The termination of two of the sinusoids and their union with the central vein (CV) is indicated by the curved arrows. Note that the wall of the vein is strengthened by connective tissue, mostly collagen, which appears as homogeneous eosin-stained material (asterisks). Fibroblasts (F) within this connective tissue can be identified and distinguished from the endothelial cell (EN) lining of the vein.
Hepatic sinusoids, liver, rat, glutaraldehyde–osmium fxation, toluidine blue ×900.
This figure shows a plastic-embedded liver specimen fixed by the method normally used for electron microscopy. In contrast to the H&E–stained preparation, it demonstrates to advantage the cytologic detail of the hepatocytes and the sinusoids (S). The hepatocytes are deeply colored with toluidine blue. Note that the cytoplasm exhibits irregular magenta masses (arrows). This is glycogen that has been retained by the glutaraldehyde fixation and stained metachromatically by toluidine blue. Also evident are lipid droplets (L) of varying size that have been preserved and stained black by the osmium used as the secondary fixative. The quantities of lipid and glycogen are variable and, under normal conditions, reflect dietary intake. Examination of the hepatocyte cytoplasm also reveals small, punctate, dark-blue bodies contrasted against the lighter-blue background of the cell. These are the mitochondria. Another feature of this specimen is the clear representation of the bile canaliculi (BC) between liver cells. They appear as empty circular profiles when cross-sectioned and as elongate channels (lower right) when longitudinally sectioned.
The sinusoidal lining cells are of two distinct types. The Kupffer cells (KC) are the more prominent cells. They exhibit a large nucleus and a substantial amount of cytoplasm. They protrude into the lumen and may give the appearance of occluding it. However, they do not block the channel. The surface of the Kupffer cell exhibits a very irregular or jagged contour because of the numerous processes that provide the cell with an extensive surface area. The endothelial cell (EN) has a smaller nucleus, attenuated cytoplasm, and a smooth surface contour.
A third cell type, the less frequently observed perisinusoidal lipocyte (Ito cell), is not seen in this micrograph. This cell would appear as a light cell containing numerous lipid droplets. The lipid droplets contain stored vitamin A.
KEY BC, bile canaliculus CV, central vein EN, endothelial cell F, fibroblast KC, Kupffer cell L, lipid droplet S, sinusoid arrows, glycogen asterisks, connective tissue of central vein curved arrows, opening of sinusoid into central vein
The gallbladder concentrates and stores bile for delivery to the duodenum. The bile is concentrated by the active transport of salt from the bile and the passive movement of water in response to the salt transport. The mucosa is characterized by a tall columnar absorptive epithe-lium that closely resembles that of the intestine and the colon in both its morphology and function. The epithelial cells are characterized by nu-merous short apical microvilli, apical junctional complexes, concentrations of mitochondria in the apical and basal cytoplasm, and complex lateral plications. In addition, Na+-K+–activated ATPase is localized on the lateral plasma membrane of the epithelial cell.
Gallbladder, human, H&E ×45.