The lymphatic system has two major functions: (1) it helps maintain fluid balance in the tissues of the body, and (2) it has a major role in the defense against infection. This chapter describes the general functions of the lymphatic system (objective 1). In the discussion of fluid balance, this chapter describes the major lymphatic pathways, lymph formation, and circulation (objectives 2-4). In discussing the defense function, it explains lymph nodes, their location, and their function (objectives 5 and 6). Specific and nonspecific body defenses, and the functions of the thymus, spleen, lymphocytes, and immunoglobulins (objectives 7-10) are discussed. Various types of immune responses, including primary and secondary responses, active and passive responses, allergic reactions, and tissue rejection reactions (objectives 11-13), are also explained.

The study of the lymphatic system completes your knowledge of how fluid is transported to and from tissues. Knowledge of the immune mechanisms of the lymphatic system is the basis for understanding how the body defends itself against specific kinds of threat.