Anlage of primary lymphatic system comes by means of formation of lateral pockets in large primary veins with thin endothelial wall under the pressure of adjacent arteries with external coat. Comunications of central canal and lateral pockets of increasing veins narrow. The pockets separate from secondary veins as lymphatic chinks with endothelial covering. Some of primary veins turn off blood flow together with lymphatic chinks as tributaries preceding venous pockets including part of protocapillary net. Lymphatic capillaries preserve very thin endothelial wall without basal membrane and lose vascular connection with blood bed. Therefore usually lymph pressure is lower than the venous and prone to the greater fluctuations right to zero. Lymphovenous connections preserve usually in the neck of human and mammals where negative venous pressure originates periodically. Thus lymphatic bed including roots in microcirculatory bed develops from venous collaterals by means of reducing their connections with venous magistrals. In conditions of intensive organogenesis and increasing blood pressure the basal membrane forms under thickenning endothelium of blood capillaries. The membrane cuts off lymphatic collaterals with thin endothelium without basal membrane. The pressure of differentiated advential coat of secondary veins is conducive to separation of venous pockets. Thus transverse gradient of blood and mechanical pressure originates in primary drainage system of parallel vessels [collateral - magistral - collateral] and diferentiates the system on secondary or true veins and primary lymphatic vessels as modificate or persistent primary veins.
The work is submitted to the International Scientific Conference «Innovative Medical Technology», Moscow-Paris, March 18-25, 2011, came to the editorial office оn 19.01.2011