The Lymphatic System in Health and Disease

The lymphatic system develops and functions in parallel with the blood circulatory system (termed the hemovasculature) and accomplishes transport of interstitial fluids, dietary lipids, and reverse transport of cholesterol, immune cells, and antigens—providing a critical homeostatic fluid balance and transmission of immune cells and mediators back to the cardiovascular system. Although the daily flow of lymph (normally 1-2 L/day under unstressed conditions) is far lower than that of daily blood flow (which is 7,500 L/day), without the adequate functioning of the lymphatics, virtually all organs and tissues would acutely suffer many different physical and inflammatory stresses ranging from edema to organ system failure. Although blood and lymphatic vessels often form in anatomic parallels to one another, our knowledge of the workings of the lymphatic system, the fine structure of lymphatic networks, how they function in different organs, and how they are regulated physiologically and immunologically are far from parallel; our knowledge of the lymphatic system still remains at only a tiny fraction of what is understood about the cardiovascular system. Although both the cardiovascular and lymphatic systems are important transport systems, what they transport and how they transport and propel these very different cargoes could not be more dissimilar. This book provides an overview of the history of the discovery (and re-discovery) of the components of the lymphatic system, lymphatic anatomy, physiological functions of lymphatics, molecular features of the lymphatic system, and clinical perspectives involving lymphatics which may be of interest to scientists, clinicians, patients, and the lay public. We provide a current understanding of some of the more important structural similarities and differences between lymphatics and the blood vascular system, their coordinated control by angiogenic and hemangiogenic growth factors and other modulators, the fate and lineage determinants which control lymphatic development, and the roles that lymphatics may play in several different diseases.