LIGHT AND ELECTRON MICROSCOPIC OBSERVATIONS OF HEPATIC HEMATOPOIESIS OF HUMAN FETUSES

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Abstract
Liver tissues obtained from 78 human fetuses between 5 wk and 10 mo. of gestation were observed with light microscope and EM. In the 3rd mo. of gestation hepatic megakaryocytopoiesis reached the maximum level and then appeared to decline. At the maximum level immature to mature megakaryocytes were usually smaller than those from adult bone marrow. They were observed between growing liver cells, within hepatic sinusoids and in the mesenchyme surrounding the liver parenchyma in the given order of frequency. Immature megakaryocytes were characterized by the presence of demarcation vesicles or tubules, and a few small round specific granules. The nucleus was mononuclear but frequently indented. With cell maturation the megakaryocytes were stained intensely by PAS[periodic acid-Schiff]-technique. The nuclei were multilobulated. Large cytoplasm was dominated by numerous specific granules and well-developed demarcation membrane system. Some megakaryocytes passed through the sinusoidal wall and possibly to hepatic sinusoids. The main site of hepatic megakaryocytopoiesis may be extravascular, more likely between liver cells. Small megakaryocytes in fetal livers are discussed in relation to the occurrence of similar megakaryocytes in various blood dyscrasias.