- Be able to describe the pathways of blood and bile flow through the liver.
- Know what organelles are prominent within the hepatocyte, and be able to relate different organelles to specific liver functions.
- Describe what surrounds the hepatocyte at various surfaces.
- Explain the organization of the bile canaliculus, space of Disse and liver sinusoid, including Kupffer cells.
- Know the organization of the classical liver lobule and Rappaport’s lobule and understand their relationship to liver functions.
- Be able to identify the gall bladder by the structure and arrangement of the various tissue layers in the wall.
LIVER AND GALL BLADDER
Slide 1 40x (liver, H&E) WebScope ImageScope Slide 194 40x (liver, H&E) WebScope ImageScope Slide 195 40x WebScope ImageScope Slide 198-1 40x ("even" slide collections, liver, Golgi silver) WebScope ImageScope Slide 198-2 40x ("odd" slide collections, liver, reticulin stain) WebScope ImageScope
Examining slide 1 at low magnification, observe numerous small, pale spots in the parenchyma, most of which are either central veins or small branches of portal veins (in portal canals) (W pg 292-3, 15.7). There may be a few larger channels, which are larger veins either entering or leaving this region of the liver. Now examine the section with the intermediate objective of your microscope, and distinguish central veins from portal veins.
The central veins (also referred to as terminal hepatic venules) are surrounded intimately by hepatocytes similar to those that make up the bulk of the liver tissue (W pg 294, 15.8). Portal veins are usually surrounded by visible connective tissue that also contains sections through one or more bile ducts and branches of the hepatic artery. Bile ducts at medium power appear in section as a circle of rather prominent nuclei. In small branches of the hepatic artery you will see primarily the ring of smooth muscle that makes up their wall. The three components together (portal vein, hepatic artery, bile duct) constitute a portal triad or "portal canal" [example] (W pg 290, 15.3 ). Look for good examples of portal canals where all three components are seen well. Of course, if you look carefully, you'll see that there is often a very thin-walled lymphatic vessel within the portal canal as well. In addition, these structure twist and turn so there may be more than one cross section of a bile duct, artery, vein, or lymph vessel, so it's not always a "triad" of structures that you'll see in the portal canal. Now, see if you can define a classic liver lobule at low power (W pg 294, 15.8).
In the hepatic parenchymal tissue (W pg 294, 15.8), note the plates of hepatocytes (the arrangement of these cells in plates is not always clear, due to plane of section and the frequent interconnections of plates). Occasional hepatocytes are binucleate. Between the plates of hepatocytes are intervening sinusoids lined by a thin endothelium (W pg 294, 15.9). Larger eosinophilic cells lining the sinusoids are mostly Kupffer cells [example] (a type of macrophage, part of the mononuclear phagocyte system) (W pg 294, 15.9). Look for Kupffer cells using slide 194 as these cells are not readily recognized in slide 1. You should be able to distinguish Kupffer cells from endothelial lining cells.
The space between the endothelial cells and hepatocytes is called the “space of Disse” and is somewhat artificially enlarged in conventional sections. Remember that blood flows from the portal veins and hepatic arteries (of the portal canals) through the sinusoids to the central veins. A classical liver lobule has a central vein in its center and has several portal triads at its periphery. Bile flows through the bile canaliculi (too small to see) to the canals of Hering to bile ducts in portal canals, to hepatic ducts of increasing sizes and to the common hepatic duct, eventually to be emptied into the duodenum via the common bile duct. If you really want to find a canal of Hering, look for a line of low cuboidal cells immediately adjacent to a portal canal [example] --the canal of Hering connects canaliculi to the bile duct.
This portal inflow system can be distinguished from the portal outflow system which lacks accompanying arteries and bile ducts. The hepatic outflow system starts with central veins which empty into sublobular veins and into collecting veins of various sizes and eventually into the hepatic veins. One characteristic of the hepatic outflow system is that it cuts through the liver parenchyma without respecting the organization of the liver lobules. The portal inflow system, on the other hand, is always located at the periphery of each liver lobule. Answer (DG6)
Slide 195 is stained with Masson trichrome and shows the distribution of collagen (blue) in connective tissue of the portal canals and less around the central veins. Staining is also visible in thin layers around the sinusoids. Note that this slide also includes some of the gall bladder, so make sure you're looking at liver [orientation].
One of the difficult concepts in the study of this organ is to understand the three-dimensional arrangement of the bile canaliculi (W pg 295, 15.10). Slide 198 (even) is a rather thick section of liver that has been treated with silver salts in a manner that specifically stains these structures. The liver cells are unstained and so are not seen. Try to gain some understanding of the “chicken-wire” arrangement of the canaliculi as they extend between all cells in the plate of hepatocytes, eventually leading to the portal canal, where the bile is delivered to bile ductules and then to bile ducts. Slide 198 (odd) is also stained with silver but under different conditions to show reticular fibers. Compare the distribution of the stains in these two slides.
B. Gall Bladder (W pg 298, 15.13) Slide 194 H&E 40x WebScope ImageScope Slide 195 trichrome 40x WebScope ImageScope Upon gross examination of slides 194 and 195 (i.e. with the naked eye or at the lowest power on the virtual microscope) you will see a portion of the gall bladder wall nestled in an indentation of the liver tissue. Examine the wall of the gall bladder with your microscope. Extensive folds of the mucosa extend into the lumen. The mucosa consists of a tall, simple columnar epithelium and its underlying connective tissue (constituting a lamina propria). No submucosa is defined. The muscularis externa consists of scattered bundles of smooth muscle. Beyond the muscularis is an adventitia consisting of rather dense connective tissue that binds the gall bladder to the liver. Where the surface of the gall bladder faces the abdominal cavity there is a serosa.
Use this section to study the liver [example] in the mouse.
Electron Micrograph Wall Charts
#122 LIVER - PORTAL AREA WebScope ImageScope In the center of the field observe the portal vein, hepatic artery and bile duct that make up the portal “triad”, and note the connective tissue that surrounds them. In the liver tissue around the portal area you will see plates of hepatocytes, with sinusoids between them. Bile canaliculi can be seen as small white spots between hepatocytes. The sinusoids are lined by endothelial cells and occasional Kupffer cells.
#123 LIVER SINUSOID WebScope ImageScope In the Kupffer cell note occasional lysosomes, which are involved in the phagocytic activities of this cell type. The endothelial lining of the sinusoid is discontinuous, allowing free passage of materials into the space of Disse (note the numerous short microvilli extending from the surface of hepatocytes into this space). There is no organized basal lamina along the endothelial cells or hepatocytes.
#124 HEPATOCYTE WebScope ImageScope Most of the typical organelles are well developed in liver cells, reflecting the many functions of these cells. Note the nucleus, rough (granular) endoplasmic reticulum, smooth endoplasmic reticulum (not labeled here), mitochondria, Golgi complex, lysosomes, peroxisomes and occasional lipid droplets. The liver cell stores glycogen and lipid. The cytoplasm contains clusters of glycogen particles (black), which can be metabolized to glucose for release into the blood when needed by the body. The glycogen occurs primarily in areas rich in smooth endoplasmic reticulum. The diverse secretory and absorptive functions of the hepatocyte take place primarily across two surfaces, shown clearly here: (1) The cell surface facing the blood in the space of Disse and adjacent sinusoid. (2) The cell surface involved in the bile canaliculus. Note the junctional complexes that seal the two sides of the bile canaliculus, and keep the bile products isolated from the blood.
DG6: What are the three classifications of liver lobules and what structures define each? Answer
- Which of the following statements regarding the 3 zones comprising a liver acinus (of Rappaport) is CORRECT?
- Zone 1 is closest to the central vein.
- Zone 2 is the first to undergo necrosis if circulation is impaired.
- Zone 3 is closest to branches of the hepatic artery.
- Zone 1 is the first to receive nutrients delivered by the portal vein.
- Zone 2 is the last to receive any toxins that may be in the blood.
- The region of the GI tract shown is:
- lower esophagus
- cardia of stomach
- pylorus of stomach
- gall bladder
- The cell indicated: [medium magnification] [high magnification]
- produces bile.
- is in the space of Disse.
- produces pancreatic pro-enzymes (such as trypsinogen).
- adds bicarbonate and water to the pancreatic exocrine secretion.
- removes sodium from the pancreatic exocrine secretion.
- secretes insulin.
- secretes glucagon.
- The asterisk is in:
- liver sinusoid
- space of Disse
- central vein
- branch of hepatic artery
- bile duct
- pancreatic intercalated duct
- pancreatic interlobular duct
- parotid gland intercalated duct
- parotid gland interlobular duct