The structure of the wall of the hepatic sinusoids in the electron microscope

Summary

• 1. The endothelial lining of the hepatic sinusoids was found to be predominantly continuous. The pictures illustrating the detachment of endothelial cells suggested that the lining is capable of closing temporary openings. Thus small gaps frequently seen in the lining may not be permanent holes during life.

• 2. The perisinusoidal space which until recently was considered to be a “potential” space, was shown in the electron micrographs as an actual space kept open by both the hepatic microvilli and the intralobular reticular fibers.

• 3. The intralobular fibers were found to vary in respect to their microfibrils from those composed of 500 to 600 A thick microfibrils to others with microtibrils of 200 A diameter and less. In view of this variation it seemed to be probable that in the adult liver (of rat and mouse) new reticular fibers continue to be formed. Indication of fibroblastic activity could be found in endothelial cells.

• 4. The hepatic microvilli either showed free endings or were closely attached to the endothelial lining. It was therefore suggested that certain substances may be taken up by the hepatic cells directly from the bloodstream via endothelium and attached villi, while other materials pass through the perisinusoidal space.

• 5. The question of the existence and of the structure of a basement membrane in the hepatic sinusoidal wall was taken up. The absence of a separate structure in the electron micrographs which could be identified as basement membrane, the results of staining the perisinusoidal space with the PAS-reaction and general histological considerations lead to the conclusion that the perisinusoidal space contains in addition to microvilli and fibers a continuous ground substance and should be therefore considered as a whole the equivalent of a basement membrane.