Histology of the Liver
Looking at a section of liver is somewhat reminiscent of looking down out of an airplane at a suburban neighborhood. One sees a very regular, almost monotonous, collection of houses in blocks demarcated by roads, with a gas station or minimart apparent at almost every intersection.
In the case of the liver, the roads are connective tissue septae which convey vascular and biliary traffic, and the clusters of houses are cord-like arrangements of hepatocytes, the parenchymal cell of the liver.
Prior to embarking on the lessons below, it would be best to review the core section Architecture of the Liver and Biliary Tract.
|Summary of Lesson|
|Sheets of connective tissue divide the liver into thousands of small units called lobules. A lobule is roughly hexagonal in shape, with portal triads at the vertices and a central vein in the middle.|
|The lobule is the structural unit of the liver and rather easy to observe. In contrast, the hepatic acinus is more difficult to visualize, but represents a unit that is of more relevance to hepatic function because it is oriented around the afferent vascular system.|
|The parenchymal cells of the liver are hepatocytes. These polygonal cells are joined to one another in anastomosing plates, with borders that face either the sinusoids or adjacent hepatocytes. The ultrastructure appearance of hepatocytes reflects their function as metabolic superstars, with abundant rough and smooth endoplasmic reticulum, and Golgi membranes. Glycogen granules and vesicles containing very low density lipoproteins are readily observed.|
|Hepatocytes make contact with blood in sinusoids, which are distensible vascular channels lined with highly fenestrated endothelial cells and populated with phagocytic Kupffer cells. The space between endothelium and hepatocytes is called the Space of Disse which collects lymph for delivery to lymphatic capillaries.|
|Bile originates as secretions from the basal surface of hepatocytes, which collect in channels called canaliculi. These secretions flow toward the periphery of lobules and into bile ductules and interlobular bile ducts, ultimately collecting in the hepatic duct outside the liver.|
|The hepatic duct is continuous with the common bile duct, which delivers bile into the duodenum. In most species, bile is diverted through the cystic duct into the gall bladder. The columnar epithelium of the gall bladder is devoted largely to absorption of water and electrolytes.|
|The Liver: Introduction and Index|
Last updated on May 11, 1997
|Author: R. Bowen|
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