The development of fetal rat liver between 12 and 21 days of gestation was studied ultrastructurally. The liver developed closely associated with hemopoietis, and so, the ultrastructural changes of hepatocytes according to hemopoietic activity were investigated.
The results observed were as follows.
1. The hepatocytes were discernible as dark cells of high electron density due to many ribosomes, rough endoplasmic ret:iculums and lipid inclusions, and as light cells of low electron density due to relatively small amount of such organelles.
2. At 13 day of´ gestation, hepatocytes with many granules were frequently found and had well developed Golgi apparati, dilatated granular endoplasinic reticulums. The granules were round in shape, surrounded by membrane, and observed with high inner, low outer electron densities. These characteristics reflected the capacity to produce proteineous substances and the maturity, and in-general, hepatocytes at 13 day of gestation were more mature than at 12 day.
3. The hepatocytes were irregular in shape due to many hemopoietic cells after 14 day of gestation and made microvilli in close contact with hemopoietic cells. Hepatocytes showed well developed Golgi apparati, RERs, mitochondria and many ribosomes, and at 17 day of gestation, immature bile canaliculi were present.
In ´summary, the great ultrastructural differences of hepatocytes between 12 and 13 day of gestation were the appearance of Golgi apparati, dilatated RERs, many ribosomes, granules and lipid inclusions reflecting the capacity to produce proteineous substances:
Besides the above, hemopoietic cells appeared for the first time at 13 day of gestation and hepatocytes were in close contact with hemopoietic cells.
From the results, the hepatocytes are supposed to produce some proteineous substances affecting the henopoiesis.
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