The functional unit of the lymphatic system- towards understanding the importance of a well-rehearsed interaction of lymphatic capillaries, collecting vessels and lymph nodes.

Lymphatic vessels and lymph nodes (LNs) are part of the lymphatic system taking care of interstitial tissue homeostasis, lipid transport and immune response. The interposition of LNs in between the lymphatic vasculature, allows the filtration of lymph fluid, cell-cell interactions and also the transfer of lymph fluid into the venous system. Impairment of the lymphatic vasculature leads to interstitial fluid congestion leading to tissue oedema as seen in acute inflammation or trauma or i.e. in lymphedema of the skin as a chronic condition. Remodelling of the lymphatic system during inflammation includes lymphangiogenesis, changed fluid transport rates and modification of LN morphology. Alterations of these processes can aggravate inflammatory processes, leading to an incomplete resolution of the inflammation and often ending in chronic inflammatory condition. Despite the development of histological markers to visualize lymphatic vessels, new imaging methods and increased knowledge about the different parts of the lymphatic system the general overview about the interplay of the different components is missing. The present review summarizes the current knowledge of the different functional units of the lymphatic transport system trying to create a model of their interplay. In a last step open questions are gathered together and possible answers discussed.