Herbert F. Helander

The Cells of the Gastric Mucosa

Publisher Summary This chapter describes the structure of the normal adult mammalian gastric mucosa, The interior wall of the gastric mucosa is thrown into folds, rugae, or plicae gastricae, which as a rule are longitudinally oriented and sometimes branching. These folds are most prominent along the lesser curvature and are more marked in the empty stomach than in the filled one. Minor furrows divide the surface of the mucosa into irregularly outlined gastric areas, which are a few millimeters in diameter. A very large number of funnel-shaped gastric pits, foveolae gastricae, can be seen all over the mucosal surface; quite often, these pits are interconnected by tiny grooves. The gastric mucosa is divided into three different zones: the cardiac zone, the fundus-corpus zone, and the pyloric zone. These zones differ from each other with respect to the depth of the gastric pits and the organization of their glands.

Quantitative analysis of mast cell structure

Fixed and embedded normal rat peritoneal mast cells were studied by light and electron microscopy, utilizing stereological methods to obtain quantitative data on their structure. The diameters of the mast cells and their nuclei averaged 10.9 and 5.8 μm respectively. The volume of the individual mast cell granule was estimated to 0.3 μm3. About 53% of the cytoplasmic volume was occupied by granules, and 2% by mitochondria. 11% of the cell volume was taken up by the nucleus. The average number of granules per cell was calculated to about 1020. Quantitative biochemical data on mast cells, extrapolated from the literature and applied to the calculated figures above, yield the following results with respect to mast granule contents‐heparin: 95 × 10−3 pg, histamine: 30 × 10−3 pg and 5‐hydroxytryptamine: 1.3 × 10−3 pg per mast cell granule.

Effect of omeprazole on gastric secretion in H+,K+-ATPase and in pepsinogen-rich cell fractions from rabbit gastric mucosa☆

In order to study the effects of the substituted benzimidazole omeprazole on gastric secretory functions, parietal cells and chief cells from rabbit gastric mucosa were separated and enriched by density gradient centrifugation in Percoll. H+,K+-ATPase activity, as well as a 100,000 dalton protein, was found to copurify with a cell fraction morphologically characterized as mainly parietal cells (purity approximately 65%), while pepsinogen copurified with a cell fraction morphologically characterized as chief cells (purity approximately 90%). A spontaneous pepsinogen release (9.9 micrograms/mg cell dry wt X 2 hr), unaffected by both atropine and omeprazole, was found in the chief cell fraction. The release was approximately doubled by both carbacholine (4 X 10(-5)M) and dibutyryl cAMP (db-cAMP, 10(-3)M). The cholinergic stimulation was selectively blocked by atropine, while omeprazole had no effect on pepsinogen release induced by either of the secretagogues. On the other hand, omeprazole inhibited both db-cAMP- and histamine-stimulated acid secretion quantified as [14C]aminopyrine (AP) accumulation in the parietal cell fraction. Cimetidine counteracted only acid secretion induced by histamine. These findings indicate that omeprazole has a specific effect on acid secretion, and are consonant with the hypothesis that the effect is due to H+,K+-ATPase inhibition.

Enzyme patterns and protein absorption in rat colon during development

Four enzymes were studied in the rat colon during perinatal development, namely, carbonic anhydrase, beta-D-galactosidase, and alkaline and acid pphosphatase. Quantitative analyses of tissue extracts revealed a peak in carbonic anhydrase activity 10 days after birth and histochemically most of the enzyme was found at the surface of the colonic mucosa. A similar localization was found for beta-D-galactosidase, which displayed a peak of activity in the 1-day-old rats. Alkaline phosphatase activity reached its maximum 5 days after birth, and by electron-microscopical histochemistry this enzyme was traced to the microvillous border, supranuclear vesicles and tubules, meconium bodies and the lateral surfaces of the principal cells. Acid hosphatase activity was also found in the microvillous border, in the supranuclear vacuoles and meconium bodies and in the Golgi apparatus. In the infant rat colon all these enzymes had higher activities and sometimes a different localization than in the adult rat, which indicates functional differences between the young and the adult animals. An example is the absorption of proteins. Peroxidase and insulin, given as enemas, were absorbed in the infant rat colon, but this capacity was much reduced after weaning.

Immunoreactivities for epidermal growth factor (EGF) and for EGF receptors in rats with gastric ulcers

SummaryThe present study was aimed at assessing whether epidermal growth factor (EGF) and its receptors are present in the gastric mucosa during the healing of gastric ulcers. Immunohistochemical, immunochemical and functional studies were performed in rats after induction of ulcers in the oxyntic mucosa. Controls, which included non-operated and sham-operated animals, displayed only rare cells in the bottom of the oxyntic glands showing EGF-like immunoreactivity. Within one day after ulcer induction, a markedly increased number of chief cells in undamaged mucosa showed intense staining. Concomitantly, there was an increased immunoreactivity for EGF receptors in the mucous neck cells. Maximal immunostaining for both compounds was observed at 3 days after ulcer induction; augmented staining was still demonstrable after 3 weeks. RIA revealed significantly increased EGF concentration in the oxyntic mucosa three days after ulcer induction, and at this stage stimulated gastric acid secretion, measured in a parallel group of chronic fistula rats, indicated significant inhibition. The transient increases in EGF-like and EGF receptor immunoreactivities may stimulate gland cell proliferation. The local release of EGF-like substances may also serve to reduce gastric acidity and thereby promote ulcer healing.

Stereological studies on the small intestinal epithelium of the rat

SummaryQuantitative macroscopic, light-microscopic and electron-microscopic studies were performed on the small intestine of fasted and non-fasted adult, male Sprague-Dawley rats. In non-fasted rats the small intestine was longer than in fasted rats. Due to the presence of villi the surface area in the duodenum and the jejunum was enlarged about six times. The microvilli on the villous crests caused a surface enlargement by 13 times in the duodenum (value corrected for overestimation due to section thickness), and 19 times in the jejunum of the fasted rats. At the base of the villi these values were about 50% lower. It was calculated that, in the fasted rats, the total enlargement of the luminal surface area — due to villi and microvilli — was 63 times in the duodenum and 81 times in the jejunum (corrected for section thickness).Differences between the villous crest epithelium and the villous base epithelium were also found with regard to the mean cell height, and the volume densities of the absorptive cell nuclei, the mitochondria, and the paracellular channels.

Quantitative ultrastructural studies on rat gastric zymogen cells under different physiological and experimental conditions

SummaryQuantitative electron microscopical measurements performed on gastric zymogen cells were aimed at determinations of size and volume density of the zymogen granules, and size of cell and nuclear profiles. 17 groups of rats each comprising 6–8 animals were investigated: five of these groups were used to study the influence of fasting and feeding, three groups were killed at different intervals after a pilocarpine injection, and four other groups were investigated after an atropine injection. The remaining five groups of rats were operated on: vagotomy was performed on one group, vagotomy + pyloroplasty on another, pyloroplasty on the third group, and antrectomy on the last two groups. The operated rats were sacrificed 4 or 10 weeks after the operations.Pilocarpine was more effective than feeding in reducing the size and the amount of zymogen granules. After atropine the size and amount of zymogen granules tended to increase. Ten weeks after pyloroplasty, vagotomy + pyloroplasty, or antrectomy the mean size of the zymogen cells was reduced.Loss of trophic vagal impulses, duodenal regurgitation, and abnormal serum gastrin levels are factors which might be responsible for the zymogen cell hypotrophy in operated rats.

Surface infrastructure of the Small Intestine Mucosa in Healthy Children and Adults: A Scanning Electron Microscopic Study with Some Methodological Aspects

Biopsy specimens of light microscopically (LM) normal small intestine mucosa from eight healthy, constitutionally short-statured children without signs of gastrointestinal disease and six healthy adults were studied by scanning electron microscopy (SEM) supplemented by transmission electron microscopy (TEM). The effects on surface morphology of various preparative procedures were also investigated, using small intestine mucosa from cats and rats. Fixation with OsO4--either alone, or following glutaraldehyde fixation--markedly changed the surface ultrastructure compared to that after glutaraldehyde fixation only. By low power SEM, some differences were observed in the appearance of the small gut mucosa between adults and young children. In adults and in children above 3 years of age, the villi were usually shaped like fingers or leaves, but in infants, ridge-shaped villi predominated. The villi showed, however, a smooth surface in both infants and adults, and medium and high power SEM displayed similar pictures, irrespective of age; here the typical structural features of the normal small gut mucosa in humans were (1) distinct extrusion zones at the crests of the villi and almost no signs of enterocyte extrusion along the sides of the villi, and (2) regular enterocytes with polygonal, flat, apical surfaces covered by a thick glycocalyx that obscured the underlying microvilli.

Some observations on knife properties and sectioning mechanics during ultramicrotomy of plastic embedding media

The edge and the trough surface of ultramicrotome glass knives were studied by interference light microscopy and electron microscopy. Particular attention was paid to the region which is commonly used for microtomy; here the bevel angle was calculated to 50–55°. The edge was serrated, even in the region used for sectioning, where the indentations measured up to 20 nm in depth. The imprints of edge serrations left on the sectioned material (Vestopal) were studied by electron microscopy. Different embedding materials displayed different degrees of compression when sectioned in the ultramicrotome: with Epon the compression was less than 10%, whereas methacrylate was compressed by more than 30%. Different trough fluids were tested: aqueous solutions of ethanol, acetone and dioxane gave less compression than pure water. However, the compression could also be reduced by exposing compressed Vestopal sections to these solutions. The direction and magnitude of the cutting force was measured with transducers during the sectioning of Vestopal blocks. Thus ∼0·3 μm wide sections cut at a feeding rate of 80 nm and a speed of 2 mm/sec required a cutting force of about 8 mN. The direction of the forces was 8–15° from the plane of cutting.

Stereological studies on the rat small intestinal epithelium

Morphological studies were carried out on the absorptive cells of the small intestine to elucidate their reaction to shunt operations and to variations in endogenous gastrin production. Adult rats were subjected to 1) antrectomy with gastro-duodenostomy, 2) antrectomy with gastro-jejunostomy, 3) antral exclusion, or 4) sham operation. Quantitative light microscopy revealed no significant differences among the different groups with regard to the height of the absorptive cells and to the internal surface area of the duodenum or jejunum. In contrast, stereological measurements at electron-microscopical level demonstrated significant differences in the apical surface area of the absorptive cells. After antral exclusion or antrectomy with gastro-jejunostomy the apical surface area in the duodenal blind loop increased by 28% and 78%, respectively, in comparison to the sham-operated rats. A reduction of this area by approximately 30-40% was registered for the jejunal absorptive cells after antrectomy or antral exclusion. Hormone levels as well as intraluminal factors are presumably responsible for these variations in the brush-border surface area.SummaryMorphological studies were carried out on the absorptive cells of the small intestine to elucidate their reaction to shunt operations and to variations in endogenous gastrin production. Adult rats were subjected to 1) antrectomy with gastro-duodenostomy, 2) antrectomy with gastro-jejunostomy, 3) antral exclusion, or 4) sham operation. Quantitative light microscopy revealed no significant differences among the different groups with regard to the height of the absorptive cells and to the internal surface area of the duodenum or jejunum. In contrast, stereological measurements at electron-microscopical level demonstrated significant differences in the apical surface area of the absorptive cells 1: After antral exclusion or antrectomy with gastro-jejunostomy the apical surface area in the duodenal blind loop increased by 28% and 78%, respectively, in comparison to the sham-operated rats. A reduction of this area by approximately 30–40% was registered for the jejunal absorptive cells after antrectomy or antral exclusion.Hormone levels as well as intraluminal factors are presumably responsible for these variations in the brush-border surface area.