General Characteristics: The stomach is divided into four regions: the cardia, fundus, corpus (body) and pylorus. The wall of the stomach consists of the usual four layers present in other parts of the gastrointestinal tract. The mucosa is relatively thick and contains numerous tubular glands. The muscularis mucosae is also thick and, in some areas, it consists of 3 layers of smooth muscle, although this layering is not always visible. Glands are absent in the submucosa. In the empty contracted stomach, the mucosa is thrown into longitudinal folds (rugae) because of the contraction of the muscularis mucosae and the loose consistency of the submucosa. The surface is further subdivided by furrows, the gastric pits. These funnel-shaped invaginations of the epithelium are continuous at their base with the tubular glands. The muscularis externa is made up of 3 ill-defined layers. The middle circular layer of the muscularis is thickened to form thepyloric sphincter, which is an “anatomic” sphincter. The lower (gastro-)esophageal sphincter does not have this thickening of the muscularis, so this is why it is called a “physiological” sphincter.
On the basis of differences in the types of glands present in the mucosa, three histological regions can be distinguished in the stomach. The first region around the cardia contains the cardiac glands. The second region, which includes the fundus and corpus, contains the gastric glands proper (also called fundic glands). The distal region of the stomach (pylorus) contains pyloric glands.
A. Cardiac glands (W pg 268, 14.6)
Slide 155 40x (gastro-esophageal junct, H&E) View Virtual Slide
Slide 160 40x (gastro-esophageal junct, PAS & Azure Blue) View Virtual Slide
These mucosal glands are composed mainly of mucous cells with pale staining cytoplasm and basally located nuclei. Present, but not seen, are stem cells and endocrine cells. In slide 155, locate the cardio-esophageal junction (W pg 268, 14.6) View Image. Note the abrupt transition from the mucosa of the esophagus with its stratified squamous epithelium to the glandular mucosa of the stomach. The cardiac gastric glands View Image are present only in a very small segment of the stomach mucosa adjacent to this junction. They are mucous glands comprised of a HOMOGENEOUS population of pale-staining columnar cells with a “bubbly” supranuclear cytoplasm. As you move further into the stomach, the cardiac glands are very quickly replaced by gastric proper (or fundic) glands which, as described below, consist of a notably HETEROGENEOUS mixture of basophilic chief cells and eosinophilic parietal cells.
Since the cardiac gastric glands are primarily mucous, they can also be be demonstrated with the PAS stain, as shown in slide 160. In this slide, the cells lining the gastric pits View Image stain very intensely with PAS due to the carbohydrate-rich, viscous mucus they secrete. The secretion of the cardiac glands is a bit more watery so they do not stain quite as intensely.
B. Gastric glands (W pg 268-272, 14.7-13).
Slide 155 40x (gastro-esophageal junct, H&E) View Virtual Slide
Slide 160 40x (gastro-esophageal junct, PAS & Azure Blue) View Virtual Slide
Slide 156 20x (stomach, H&E) View Virtual Slide
Slide 156 40x (stomach, H&E) View Virtual Slide
Slide 157 20x (stomach, H&E) View Virtual Slide
Slide 157 40x (stomach, H&E) View Virtual Slide
"Gastric" or "fundic" glands are characteristic of the mucosa throughout the fundus and corpus regions of the stomach. At low magnification, notice that the gastric pits are relatively more shallow here View Image and the tubular gastric or fundic glands are relatively much longer than those in the cardia or pylorus. Observe that the tall columnar cells lining the luminal surface and pits have basally located nuclei and lightly staining cytoplasm. Most of these cells secrete mucus, that is stored in the apical cytoplasm. You can see these cells in the stomach preparation stained with PAS (which will stain mucus and other glycoproteins) in slide 160. In this slide, the mucous cells of the gastic pits stain quite intensely. Also identifiable are lighter-staining "mucous neck cells" present in the neck region of the gastric glands and mucus-secreting cells of the cardiac glands found near the gastro-espophageal junction.
Moving into the body of a fundic gland, identify the parietal and chief cells in slides 155 View Image [ORIENTATION], slide 156 View Image[ORIENTATION], and slide 157 View Image[ORIENTATION]. Parietal cells are large, ovoid to pyramidal shaped cells with their broad side adjacent to the basement membrane. Each cell contains a round, centrally located nucleus and reveals a lightly eosinophilic cytoplasm that appears granular due to the presence of many mitochondria. The chief cells are present in the lower one-third to one-half of the gastric glands. The apical cytoplasm of these cells may appear granular due to the presence of zymogen granules, that may stain bright red in H&E preparations (as in slide 157). However, in other preparations (slides 155 and 156), the pepsinogen has been extracted and the empty secretory granules resemble many glass beads in the supranuclear cytoplasm. The base of the cytoplasm, on the other hand, is distinctly basophilic.
Other cells of the gastric glands, such as undifferentiated (stem) cells and various endocrine cells, will NOT be studied in this laboratory session as they are not readily identifiable in the stomach, but you should be aware of their general characteristics. Notice the presence of a large number of lymphocytes and plasma cells in the lamina propria between the gastric glands, and, in some areas, aggregated as lymphoid nodules View Image (which will be studied in greater detail along with other lymphatic tissues but you should at least be able to identify them here). Also, notice that the strands of smooth muscle fibers from the inner layer of the muscularis mucosae extend between the glands toward the surface. The contraction of these strands may help the emptying of the glands.
C. Pyloric glands (W pgs 273, 14.14-15)
Slide 162 20x (gastro-duodenal junct, H&E) View Virtual Slide
Slide 162 40x (gastro-duodenal junct, H&E) View Virtual Slide
In slide 162, you can see the transition from pylorus of the stomach to duodenum of the small intestine. The pyloric region of the stomach is characterized by a thick wall due to the presence of the pyloric sphincter muscle View Image, which is comprised primarily of the inner circular layer of the muscularis externa. Compare its wall thickness with that of the adjacent duodenum (W pg 273, 14.15). The pyloric glands View Image at the base of each gastric pit [ORIENTATION] are also composed again of a mostly HOMOGENEOUS population of mucous cells that are similar in appearance to those in cardiac glands although the pits are much deeper compared to cardiac glands. Present, but not seen, are stem cells and endocrine cells. An occasional parietal cell may be also found. Note that the bases of the pyloric glands abut the muscularis mucosae whereas in the duodenum, you will see abundant glands (Brunner's glands) DEEP to the muscularis mucosae (i.e. in the SUBMUCOSA).
Just in case you are worried about identifying cardiac glands versus pyloric glands, it is admittedly very difficult to tell these two apart based only on high-mag views, but you can always use contextual information to help you out: cardiac glands will be right near the gastro-esophageal junction whereas pyloric glands are at the gastro-duodenal junction.
