Electron microscope observations on chick embryo liver: Glycogen, bile canaliculi, inclusion bodies and hematopoiesis

Abstract

Chick embryo livers of different incubation ages (6–18 days) have been studied in the electron microscope. Three fixation procedures and a variety of embedding materials were used. In particular, the glycogen, bile canaliculi, lipid inclusions, and capillaries containing young blood cells were studied. The variable appearance of the glycogen is illustrated. It is often seen as distinct granules which are as large as 33 m μ , but in other cases these granules become indistinct and are seen only under very low contrast. Furthermore, single granules may fuse (probably when polymerization damage is present) and then the glycogen appears in form of larger clumps. Attempts to demonstrate digestion of the glycogen by salivary amylase, applied directly on the plastic-containing sections, were successful in one instance. The bile canaliculi are well established in livers 6 days old. They are bounded by a variable number of liver cells. “Terminal bars” are not seen at this stage. Certain inclusion bodies are interpreted as lipid bodies. The gradual development of a dense mass in their center (presumably fat), and of stacked lamellae at their periphery (presumably phospholipid) is illustrated. It is believed that the central mass and the peripheral lamellae within these inclusions are being formed from the inclusion body “matrix.” Perhaps these pictures illustrate the synthesis of fat and of phospholipid. In old (18-day) embryos the lamellae (presumed phospholipid) are rarely seen. Blood capillaries are characterized by a continuous endothelium in embryos 6 days old, but they show a discontinuous endothelium after about 8 days of incubation. Endothelial cells are seen to undergo division as they differentiate to form young erythroblasts. The electron microscope observations on this intracapillary erythropoiesis are closely comparable with early observations made with the light microscope.