Scientific journal
European Journal of Natural History
ISSN 2073-4972


Petrenko V.M.
Mechanic of anlage of haemopoietic organs is not described in literature. Anlage of lymph nodes takes place when blood vessels with their more thick walls invaginate into increasing lumen of embryonic lymphatic collectors together with their endothelial wall. Intervascular connective tissue of invagination accumulates lymphocytes gradually. Increasing invagination twists and narrows the lumen of matrical lymphatic vessel, which is divided on three segments - afferent, efferent and intermediate (primary marginal sinus of anlage of lymph node). The invagination takes place on path of lymph flow and slow down it with division on two flows: direct lymph flow skirts the stromal anlage of lymph node into lenthening primary marginal sinus and undirect, trancfussional lymph flow penetrates the stromal anlage of lymph node where probably fragments of degenerating cells, tissues and organs settle including the partitions of lymphatic sacs and trunks. The fragments can induce migration of blood cells from blood microvessels of the invagination into its connective tissue, the stromal anlage of lymph node with its cleaning (macrophages) and transformation into lymphoid anlage of lymph node. Haemopoiesis in the (embryonic) liver takes place about sinusoides which are appeared due to that hepatic trabeculaes constrict and divide subintestinal vein or venae vitellinae and umbilicales. Haemopoiesis in the bones begins in foetuses of third month about venous sinuses which occur in this period. Intensive sedimentation of calcium in bones begins in foetuses of fourth month and red bone marrow becomes the centre of haemopoiesis in foetuses of fifth month. It is possible that walls of bones cavities limiting of dilatation of bone marrow and veins promote formation of sinusoides and entrance of blood cells into blood flow. Intensive proliferating epithelial anlages of thymus «wall up» blood microvessels. In embryos of 7-8 weeks the anlages «descend» from cervical region into thoracical cavity and find in solid surroundings of muscles, clavicles, ribs, sternum and heart. Such case limits outer growth of anlages of thymus, promotes their approach and junction, formation of blood thymus barrier. In this period mesenchyma of thymus is loosened and blood microvessels widen in connection with production of proteoglycans, blood and thymosin flow out are lightened that stimulates influx lymphocytes from blood into epithelial anlages of thymus. Anlage of spleen takes place in embryos of 5-6 weeks, in solid surroundings of intensive growing organs (liver, stomack, pancreas, mesonephros, gonada, kidney and suprarenal gland) - external cuff of spleen instead of compact fibrose capsule which forms in foetuses. And compact mesenchyma in anlage of spleen limits widening of protocapillaries which is uneven. In embryos of 7-8 weeks stroma of spleen is loosened, protocapillaries transformate into venous sinuses. Besides, venous congestion spring up in anlage of spleen in connection with its removing from hepatic portal vein, its roots and tributaries. They are «cut off» by means of muscular coat of stomack and compact epithelial anlage of pancreas. But even in foetuses of 9-10 weeks intraorganic veins of spleen persist endothelial walls and thickening of its extraorgenic veins is very small. At last in embryos of 5-6 weeks turns of stomack about its lesser curvature are accompanied by twisting of dorsal mesogastrium, deformation and constriction of its blood vessels, inhibition of blood flow from spleen.