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ductule ductule

The intrahepatic ductule (canal of Hering). a. Photomicrograph showing an area near a portal canal. The terminal branch of a portal vein (lower right) accompanied by a small intrahepatic ductule (canal of Hering) are evident. The arrow indicates the area where a bile canaliculus is draining into the intrahepatic ductule. Note that the intrahepatic ductule is surrounded by hepatocytes, in contrast to the bile duct, which is embedded in the connective tissue of the portal canal. x800. b. Electron micrograph showing an intrahepatic ductule.

The ductule collects bile from the bile canaliculi. It is close to the hepatocytes, but the actual connection between bile canaliculi and the intrahepatic ductule is not evident in this plane of section. The ductule is composed of cuboidal epithelium (CE) surrounded by a complete basal lamina (BL). The narrow space (asterisks) into which microvilli of hepatocytes project is the periportal space (of Mall), not the perisinu-soidal space (of Disse). x 6,000.

Hepatocytes are relatively long-lived for cells associated with the digestive system; their average lifespan is about 5 months. In addition, liver cells are capable of considerable regeneration when liver substance is lost to hepatotoxic processes, disease, or surgery.

The hepatocyte cytoplasm is generally acidophilic. Specific cytoplasmic components may be identified by routine and special staining procedures, including

• Basophilic regions that represent rough endoplasmic reticulum (rER) and free ribosomes.

• Numerous mitochondria; as many as 800 to 1000 mitochondria per cell can be demonstrated by vital staining or enzyme histochemistry

• Multiple small Golgi complexes seen in each cell after specific staining

• Large numbers of peroxisomes demonstrated by im-munocytochemistry

• Deposits of glycogen stained by means of the periodic acid-Schiff (PAS) procedure. However, in a well-preserved hematoxylin and eosin (H&E) preparation, glycogen is also visible as irregular spaces, usually giving a fine foamy appearance to the cytoplasm.

• Lipid droplets of various sizes seen after appropriate fixation and Sudan staining. In routinely prepared histologic sections, round spaces are sometimes seen that represent dissolved lipid droplets. The number of lipid droplets increases after injection or ingestion of certain hepatotoxins, including ethanol. • Lipofuscin pigment within lysosomes seen with routine H&E staining in various amounts. Well-delineated brown granules can also be visualized by the PAS method.

As noted above, the liver cell is polyhedral; for convenience, it is described as having six surfaces, although there may be more. A schematic section of a cuboidal hepatocyte is shown in Fig. 17.12. Two of its surfaces face the perisi-nusoidal space. The plasma membrane of two surfaces faces a neighboring hepatocyte and a bile canaliculus. Assuming that the cell is cuboidal, the remaining two surfaces, which cannot be seen in the diagram, would also face neighboring cells and bile canaliculi. The surfaces that face the perisinusoidal space correspond to the basal surface of other epithelial cells; the surfaces that face neighboring cells and bile canaliculi correspond to the lateral and apical surfaces, respectively, of other epithelial cells.

Peroxisomes are numerous in hepatocytes

Hepatocytes have as many as 200 to 300 peroxisomes per cell. They are relatively large and vary in diameter from 0.2 to 1.0 pm (see Fig. 17.13a). Peroxisomes are a major site of oxygen use and in this way perform a func tion similar to that of mitochondria. They contain a large amount of oxidase that generates toxic hydrogen peroxide, H,02. The enzyme catalase, also residing within peroxisomes, degrades hydrogen peroxide to oxygen and water. These types of reactions are involved in many detoxification processes occurring in the liver, e.g., detoxification of alcohol. In fact, about one half of the ethanol that is ingested is converted to acetaldehyde by enzymes contained in liver peroxisomes. In humans, catalase and n-amino acid oxidase, as well as alcohol dehydrogenase, are found in peroxisomes. In addition, peroxisomes are also involved in breakdown of fatty acids (fi-oxidation) as well as gluconeogenesis and metabolism of purines.

sER can be extensive in hepatocytes

The sER in hepatocytes may be extensive but varies with metabolic activity (see Fig. 17.13b). The sER contains enzymes involved in degradation and conjugation of toxins and drugs as well as enzymes responsible for synthesizing cholesterol and the lipid portion of lipoproteins. Under conditions of hepatocyte challenge by drugs, toxins, or metabolic stimulants, the sER may become the predominant organelle in the cell. In addition to stimulating sER

Golgi apparatus

LUMEN OF HEPATIC SINUSOID collagen fibers it0 cell

space of Disse zonula occludens bile canaliculus mitochondria

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