[Ultrastructural organization of the endotheliocytes of human liver sinusoids in the prenatal period].

Structure of endotheliocytes of the human liver sinusoids during 4-5-9 months of intrauterine development has been studied electron microscopically. At early stages of embryogenesis the liver sinusoids are covered with continuous endothelium. As cytodifferentiation progresses, formation of zonality in cytoplasm of endotheliocytes is observed. In the most thinned parts of cytoplasm single fenestrae, situating irregularly appear. As the fetus is growing, the number of diafragmented fenestrae increases their arrangement becomes more regular; together with accidental, claster arrangement of the fenestrae is observed. Open intra- and intercellular fenestrae of endotheliocytes appear in the second half of the intrauterine development. For endotheliocytes of the fetal liver sinusoids presence of transitory migrational pores is specific; they are maximally thinned areas of endotheliocytic cytoplasm, that emerge at the moment of diapedesis of the blood formed elements across the endothelial lining. High tempo of histogenesis is specific for endothelium of the liver sinusoids; the endothelium of a continuous type differentiates into the specialized--sinusoid endothelium.