Lymphatic System

Wayne G Kimpton, University of Melbourne, Melbourne, Australia
Elizabeth A Washington, University of Melbourne, Melbourne, Australia

Published online: September 2009

DOI: 10.1002/9780470015902.a0000523.pub2

The lymphatic system consists of a network of vessels lined with endothelial cells and interconnected lymph nodes which are distributed throughout most of the body. It functions as a tissue drainage system which controls blood volume and extracellular fluid volume and prevents tissue oedema. The lymphatic system collects tissue fluids and cells from most organs and tissues and transports it as lymph via a combination of intrinsic and extrinsic lymphatic pumps, ultimately discharging the lymph into blood. It also has an important biological role in the turnover of macromolecules which make up the extracellular matrix, fat absorption from the gut and immune function. Large numbers of lymphocytes migrate from the bloodstream into tissues and lymph nodes every day and the lymphatic system has the essential role of returning these cells to the blood, integrating the widely dispersed organs and tissues that make up the immune system.

Key Concepts

  • The lymphatic system comprises a network of vessels lined by endothelial cells.
  • Lymphatic vessels drain nearly all tissues and organs in the body and interconnect lymph nodes.
  • Lymphatics are essential for returning proteins, fluids and cells to blood, absorbing fat from the gut and are involved in the homeostasis of interstitial macromolecules.
  • The lymphatic system is a key regulator of extracellular fluid volume and is involved in preventing oedema.
  • The lymphatics play a central role in integrating the immune system.

Keywords: lymph; tissue fluid homeostasis; lymphocytes; tissue oedema; lymph nodes

Figure 1. The lymphatic system drains most tissues and organs in the body, and interconnects the lymph nodes. Reprinted by permission from Macmillan Publishers Ltd. Brown P (2005) Lymphatic system unlocking the drains. Nature 436: 456–458.
Figure 2. Scheme showing the principal pathways of lymph flow in mammals. PLN, peripheral lymph node and MLN, mesenteric lymph node.
Figure 3. Scheme of a peripheral lymph node showing the pathways by which cells enter and leave the node. Afferent lymphatics consist of an initial lymphatic which drains into a collecting lymphatic. These collecting lymphatics are characterized by a smooth muscle wall and bicuspid valves (see enlargement). Afferent lymph delivers approximately 10% of the lymphocytes entering a lymph node with the remaining 90% entering from blood via specialized venules within the node. In most mammals, lymphocytes leave the lymph node via efferent lymphatics.
Figure 4. Scheme showing pathways of lymphocyte recirculation. The journey from blood through lymph nodes and back into lymph takes approximately 1 day. Tissue-specific streams direct gut-homing cells to the intestines and skin-homing cells to skin. Lymphocytes are added to the pool from their sites of production in thymus and bone marrow. PLN (peripheral lymph node) and MLN (mesenteric lymph node).
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 Further Reading
    Alitalo K, Tammela T and Petrova TV (2005) Lymphangiogenesis in development and human disease. Nature 438: 946–953.
    Boulton M, Flessner M, Armstrong D, Hay J and Johnston M (1998) Determination of volumetric cerebrospinal fluid absorption into extracranial lymphatics in sheep. American Journal of Physiology 274: R88–R96.
    Cahill RNP, Poskitt DC, Frost H and Trnka Z (1977) Two distinct pools of recirculating lymphocytes: migratory characteristics of nodal and intestinal T lymphocytes. Journal of Experimental Medicine 145: 420–428.
    book Fraser JRE, Cahill RNP, Kimpton WG and Laurent TC (1996) "Lymphatic system". In: Comper WD (ed.) Tissue Function, Tissue Function, vol. 1. The Netherlands: Harwood Academic Publishers.
    Gashev AA (2008) Lymphatic vessels: pressure- and flow-dependent regulatory reactions. Annals of the New York Academy of Sciences 1131: 100–109.
    Karpanen T and Mäkinen (2006) Regulation of lymphangiogenesis – From cell fate determination to vessel remodelling. Experimental Cell Research 312: 575–583.
    book McDowell J and Windelspecht (2004) The Lymphatic System. Westport, CT: Greenwood Press.
    book Reed RK, McHale NG, Bert JL, Winlove CP and Laine GA (eds) (1995) Interstitium, Connective Tissue and Lymphatics. London: Portland Press.
    Ristevski B, Brecker H, Cybulsky M et al. (2006) Lymph, lymphocytes, and lymphatics. Immunologic Research 35: 55–63.
    book Yoffey JM and Courtice FC (1970) Lymphatics, Lymph and the Lymphomyeloid Complex. London: Academic Press.

Related Sub-Topics:

Tissues of the Immune System
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Article Title: Lymphatic System
 
How to Cite close
Kimpton, Wayne G, and Washington, Elizabeth A(Sep 2009) Lymphatic System. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0000523.pub2]