Of all the body systems, the lymphatic system is perhaps the least familiar–yet, without it, the circulatory system would quickly shut down from hypovolemic shock and the immune system would be seriously compromised. This chapter discusses the role of the lymphatic system in maintaining fluid balance in the body and protecting it against infection and disease.

The lymphatic system is closely allied with the immune system in providing us with a defense against foreign invaders. As the lymphatic system collects tissue fluid, it picks up pathogens that may be present in it. On its way back to the bloodstream, the fluid flows through numerous lymph nodes, where dense populations of lymphocytes and macrophages are strategically positioned to detect such pathogens and mount a quick response. Without this defense, the human body would be an ideal place for microorganisms to live. Our homeostatic mechanisms would ensure a constant warm temperature, ample water, and a continual supply of nutrients. Because the lymphatic system enables the immune system to function efficiently, it is appropriate that we consider these two systems together.

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