Foregut Lumen Research Articles

Intraluminal duodenal “windsock” diverticulum

Intraluminal duodenal diverticulum (IDD) is a rare developmental anomaly usually found in the second portion of the duodenum. The cause appears to be a failure of recanalization of the occluded foregut lumen of the human embryo, resulting in a fenestrated mucosal membrane [1]. A small aperture in this diaphragm will gradually cause it to elongate caudally in response to duodenal peristalsis to form the so called “wind-sock” configuration. Symptoms are nonspecific and generally depend on the degree of duodenal obstruction; 25% of cases are associated with GI bleeding. In most documented cases, IDD was diagnosed radiologically, but the value of endoscopy for diagnosis and treatment has been amply demonstrated

Intraluminal duodenal “windsock” diverticulum; Case Report and discussion

Intraluminal duodenal diverticulum (IDD) is a rare developmental anomaly usually found in the second portion of the duodenum. The cause appears to be a failure of recanalization of the occluded foregut lumen of the human embryo, resulting in a fenestrated mucosal membrane [1]. A small aperture in this diaphragm will gradually cause it to elongate caudally in response to duodenal peristalsis to form the so called “wind-sock” configuration. Symptoms are nonspecific and generally depend on the degree of duodenal obstruction; 25% of cases are associated with GI bleeding. In most documented cases, IDD was diagnosed radiologically, but the value of endoscopy for diagnosis and treatment has been amply demonstrated.

Duodenal Chemosensing of Short-Chain Fatty Acids: Implications for GI Diseases.

Short-chain fatty acids (SCFAs), the main bacterial fermentation products in the hindgut of hindgut fermenters, are also present in the foregut lumen. We discuss the impact of SCFAs in the duodenal defense mechanisms and in the gastrointestinal (GI) pathogenesis. Luminal SCFAs augment the duodenal mucosal defenses via release of serotonin (5-HT) and glucagon-like peptide-2 (GLP-2) from enteroendocrine cells. Released GLP-2 protects the small intestinal mucosa from nonsteroidal anti-inflammatory drug-induced enteropathy. SCFAs are also rapidly absorbed via SCFA transporters and interact with afferent and myenteric nerves. Excessive SCFA signals with 5-HT3 receptor overactivation may be implicated in the pathogenesis of irritable bowel syndrome symptoms. SCFA production exhibits diurnal rhythms with host physiological responses, suggesting that oral SCFA treatment may adjust the GI clocks. SCFAs are not only a source of energy but also signaling molecules for the local regulation of the GI tract and systemic regulation via release of gut hormones. Targeting SCFA signals may be a novel therapeutic for GI diseases and metabolic syndrome.

Thyroid bud morphogenesis requires CDC42- and SHROOM3-dependent apical constriction.

ABSTRACTEarly development of the gut endoderm and its subsequent remodeling for the formation of organ buds are accompanied by changes to epithelial cell shape and polarity. Members of the Rho-related family of small GTPases and their interacting proteins play multiple roles in regulating epithelial morphogenesis. In this study we examined the role of Cdc42 in foregut development and organ bud formation. Ablation of Cdc42 in post-gastrulation mouse embryos resulted in a loss of apical-basal cell polarity and columnar epithelial morphology in the ventral pharyngeal endoderm, in conjunction with a loss of apical localization of the known CDC42 effector protein PARD6B. Cell viability but not proliferation in the foregut endoderm was impaired. Outgrowth of the liver, lung and thyroid buds was severely curtailed in Cdc42-deficient embryos. In particular, the thyroid bud epithelium did not display the apical constriction that normally occurs concurrently with the outgrowth of the bud into the underlying mesenchyme. SHROOM3, a protein that interacts with Rho GTPases and promotes apical constriction, was strongly expressed in the thyroid bud and its sub-cellular localization was disrupted in Cdc42-deficient embryos. In Shroom3 gene trap mutant embryos, the thyroid bud epithelium showed no apical constriction, while the bud continued to grow and protruded into the foregut lumen. Our findings indicate that Cdc42 is required for epithelial polarity and organization in the endoderm and for apical constriction in the thyroid bud. It is possible that the function of CDC42 is partly mediated by SHROOM3.

SCFA transport in rat duodenum.

Bacterial or ingested food-derived short-chain fatty acids (SCFAs) are present in the duodenal lumen. Acetate, the most abundant SCFA in the foregut lumen, is absorbed immediately after ingestion, although the mechanism by which this absorption occurs is not fully understood. We investigated the distribution and function of candidate SCFA transporters in rat duodenum. The Na(+)-coupled monocarboxylate transporter-1 (SMCT1) was localized to the brush border, whereas the pH-dependent monocarboxylate transporter (MCT) 1 and MCT4 were localized to the duodenocyte basolateral membrane. In Ussing chambered duodenal mucosa, luminal acetate dose-dependently increased short-circuit current (Isc) in the presence of serosal bumetanide and indomethacin by a luminal Na(+)-dependent, ouabain-sensitive mechanism. The Isc response was inhibited dose-dependently by the SMCT1 nonsubstrate inhibitor ibuprofen, consistent with net electrogenic absorption of acetate via SMCT1. Other SCFAs and lactate also increased Isc. Furthermore, duodenal loop perfusion of acetate increased portal venous acetate concentration, inhibited by coperfusion of ibuprofen or a MCT inhibitor. Luminal acetate perfusion increased duodenal HCO3 (-) secretion via capsaicin-sensitive afferent nerve activation and cyclooxygenase activity, consistent with absorption-mediated HCO3 (-) secretion. These results suggest that absorption of luminal SCFA via SMCT1 and MCTs increases duodenal HCO3 (-) secretion. In addition to SCFA sensing via free fatty acid receptors, the presence of rapid duodenal SCFA absorption may be important for the suppression of luminal bacterial colonization and implicated in the generation of functional dyspepsia due to bacterial overgrowth.

The larval alimentary canal of the Antarctic insect, Belgica antarctica

On the Antarctica continent the wingless midge, Belgica antarctica (Diptera, Chironomidae) occurs further south than any other insect. The digestive tract of the larval stage of Belgica that inhabits this extreme environment and feeds in detritus of penguin rookeries has been described for the first time. Ingested food passes through a foregut lumen and into a stomodeal valve representing an intussusception of the foregut into the midgut. A sharp discontinuity in microvillar length occurs at an interface separating relatively long microvilli of the stomodeal midgut region, the site where peritrophic membrane originates, from the midgut epithelium lying posterior to this stomodeal region. Although shapes of cells along the length of this non-stomodeal midgut epithelium are similar, the lengths of their microvilli increase over two orders of magnitude from anterior midgut to posterior midgut. Infoldings of the basal membranes also account for a greatly expanded interface between midgut cells and the hemocoel. The epithelial cells of the hindgut seem to be specialized for exchange of water with their environment, with the anterior two-thirds of the hindgut showing highly convoluted luminal membranes and the posterior third having a highly convoluted basal surface. The lumen of the middle third of the hindgut has a dense population of resident bacteria. Regenerative cells are scattered throughout the larval midgut epithelium. These presumably represent stem cells for the adult midgut, while a ring of cells, marked by a discontinuity in nuclear size at the midgut-hindgut interface, presumably represents stem cells for the adult hindgut.

On the shape of foregut lumen in sea spiders (Arthropoda: Pycnogonida)

The shape of foregut lumen in both the pharyngeal and the oesophageal regions has been examined from serial histological sections in 16 species of pycnogonids covering all extant families. Each species has a Y-shaped foregut lumen in transverse section. This result shows that some previous authors misoriented the lumen as inverted Y-shaped. The triradiate Y-shaped foregut lumen has been found among ecdysozoans including tardigrades, onychophorans and scatteringly arthropods. At present, it is not clear whether the Y-shaped state of the characteristic in pycnogonids is convergent or symplesiomorphy with that in tardigrades and onychophorans.

Ultrastructure of the foregut and associated glands in the lung fluke, Paragonimus miyazakii (Digenea: Troglotrematidae), with particular reference to their functional roles.

The foregut and associated glands of a digenetic trematode, Paragonimus miyazakii, were examined in the forebody by transmission and scanning electron microscopy as well as by light microscopy, and their functional roles were discussed. The foregut is lined with a general tegument without spines and sensory receptors throughout its length, although it consists of the mouth, pharynx, and esophagus. This foregut tegument is regionally and intraregionally modified in appearance, suggesting the performance of auxiliary functions in digestion. This appearance is characterized by long, frequent cytoplasmic extensions of the apical tegument around the middle portion of the mouth and the anterior esophagus. Electron-dense granules and multimembranous and multilamellar bodies are developed in the tegument to various degrees, and elaborately in the apical layer of the prepharynx. A single type of unicellular gland is embedded in the antero-middle part of the worm in small groups. The gland cells synthesize clear secretory granules as a chief product, each granule with a pleomorphic, dense, core-like inclusion. Mature granules are elliptical in shape, approximately 500 nm in diameter, and are subsequently discharged into the prepharyngeal foregut lumen after passing through the elongated cytoplasm of the gland cell. In the prepharynx and pharynx, host blood cells are apparently processed for digestion. In the wide lumen of the esophagus, foodstuff could undergo sufficient digestion prior to absorption by the cecal epithelium.

The maltase of the house cricket Acheta domesticus L. (orthoptera: gryllidae)

1. 1. The optimal pH of maltase of the house cricket was 5.6 and the optimal temperature was 40°C. The apparent activation energy was 5300 cal/mol 2. 2. The 50% inactivation time for maltase at 50°C was 69 min and the 50% inhibition concentration for mercuric chloride was 163μmole. 3. 3. Maltase was only produced by the caecal tissues but its highest activity was found in the foregut lumen and after 5 days of starvation, only 44.6% of the total maltase activity remained.

Experimental transmission of murine typhus by Xenopsylla cheopis flea bites

Transmission of Rickettsia typhi to rats by the bites of Xenopsylla cheopis (Rothschild) fleas was investigated. Procedures rigorously excluded the possibility of contamination of the host skin by flea faeces. Fleas with R. typhi infection (21-25 days post-infection) which fed through bolting cloth (45 min exposure to ten fleas) transmitted rickettsiae with a success rate of 20%. Infective fleas allowed free access to their host for 8 h (10-15 fleas/rat) gave transmission rates of 45-68%. They were also capable of inoculating R. typhi through a membrane of rat skin on a feeder. Only fleas which had been infected for 21 days or longer transmitted R. typhi orally. Oral transmission appeared to be the result of regurgitation of rickettsiae present in the foregut lumen rather than through salivary secretions.

Organization of protein digestion in adult Calosoma calidum (Coleoptera: Carabidae)

Organization of protein digestion was examined in adult male Calosoma calidum (Carabidae) fed either ground-beef or waxmoth larvae ( Galleria mellonella). Although trypsin activities in the foregut are consistently higher than those in the midgut, the luminal contents of each region are in equilibrium. Movement of fluids between the midgut and foregut is brought about by muscular contractions of the proventriculus. A 42% fall in trypsin activity of the foregut after feeding on ground-beef is due largely to disgorged enzymes being left on the food. A far higher proportion of disgorged trypsin is recovered when C. calidum feed on waxmoth larvae; beetles ingest about 74% prey protein and yet avoid ingesting digestively refractory solids. The retention of undigested macromolecules in the midgut and foregut lumen was determined using [ 14C]inulin labelled waxmoth larvae. Nine per cent and 25% of the radiolabel was passed in the faeces in 2 and 4 days respectively, whilst 59 and 91% of the weight gained at feeding was lost in the same intervals. The role that the peritrophic membrane and pyloric valve play in this process, as well as its implications for enzyme conservation, is discussed.

Reexamination of the origin and early development of the human larynx.

The respiratory primordium buds off the primitive foregut and grows caudally, on a lengthening stalk; the cephalic end of the stalk develops into the glottis and infraglottis, and the rest becomes the trachea. Compression by pharyngeal mesoderm cephalic to the respiratory diverticulum obliterates the foregut lumen ventrodorsally as far cranially as the 4th pharyngeal pouches, forming an epithelial lamina with a narrow pharyngoglottic duct along its dorsal border. The mesoderm also raises an epiglottic and two arytenoid swellings in the pharyngeal floor at the level of the 4th pouches; the triangular 'cecum', bounded by these swellings, grows caudally along the ventral border of the epithelial lamina to just above the glottis. Beginning at stage 21, the epithelial lamina separates cephalocaudally, bringing the cecal lumen into continuity with the pharyngoglottic duct to form the laryngeal vestibule; when the separation is complete, the vestibule is continuous with the infraglottic cavity. Meanwhile, bilateral pouches arising from the caudal end of the cecum form the ventricles, the lower lips of which become the vocal folds, and the pharyngeal mesoderm surrounding the laryngeal cavity gives rise to the laryngeal cartilages and intrinsic musculature. The cricoid chondrifies bilaterally from a single center in the ventral arch of a precartilaginous template that encircles the infraglottic cavity, and on meeting forms the dorsal lamina. Each arytenoid chondrifies from a single center, and each half of the thyroid cartilage chondrifies from two. Anlagen for the intrinsic muscles appear during stage 17, sites of individual muscles are recognizable by stage 23, and myofibrils are present by the 12th week.

Initiation of feeding and salinity tolerance in the pacific lamprey Lampetra tridentata

Changes in salinity tolerance were determined during metamorphosis in Lampetra tridentata. Lampreys in Phase 5 of metamorphosis were unable to withstand salinities>13.4‰S, while those in Phase 6 survived direct transfer to sea water (30‰S). This abrupt change in tolerance coincided with the opening of the foregut lumen. Parasitic feeding began at the end of Phase 7 of metamorphosis following the completion of tooth development.

Association of Virus-like Particles with the Foregut of the Aphid Cavariella aegopodii Transmitting the Semi-persistent Viruses Anthriscus Yellows and Parsnip Yellow Fleck

SUMMARY The aphid Cavariella aegopodii transmits anthriscus yellows virus (AYV) and parsnip yellow fleck virus (PYFV) in a semi-persistent manner and loses them on moulting. It transmits PYFV only when it is also carrying AYV. The particles of AYV have not been seen in preparations or sections from infected plants but those of PYFV are isometric, about 30 nm in diam. in negative stain. Groups of a few to several hundred virus-like particles about 20 to 28 nm in diam. were seen by electron microscopy in the foregut of C. aegopodii transmitting AYV or the AYV/PYFV complex but not in aphids fed on healthy plants or on a source of PYFV alone. The particles were surrounded by densely staining material, which was in turn embedded in a matrix of lightly staining material (M-material), overlying a 15 to 20 µm-long portion of the intima lining the ventral wall of the pharynx (anterior portion of the foregut). In this region the intima is thickened and formed into several spike-like protrusions. The M-material also occurred in aphids fed on healthy plants, but less commonly than in those fed on infected plants. In some aphids that were fixed immediately after feeding on AYV-infected plants, additional groups of virus-like particles were found free in the foregut lumen. The particles in the matrix were not found until the aphids had fed on AYV-infected plants long enough to acquire transmissible virus, but they were still present in aphids that had fed for 2 h on 10% sucrose after feeding for 24 h on a source of AYV. In moulting aphids, the matrix, with associated virus-like particles, remained attached to the old pharynx lining. It is thought that the virus-like particles are those of AYV and that the matrix is the specific site of retention within the aphid. No differences were observed between aphids carrying AYV and those carrying both AYV and PYFV, and it is not known whether some of the particles found in insects carrying both viruses are those of PYFV.