Ontogeny and phylogeny of lymphatics: embryological aspect

The lymphatic system was first described by Hippocrates in 460-377 BC and further confirmed as one of the two major circulatory systems together with the blood vascular system by Gasparo Aselli in 1627. Despite these findings, this major circulatory system has been largely neglected for three centuries primarily due to limited knowledge, being often an invisible auxiliary to the blood vascular system and as such being considered less important. However, our understanding of the lymphatic system has significantly advanced over the last two decades with many landmark discoveries in lymphatic research, especially in the areas of cellular and molecular biology of lymphatic endothelial cells (LECs). This chapter will discuss the lymphatic system in detail, along with recent advances in our understanding of the embryonic development of the lymphatic vasculature, including the molecular mechanisms to mediate lymphangiogenesis. These advances have brought to light the molecular control of physiological and pathological lymphangiogenesis and subsequently changed the paradigm to re-evaluate the lymphatic system’s essential role in the human circulatory system.