High-endothelial postcapillary venules in the fetal palatine tonsil

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.