mimic true pathology. Fixatives should be isotonic and isothermic to the cells4; although different labs have their own preferences, 1.5% to 2.5% buffered gluteraldehyde is universally accepted.
Table 5.1 Ultrastructural features that can be used to judge the quality of tissue preservation
The tissue becomes less homogenous in electron density (exaggerated contrast).
The tissue has a pale and extracted appearance.
Details are compromised at higher magnification, resulting from the uneven loss of phospholipids, membranous structures, matrix, and ribosomes.
The cell membranes of discohesive cells, such as Kupffer cells, frequently show discontinuities at high magnification.
There is loss of mitochondrial detail. The mitochondria appear contracted or distended and partly disintegrated. The cristae are poorly preserved.
Among cytoplasmic contents, lipid, glycogen, and ribosomes are poorly preserved.
Among organelles, the smooth endoplasmic reticulum and Golgi apparatus are poorly preserved.
The cytoplasm shows irregular rarefactions representing lost liposomes, glycogen, endoplasmic reticulum, Golgi apparatus, and vesicles.
Lipofuscin shows moderate alterations.
Cell nuclei show peripheral condensation of their chromatin, with incomplete preservation of the nuclear membranes. The nuclear pores are difficult to identify.
Cellular borders, including cilia and microvilli, are well defined.
Intercellular junctions, such as desmosomes are well preserved.
Closely packed rough endoplasmic reticulum is well preserved.
Lysosomes, including large secondary lysosomes with phagocytized material, are usually well preserved.
Collagen and basement membranes are well delineated.
Microfilaments, such as seen in the pericanalicular region, are relatively well preserved.
to the high level of endocytosis on this surface, the underlying cytoplasm contains many pinocytotic vesicles.
Figure 5.1 The normal hepatocyte. Normal hepatocytes (upper center) have a polyhedral appearance, with voluminous cytoplasm, abundant glycogen contents and numerous organelles.
Figure 5.2 The normal hepatocyte. Lipid droplets can be found in small numbers within the cytoplasm of hepatocytes under normal conditions.
cell-to-cell communication,29,30 and tight junctions that seal the bile canaliculi.
Figure 5.3 The normal hepatocyte. Lipofuscin consists of coarse, electron-dense granules, lipid droplets, and a heterogeneous matrix.
Figure 5.4 The normal hepatocyte. Hemosiderin consists of lysosomal aggregates of finely granular electron-dense material.
Figure 5.5 The normal hepatocyte: hepatocellular poles. Hepatocytes have three poles: the sinusoidal pole (upper right corner), the lateral poles (long white arrows), and the canalicular pole (short black arrow).
The rough endoplasmic reticulum is the site of protein synthesis, especially proteins for secretion.34 The tubules of the smooth endoplasmic reticulum (Fig. 5.12) are devoid of ribosomes, and are located more toward the periphery of the hepatocyte; smooth endoplasmic reticulum is usually associated with rich collections of glycogen.20,35, 36, 37 The smooth endoplasmic reticulum is the site of remarkable metabolic activity, including cytochrome P450 (located in endoplasmic reticulum membranes)20; its functions include lipid synthesis, glycogen and glycoprotein metabolism, bile acid synthesis, and drug detoxification. The latter function is reflected ultrastructurally by the expansion and shrinkage of the smooth endoplasmic reticulum in response to administration and withdrawal, respectively, of certain medications.20,35,38, 39, 40, 41
Figure 5.11 The normal hepatocyte: rough endoplasmic reticulum. The rough endoplasmic reticulum is a network of continuous membranes and tubules. It is characteristically studded by ribosomes (finely granular deposits along the membranes, arrow).
within the cytoplasm.48 They are more numerous in Zone 3 hepatocytes. It is essential to examine electron microscopy images methodically for the presence of peroxisomes within hepatocytes in every case; the absence of peroxisomes, characteristic of Zellweger syndrome, can be otherwise easily missed.
Figure 5.15 The normal hepatocyte: nuclear inclusions. Nuclear inclusions such as glycogen inclusions are often seen in pathologic conditions, but can occasionally be seen in normal hepatocytes.
around the bile canaliculus.50, 51, 52 In the pericanalicular region, microfilaments are visible as an organelle-free ectoplasmic zone, which acts as miniature musculature for the bile canaliculi, facilitating bile flow.32,53,54
Another characteristic feature of sinusoidal endothelial cells is the presence of numerous pinocytotic pits and vesicles. Each endothelial cell is loosely attached to its neighboring endothelial cells by junctions.62 Unlike other endothelia, the sinusoidal endothelium lacks a basement membrane.9
Figure 5.17 The normal hepatocyte: zonal differences. Peroxisomes can be increased in Zone 3 hepatocytes, sometimes outnumbering mitochondria.
Figure 5.20 Hepatic stellate cells. Hepatic stellate cells have round to oval, eccentrically placed nucleus, and many large lipid droplets occupying most of the cytoplasm.
necrosis. In practice, general ultrastructural patterns of hepatocyte injury include the following:
Figure 5.25 Hepatocellular injury: ballooning. Ballooning degeneration is characterized by marked and diffuse dilatation of the endoplasmic reticulum
Figure 5.27 Hepatocellular injury: oncocytic change. Hepatocytes with oncocytic change are packed with numerous mitochondria.