RESUMO
In the 18th week of the prenatal life large light cells of mesenchymal origin enter the crypt epithelium of the palatine tonsil to start its reticularisation. They are considered precursors of Langerhans cells.
Assuntos
Células de Langerhans/citologia , Tonsila Palatina/embriologia , Células Epiteliais/citologia , Humanos , Células de Langerhans/ultraestrutura , Tonsila Palatina/citologiaRESUMO
Postcapillary high-endothelial venules were studied in the palatine tonsils of 48 fetuses and 19 children aged from the 10th gestational week to the end of the first year of life. Light microscopy was used to study their localization and distribution in extrafollicular lymphatic tissue in histological sections. The anlage of the venules was detected as early as in the 14th gestational week. Transmission electron microscopy was used to study the ultrastructure of high-endothelial cells and adjacent connective tissue structures of the venular wall.
Assuntos
Endotélio Vascular/embriologia , Tonsila Palatina/embriologia , Endotélio Vascular/ultraestrutura , Idade Gestacional , Humanos , Recém-Nascido , Tonsila Palatina/irrigação sanguínea , Vênulas/embriologia , Vênulas/ultraestruturaRESUMO
Migration of lymphoid cells through the wall of postcapillary venules was studied in the palatine tonsils of five human fetuses. The direction of the migration of lymphoid cells as observed in the early fetal period seems to be mostly from the lumen of the venule into the tonsillar parenchyma. Migration starts with the adherence of the lymphocyte by means of a cytoplasmic projection to the cellular surface of a high-endothelial cell. The projection slips between two neighbouring endothelial cells and extends to settle on the basal membrane of the endothelium. After the disruption of the basal lamina the lymphocyte migrates into the subendothelial connective tissue and further into the extrafollicular tissue of the tonsil. The possibility of transendothelial migration of lymphoid cell through the wall of the postcapillary venule is discussed. Even in case, when the lymphocyte appears to be completely enveloped by the cytoplasm of the endothelial cell it may be in reality the intercellular migration--the lymphoid cell is pressed into the cytoplasm of an endothelial cell.