Anatomy and Function of the Lymphatic System

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Chapter 482 Anatomy and Function of the Lymphatic System

Richard L. Tower, II, Bruce M. Camitta

The lymphatic system participates in many biologic processes, including fluid homeostasis, absorption of dietary fat, and initiation of specific immune responses. This system includes circulating lymphocytes, lymphatic vessels, lymph nodes, spleen, tonsils, adenoids, Peyer patches, and thymus. Lymph is an ultrafiltrate of blood and is collected by lymphatic capillaries that are present in all organs except the brain, bone marrow, retina, cartilage, epidermis, hair, and nails. These capillaries join to form progressively larger vessels that drain regions of the body. During their course, the lymphatic vessels carry lymph to the lymph nodes. In the nodes, lymph is filtered through sinuses, where particulate matter and infectious organisms are phagocytosed, processed, and presented as antigens to surrounding lymphocytes. These actions stimulate antibody production, T-cell responses, and cytokine secretion (Chapter 117). Lymph is ultimately returned to the intravascular circulation.

The composition of lymph can vary with the site of lymph drainage. It is usually clear, but lymph drained from the intestinal tract may be milky (chylous) because of the presence of fats. The protein content is intermediate between that of an exudate and that of a transudate. The protein level may be increased with inflammation and in lymph drained from the liver or intestines. Lymph also contains variable numbers of lymphocytes and antigen-presenting cells.

Embryonic lymphatic development (primary lymphangiogenesis) proceeds from the stage of lymphatic competence, through lymphatic commitment, specification, coalescence, and maturation. Secondary lymphangiogenesis occurs in the settings of wound healing and inflammation. Many genes are now known to be crucial to normal lymphatic development and function, including Prox1, vascular endothelial growth factor-C (VEGF-C), and vascular endothelial growth factor receptor-3 (VEGFR-3).

Alders M, Hogan BM, Gjini E, et al. Mutations in CCBE1 cause generalized lymph vessel dysplasia in humans. Nat Genet. 2009;41:1272-1274.

Alitalo K, Tammela T, Petrova TV. Lymphangiogenesis in development and human disease. Nature. 2005;438:946-953.

Cueni LN, Detmar M. The lymphatic system in health and disease. Lymphat Res Biol. 2008;6:109-122.

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