyriformis GL-9

Summary Evidence is presented in support of the hypothesis that the contents of digestive vacuoles in refed starvedTetrahymena pyriformis GL-9 are egested from the cell in approximately the sequence of their order of formation. The investigations involved measurements of the rates of disappearance of digestive vacuoles from the cells and the subsequent appearance of egested globules in the surrounding medium using both cultures and individual cells. The cells were first fed peptone and latex particles for a period and then this type of vacuole formation was suppressed by the addition of excess carmine particles (or the process was repeated with the particles in reverse order). Thus two types of morphologically distinct digestive vacuoles could be produced and observed microscopically. These observations suggest that the temporal nature of the movement of the digestive vacuoles through the cell result in the temporal nature of egestion and that no selective mechanism occurs at egestion. Thus digestive vacuoles are thought to pass through the cell from cytopharynx to cytoproct in approximately the order formed and at approximately constant rate. Under conditions of excess nutrients, where the cells become filled with digestive vacuoles, they seem to be able to maintain an approximately uniform number of digestive vacuoles within themselves by maintaining approximately constant and equal rates of vacuole formation and egestion. The maximum rates of latex or carmine vacuole formation or egestion found in single cells were approximately 0.3–0.4 vacuoles per cell per minute. The results are discussed.     

Histological and ultrastructural study of the digestive tract of rice field eel, Monopterus albus

The histological characteristics of the digestive tract and the ultrastructure of mucosal cells of the stomach and intestine of rice field eel, Monopterus albus, are described to provide a basis for future studies on its digestive physiology. The digestive tract of the rice field eel is a long and coiled tube composed of four layers: mucosa, lamina propria‐submucosa, muscularis and serosa. The pharynx and oesophagus mucosa is lined with a stratified epithelium. The stomach includes the cardiac and pyloric portions and the fundus. Many gastric pits are formed by invaginations of the mucosal layer and tubular gastric glands formed by the columnar cells in the fundus. The intestine is separated from the stomach by a loop valve and divided into a proximal portion and a distal portion. The proximal intestinal epithelium consists of columnar cells with microvilli towards the lumen and goblet cells. The enterocytes are joined at the apical surface by the junctional complex, including the evident desmosomas. Numerous lysosomes and some vesicles are evident in the upper cytoplasm of the cells, and a moderate amount of endoplasmic reticulum and lysosomes are scattered in the supranuclear cytoplasm. The epithelium becomes progressively thicker and the folds containing large numbers of goblet cells are fewer and shorter in the distal portion of the intestine. At the ultrastuctural level, the columnar cells of the tubular gastric glands have numerous clear vacuoles and channels. A moderate amount of pepsinogen granules are present in the stomach. The enterocytes of the intestinal mucosa display a moderate amount of endoplasmic reticulum and lysosomes, and long and regular microvilli.     

Functional morphology of the developing alimentary canal in the holothurian Eupentacta fraudatrix (Holothuroidea, Dendrochirota)

Development of the digestive tract of the holothurian Eupentacta fraudatrix was examined using light and transmission electron microscopy. After the blastopore closes, the gut rudiment loses its connection with the blastoderm and becomes an enclosed, tubular chamber, ending blindly at both ends. The differentiation of the digestive and coelomic epithelia is mainly completed by day 12. Since no transient cell types are observed, this differentiation is definitive. By day 20, the mouth and anal openings appear. The cuticular lining in the anterior part of the gut rudiment has an endodermal origin and differentiates before the mouth is formed. The rest of the gut lining is composed of enterocytes typical of holothuroid intestine. At the early stages of development, mitotic figures are encountered among nonspecialized cells of the gut primordium. In more developed digestive epithelium, vesicular enterocytes are capable of mitotic division. Dividing enterocytes retain secretory vacuoles; thus mitosis occurs in actually differentiated cells. After mouth and anus formation, the oesophagus, stomach, intestine and rectum can be distinguished. In the wall of the stomach, powerful musculature is formed.     

The subcellular localisation of certain crop-juice esterases in the digestive gland ofCepaea (Mollusca: Helicidae)

Summary Three methods have been used to localise specific crop-juice esterases within the cells of the digestive gland ofCepaea nemoralis andC. hortensis. A comparison withHelix aspersa has also been made. Autolysis experiments showed that Est. 1 and Est. 9 were very resistant to denaturation and might therefore be of lysosomal origin. Ultracentrifugation of digestive gland homogenates suggests that these same esterases are within vacuoles and this is confirmed by histochemical studies at the electron microscope level using thiolacetic acid as a substrate. It is shown electrophoretically that only esterases within set 1 (Oxford, 1977), which includes Est. 1 and Est. 9, hydrolyse this substrate to any marked extent. Thiolacetic acid esterase activity is found within the phagolysosomes and endoplasmic reticulum of digestive cells. It is suggested that at least some of the digestive enzymes present in the crop juice originate within phagolysosomes and are specifically released from digestive cells.     

Symbiotic Chlorella sp. of the ciliate Paramecium bursaria do not prevent acidification and lysosomal fusion of host digestive vacuoles during infection

Summary. Each symbiotic Chlorella sp. of the ciliate Paramecium bursaria is enclosed in a perialgal vacuole derived from the host digestive vacuole, and thereby the alga is protected from digestion by lysosomal fusion. Algae-free cells can be reinfected with algae isolated from algae-bearing cells by ingestion into digestive vacuoles. To examine the timing of acidification and lysosomal fusion of the digestive vacuoles and of algal escape from the digestive vacuole, algae-free cells were mixed with isolated algae or yeast cells stained with pH indicator dyes at 25 ± 1 °C for 1.5 min, washed, chased, and fixed at various time points. Acidification of the vacuoles and digestion of Chlorella sp. began at 0.5 and 2 min after mixing, respectively. All single green Chlorella sp. that had been present in the host cytoplasm before 0.5 h after mixing were digested by 0.5 h. At 1 h after mixing, however, single green algae reappeared in the host cytoplasm, arising from those digestive vacuoles containing both nondigested and partially digested algae, and the percentage of such cells increased to about 40% at 3 h. At 48 h, the single green algae began to multiply by cell division, indicating that these algae had succeeded in establishing endosymbiosis. In contrast to previously published studies, our data show that an alga can successfully escape from the host’s digestive vacuole after acidosomal and lysosomal fusion with the vacuole has occurred, in order to produce endosymbiosis. Correspondence and reprints: Biological Institute, Faculty of Science, Yamaguchi University, Yoshida 1677-1, Yamaguchi 753-8512, Japan.     

Fine structure and absorption of ferritin in the digestive organs of Loligo vulgaris and L. Forbesi (Cephalopoda,Teuthoidea)

The digestive organs possibly involved in food absorption in Loligo vulgaris and L. forbesi are the caecum, the intestine, the digestive gland, and the digestive duct appendages. The histology and the fine structure showed that the ciliated organ, the caecal sac, and the intestine are lined with a ciliated epithelium. The ciliary rootlets are particularly well developed in the ciliated organ, apparently in relation to its function of particle collection. Mucous cells are present in the ciliated organ and the intestine. Histologically, the digestive gland appears rather different from that of other cephalopods. However, the fine structure of individual types of squid digestive cell is actually similar to that of comparable organs in other species, and the squid cells undergo the same stages of activity. Digestive cells have a brush border of microvilli, and numerous vacuoles, which sometimes contain “brown bodies.” However, no “boules” (conspicuous protein inclusions of digestive cells in other species) could be identified in their cytoplasm; instead only secretory granules are present. In the digestive duct appendages, numerous membrane infoldings associated with mitochondria are characteristic features of the epithelial cells in all cephalopods. Two unusual features were observed in Loligo: first, the large size of the lipid inclusions in the digestive gland, in the caecal sac, and in the digestive duct appendages; and second, the large number of conspicuous mitochondria with well-developed tubular cristae. When injected into the caecal sac, ferritin molecules can reach the digestive gland and the digestive duct appendages via the digestive ducts, and they are taken up by endocytosis in the digestive cells. Thus, it appears that the digestive gland of Loligo can act as an absorptive organ as it does in other cephalopods.     

Light and electron microscope localization of beta-glucuronidase activity in the stomach and digestive gland of the marine gastropod Littorina littorea

Summary An azo dye technique was used to investigate localization of the acid hydrolase,-glucuronidase, at light and electron microscope level in the stomach and digestive gland of the marine periwinkleLittorina littorea. Activity for-glucuronidase was located principally within digestive cells of the digestive gland and also associated with the microvillous border and epithelial cells lining the stomach. At the light microscope level all digestive tubules showed activity which appeared essentially restricted to the large heterolysosomes of the digestive cells. However not all digestive cells showed activity. In the electron microscope, reaction product was apparent in all types of macrovesicle in the digestive cells although not all stained positively. Heterophagosomes typically showed reaction product around their periphery or associated with the electron opaque contents. Activity was commonly seen around the apical edge of heterolysosomes where merging of heterophagosomes into heterolysosomes was apparent. Reaction product was commonly located within small electron lucent vesicles which lined the internal membrane of the heterolysosomes but sometimes also associated with flocculent, electron opaque contents. In the stomach dense clusters of reaction product were visible in lysosomes in the basal region of the epithelial cells and in the large granular inclusions of the secretory cells.     

On the Fine Structure of the Alimentary Tract of Cephalodiscus gracilis (Pterobranchia,Hemichordata)

The U-shaped alimentary tract of Cephalodiscus is of exclusively epithelial structure; on the basis of fine structural criteria the entire tract can be divided into two large subdivisions: an anterior one with mouth, mouth cavity, pharynx and oesophagus, and a posterior one with stomach and intestine. The anterior subdivision is built up of a relatively uniform, innervated, pseudostratified, ciliated epithelium with mucus cells which are concentrated in the initial parts of the mouth cavity. Cilia and mucus presumably constitute a mechanism transporting food particles into the stomach. In the area of the gill slits specific vacuolated cells occur which may lend rigidity to the walls of the slits. The gastric epithelium consists of prismatic cells characterized by, among others, large inclusion bodies, which may represent digestive vacuoles, small dense rod-shaped granules and an elaborate system of microridges, at the base of which abundant endocytotic vesicles occur. The dorsal gastric pouch contains cells rich in rough ER and secretory granules, probably containing digestive enzymes. Thus morphological evidence points both to intra- and extracellular digestion. The intestinal epithelium resembles that of the stomach, however, it is lower, its organelles are fewer and it bears, beside cilia, mainly microridges, which towards its distal end become sparse. Both in the gastric and intestinal epithelium small granulated cells have been found, which presumably represent endocrine cells.     

The gut of the juvenile African lungfish Protopterus annectens: A light and scanning electron microscope study

We describe the microstructure of the alimentary canal of the juvenile lungfish Protopterus annectens. Following the oesophagus, the gut is formed by a long segment that extends down to the pyloric valve. This segment, classically named stomach, is lined by a transitional epithelium but lacks all characteristics of the vertebrate stomach. It has been defined here as the intestinal vestibule. The spiral valve is divided into a first large chamber, which contains mucosal ridges, and a second smooth portion. The entire spiral valve is lined with a pseudostratified columnar epithelium that contains approximately six cell types: enterocytes, goblet cells, ciliated cells, leukocytes, dark pigment cells, and vascular cells. Enterocytes and goblet cells show a high number of cytoplasmic vacuoles. The number and size of the vacuoles, and the number of ciliated cells, decreases from the anterior toward the posterior end, suggesting that most of the digestive processes take place in the anterior part of the spiral valve. The epithelium overlies a lamina propria in the first large chamber and a vascular plexus in the smooth portion. The cloaca has a thick muscular wall covered by a transitional epithelium. An extensive lymphatic system formed by capillaries and lymphatic micropumps is present along the entire wall of the alimentary canal. J. Morphol., 2011. © 2011 Wiley‐Liss, Inc.     

STRUCTURE AND REPRODUCTION OF THE ALGAL SYMBIONTS OF HYDRA VIRIDIS1

The algal symbionts of Hydra viridis are found within vacuoles of the gastrodermal digestive cells of the host. Electron microscopy reveals that the symbionts possess cell walls, and that their reproductive cycle follows the general pattern of free-living Chlorella. Nuclear and chloroplast divisions arc followed by formation of new cell walls, the Golgi apparatus being quite active during cell wall synthesis. Autospores are released when the parent wall ruptures. The autospores are then usually segregated into separate animal vacuoles. Remnants of the ruptured parent wall persist in the vacuoles for an indefinite period. The ruptured parent walls curl at the breakage clefts, forming double-layered scroll-like structures. The fate of these wall remnants has not been firmly established. Long-term starvation of the animals does not result in a detectable change in the structure of the symbionts, and they continue to divide and to store carbohydrate as starch grains.     

Regeneration of the epithelial lining of the stomach after autotomy of a disk in the brittle star Amphipholis kochii (Lütken) (Echinodermata: Ophiuroidea)

The regeneration of the epithelial lining of the stomach of the brittle star Amphipholis kochii after autotomy of the aboral part of the disk was studied. It was shown that a part of the stomach epithelium remained after autotomy. Its cells participated in regeneration of the epithelium during restoration of the lost digestive system. There was a partial dedifferentiation of the epithelium cells of stomach, their migration and proliferation; cells of the stomach retained some specialized cytoplasmic structures, secretory vacuoles, and pinocytic vesicles. Migration of ectodermal cells of the esophagus in the damaged area was also recorded.     

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.     

Development of the digestive system of Argentine hake,Merluccius hubbsi,larvae

The Argentine hake Merluccius hubbsi is an important fishery resource of the Southwestern Atlantic Ocean and it is also a potential species for cultivation. In this work, the digestive system development in field-caught hake larvae was studied using histological and histochemical approaches. The digestive tract of larvae was divided into: oropharyngeal cavity (OPC), esophagus, stomach (that develops in the preflexion stage), and intestine. The annexed digestive glands consisted of the liver and the exocrine pancreas. At the beginning of the preflexion stage, teeth were developed in the OPC. There were mucous cells in the esophagus secreting different glycoconjugates from hatching. The enterocytes in the posterior intestine exhibited supranuclear vesicles associated with protein absorption. Mucous cells were observed in the posterior intestine in the preflexion stage and, in the anterior region, ending the flexion stage. Each type of glycoconjugates has a specific role. Acidic mucins lubricate and protect from mechanical damage, sialomucines protect from bacterial infections and neutral mucins regulate the acidity of mucus secretion, protect against abrasion and participate in the formation of the chyme, indicating a pregastric digestion. The liver was present since hatching with pancreatic tissue inside and increased in size acquiring the typical structure with hepatocyte cords, sinusoids, vacuoles, and hepatic duct. The hepatocytes vacuolization increased with larval development. The pancreas became extra-hepatic, with basophilic acinar cells and acidophilic zymogen granules. Throughout the ontogeny, the increased structural and functional complexity of the digestive system reflected the transition to exogenous feeding and nutritional increasing needs.     

Morphological and histochemical features of the digestive tract of Leiarius marmoratus (Gill, 1870)

Leiarius marmoratus, a freshwater catfish from Pimelodidae family, shows great biological and commercial relevance because of its geographic distribution and adaptation to fish-farm. The knowledge of the morphological characteristics of the digestive tract is fundamental to the understanding of fish physiology and nutrition, which helps in the planning of diets to provide better management and success in fish farming. Thus, this work described the morphology and histochemistry of the digestive tract of L. marmoratus adults. After euthanasia, the animals were dissected for analysis of the digestive tract. The oesophagus is a short and distensive organ with longitudinal folds that allow the passage of large food, e.g., other fishes. Oesophageal mucosa layer shows a stratified epithelium with goblet cells and club cells. The secretion of goblet cells is composed of neutral and acidic mucins that are anchored in the epithelium luminal face by epithelial cells fingerprint-like microridges, lubricating the surface to facilitate the food sliding. Club cells have protein secretion that can be involved in alarm signals when epithelium is damaged and in immunological defence. The saccular stomach is highly distensible to store large food. Gastric mucosa layer is composed of epithelial cells with intense secretion of neutral mucin to protect against self-digestion of gastric juice. Cardiac and fundic regions of stomach show well-developed gastric glands composed of oxynticopeptic cells. These cells have numerous mitochondria, highlighting their intense activity in the synthesis of acid and enzymes. The intestine is divided into three regions: anterior, middle and posterior. Although it is a short tube, intestine shows longitudinal folds and microvilli of enterocytes to increase the contact surface. These folds are higher in the anterior region of the intestine, highlighting their function in digestion and absorption. Intestinal goblet cells have acidic and neutral mucins that lubricate the epithelium and aid in digestive processes. These cells increase in number towards aboral, and they are related to the protection and lubrication to expulsion of faecal bolus.     

Selectivity of Ingestion and Digestion in the Chrysomonad Flagellate Ochromonas malhamensis

Ochromonas malhamensis cells were allowed to feed on autoclaved Aerobacter aerogenes, biochemically inert polystyrene latex particles of comparable size, shape and density, or a combination of these to determine if this protozoan is capable of phagotrophic selectivity under defined experimental conditions. Electron microscopic examination of Gomoristained food vacuoles indicated that the type of particle ingested was determined entirely by the type available. Apparently the biochemical or physical configuration of the particle surface is not decisive in particle selection. Gomori acid-phosphatase reaction product, which indicates digestive enzyme activity, was present in all particle-containing vacuoles, suggesting that digestive activity in O. malhamensis is due to the presence of particulate material in the vacuole, but not necessarily to the nature of the particle.