Studies on the microvascularization of the digestive tract by scanning electron microscopy of vascular corrosion casts. 1. Large intestine in rats and guinea pigs.

The colonic microvascularization of 10 adult Sprague-Dawley rats and guinea pigs (Cavia porcellus was studied by scanning electron microscopy of microvascular corrosion casts. The tunica muscularis is supplied by branches of the submucosal arteriolar plexus, according to the arrangement of muscle layers, longitudinally and transversally arranged capillaries are distinguished. The mucosal capillaries show a honeycomb pattern and mimic the openings of the mucosal glands. Parallel to the luminal aspect of the large intestine, the mucosal capillary loops often arise from the submucosal arterioles at the most abluminal aspect of the mucosa; however, some arterioles end just subjacent to these capillaries. The submucosal veins are located just subjacent to the capillaries of the lamina propria. The rat and guinea pig colonic vascular architecture revealed no differences, neither did the capillary density in different parts of the large intestine.     

Microvasculature of the feline stomach

The feline gastric microvasculature was studied by corrosion of the injected vascular bed, which allowed evaluation of the vascular pattern of the different tunics. The serosal pattern consisted of numerous interconnected capillary vessels, forming a delicate network. Submucosal arteries supplied the muscular tunic through numerous anastomosing vessels that followed the direction of the smooth muscle fibers. The entire mucosal tunic was supplied by arterioles derived from the submucosal plexus; these gave rise to capillaries that surrounded the gastric glands and terminated in a diffuse, anastomosing subepithelial capillary network. Venules coursed through the mucosa in a perpendicular manner, forming submucosal veins.     

Microangioarchitecture of gastric mucosa in man: antrum ventriculi

The blood vessels of the antrum area of human gastric tunica mucosa have been studied by scanning electron microscopy and compared with vertical and horizontal serial sections of perfusion-fixed antrum mucosa. In contrast to previous studies on the oxyntic corpus mucosa, where two superimposed capillary layers could be seen, the antrum mucosa presents only one capillary layer. It extends from the lymphatic follicles above the lamina muscularis mucosae up to the luminal surface. No further arterioles exist in the glandular part of the antrum mucosa. The luminal aspect of the capillaries show thin, honeycomb-like capillaries, differing from our previous findings in the corpus area. There the capillaries are wide and circulate in a dense, convoluted way. Arteriovenous anastomoses again could not be seen in the examined tissue. The differences in gastric microangioarchitecture might be explained by the extent of the glandular part in both regions. The findings in the antrum area very much resemble the basal capillary layer in the corpus mucosa. The critical height for one capillary layer in the glandular tissue of human gastric mucosa is estimated to be approximately 1 mm. Larger diameters, as in the oxyntic corpus mucosa, might require a second capillary layer.     

Comparative mucosal microvasculature of the mammalian stomach

The comparative morphology of the gastric mucosal microvasculature was investigated using the corrosion casting technique. The vascular pattern consisted of a hexagonally arranged capillary plexus surrounding the gastric glands and terminating in venules running perpendicular to the mucosal axis. Vessels of the pyloric antrum demonstrated an acute angle between capillaries and venules, whereas vessels of the gastroduodenal junction changed from a honeycomb pattern to a leaf-like arrangement.     

Somatostatin in human enteric nerves

Summary Somatostatin-immunoreactive nerves and endocrine cells were localized by use of immunohistochemistry in human stomach, small and large intestine. The nature of the immunoreactivity in acid extracts of separated layers of intestine was determined with separation by high pressure liquid chromatography followed by detection with radioimmunoassay; authentic somatostatin-14 was found in the external musculature, which contains nerves, and in the submucosa and mucosa, which contain both nerve fibres and endocrine cells.The distribution of somatostatin nerves in the gastric antrum, duodenum, jejunum, ileum, ascending and sigmoid colon, and rectum is described. In the intestine many positive perikarya and fine varicose fibres were seen. Mucosal fibres formed a sub-epithelial plexus and a looser network in the lamina propria; this nerve supply was less dense in the large intestine. Submucous ganglia contained positive perikarya and terminals; many terminals formed pericellular baskets, mainly around non-reactive cells. A small number of nerve fibres were associated with submucosal blood vessels. The innervation of the circular and longitudinal muscle was sparse. Positive nerve terminals were seen in the myenteric plexus, although fewer than in the submucous ganglia; positive perikarya were scarce in myenteric ganglia. Somatostatin-immunoreactive nerves were found in the muscle layers and myenteric plexus of the gastric antrum, but were not detected in the antral mucosa and all layers of the gastric body.The distribution of human enteric somatostatin nerves is compared to that in small laboratory animals, and possible roles for these nerves are discussed.     

Structure and mucous histochemistry of the intestinal respiratory tract of the mud loach, Misgurnus anguillicaudatus (Cantor)

The straight intestinal tract of the mud loach Misgurnus anguillicaudatus was divided into an intestine and rectum which consisted of a mucosa (epithelial layer), lamina propria‐submucosa, muscularis and serosa. The intestine and rectum have shorter mucosal folds and a thinner wall. Extensive vascular capillary networks were present in the mucosa of the intestine and the rectum. The diffusion distance between the vascular capillaries and the lumen in the intestinal and rectal mucosal epithelium was about 11.2 μm (±1.12). The majority of the epithelial mucous cells contain acidic mucins although there are small amounts of a mixture of acidic and neutral mucins. The intestinal tract of M. anguillicaudatus is probably modified to suit its role of respiration for the deficient oxygen supply within their environment.     

Mucosal microvascular organization of the rat colon

The mucosal microvascular architecture of the rat colon is described from vascular casts and intravital microscopy. Arterial break-up into the mucosal capillary bed invariably occurs at the submucosal/mucosal interface. The mucosal capillaries drain into venules only at the opposing, luminal aspect, i.e., mucosal venules transverse the mucosa without receiving further capillary tributaries. Intravital microscopy of luminal flow confirmed cast predictions. Further, capillary flow was unusually unidirectional, i.e., rarely static or reversible. The possible functional importance of this particular microvascular architecture to water absorption in the colon is discussed.     

Mast cells and cells producing alpha-endorphin in the mucosa of the antral section of the stomach

The distribution of mast cells, alpha-endorphine-producing cells (AER-cells) and argyrophilic cells in lamina propria of the antral mucosa was determined quantitatively in 13 normal men. The cells were detected by histochemical and immunohistochemical (PAP) methods. The form and site of AER-cells resembled those of mast cells and mucosal argyrophilic cells (in lamina propria). The authors assume that part of human gastric mucosal cells have argyrophilic properties and contain alpha-endorphine.     

Cell proliferation in Walker tumour growing in the stomach wall.

Tumour cells from a Walker carcinosarcoma 256 were implanted in the gastric mucosa in rats. The tumour grew and infiltrated the lamina propria and the submucosal space after 7 days. It appeared to grow faster in the submucosal space than in the lamina propria. The cell proliferation was therefore studied separately in: (1) the tumour in the lamina propria, (2) the main tumour mass and (3) the tumour periphery, defined as the cells located within the outer 100-120 mum of the tumour. Mitoses arrested with vinblastine, cells labelled with tritiated thymidine and the grain count per labelled cell were studied at the three different sites. The rate of cell proliferation in the tumour was highest in the lamina propria, lower in the centre of the main tumour mass, and lowest at the periphery. Cell loss might explain the discrepancy between the rate of cell proliferation and the actual tumour growth. The factors that influence tumour cell proliferation in the different parts of the tumour are discussed.     

Specific attachment of mesenteric IgA lymphoblasts to specialized endothelium of intestinal mucosa lamina propria capillaries

The bulk of IgA secreted in the gut is mostly contributed by locally dwelling plasma cells derived from B cells originating in the gut-associated lymphoid tissues (GALT). These IgA cells originate in Peyer's patches and recirculate, returning to the gut upon maturity. The precise mechanism of homing to secretory mucosae is to date not fully understood. It has been demonstrated, however, that specialized endothelium of small vascular spaces in peripheral nodes (PN) and endothelia of mucosal vessels are the site of receptor recognition for B and T cells. In their sojourn, IgA blasts have been shown to stop momentarily in mesenteric nodes (MN) before proceeding to their final destination, the lamina propria (LP) of the gut mucosa. They then develop into IgA-secreting plasma cells. In the present work, we show that IgA MN lymphoblasts, when compared to PN lymphoblasts, attach preferentially to LP venule and capillary endothelium, The B-cell maturation in the mesenteric lymph nodes, where IgA is the sole membrane-bound immunoglobulin, allows attachment of most of these cells. Our work suggests that the site of exit of IgA cells from the circulation are these specialized lamina propria venules and capillaries.     

CELL PROLIFERATION IN WALKER TUMOUR GROWING IN THE STOMACH WALL

Tumour cells from a Walker carcinosarcoma 256 were implanted in the gastric mucosa in rats. The tumour grew and infiltrated the lamina propria and the submucosal space after 7 days. It appeared to grow faster in the submucosal space than in the lamina propria. The cell proliferation was therefore studied separately in: (1) the tumour in the lamina propria, (2) the main tumour mass and (3) the tumour periphery, defined as the cells located within the outer 100–120 μm of the tumour. Mitoses arrested with vinblastine, cells labelled with tritiated thymidine and the grain count per labelled cell were studied at the three different sites. The rate of cell proliferation in the tumour was highest in the lamina propria, lower in the centre of the main tumour mass, and lowest at the periphery. Cell loss might explain the discrepancy between the rate of cell proliferation and the actual tumour growth. The factors that influence tumour cell proliferation in the different parts of the tumour are discussed.     

Effect of proximal selective vagotomy on gastric prostaglandin content in the Shay-rat ulcer model

During Shay-ulcer formation damages to the barrier of the gastric mucosa develop even before the appearance of macroscopic ulceration. Proximal selective vagotomy prevents these damages. Following pyloric ligation the prostaglandin content of the mucosa changes in parallel with the injuries of the mucosal barrier: TXB2 content of the forestomach increases, while PGF2 alpha content of both the forestomach and the antrum decreases. Following PSV operation the 6-keto-PGF1 alpha content of the mucosa decreases, whereas PGF2 alpha and TXB2 contents exhibit no alteration. As a combined effect of proximal selective vagotomy pretreatment and pyloric ligation the 6-keto-PGF1 alpha and PGF2 alpha contents of the mucosa remain low and the TXB2 increase, otherwise detectable after pyloric ligation, does not take place.     

The innervation of the human antro-pyloric region: organization and composition.

Although the composition of the gastric innervation has been determined in animal models, relatively little known about the innervation of the human antro-pyloric region. We used immunocytochemical techniques to establish the localization and co-expression of neuropeptides and nitric oxide in the human antrum and upper duodenum. Our results demonstrate the existence of a clearly defined submucosal plexus in the antral region that is absent in rats and guinea pigs. The abundant innervation of the lamina propria contains 3 major nerve populations: VIP- and NOS-, SP- and CGRP-, and GRP-immunoreactive. For the first time, NOS-containing nerve fibers were observed throughout the length of the antral glands. Within the antrum somatostatin was confined to endocrine cells, however, at the pyloric sphincter both enteric plexi contained immunoreactive neurons and nerve fibres. Within the pyloric sphincter CGRP- and SP-immunoreactive fibres were significantly increased, correlating with the presence of large ganglia in the submucosal plexus. In conclusion, the organization and composition of the innervation of human antro-pylorus differed substantially from that reported in other mammals. The presence of an abundant mucosal innervation paralled by a well-defined submucosal plexus indicates that the functional regulation of the gastric-pyloric region will be distinct from that of smaller animal models.     

Histology and mucin histochemistry of the gastrointestinal tract of the mud loach, in relation to respiration

The gastrointestinal tract of the mud loach Misgurnus mizolepis was divided into an oesophagus, stomach, intestine and rectum which consisted of a mucosa (epithelial layer), lamina propria-submucosa, muscularis and serosa. The intestine and rectum have shorter mucosal folds and a thinner wall than those of the oesophagus and the stomach. Extensive vascular capillary networks were present near the luminal surface of the intestine and the rectum. The diffusion distance between the vascular capillaries and the viscus lumen in the intestinal and rectal mucosal epithelium was 0·7 μm (±0·11). The intestine and rectum of Misgurnus mizolepis probably have a respiratory function to address the deficient oxygen supply within their environment. The epithelial mucous cells contained acidic or a mixture of acidic and neutral mucins, the former being the most common.     

Regeneration of endocrine cells in the stomach

A mucosal defect was produced by cryosurgery in the antral and the fundic wall of the rat stomach, and regeneration of gastric endocrine cells was studied 50, 100 and 200 days after operation. Fifty days after the operation, the mucosal defect was completely covered with regenerated epithelium. The regenerated mucosa both in the antral and in the fundic region consisted of mucinous glandular structures. The regenerated mucosa in the corpus remained pseudopyloric in type even 200 days after operation. Regardless of the time after operation, regeneration of endocrine cells was always observed. We could identify G cells and EC cells in the regenerated mucosa of the antrum, and EC cells, A cells and AL cells in the regenerated mucosa of the corpus, respectively. By electron microscopy, endocrine-exocrine cells were frequently encountered. These cells had two different types of intra-cytoplasmic granules; one was an endocrine-specific, small electron-dense granule, and the other a large, lucent mucin droplet-like granule. These findings indicate that the endocrine cells of the stomach are formed from endodermal precursor cells.     

The microscopic anatomy of the oesophagus, stomach and intestine of the channel catfish, Ictalurus punctatus

An anatomical study of the digestive tract of the channel catfish revealed that the oesophageal mucosa was longitudinally folded and that secondary folds were occasionally located on the primary longitudinal folds. The infoldings were more numerous near the stomach. The stratified squamous epithelium covering the folds was made up of a basal layer, large mucous cells and simple squamous cells on the surface. The epithelium on the side of the folds consisted primarily of mucous secreting cells. Taste buds were observed between mucous cells on the apical portion of the oesophageal folds and were more prevalent in the cranial part of the oesophagus. The remaining layers of the oesophagus were: a lamina propria-submucosa, tunica muscularis and adventitia or serosa.
The J-shaped stomach had two regions: a large sac-shaped region containing gastric glands and a smaller, nonglandular pyloric region. The large rugae of the stomach became gradually smaller near the pylorus. There was a well developed pyloric sphincter. The mucosa included a simple columnar epithelium, a lamina propria and adventitia or serosa.
The intestine could be differentiated into a thick ascending segment, a descending segment, a thin convoluted segment and a thicker terminal segment, the rectum. Many mucosal folds containing branched villi characterized the ascending segment of the intestine. The descending and convoluted segments contained fewer folds with shorter and less-branching villi and were smaller in diameter and thinner walled. Descending and convoluted segments were also mildly convoluted and accounted for 80% of the total length of the intestine. An intestinal valve with a sphincter marked the beginning of the rectum. There was an approximately four-fold increase in the thickness of the tunica muscularis of the terminal segment of the intestine.     

Selective ablation of spinal afferent neurons containing CGRP attenuates gastric hyperemic response to acid.

The gastric mucosa, in particular submucosal blood vessels, are innervated by afferent neurons containing neuropeptides such as calcitonin gene-related peptide. Stimulation of sensory neurons innervating the gastric mucosa increases submucosal blood flow. Since sensory neurons supplying the stomach are of dual origin from nodose and dorsal root ganglia, we examined the effect of selective ablation of either the vagal or spinal sensory innervation to the upper gastrointestinal tract on the increase in gastric mucosal blood flow in response to acid back diffusion into the gastric mucosa. Perineural application of capsaicin to the celiac/superior mesenteric ganglia, but not to the vagus nerves, significantly inhibited by 53% the hyperemic response to acid back diffusion. Tissue levels of immunoreactive calcitonin gene-related peptide in the gastric corpus were significantly reduced (by 73%) by periceliac capsaicin treatment, but unaffected by perivagal capsaicin treatment. These data suggest that spinal capsaicin-sensitive afferents containing calcitonin gene-related peptide immunoreactivity are involved in mediating increases in gastric mucosal blood flow. This increase in gastric mucosal blood flow mediated by sensory neurons may act as a protective mechanism against mucosal injury, similar to responses seen in other tissues such as skin.