Biomechanics of Lymph Transport

Abstract

While lymphatics were probably observed by members of ancient schools, the first documented description of lymphatics in the dog mesentery is by the Italian Asellius in 1622. About 1652 the Swedish scientist Olaus Rudbeck at the University of Uppsala and independently the Danish anatomist Thomas Bartholin gave the first descriptions of lymphatics as a unidirectional transport system which carries fluid from the interstitial tissue compartment via a network of lymphatic conduits and nodes to the thoracic ducts and back into the venous circulation (Grotte, 1979). In addition to interstitial fluid, the lymphatics carry colloid particles of different sources as well as blood cells, such as lymphocytes. With the exception of the brain, virtually all organs have lymphatics. Man generates several liters of lymph fluid every day. While the flow rates in individual lymphatics are low compared with flow rates in the vascular system, the amount of fluid being transported by each lymphatic is still large. Even relative short interruption of the lymph flows lead to rapid swelling of lymphatics and the interstitial space. In spite of a colorful research history older than three hundred years, no consensus has been reached to explain the mechanism(s) by which interstitial fluid is carried into the terminal endings of the lymphatics and by which lymph fluid is retained and transported inside the initial lymphatics. Once lymphatic fluid reaches the contractile segments of the lymphatic system, fluid propulsion is achieved by peristaltic smooth muscle contractions and lymphatic valves to prevent reflow. While many aspects of peristaltic lymph pumping have been explored, the mechanism of lymph formation and transport in regions without lymphatic smooth muscle is, however, without even the most basic understanding. It will be the focus of the present discussion.