[The ultrastructural characteristics of the organization of the postcapillary venules of a lymph node].

A comparative investigation has been undertaken to study the initial and terminal parts of the postcapillary venules (PCV) in the rat lymph nodes in order to reveal certain structural peculiarities of endothelium in the actively functioning venular zones at a transmural transport of lymphocytes. Certain morphological peculiarities have been detected in the endothelial lining at the place where it passes from the capillary into the PVC, as well as in the initial and terminal parts of the PVC. Decrease or/and absence of tight junction near apical surfaces of endotheliocytes has been stated in the terminal parts of the venule, while similar contacts are present in the initial parts of the vessel. It has also been proved that there are some specific peculiarities in the structure of the PVC lymph node: high endothelium, great number of lymphocytes in the wall of the venule. It has been stated that not all endotheliocytes, to the same extent, participate in the transmural transport of lymphocytes. It is demonstrated by different structural organization of these cells.