GI System Intro - Unit 2
Layers of tubular GI organs
Slides
Canine esophagus - glass slide #150
St. Squam. Epith.:
The esophagus is the tubular organ that conveys food from the pharynx to the stomach. The tunica mucosa consists of three sub-layers: a thick non-cornified stratified squamous epithelium, a dense lamina propria that contains large amounts of elastic fibers, and in the caudal portions in most species, a muscularis mucosae.
Topic: St. Squam. Epith.
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
Lamina propria:
The lamina propria in this example is relatively dense and thick compared to other GI system tubular organs. Elastic fibers are common, though not visualized with the triple stain on this section.
Topic: Lamina propria
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
Musc. mucosa:
The muscularis mucosa is smooth muscle whose function is to provide motility to the mucosal surface. In the esophagus it is found in the caudal portions, near the stomach. Note that it is not a continuous layer in this example from the dog.
Topic: Musc. mucosa
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
T. submucosa:
The tunica submucosa consists of collagenous connective tissue with elastic fibers and a large number of tubuloacinar (tubuloalveolar) mucous glands, which secrete a lubricant for the esophageal lumen.
Topic: T. submucosa
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
Submucosal glands:
Submocosal glands provide lubrication to the mucosal epithelium. Pay attention to their exact location within the succession of layers.
Topic: Submucosal glands
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
T. muscularis:
The tunica muscularis may be smooth or striated muscle, or a mixture of both, depending upon the species. This muscle is generally disposed as an inner circular and an outer longitudinal layer.
Topic: T. muscularis
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
T. adventitia:
The outer layer of the esophagus is a tunica adventitia that is continuous with the surrounding connective tissue.
Topic: T. adventitia
1 = Mucosa (Strat. squamous); 2 = Lamina propria; 3 = Muscularis mucosa; 4 = Tunica submucosa; 5 = Submucosal glands; 6 = Tunica muscularis; 7 = Tunica adventitia
Esophageal-cardiac juction from the dog - glass slide #151
Esophagus:
This is a longitudinal section of the junction of the esophagus with the stomach. Note the abrupt change from the stratified squamous epithelium of the esophagus to the simple columnar epithelium of the stomach.
Topic: Esophagus
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
Cardiac stomach:
This is a longitudinal section of the junction of the esophagus with the stomach. Note the abrupt change from the stratified squamous epithelium of the esophagus to the simple columnar epithelium of the stomach.
Topic: Cardiac stomach
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
Esophageal Musc. mucosa:
The muscularis mucosa is smooth muscle whose function is to provide motility to the mucosal surface. In the esophagus it is found in the caudal portions, near the stomach. The stomach has a thick muscularis mucosae, strands of which project into the lamina propria between the mucosal glands.
Topic: Esophageal Musc. mucosa
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
Submucosal glands:
The submucosal glands of the esophagus stop just beyond the point where the esophageal epithelium ends.
Topic: Submucosal glands
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
Stomach mucosa:
A profusion of branched simple tubular mucosal glands empty into the stomach lumen. They project from the base of small mucosal depressions called gastric pits into the lamina propria (no deeper than the muscularis mucosa). The submucosa of the stomach contains no glands.
Topic: Stomach mucosa
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
T. submucosa:
Clearly, the esophageal submucosal glands are deep to the muscularis mucosa in the esophagus but are not carried into the stomach, where no glands are found in the submucosa.
Topic: T. submucosa
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
Stomach Musc. mucosa:
The inner margin of the submucosa is the muscularis mucosa. One of the keys to recognizing the various tubular GI organs is to be able to positively identify the muscularis mucosa.
Topic: Stomach Musc. mucosa
1 = Espophageal mucosa (Strat. squamous); 2 = Cardiac region of gastric mucosa; 3 = Lamina propria; 4 = muscularis mucosa; 5 = Submucosal glands; 6 = Tunica submucosa; 7 = Tunica muscularis
Porcine cardiac stomach - glass slide #152
Gastric pits:
This is the tunica mucosa of the cardiac stomach from a pig. Locate the tunica mucosa on glass Slide 152 and note the following features. The cells of the mucosal glands of the cardia are homogeneous and secrete mucus. The lamina propria contains a large number of cells, many lymphocytes and plasma cells although a few granulocytes and mast cells can be found. Locate the large aggregate of lymphoid tissue on the Slide and note that it penetrates through the muscularis mucosae into the submucosa.
Topic: Gastric pits
Blue arrows = gastric pits; Red arrows = gastric glands - cardiac region
Mucosal glands:
Just as cells of the gastric pits, the cells of the mucosal glands in the cardiac stomach also secrete mucins. However, the gland cells differ in appearance from those lining the gastric pits. The un-released secretory material in the (deeper) glandular cells appears different from the pale mucins present in the surface epithelium.
Topic: Mucosal glands
Blue arrows = gastric pits; Red arrows = gastric glands - cardiac region
Muscularis mucosa:
Note the prominent muscularis mucosa in the porcine stomach.
Topic: Muscularis mucosa
Green arrows = muscularis mucosa; Red arrows = aggregate of lymphocytes and scattered inflammatory cells; Blue arrows = gastric glands (cardiac type).
Fundic mucosa, goat abomasum - glass slide #149
Gastric pits:
Gastric pits in the fundic stomach are intermediate in depth between those found in the cardiac region and those found in the pyloric region. Compare these to the others
Fundic glands
The mucosal glands of the gastric/fundic region are the most cytologically diverse glands of the stomach. This large micrograph gives many good examples of each of the four cell types. The next image and page contains labeled micrographs drawn from this image. Use these Images and glass slides 151 and 149 to positively identify examples of each cell type.
Fundic gland cells:
The next page contains labeled micrographs drawn from this zooming image. Use these Images and glass slides 151 and 149 to positively identify examples of each cell type: 1. Mucous neck cells; 2. Parietal cells; 3. Chief cells; 4. Enteroendocrine cells.
Topic: Fundic gland cells
Blue arrows = Mucous neck cells; Red arrows = Parietal cells; Yellow arrows = Chief cells; Green arrows = Enteroendocrine cells.
Muscularis mucosa
The muscularis mucosa is the boundary of the lamina propria, which contains all of the fundic glands.
Cells of the fundic stomach
Mucous neck cells:
Mucous neck cells: These mucous secreting cells are found at or near the neck of the fundic gland. The flattened nuclei are displaced to the base of the cell with the mucous secretion occupying the apical portions of the cell.
Parietal cells:
Parietal cells are much larger than other cells here and stain with acidophilic dyes due to acid production and release. Note pale staining areas of canaliculi.
Chief cells:
Chief cells are the most common fundic gland cell, often the zymogens are washed-out.
Enteroendocrine cells:
Enteroendocrine cells are found throughout the GI tract. They stain darker than other glandular cells, and are found near the basement membrane of the glands.
Surface mucous cells:
Surface mucus cells actively protect the stomach surface, and are constantly replaced. They are typically columnar cells with ample apical mucus. It is common to find them somewhat damaged in histological specimens.
Pyloric stomach - porcine - glass slide #154
Pyloric pits:
Glass Slide 154 is a section of the pyloric region from the stomach of a pig. Note that the gastric pits (spaces open to the lumen) are very deep in the pyloric region, which distinguishes it from the other regions.
Topic: Pyloric pits
Blue arrows = bases of the pyloric pits.
Pyloric glands:
The mucosal glands in this area are mucous in character with scattered of enteroendocrine cells near the basement membrane. This is the best slide for identifying enteroendocrine cells, particularly near the base of the mucosal glands. In that same region you should also be able to find mitotic fugures of dividing gland epithelial cells.
Topic: Pyloric glands
Blue arrows = enteroendocrine cells among pyloric gland mucus-secreting cells.
Muscularis mucosae
Again, note the prominent and thick muscularis mucosa - this in the pyloric region of the stomach.
Rumen - glass slide #155
Papillae:
The ruminant forestomach is lined by a slightly cornified stratified squamous epithelium. It has an irregular proximal border that is similar to the dermal-epidermal junction of the skin. The stratum spinosum consists of several layers of large cells with many desmosomes. The stratum granulosum is not always present. The stratum corneum contains vacuolated cells, many of which seem filled with bacteria. On glass Slide 155, note the lumenal surface of the rumen is covered with many paddle-shaped papillae. The papillae vary in size and shape from one area of the rumen to another and also change with variations in diet, but they lack secondary processes.
Topic: Papillae
Green arrows = lamina propria/submucosa; Blue arrows = papillae
Lamina propria/submucosa:
Since the muscularis mucosae is absent in the rumen, the subepithelial connective tissue is called a lamina propria-submucosa. The tunica muscularis consists of inner circular and outer longitudinal layers of smooth muscle. A tunica serosa covers the outermost aspect of the rumen.
Topic: Papillae
Green arrows = lamina propria/submucosa; Blue arrows = papillae
Reticulum - glass slide #156
Papilla:
The tunica mucosa of the reticulum is highly folded giving a rough surface. Recall the honeycomb appearance of the papillae when viewed grossly. At the microscopic level, we will compare the structure of the tunica mucosa at the base with that found in the free edge of the papillae.
2° process:
Secondary processes of the papillae of the reticulum increase the surface area and may serve a mechanical function in the separation of fine and coarser particles of ingesta.
Topic: 2° process
Blue arrows = secondary processes.
Musc. mucosae:
The edges (ends) of the folds contain a heavy muscularis mucosae. This band of smooth muscle is continuous from one fold to another near the free edge, but is not found at the base of the mucosal folds.
Topic: Musc. mucosae
Blue arrows = muscularis mucosae
L. prop./submucosa:
Notice that the base of reticular papillae contain no muscularis mucosa. Thus, the tips of the papillae are independently motile while the bases are not.
Topic: L. prop./submucosa
Blue arrows = region of lamina propria/submucosa.
Omasum - glass slide #157
Papilla:
Microscopically, the omasum differs from the rumen and reticulum in several ways. Note the papillae are made of long folds of tunica mucosa that arise at the greater curvature and sides of the inner omasum. The folds are covered by stratified squamous epithelium.
2° processes:
The mucosal folds of the omasum have fewer branches than those found in the reticulum.
Topic: 2° processes
Blue arrows = secondary process of the omasum
Musc. mucosae:
The muscularis mucosae extend from the tips down to the base in omasal folds, in contrast to the reticulum. There is a double layer of muscularis mucosae in each fold and a thin frond of the tunica muscularis can extend into the omasal fold between the layers of muscularis mucosae. The balance of the omasal wall is similar to the other forestomachs.
Topic: Musc. mucosae
Blue arrows = muscularis mucosa, sometimes blending with projections of the tunica musularis.