Light and electronmicroscopic observations on hepatic hematopoiesis of human fetuses. I. Granulocytopoiesis in the hepatic mesenchymal tissue.

Focusing on hematopoiesis, especially granulocytopoiesis, livers from ten human fetuses between 7 to 13 weeks of gestation were observed with light and electron microscope. In the hepatic mesenchymal tissue variable number of granulocytes in varying stage of maturation were found from 10 to 13 weeks of gestation. The granules of neutrophils in human fetal livers were classified into three distinct types. The first granules appeared in myeloblasts. The second granules, possibly formed in Golgi complex, were more larger and observed after the promyelocytic stage. The third granules, predominant in mature neutrophils, were pleomorphic. Other than granulocytic, erythrocytic and stromal cells, unclassifiable cells were occasionally encountered. The role of mesenchymal tissues in the granulocytopoiesis, the development of fetal neutrophils and the problem of hematopoietic stem cells were discussed.