The three-dimensional microstructure of the liver. A review by scanning electron microscopy.

The improvement in scanning electron microscopy (SEM) techniques has permitted us to describe the microstructure of the liver. By SEM, the liver peritoneal surface is composed of flat mesothelial cells possessing microvilli and cilia. Hepatic sinusoids connect the portal vessels with the terminal branches of the hepatic vein (central veins). Endothelial cells of the portal space arteries are elongated and arranged longitudinally, while those of the central and portal veins are polygonal and flattened, possessing microvilli. The sinusoidal endothelial cells show both small fenestrations (sieve plates), up to 200 nm in diameter, and large ones, up to 1 micron. Within the sinusoids are seen bridging structures, covered by fenestrated endothelium, seeming to have a fibrillar core. Kupffer cells resemble macrophages, showing microvilli, blebs, lamellipodia and filopodia. Within the Space of Disse are seen the fat-storing cells, having laminar dendritic projections. The polyhedral liver cell faces the Space of Disse (vascular pole) or faces an adjacent hepatocyte (biliary pole). Vascular facets are evenly covered by microvilli. Biliary facets show a central longitudinal depression, bordered by microvilli (bile hemicanaliculi). Canaliculoductular junction and bile duct epithelia show blebs, microvilli and cilia. Up to now, fetal liver and liver pathology have been scarcely investigated by SEM: in the future, they can be successfully approached by three-dimensional studies.