Lymphatic channels and lymphoid structures cooperate with each other to provide hemostasis in the body. This is indetermined by their set up in close association with veins. Lymphatic channels differentiate as a collateral part of the venous bed excluded from the blood flow. Spleen and thymus lie off the transport conduits that carry lymph, as well as the red bone marrow. Unlike the other lymphoid structures, they do not participate in lymph drainage from other organs; and in the process of evolution and ontogenesis, they form together with the predecessors of the lymph vessels - venous sinuses. Lymphatic «instability» of thymus, spleen and the red bone marrow is their typical feature from the moment of their formation, when mesenchymal cells cluster around venous sinuses, where the blood flow slows down and the blood gets a better contact with the perivasal tissue. The rest lymphoid structures originate in association with lymphatic sacs or vessels. Their forerunners are the merging lymphatic clefts, which appear from the pockets, separated from the primary veins. Lymphocytes begin to colonize a lymphoid organ after peripheral lymph collectors have been formed - intercleft membranes collapse, and decay products of other structures (antigens) get inside.
The work was submitted to international scientific conference «Medical, social and economic problems of population health preservation», Turkey, May 20-27, 2009. Came to the editorial office on 10.09.2009.