Reading: R&R, Chapter 17
SLIDE 65d liver, rat (H&E)
(RR&K p521, Fig. 1,2; p523 Fig. 1)
This slide contains a thin plastic section of the rat liver stained with H&E. Using low power, locate a classic lobule and a liver acinus. Note the arrangement of the portal triad, hepatocytes, sinusoids, and central veins within the lobule and acinus.
At higher power, identify the portal triad with hepatic artery, portal vein, bile duct and connective tissue. The portal vein is the largest vessel to have a thin wall. The hepatic artery is small, with 1-3 muscle layers in the tunica media. The bile duct is lined with simple cuboidal epithelium. The lymphatic vessels generally collapse and are difficult to identify. The hepatic sinusoids are difficult to see on this slide. The wall of the sinusoid is lined with endothelial cells and Kupffer cells. Identify nuclei of the Kupffer cells, which tend to be larger and more ovoid than the flattened endothelial cells.
Observe, that hepatocytes are mono- and binucleate cells, and the presence of small and large nuclei. The ergastoplasm of the hepatocytes appears as darkly stained, irregularly shaped areas in the cytoplasm (use the high dry or oil immersion lens). The central vein is lined by endothelial cells with minimal underlying connective tissue. Sometimes you can visualize the continuation of a sinusoid with the central vein. Examine the serosa of this organ.
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SLIDE 65e liver, rat (toluidine blue)
(RR&K p523 Fig. 2)
This slide contains a small, thin plastic section of the rat liver stained with toluidine blue. Using low power, examine the portal triads, hepatocytes, sinusoids, and central veins within the classic lobule and hepatic acinus.
At higher power, identify the portal triad with hepatic artery, portal vein. bile duct and connective tissue. The portal vein is the largest vessel to have a thin wall lacking any noticeable smooth muscle. The hepatic artery is small, with 1-3 muscle layers in the tunica media. The bile duct is lined with simple cuboidal epithelium. Observe the wall of hepatic sinusoids lined with endothelial cells and Kupffer cells. Identify nuclei of the Kupffer cells, which tend to be larger and more ovoid than the flattened endothelial cells. The space of Disse is well preserved on this plastic section of liver, and is clearly visible between the sinusoidal endothelial cell and the hepatocyte. What is the function of the space of Disse? Examine the hepatocytes with the 40x objective and locate the basal, lateral, and apical surfaces. Identify the bile canaliculi. Then, with the oil immersion lens examine cellular details of the cell. You should be able to see the mitochondria (round, dark staining granules) and the glycogen containing areas (metachromatic patches in magenta color free of mitochondria) in the cytoplasm. Lipid droplets of varying size stained dark blue or black are also present in some of the cells. The lipid droplets are round and usually much larger than the mitochondria. Some hepatocytes contain excessive lipid droplets. These cells store vitamin A and have been referred to as lipocytes (Ito cells). The central vein is lined by endothelial cells with minimal underlying connective tissue. Sometimes you can visualize the continuation of a sinusoid with the central vein.
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SLIDE 65a liver, human (H&E)
(RR&K p521, Fig. 1,2; p523 Fig. 1)
This is a typical paraffin-embedded slide of the human liver. Using low power, review the histology of the liver. Observe the organization of the portal triads, hepatocytes, sinusoids, central veins and hepatic veins in relationship to the classic lobule and hepatic acinus. At higher power, identify the portal triad with hepatic artery, portal vein, bile duct and connective tissue. Observe the wall of hepatic sinusoids lined with endothelial cells and Kupffer cells. Examine the hepatocytes with the 40x objective and locate the basal, lateral, and apical surfaces. Identify the bile canaliculi. Hepatocytes will have 1 or 2 nuclei. The ergastoplasm of the hepatocytes appears as pale blue stained, irregularly shaped areas in the cytoplasm (use the high dry or oil immersion lens). Lipid droplets of varying size appear as unstained holes in the cell.
The central vein is lined by endothelial cells with minimal underlying connective tissue. Sometimes you can visualize the continuation of a sinusoid with the central vein. The hepatic vein can be distinguished from the central vein by its thick wall of dense connective tissue which the central vein lacks.
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SLIDE 66a gallbladder (H&E)
(RR&K p527, Fig. 1,2,3,4)
The gallbladder can be considered as an extrahepatic bile duct, which become modified to store and concentrate the bile. Examine the various layers of the wall of the gallbladder: mucosa, muscularis externa, and serosa or adventitia. The mucosa has many folds projecting into the lumen. Identify the luminal surface of the gallbladder on your slide. The tall columnar epithelium of the gallbladder resembles that of an intestinal villus, except for a poorly defined striated border and lack of goblet cells. Distended intercellular spaces can be seen between the columnar epithelial cells. Deep to the epithelium, lamina propria possesses many capillaries and larger blood vessels. In addition, identify outpocketings of the mucosa called Rokitansky-Aschoff sinuses, which extend into the muscularis externa. External to the lamina propria is a muscularis externa represented by irregular layer of smooth muscle cells. There is no submucosa in the gallbladder. Note the peritoneal coverage of the gallbladder; both serosa and adventitia are present.
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SLIDE 64a pancreas, human (H&E)
(RR&K p529, Fig. 1,2; p512 Fig. 17.15)
This is a thin section of human pancreas embedded in plastic.
The exocrine component of pancreas is represented by the glandular tissue that forms pancreatic acini. Individual acini are very similar to the serous acini of salivary glands, but they lack myoepithelial cells. At low power identify lobules, which are separated from each other by connective tissue septa. Observe the acini, intercalated and intralobular ducts within the lobule. The acini consist of columnar secretory cells. The wide basal portion of these cells contain ergastoplasm while the narrow apical portion have eosinophilic secretory vesicles. Outside the acinus is a capillary network. Do not confuse the endothelial cells with myoepithelial cells which are not present in the pancreas. Intercalated ducts are lined by squamous cells. The proximal portion of intercalated duct protrude into the acinus and those duct cells are referred to as centroacinar cells The intralobular ducts are lined with simple cuboidal cells. Identify the interlobular ducts embedded in the thick connective tissue septa between lobules.
The endocrine component of the pancreas consists of group of cells called the islets of Langerhans. The islets are scattered within the glandular tissue of the pancreas. Note that islet cells have much less cytoplasm than the acinar cells and stain pink in this H&E preparation. These islets have associated with them an extensive fenestrated capillary network.
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SLIDE 65p liver, cirrhosis (H&E)
(RR&K p521, Fig. 1,2; p523 Fig. 1)
Cirrhosis is a disease of the liver in which hepatocytic injury induces diffuse architectural disorganization and varying degrees of fibrosis accompanied by nodular regeneration of hepatic tissue. Scan your slide on low magnification and note the various amounts of fibrous tissue scars formed in response to loss and injury of hepatocytes. Connective tissue is infiltrated by lymphocytes and often contains portal triads. Very often, lobules lack central veins and have abnormal vascular architecture. In some areas on your slide note extensive accumulation of the lipid droplets in the cytoplasm of hepatocytes. Some hepatocytes contain eosinophilic inclusions that take a form of "candle drippings" known as Mallory bodies or alcoholic hyalin. Accumulation of brown lipofuscin pigment is also evident in some cells. Observe small areas of necrosis marked by clusters of red-stained neutrophils. This is a good slide to review normal histology in the areas not affected by cirrhosis. Observe well-preserved Kupffer cells in the endothelium of enlarged sinuses.
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The liver, gallbladder, and pancreas are all important in digestion. The liver and pancreas serve both exocrine and endocrine purposes. The liver is involved in bile formation, detoxification, glucose storage, lipoprotein synthesis, synthesis of various proteins, and many other functions. The pancreas releases digestive enzymes and also hormones involved in glucose homeostasis.