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Digestive Glands

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Slide 1: Low power, pig liver. In this animal the hepatic lobules are surrounded by a significant amount of connective tissue. The separation seen here is some what exaggerated due to a shrinkage artifact. Note central veins and portal spaces. The zonation of staining within a lobule is very evident. What might be the cause of this zonation? (Answer: 02 and nutrient availability, etc.)  

Slide 2: Low power human liver. Hepatic lobules are not as clearly delineated as in the pig. Locate central veins and portal spaces. Attempt to describe the limits of the classic lobule, the portal lobule and the liver acinus.  

Slide 3: Higher magnification of liver parenchyma between portal spaces and central veins. Describe the liver acinus. In what direction is the blood flowing? (Ans: towards the cental veins).  

Slide 4: Central vein. Note binucleate parenchymal cells, sinusoidal spaces and sinusoids joining the central vein.  

Slide 5: Portal area. Surrounded by connective tissue are branches of the portal vein (large lumen longitudinally sectioned), the hepatic artery (cross sectioned), a bile duct. The endothelially lined empty space is the accompanying lymphatic vessel.  

Slide 6: Liver, plastic embedded secrtion, rat methylene blue-Azure A. (Remember seeing this image in the Cell Biology course?).  

Slide 7: Low power TEM (no, EM's are not in color - we added the colors afterward). Hepatocyte borders are red - solid lines for lateral surfaces, dotted for sinusoidal ones. Bile canaliculi are yellow and sinusoidal lining cells are outlined in blue. A perisinusoidal "fibroblast" (of Ito or fat-storing cell) is outlined in green and an adjacent xs of a reticular fiberbundle is a green cross-hatched oval. Compare the nuclei and mitochondria with slide 13-6. Note the binucleate cell and prominent nucleoli.  

Slide 8: TEM. A fat storing cell (of Ito), which resides in the space of Disse, is outlined in blue. The sinusoidal plasmalemma of the hepatocyte (and its microvilli) are outlined in green. The fenestrated sinusoidal endothelium is outlined in red. Note the few small collagen (reticular) fibers also in the space of Disse.  

Slide 9: Sinusoids - injected preparation.  

Slide 10: Bile canaliculi demonstrated histochemically by ATPase or alkaline phosphatase activity.  

Slide 11: Reticular fibers (specially stained and in the space of Disse) and a central vein.  

Slide 12: PAS-H reaction for glycogen. The glycogen is shifted to one side of each cell (diffusion artifact) and the tissue is overstained. Note the biucleate hepatocytes.  

Slide 13: Portal space and parenchyma. Rat injected with TiO2 to demonstrate the phagocytic Kupffer cells sitting in the sinusoidal spaces. Find a bile ductule in xs and an obliquely sectioned canal of Herring as well as an obliquely sectioned portal vein.  

Slide 14: Larger hepatic bile ducts in a portal tract, surrounded by connective tissue (human liver). Note the limiting plate of hepatocytes.  

Slide 15: Liver, very low power. The hepatic portal vein is accompanied along its course by branches of the hepatic artery and the biliary system. The large vessel running diagonally across the field is a hepatic portal vein in a portal tract. Contrast it with the large branched vessel without "sidekicks". It is a collecting vein and its branches are sublobular veins (it will drain into one of the hepatic veins). Next slide is a higher mag of this vessel. Note also the thin CT layer at the surface of the organ - Glisson's capsule.  

Slide 16: Sublobular veins draining into a collecting vein - note the lack of any parallel vessels or ducts.  

Slide 17: Liver, human, plastic embedded section. This slide was labelled "normal". What is not quite so normal about it? (Ans. Some fatty degeneration which is apparent,even at this low power).  

Slide 18: Low power of two regions of the gallbladder wall. Upper = near the neck. Here the muscle layer is thin, the folds of the wall rather short and sparse and a mesothelial covering is absent (i.e. no adventitia). The body of the gland (below) has a thicker muscle layer, longer, more numerous and complex folds and on the surface toward the peritoneal cavity, a serosa (i.e. a mesothelial covering). Other sections (not illustrated here, will not have a serosa but will have a thin C.T. which merges with Glisson's capsule of the liver).  

Slide 19: Higher mag of body of gall bladder. Note the simple and complex mucosal folds, the adjacent smooth muscle layer (no submucosa delimited from the mucosa by a muscularis mucosa) and serosa.  

Slide 20: Gall Bladder, Human, Simple columnar epithelium, no goblet cells, no muscularis mucosa, no intestinal glands, folds not villi.  

Slide 21: Monkey gall bladder, plastic embedded section. Note the simple columnar epithelium, lack of a brush border and no goblet cells.  

Slide 22: Cystic duct, monkey. Resemblance to the gall bladder proper is unmistakable. In fact, from this field alone it is impossible to distinguish the two.  

Slide 23: Parotid (monkey). At low power it is easy to distinguish the lobes and lobules of the gland and to identify the intralobular (striated) ducts and the interlobular (excretory) ducts. The smallest (intercalated) ducts cannot be identified here. The overall purplish tint in an H&E prep. is due to the high RER content of the glandular cells. Shrinkage artifact is particularly noticable at the periphery of the lobes.  

Slide 24: High power of 13-23. Distinguish the different ducts (hints of intercalated ducts (ID) in l.s. can be found if you look carefully at the enlarged image).  

Slide 25: Hp of paraffin section of parotid similar to 13-24. Find two striated ducts (SD) and two ID's in xs. ID's are extensive but not easily found at first because of their small diameter. Most sections are not good xs or ls but are oblique and do not include the very small lumen. Any oval, fairly euchromatic nucleus (often in a lighter cytoplasm) is a piece of an ID. The cytoplasm of the acinar cells appears "foamy" because of poor preservation of the apical zymogen granules.  

Slide 26: Parotid, human, section near the hilus of the gland with many ducts. Plastic embedded section (1.5 um). Blood vessels run with the excretory ducts and here are filled with blood (bright pink). Although most texts describe the human parotid as "almost entirely serous", this field has some mucous elements - almost all with serous demilunes. Can you find them?  

Slide 27: Hp. of 13-26. Acinar cells have basal basophilia (RER) and better preservation (not 100%) of the zymogen granules. Acinar lumina are very small and most acini are not sectioned through them. Find the 2 large striated ducts and the 3 or 4 ID's cut obliquely or in ls (light pink cytoplasm similar in color to that of the SD's).Also locate some probable myoepithelial cell nuclei. Capillaries and venules have deep pink rbc in them.  

Slide 28: Hp of 13-26 showing mucous and serous secretory elements - compare their nuclear morphology (mucous = flattened near the base, serous = round). Remember that this field is atypical; the amount of mucous secretory elements in the parotid is very small. Find the 2 ID's that are sectioned through their lumina . Besides vessels and fibroblasts what other elements can you identify in the CT. (Ans: plasma cells - what do they contribute to the saliva? - secretory IgA).  

Slide 29: Another plastic embedded section of parotid. Poor zymogen granule preservation but you should be able to locate parts of 4 or 5 ID's and 4 SD's.  

Slide 30: Adult parotid showing some intralobular fat. There are several large excretory ducts and a small amount of interlobular adipose tissue. Compare with 13-31.  

Slide 31: Low power of a mature adult parotid (a thick section gives an intense color). Fat is accumulating and the amount of acinar tissue is reduced.  

Slide 32: Hp of part of 13-31. Note the large excretory duct with secretory material in it, the fatty intralobular CT and the acinar elements.  

Slide 33: Hp of 13-25. Identify the intralobular duct and acini.  

Slide 34: Adult human submandibular gland, low power. As with the other salivary glands the basic lobe and lobule structure is evident. The human gland is mixed but with a predominance of serous elements.  

Slide 35: Hp of 13-34. Blood vessels are found in interlobar and interlobular CT septa accompanying ducts.  

Slide 36: Higher mag of a thicker paraffin section. Here it is easy to differentiate fat from mucous acini, most of which have serous demilunes. Intralobular (striated ducts) are clear but ID's are not. In the submandibular gland they are much shorter than in the parotid (see next slide).  

Slide 37: Well preserved paraffin section of human submandibular gland (note zymogen granules in serous cells). Find the xs of an ID and near it an obliquely sectioned one.  

Slide 38: Monkey submandibular gland, plastic embedded section. This gland was fixed by vascular perfusion under high pressure - thus blood vessels are dilated and of maximum size (but empty of blood elements). Note the very extensive capillary network - especially those caps which indent the basal surfaces of the striated ducts. Find the one mucous acinus and the single ID (which shows a nice myoepithelial cell).  

Slide 39: Mixed acini in the submandibular gland of a rat. Mucous acini with serous demilunes. Note the basal striations of the duct cells and junctional complexes ("terminal bars") on the luminal side of the duct.  

Slide 40: The excretory ducts of the salivary glands go from simple columnar epith. to pseudostratified to stratified epithelium near their junction with the oral mucosa. This is a major excretory duct of the submandibular gland. It is almost completely lined by a pseudostratified columnar epithelium.  

Slide 41: Basal myoepithelial cells with their smaller, darker nuclei can be found associated with the striated duct in the corner which bends and is obliquely sectioned. They can also be seen associated with an intercalated duct just above this striated duct. Serous elements predominate and are seen as demilunes on mucous acini. This is actually parotid gland not sublingual (the human parotid has a very small percent of mucous secretory elements) but we would not ask you to identify a field such as this as a parotid. Human, plastic embedded section.  

Slide 42: The human sublingual gland has the most mucous elements of the three major salivary glands but unlike many lower animals many mucous acini have serous demilunes. ID's are not prominent and intralobular ducts are short and their striations rudimentary. This section is somewhat misleading because of the apparent absence of major excretory ducts.  

Slide 43: This slightly light, low power slide shows excretory ducts and some lymphocytic infiltration of the CT.  

Slide 44: At this mag the intralobular ducts are apparent as are the serous demilunes.  

Slide 45: In this plastic embedded section the demilunes are easier to define. Compare with 13-46 and 13-44.  

Slide 46: What are the structures seen in the CT of this sublingual gland? (Ans: a parasympathetic ganglion and an obliquely sectioned nerve bundle).  

Slide 47: Major sublingual excretory duct. How would you classify its epithelium? (Ans: Stratified columnar epithelium).  

Slide 48: L.p. Duodenum, pancreas, pancreatic duct. Monkey. What are the light patches in the pancreas? (Ans: islets of Langerhans).  

Slide 49: Hp of 13-48. Pancreas and pancreatic duct. What is the smooth muscle layer between them? (Ans: muscularis externa of the duodenum - look back at 13-48). What type of epithelium does the duct have (Ans: simple columnar epithelium).  

Slide 50: Hp of 13-48. Islet and exocrine tissue. Find the ID's (light pink cytoplasm). This is a thick paraffin section but basal basophilia is evident although zymogen granules are harder to identify. Islet cells lack both the extensive RER and zymogen granules of the serous cells and thus stain much less intensely.  

Slide 51: Human adult pancreas, low power, Mallory stain. As with the other glands of the digestive tract the lobulated structure is apparent (emphasized here by the blue stained collagen of the CT). Also clear is the fat within the CT. Pick out the islets (They are delimited by shrinkage artifact).  

Slide 52: Hp of 13-51. Acinar and islet tissue both show shrinkage. Note how large the fat cells are. Did you find all 6 islets?  

Slide 53: Routine paraffin/H&E section of pancreas. Compare with 13-52. Deceptive because no ducts are evident.  

Slide 54: Hp of same preparation as 13-54. Note the light staining ducts. Find an acinus where the section makes it appear as though an ID cell is "floating" in the center of the acinus. This is the so called centroacinar cell that is diagnostic of pancreatic exocrine tissue.  

Slide 55: Plastic embedded section which shows why centroacinar cells appear as they do. Note the three good examples in this field of acinar tissue enveloping the ends of intercalated ducts.

Imagine cross sections of these - if the sections go through the nucleus of an ID cell it will appear (because of its light cytoplasm) to "float" inside the acinar lumen. See next slide.  

Slide 56: Pancreatic acinus with a centroacinar cell, plastic embedded section.  

Slide 57: Monkey pancreas, plastic embedded section. CT has blood vessels and 2 excretory ducts. Intralobular ducts and ID's can be picked out by their light cytoplasm and are often filled with intensely staining secretory material.


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