OBJECTIVES: At the end of this laboratory you should be able to:

1. Recognize liver, gall bladder, and pancreas.

2. Identify and understand the functional significance of the vascular supply and bile drainage of the liver.

3. Identify and discuss the structural and functional arrangement of the classical hepatic lobule, portal lobule, and the liver acinus.

4. Identify bile canaliculi and perisinusoidal spaces of Disse in the liver at the light and electron micrograph level.

5. Recognize the hepatocyte organelles and inclusions in electron micrographs and give their function.

6. Identify excretory ducts, interlobular ducts, intercalated ducts, acinar and centroacinar cells in the pancreas. You should also be able to distinguish between the islets of Langerhans and the remaining parenchyma of the pancreas.

SLIDES FOR THIS LABORATORY: 58, 80, 88, 89, and Supplemental Slides 102, 103, and 124.

Slide 88 Human liver.

The principal parenchymal cell is the hepatocyte which all look very similar with H & E staining. Some hepatocytes are binucleate . The connective tissue present is mostly seen at the border regions between classic liver lobules . Note the connective tissue covering the uncut surfaces of this section. This is Glisson's capsule . Observe how the connective tissue septae dividing the lobules are continuous with the capsule

You can easily observe the components of the classic lobule on this slide. Find central veins and identify the plates (or cords) of hepatic cells that radiate out from the central vein. These cords of hepatic cells are separated by sinusoids . At the 6 apices of the classic lobule, observe the portal triads made up of hepatic (portal) artery, portal vein, bile duct, and lymphatic vessels. The lymphatic vessels are not visible in this preparation. Also locate sublobular veins which are found separate from the hepatic (portal) artery, portal vein, and bile duct. Sublobular veins coalesce into the hepatic vein which carries blood from the liver to the vena cava.

In addition to the classic liver lobule you should also envision the portal lobule and the liver acinus .

Supplemental Slide 102 Liver.1.5 µm, monkey.

Observe the finer details of the hepatocytes , the space of Disse , and occasionally Kupffer cells .

Supplemental Slide 124 Liver, PAS and H&E.

Kupffer cells are seen best in this slide. Recall that these cells are macrophages and contain particulate matter.

Slide 89 Liver, Van Gieson and silver stain.

In this slide, reticular fibers and collagen fibers have been stained. Note the extensive network of reticular fibers which literally cradle the liver cells. Compare the distribution of collagen and reticular fibers.

Slide 58 Gall bladder.

The gall bladder functions to concentrate and store bile. It is a hollow, pear shaped organ with walls composed of three layers: a mucosa , muscularis externa , and adventitia (serosa). Notice the very tall, simple columnar epithelium of the mucosa which is thrown into numerous villus-like folds . The lamina propria of the mucosa is highly vascular with no lymphatics. Note the arrangement of the smooth muscle in the muscularis externa with longitudinal fibers closer to the lamina propria and circular fibers more peripheral (no muscularis mucosa or submucosa exists).

Slide 80 . Pancreas.

The exocrine component of the pancreas is a compound tubuloacinar gland with a complex series of ducts that convey the exocrine secretion of the pancreas to the duodenum. Observe the serous acini of the pancreas. Each acinus is composed of acinar cells . Note the intense basophilia in the basal portion of the acinar cells and eosinophilia of the apical portion. Some acini reveal the centrally located centroacinar cells . These cells are the beginning of intercalated ducts lined with a simple low columnar or cuboidal epithelium. The intercalated ducts empty into the intralobular ducts which have a cuboidal epithelium. These ducts empty into the interlobular ducts which run within the connective tissue septa dividing the pancreas into lobules. The interlobular ducts coalesce to form the pancreatic duct which empties into the duodenum.

The endocrine portion of the pancreas, the islets of Langerhans , are seen as islands of pale staining cells spread through the organ. Defer your detail study of these until the endocrine glands are covered in a later laboratory.

Note: the pancreas can be distinguished from the parotid gland in that the pancreas does not have striated ducts, and the pancreas has the characteristic islets of Langerhans.

Supplemental Slide 103 Pancreas, 1.5 µm, human.

Again, observe the characteristic features of the exocrine pancreas: serous acini , acinar cells , centroacinar cells , intercalated ducts , intralobular ducts , and interlobular ducts .