Ultrastructure of the liver and biliary tract in health and disease.

Abstract

Ultrastructural studies with the transmission (TEM) and scanning (SEM) electron microscopes have added greatly to our knowledge of cellular structure and function in the liver. The normal polyhedral hepatocyte has numerous subcellular organelles, such as mitochondria, peroxisomes, lysosomes and complex rough (rer) and smooth (ser) endoplasmic reticulum. The normal hepatocyte stores glycogen, and sometimes lipid droplets, and secretes bile through the bile canaliculi between adjacent liver cells. It receives nutrients from the sinusoidal lumen across a fenestrated endothelium which is separated by the Space of Disse' from the plasma membrane. The Space of Disse' contains a scant network of reticulin fibers but no basal lamina. Two types of parasinusoidal cells are found in Disse's space: the fat storing cells of Ito, and the Pit cells which may have an endocrine function. The diseased liver has yielded much information in studies with TEM and SEM. The studies with TEM have been most helpful in studying the etiology of infectious diseases such as hepatitis B; have revealed organelle changes such as megamitochondria in cirrhosis and the fibrillar nature of alcoholic hyaline; have led to the identification of specific deposits in metabolic and storage diseases such as hemochromatosis (iron). Wilson's disease (copper), and alpha-1-antitrypsin deficiency (glycoprotein) have proven useful in identifying drug induced liver cell changes such as proliferation of SER and cholestasis, and are useful for identifying specific cell types in inflammatory and neoplastic diseases. In the future, both TEM and SEM coupled with histochemical, cytochemical, immunohistochemical and other analytic techniques will continue to add greatly to our understanding of the liver in health and disease.