The ultrastructure of the alimentary tract of the skin-penetrating larva of Nippostrongylus brasiliensis (Nematoda)

The structure of the alimentary tract of the third stage infective larva of Nippostrongylus brasiliensis has been described. The cuticle which lines the buccal cavity and oesophagus differs from that which lines the mouth and covers the external surface of the nematode. The oesophagus is a cellular structure and is not, as previously thought, a syncytium. The secretory granules of the oesophageal glands are surrounded by multi-layered membranes which give a myelinated appearance to the granules. The cells of the oesophago-intestinal junction are lined with cuticle and are presumably part of the stomodaeum. The intestine is thin-walled and the cells bear short, widely spaced microvilli. The lumen of the intestine contains whorls of membranes which are probably phospholipid and could act as a food reserve for the larva. The rectum and anus are lined with cuticle.     

The ultrastructure of the microfilaria of Brugia, Nematoda: Filarioidea

The microfilaria of Brugia pahangi is a differentiated nematode larva. The basic nematode body plan is present showing cuticle, hypodermis, dorsal, ventral, and lateral cords, muscle cells, longitudinal nerves, papillary nerves, amphids and phasmids. Secretory granules are present in ganglionic cells and in axons in the nerve ring. There is no differentiated pseudocoelom. There is only a single row of muscle cells between each pair of cords. The excretory cell complex is similar in structure to the hypodermal gland cells of other nematodes. The alimentary canal of the microfilaria is very much modified. The pharyngeal cells are attached to the pharyngeal thread which is circular in cross section and there is no pharyngeal musculature. The intestine is represented by the solid mass of the inner body within paired intestinal cells. The intestine is separated from the rectum. The three rectal cells form a syncytium of villi in the anal vesicle. The structure in Brugia is related to the ultrastructure of other microfilariae and it is concluded that the evolution of the modifications of the basic larval structure is due to the small size of these nematodes as a consequence of their adaptation to a parasitic mode of life in the capillaries of the vertebrate host with transmission through an intermediate arthropod vector.     

Embryology of the sheep. II. The alimentary tract and associated glands

The day-by-day development of the alimentary system of the sheep embryo from 14 to 34 days is documented and described. This includes development of the mouth, the pharynx and its derivatives, esophagus, stomach, intestine, cecum, pancreas and liver. This work provides standards within the normal range of development of the ovine alimentary system on which studies of abnormal development can be based.     

Morphology of the epithelium in the alimentary tract of the larval lamprey,Petromyzon marinus L.

The alimentary tract of the ammocoete of the lamprey, Petromyzon marinus L., is divisible into three morphologically distinct regions: the oesophagus, the anterior intestine, and the posterior intestine. The epithelium of the oesophagus possesses mucous, ciliated, and columnar cells and appears to be specialized for movement of food particles. The epithelium of the anterior intestine possesses secretory cells with numerous zymogen granules, ciliated cells, and columnar-absorptive cells. Although some absorption occurs in the anterior intestine, the main function of this region seems to be the release of digestive enzymes and the continued movement of food particles. The epithelium of the posterior intestine is entirely comprised of columnar absorptive cells, namely tall (light and dark) columnar and low columnar, and the primary function of this region is one of absorption. The epithelium of the hindgut resembles that of the archinephric duct (Youson and McMillan, '71). The morphology of the alimentary tract of ammocoetes suggests that some differentiation and renewal of cell types may occur in the epithelium of the three regions. Comparison of the alimentary tract of larval lamprey with that of other vertebrates indicates that the gut of the ammocoete represents a less specialized level of vertebrate development.     

玛曲渔场几种裂腹鱼类消化道的形态结构与其食性的相互关系

本文对玛曲渔场几种裂腹鱼类消化道的大体形态及显微结构进行了观察与比较,并对其结构与食性的关系作了初步探讨,结果如下:(1)这几种裂腹鱼类消化道的大体形态同林浩然(1962)报道的鲤科鱼类者一致,但显微结构差异甚大。与Mohsin(1961)报道的G.giurus鱼的显微结构相似。(2)各种硬骨鱼类分泌粘液的细胞组成不同,这种组成与食性有关。食道上皮除复层鳞形上皮外,还有复层柱状上皮。食道肌层的纤维走向与肠部者相反。(3)鱼类消化道的形态结构与其食性一致,主要表现在口腔、咽、食道和肠的长短方面。肠的显微结构,几乎没有对特有食性的适应变化。       

Trade-off between digestion and respiration in two airbreathing callichthyid catfishes Holposternum littorale (Hancock) and Corydoras aeneus (Gill)

In callichthyid catfishes, the posterior intestine is modified to function as an air breathing organ by being air-filled, thin-walled and highly vascularized. These modifications make it unsuitable for digestive functions and digesta has to be transported quickly through this region to minimize disruption of vital respiratory functions. However, the weak muscles of the wall of the respiratory intestine make this problematic. It is hypothesized that the unidirectional ventilatory air current within the respiratory intestine is responsible for the quick transport of digesta through the respiratory intestine. To verify this, movement of digesta through the alimentary tract was examined in Hoplosternum littorale and Corydoras aeneus that were either allowed to breathe air or prevented from air breathing. When air breathing was prevented, digesta was not transported to the rectum in H. littorale and there was a 94% reduction in the amount of digesta in the rectum of C. aeneus. This study suggests that the anterior digestive intestine facilitates the passage of air although it is filled with digesta. The anterior digestive intestine packages digesta into a string of slightly compressed boluses, creating an air channel in the digestive intestine thus allowing air to pass unimpeded.     

Ultrastructure of Enteronephridia and General Description of the Alimentary Canal in Trochonerilla mobilis and Nerillidium troglochaetoides (Polychaeta,Nerillidae)

The alimentary canals of Trochonerilla mobilis and Nerillidium troglochaetoides consist of a ventral pharyngeal organ, oesophagus, stomach, intestine, and rectum. Prominent salivary glands lying lateral to the oesophagus discharge their secretions into the buccal cavity. Ciliated canals, the enteronephridia, embedded in the intestinal epithelium, open into the stomach near its border to the intestine. The ventral pharynx comprises a muscle bulb connected to a tonguelike organ by an investing muscle. The whole alimentary canal is ciliated except for the intestine of T. mobilis. The stomach is built up of absorptive cells and posteriorly also of secretory cells, whereas the intestine consists of only one cell type which is considered to be mainly absorptive. A typical microvillar brush border is present only in the intestine of T. mobilis; elsewhere the density of microvilli is low or the cells have irregular apical processes. In N. troglochaetoides the intestine has a ventral ciliary gutter laterally bordered by cells with highly specialized microvilli. The enteronephridia — 3 in N. troglochaetoides and 13 in T. mobilis — are unicellular tubes up to 130 μm long with a microvillar brush border and other cytological features typical for nephridial ducts. These structures are not known in any other polychaete taxon.     

On the morphology of the alimentary tract of flatfishes (Pleuronectiformes)

The changes during the life cycle in the relative length of certain parts of the alimentary tract, buccal-pharyngeal cavity, oesophagus-stomach, intestine, rectum—are investigated in the five North Sea flatfish species, viz. turbot, brill, plaice, dab, sole. According to the average ratio between the length of the alimentary tract and the food preference three main groups are distinguished.     

Movements of the large intestine in the anuran larvae, Xenopus laevis

1. The contractile behavior of the large intestine of Xenopus laevis tadpoles was studied. 2. The large intestine is divided into a colon and rectum, and shows three types of movements: rhythmic ascending (antiperistaltic) waves of contraction originating at the anal end of the large bowel, rhythmic longitudinal contractions in the rectum and colon, and irregular contractions. The first two patterns occur in the large bowel in situ and thus appear mature. The last one occurred only in older preparations, and thus appeared pathological. 3. Antiperistaltic waves of contractions and longitudinal contractions are generated independent of each other, suggesting that circular muscles and longitudinal muscles contract separately. 4. Acetylcholine, adrenaline and noradrenaline augment motility. 5. The premetamorphic motility of the large bowel is similar to that seen in adult frogs. Comparable motility was not observed elsewhere in the larval alimentary tract. The large intestine appears to be the first portion of the anuran alimentary tract to acquire the adult physiological and morphological profile.     

Gangliosides of the human gastrointestinal mucosa.

Gangliosides of the human alimentary mucosa were purified and analysed with thin-layer chromatography and gas chromatography. The content of ganglioside neuraminic acid was 0.16 mumol/g dry weight in the stomach, 0.07 mumol/g dry weight in the small intestine and 0.11 mumol/g dry weight in the large intestine. Mono- and disialosylhemosides were the major gangliosides, on a molar basis 68% of the total found in the stomach and 44% of the total in the small and large intestine. Considerable amounts of more complex gangliosides were found, especially in the small and large intestine, in which the molar content of tri- and tetraglycosylgangliosides containing galactosamine made up 38% of the total. Two glucosamine-containing gangliosides were also found, the probable structures of which were mono- and disialotetraglycosylceramide. The presence of the latter is reported for the first time.     

Ultrastructure of the Alimentary Canal in Five-Month-Old Pentactulae of the Holothurian Eupentacta fraudatrix

Five-month-old pentactulae (juveniles) of the holothurian Eupentacta fraudatrixpossess a well-developed alimentary canal comprising an esophagus, a stomach, an intestine, and a rectum. The intestine in turn consists of five parts. The esophagus, stomach, and rectum are lined with a cuticular epithelium. The intestinal lining lacks a cuticle and is composed of mainly polyfunctional vesicular enterocytes. Granular enterocytes are less abundant; their cytoplasm contains electron-dense granules, which are probably zymogenic. The gut connective tissue consists of electron-lucent ground substance with collagen fibers and embedded coelomocytes. The gut mesothelium is composed of myoepithelial and peritoneal cells and contains the neurons of the hyponeural nerve plexus.     

Immnunohistochemical detection of phthalate esters in the alimentary canal of Tilapia spp.

An examination of the occurrence and distribution of phthalate esters in the alimentary canal of a polyhybrid of Tilapia gave evidence of different and selective patterns of distribution in the organ tissues: the phthalate esters were shown to be concentrated in the stomach and anterior intestine. The restricted distribution of phthalate esters can have implications for the physiology of the digestive system. The phthalates, stored in the oxyntic cells of the gastric tubular glands, probably interfere with the digestive process. The strategic location of the enterocytes in the anterior intestine implies that they can hamper the reabsorption of digestion products. The endocrine disrupting effects known for these chemicals are probably related to the absorption of them via the alimentary canal.     

Developmental expression of adenosine deaminase in the upper alimentary tract of mice

The distribution and localization of adenosine deaminase (ADA) was studied during postnatal development of the alimentary tract in mice. There was detectable enzyme activity in all organs examined, but a range of more than 10,000 fold in the relative levels of specific activity was observed among adult tissues. A comprehensive survey of multiple adult tissues revealed that the highest levels of ADA occur in the upper alimentary tract (tongue, esophagus, forestomach, proximal small intestine). Immunohistochemical analysis revealed that ADA was predominantly localized to the epithelial lining of the alimentary mucosa: the keratinized squamous epithelium that lines the forestomach, esophagus, and surface of the tongue; and the simple columnar epithelium of the proximal small intestine (duodenum, proximal jejunum). Biochemical analysis revealed that ADA was one of the most abundant proteins of these mucosal tissue layers, accounting for 5%-20% of the total soluble protein. Tissue-specific differences in ADA activity correlated both with levels of immunoreactive protein and RNA abundance. The level of ADA activity in the upper alimentary tissues was subject to pronounced developmental control, being low at birth and achieving very high levels within the first few weeks of postnatal life. The appearance in development of ADA-immunoreactivity coincided with maturation of the mucosal epithelium. These results suggest that ADA is subject to strong cell-specific developmental regulation during functional differentiation of certain foregut derivatives in mice.     

Feeding and gut physiology in Acanthopleura spinigera (Mollusca)

The morphology and histology of the alimentary canal of the rock chiton Acanthopleura spinigera are described and the ability of regions of the gut to digest specific substrates investigated. The oesophagus is produced into a pair of thin-walled lateral pouches, the salivary glands or "sugar glands" which empty into the stomach. Folds of the capacious stomach are almost obscured by the large digestive gland over which is coiled the intestine. Histologically the gut consists of an outer layer of connective tissue, an inner muscular layer and a ciliated epithelium which varies in thickness from one region to the next. Proteases are most active in the stomach, digestive gland and anterior intestine at pH 6·5 and in the posterior intestine at pH 7·5-8·5. The digestion of lipoidal substance was greatest in the stomach and digestive gland and least in anterior intestine. There was little increase in the amount of digestion product obtained after 20 hours incubation. All regions of the alimentary canal and salivary gland were capable of digesting carbohydrates except that many low molecular weight carbohydrates were digested by salivary gland extracts only. The amylases were most active at pH 6–6·5. It is concluded that digestive enzymes are distributed throughout the intestinal tract but the amount of enzyme present varies from region to region, and is greatest just after feeding.     

Cell renewal in the epithelium of the alimentary tract of the larval lamprey,Petromyzon marinus L.

Light microscopic autoradiography with ³H-thymidine demonstrates that the three regions of the alimentary tract in the larval (ammocoete) lamprey, Petromyzon marinus L., possess different patterns for renewing their epithelium. In the oesophagus, columnar and mucous cells originate from stem cells located at the bases of folds and migrate to the tops of the folds where they are apparently extruded. Ciliated cells, located only at the tops of the folds, seem to differentiate from migrating columnar cells. In the anterior intestine, stem cells are present throughout the epithelium so that there is limited migration of cells and their extrusion occurs randomly. In the posterior intestine, the stem cells located at the bases of the typhlosole provide a continuous population that differentiates and migrates to the top of the typhlosole and to the opposite epithelial wall where they are presumably extruded. The rates of cell renewal in all three epithelial regions of the alimentary tract are slower in animals maintained at 10 ± 1°C compared with those kept at 21 ± 1°C. Comparatively, ammocoetes have the least specialized system for cell renewal known in the alimentary tract of a vertebrate.     

Analysis of the role of adrenergic receptors in the regulation of small intestine motor activity in sheep

In sheep with chronic fistulae of the small intestine and rumen the participation of alpha- and beta-adrenergic receptors in the regulation of the motor activity of the small intestine was studied by the method of pharmacological analysis. The movements of the fistulated parts of the alimentary tract were recorded by the balloon method. Slow intravenous infusion of isoprenaline inhibited the contractions of the small intestine. This inhibitory effect of isoprenaline was abolished by propranolol. Intravenous phenylephrine inhibited the motor activity of this intestinal part as well. The effect of phenylephrine was abolished by pretreatment with dihydroergotamine. In the small intestine of sheep stimulation of the alpha and beta adrenergic receptors decrease the motor activity of intestine.     

Expression of the poliovirus receptor in intestinal epithelial cells is not sufficient to permit poliovirus replication in the mouse gut.

Although the initial site of poliovirus replication in humans is the intestine, previously isolated transgenic mice which carry the human poliovirus receptor (PVR) gene (TgPVR mice), which develop poliomyelitis after intracerebral inoculation, are not susceptible to infection by the oral route. The low levels of PVR expressed in the TgPVR mouse intestine might explain the absence of poliovirus replication at that site. To ascertain whether PVR is the sole determinant of poliovirus susceptibility of the mouse intestine, we have generated transgenic mice by using the promoter for rat intestine fatty acid binding protein to direct PVR expression in mouse gut. Pvr was detected by immunohistochemistry in the enterocytes and M cells of transgenic mouse (TgFABP-PVR) small intestine. Upon oral inoculation with poliovirus, no increase in virus titer was detected in the feces of TgFABP-PVR mice, and no virus replication was observed in the small intestine, although poliovirus replicated in the brain after intracerebral inoculation. The failure of poliovirus to replicate in the TgFABP-PVR mouse small intestine was not due to lack of virus binding sites, because poliovirus could attach to fragments of small intestine from these mice. These results indicate that the inability of poliovirus to replicate in the mouse alimentary tract is not solely due to the absence of virus receptor, and other factors are involved in determining the ability of poliovirus to replicate in the mouse gut.     

Inability of human clinical strains of Helicobacter pylori to colonize the alimentary tract of germfree rodents

Several attempts were made to colonize the alimentary tract and infect germfree BALB/c mice and germfree Sprague-Dawley rats with two human isolates of Helicobacter pylori. The alimentary tracts of mice, sacrificed at intervals between 1 day and 20 weeks after oral challenge, were culture negative for H. pylori. The alimentary tract, kidney, liver, and mesenteric lymph nodes were culture negative for H. pylori 5 h after intravenous challenge. Growth of H. pylori was inhibited by homogenates of murine stomach, small intestine, liver, and mesenteric lymph nodes. Germfree rats and mice do not appear to be readily colonized or infected by human strains of H. pylori.     

Growth of the alimentary tract with aging in chickens.

There is a mathematical model supporting that when growth rate of the chickens is maximized and not constrained by the food-availability, the optimal relationship between body mass and alimentary tract mass should conform to a two-segmented straightened line with different slopes. In the present work we have studied the model using the mass of the intestines as an indicator of growth of the alimentary tract of the Gallus gallus domesticus L. We have observed the slope change of the two segments around a body weight of 90 g that corresponded to two-week-old animals and, at this age it was supposed that the differentiation of the intestine reach the maximum.