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Digestive Tract

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Slide 1: Lip - find the inner and outer surfaces, vermillion border, and obicularis oris muscle. Hint, the outer surface has a lightly keratinized epithelium. It would be much easier to identify if it had hair follicles (see the next image).  

Slide 2: Lip - outer surface. Note the hair follicles and thin skin.  

Slide 3: Lip - the red or vermillion border. Note the blood vessels below epithelium and he deep dermal papillae indenting the inner surface of the epithelium. Name the muscle tissue, specifically and by type (Ans: obicularis oris, skeletal muscle).  

Slide 4: Lip - inner (oral) surface of the same lip as seen in slides 2 and 3. The labial glands are mixed sero-mucous, i.e., mixed. Note the orbicularis oris muscle.  

Slide 5: Tongue - the upper surface with filliform and fungiform papillae. PAS-H stain, rodent. Note the heavy keratinization of the filliform papillae. It is an exception to the general finding that wet cavity lining epithelia lack cornified layer.  

Slide 6: Tongue - oral suface (at the edge of the tongue) with foliate papillae, H&E, rabbit.  

Slide 7: Tongue - A circumvallate papilla - where are these found? What type of secretory product do von Ebner's glands produce? (Ans: V at the back of the tongue; serous product probably containing one or more binding proteins). Note the trench around the papilla and the gland ducts; locate the taste buds.  

Slide 8: Taste buds -H&E- are nerve endings present? Yes, but you don't see them unless they are specially stained. Probable type of papillae? (Ans: folliate, 2 adjacent).  

Slide 9: Fungiform papilla, the oral surface taste buds and adjacent filliform papillae.  

Slide 10: Tongue. Skeletal muscle x.s. and l.s. Serous and mucous glands and a myelinated nerve bundle. Compare the mucous glands with the scattered adipocytes in the connective tissue.  

Slide 11: In this low power image find the oral surface - stratified squamous epithelium and mucous glands and then the nasal surface - pseudostratified columnar epithelium with associated seromucous glands. Which surface is the oral? (Ans: bottom of the field)  

Slide 12: Upper esophagus, cross section of the wall at low power, H&E. Note the thick muscularis mucosa. Name and find the layers.  

Slide 13: Mid-esophagus, x.s. What type of external muscle tissue do you expect to find here? (Answer: mixed - both skeletal and smooth muscle). How can you tell, even at this low power, that this section is from above the diaphragm? (Ans: the presence of an adventitia not a serosa).  

Slide 14: Gastro-esophageal junction - Identify cardiac region of stomach. Lymphoid accumulation is common in the connective tissue beneath epithelial junctions.  

Slide 15: Mucosa at gastro-esophageal junction at higher power than previous  

Slide 16: Rugae - Fundus. Are rugae distensible? (Ans: yes, think Thanksgiving dinner!). Even at this very low power the basophilia of the deeper region of the gastric glands is apparent.  

Slide 17: Surface mucous cells (recall that "mucous", an adjective, refers to a glandular cell type while "mucus", a noun, refers to what the cell secretes) -- mucinogen droplets contain neutral glycoproteins. Plastic embedded section, monkey.  

Slide 18: Cardiac region - cardiac mucous glands, here cut mostly in cross section. Compare the gastric pits (larger lumina, also mostly in cross section) with the glands.  

Slide 19: Low power image of the fundic region. Note the basophilic zone in the mucosa. What is the predominant cell type in this zone? (Ans: chief cell- containing lots of RER). The deep staining on the peritoneal surface is an artifact (trapped stain).  

Slide 20: Gastric mucosa, monkey. The luminal surface mucous cells are not well preserved. Locate: parietal cells, chief cells, and the muscularis mucosa.  

Slide 21: Fundic region at higher power, the lumen would be above the top of the field. Note the gastric pit and the region where the fundic gland (or gastric gland) begins. Note a cell in prophase of mitosis. Is the muscularis mucosa part of the mucosa? (Ans: yes).  

Slide 22: Fundic region, lumen to the top of the image. Plastic embedded section, obliquely sectioned. Identify surface mucous cells, and mucous neck cells (look for basal nucleus and vacuolated cytoplasm), parietal cells ("fat", acidophilic, large nucleus near center of cell), chief cells (deeper staining cells in lower region of gland). Find at least 2 probable endocrine cells.  

Slide 23: Fundic region. Base of fundic gland in cross section, paraffin embedded, rather thick section. Note the foamy appearance in apex (poorly preserved zymogen granules) and basophilia in the base of chief cells. Find some parietal cells.  

Slide 24: Fundic region, plastic embedded section. The deeper staining at the bases of the chief cells is RER (would be blue if this image had any blue!). Can you see regions of the secretory canaliculus in parietal cells? Where is the endocrine cell? (Ans: the cell with clear cytoplasm at the left of the field).  

Slide 25: Endocrine cells of the gastric mucosa of a dog. Argentaffin reaction (which is a silver impregnation technic) and eosin counterstain, no nuclear stain. Where are these cells found? (Ans: within the epithelium of the glands: note the muscularis mucosa to the bottom left of the field).  

Slide 26: Pyloric mucosa. Note the deep pits and mucous glands. Compare to the cardiac region.  

Slide 27: Myenteric plexus (Auerbach's plexus) between layers of the muscularis externa. Find at least 12 perikarya (not all are sectioned through their nuclei). Distinguish this plexus from Meissner's plexus by location and function. Remember that the stomach has 3 layers of muscularis externa (unlike the 2 layers in most of the rest of the gut) that run rather obliquely.  

Slide 28: Submucosal (Meissner's) plexus. Generally, fewer perikarya together than in the myenteric plexus. It is located the CT of the submucosa.  

Slide 29: Pyloroduodenal junction. Note pyloric sphincter; the mucous nature of both the pyloric region gastric glands as well as Brunner's glands. The duodenal beginning is marked by the appearance of villi (more leaf-like than finger-like) and glands beneath the muscularis mucosa (submucosal= Brunner's). Diffuse lymphocytic infiltration as well as isolated nodules (as the one seen here) are often seen.  

Slide 30: Plicae circularis or valves of Kerkring are circularly arranged permanent (nondistensible) folds. Duodenum - note Brunner's glands in the submucosa. Note the variable shaped villi. Monkey.  

Slide 31: Duodenum with Brunner's glands. Note the duct traversing the muscularis mucosa and opening on to the surface between 2 villi. Note also the intestinal glands (crypts of Lieberkuhn).  

Slide 32: Duodenum - Brunner's glands. Note the strands of muscularis mucosa with glands above and below it. Human.  

Slide 33: Duodenum - Brunner's glands, x.s. Note the mucous-type morphology of the cells and the wide glandular lumina. Monkey, plastic embedded section.  

Slide 34: Jejunum at low power. Note the 3 plicae circularis.  

Slide 35: Jejunum, higher power image of previous slide. Note the dilated lacteals in the villi. Where is the lamina propria in this slide? (Ans: between the lacteals and the basal lamina of the epithelium,)  

Slide 36: Jejunal villi at higher magnification without distended lacteals. Note the smooth muscle cells in the core of the villi, the very cellular lamina propria and the tall simple columnar epithelium with goblet cells and a striated (brush) border. Also note the intraepithelial lymphocytes.  

Slide 37: Jejunum villi - note brush border, goblet cells and capillaries filled with intensly staining red cells. Plastic embedded section. What's happening at the tip of one of the villi? (Ans: an effete cell is being extruded). The basal aspect of many of the cells of the lining epithelium have shrunken away from the basal lamina (artifact).  

Slide 38: Jejunum villi - PAS-H stain. What three structures are PAS+? (Ans. Goblet cell mucus (mucinogen), brush border glycocalyx and basal lamina),  

Slide 39: Paneth cells are located at the bases of the intestinal glands (crypts) and are found in the small and large intestine and appendix. Here the secretory granules in their apical cytoplasm are weakly PAS+. The very deeply PAS+ cells furthur up the glands are goblet cells. PAS-H stain  

Slide 40: Jejunum, plastic embedded section. Locate the Paneth cells, mitotic figures, endocrine cell, and plasma cells in the lamina propria. Note the thin muscularis mucosa.  

Slide 41: Ileum, low power image. Note the large, confluent Peyer's patches. Monkey.  

Slide 42: Ileum, human, in an area without Peyer's patches. Note the plicae, dilated submucosal blood vessels (not characteristic) and robust muscularis externa.  

Slide 43: Ileum mucosa close to the jejunum, (mostly) crypts. Note the mitotic figures and rather abundant goblet cells.  

Slide 44: Ileum mucosa (lower) - Note the increase in the number of goblet cells compared to slide 43.  

Slide 45: Appendix, low power. (You might compare with slide #36 from unit 9). Note the absence of villi, the mesentery and the lymphoid nodules. Its small lumen, and the absence of taneia coli differentiate it from the rest of the large intestine.  

Slide 46: Appendix mucosa, human. Now that's lymphocytic infiltration!  

Slide 47: Colon, low power. Note that there are no plicae or villi and that the intestinal glands are straight. There are no taenia coli in this image.  

Slide 48: Lymphocytic infiltration of the mucosa and submucosa; higher mag. image than slide 47. Note the great abundance of goblet cells; the absorptive cells are squashed between them and it is difficult to appreciate that absorpitve cells are in the epithelium at all.  

Slide 49: A low power image showing a taenia coli (thickening of the external longitudinal muscle layer). How many taenia are there? (Ans: 3). Monkey.  

Slide 50: An oblique section of the colon mucosa. Note the abundance of goblet cells in the obliquely sectioned intestinal glands. Find the muscularis mucosa.  

Slide 51: Absorptive cells and goblet cells of the colon mucosa. Plastic embedded section. This well preserved, thin section shows the absorptive cells well. Monkey  

Slide 52: The bases of two intestinal crypts with well stained Paneth cells.  

Slide 53: Rectum, probably monkey. Note the lack of a serosa.  

Slide 54: Recto-anal junction, high mag. Note the goblet cells and lymphocytic infiltration of the lamina propria at this junction region. What type of epithelium is found in the anal region? (Ans: stratified squamous epithelium).  

Slide 55: Recto-anal junction, low power. Note the lymphocytic infiltration and Pacinian corpuscles (what might their function be here?), as well as the internal sphincter. (Ans: receptors for deep pressure).  

Slide 56: Meissner's plexus (submucosal plexus) with a dozen or so perikarya. Plastic embedded section, jejunum, monkey. Compare with slide #28. Identify the obliquely sectioned epithelium to one side and the smooth muscle to the other. Find the arteriole, venule and lymphatic. (Hint: the lymphatic is very large and empty).  

Slide 57: Auerbach's plexus (myenteric plexus) in muscularis externa of the small intestine. Compare with slide #27. The muscle layers of the small and large intestine are more regular than those of the stomach which has an extra oblique layer. Plastic embedded section. Neuronal perikarya lack their typical basophilia in this preparation but can be identified based on size and nuclear morphology. This slide also has well preserved smooth muscle.  

Slide 58: Portions of 2 enterochromaffin cells (EC), which secrete 5-hydroxy-tryptamine. How did these cells get this name? TEM.  

Slide 59: A G cell which secretes gastrin. Note that unlike may other enterendocrine cells it does reach the glandular lumen (to the top of the field). TEM

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