The Lymphatic System

The lymphatic system is important for immunity and augments the circulatory system by returning a portion of the interstitial fluid to the blood. The lymphatic system consists of a series of vessels and lymph nodes, as well as discrete organs and diffuse patches of immune tissue scattered throughout the body.

The lymphatic vessels penetrate virtually all of the tissues of the body and absorb interstitial fluid. That fluid is moved through the lymphatic vessels by the pressure exerted on the vessels from surrounding tissues. For example, when muscles contract they squeeze intramuscular as well as surrounding lymphatics, and push the fluid forward. Valves in the lymphatic vessels prevent the fluid from flowing backwards. As the fluid within the lymphatic vessels flows forwards, it passes through lymph nodes which filter the fluid. Lymphatic vessels which carry fluid into the lymph nodes are called afferent lymphatic vessels. Lymphatic vessels which carry the filtered fluid out of the lymph nodes are called efferent lymphatic vessels. The lymph nodes contain macrophages, large cells which engulf particles of foreign matter and bacteria. There are also lymphocytes which respond to the presence of foreign antigens, especially proteins.

There are two basic classes of lymphocytes: B lymphocytes and T lymphocytes. Both originate in the bone marrow, but migrate to other tissues to mature and become active in immunity. Some B lymphocytes respond to foreign antigens by forming plasma cells. Plasma cells produce antibodies (immunoglobulins) which move through the lymphatic vessels into the blood to attack antigens. Some T lymphocytes respond to infection by reproducing and forming cytotoxic T cells ("killer cells") which move into the blood to fight infection. When challenged by an antigen (as during an infection) some B and T lymphocytes do not immediately produce antibodies or become phagocytic. These lymphocytes become memory cells which remain within the lymphatic tissue but are prepared to produce an enhanced immune response if there is a subsequent exposure to the same antigen.

The lymphatic fluid may pass through many series of vessels and nodes. Finally, the fluid is slowly moved through larger and larger lymphatic vessels, and enters the thoracic duct, a large vessel which runs from the abdominal cavity up to the heart. The abdominal lymphatic vessels also absorb lipids from the digestive system. Hence, the fluid in the thoracic duct has a milky appearance and is called chyle. From the thoracic duct, the chyle is emptied into the superior vena cava. In this way, the fluid which has been lost from the blood as it went through the small capillaries of the body is returned to the blood before it re-enters the heart.

Lymph nodes and lymphatic vessels are not distributed evenly throughout the body. The greatest concentrations are located around the neck, and where the limbs join the trunk. For example the occipital lymph nodes and superficial cervical lymph nodes filter fluid draining from the head and neck. The subclavicular lymph nodes drain fluid from the arms and the breasts. The nodes of the subclavicular chain may become infiltrated with cancerous cells when there is cancer of the breast. The inguinal lymph nodes filter fluid from the legs and external genitals. In some respects the spleen is like a large lymph node. It filters blood and is a storehouse both for lymphocytes and erythrocytes. During emergencies, the spleen can contract and force stored cells into the blood to raise the blood pressure and increase oxygen transportation.

The thymus is also a component of the lymphatic system. The thymus stores maturing T lymphocytes and so is vital to immune processes. Failure of the thymus to develop properly, as in DiGeorge's Syndrome, severely impairs immunity.

Apart from the lymph nodes, spleen and thymus, there are diffuse patches of lymphatic tissue scattered throughout the body, especially in the digestive system. The palatine tonsils, pharyngeal tonsils and sublingual tonsils contain many lymphocytes and probably help to combat infectious pathogens which are taken in with our food. Along the length of the alimentary canal, there are concentrations of lymphatic tissue, called Peyer's patches, which probably have the same function. The importance of the lymphatic system can be appreciated from the high rates of mortality among people with congenital deficiencies and Acquired Immune Deficiency Syndrome (AIDS).

 

English - French Lexicon

afferent lymphatic vessel: vaisseau lymphatique afferent;antibody: anticorps;antigen: antigène  ;B lymphocyte: lymphocyte b;bone marrow: moelle osseuse;cytotoxic T cell (killer cell): lymphocyte T cytotoxique (cellule tueuse);efferent lymphatic vessel: vaisseau lymphatique efférent;immunity: immunité;immunoglobulin: immunoglobuline;lymph node: ganglion lymphatique;lymphatic vessel (lymphatic duct): vaisseau lymphatique;lymphocyte: lymphocyte;macrophage: macrophage;memory cell: cellule-mémoire; Peyer's patch: plaque de Peyer;plasma cell: plasmocyte;spleen: rate;T lymphocyte: lymphocyte t;tonsil: amygdale;thoracic duct: canal thoracique;thymus: thymus


English - Japanese Lexicon

afferent lymphatic vessel: 輸入リンパ管 (yunyuulinpakan); antibody: 抗体 (koutai); antigen:抗原 (kougen); B lymphocyte: Bリンパ球 (B linpakyuu); bone marrow: 骨髄 (kotsuzui); chyle: 乳び (nyuubi); cytotoxic T cell (killer cell): 細胞傷害性 T 細胞 (saiboushougaisei T saibou); efferent lymphatic vessel: 輸出リンパ管 (yushutsulinpakan); immunity: 免疫性 (menekisei); immunoglobulin: 免疫グロブリン (menekiguroburin); superficial inguinal lymph nodes: 浅鼠径リンパ節 (sensokeilinpasetsu); interstitial fluid: 組織間液 (soshikikaneki); lymph node: リンパ節 (linpasetsu); lymphatic vessel (lymphatic duct): リンパ管 (linpakan); lymphocyte: リンパ球 (linpakyuu); macrophage: 大食細胞 (daishokusaibou); memory cell: 記憶細胞 (kiokusaibou); occipital lymph nodes: 後頭リンパ節 (koutoulinpasetsu); palatine tonsil: 口蓋ヘン桃 (kougaihentou); Peyer's patches: パイエル板 (paieruban); pharyngeal tonsils: 咽頭ヘン桃; plasma cell: 形質細胞 (keishitsusaibou); superficial cervical lymph nodes: 浅頚リンパ節 (senkeilinpasetsu); spleen: 脾臓 (hizou); sublingual tonsil: 舌ヘン桃 (zetsuhentou); subclavicular lymph nodes: 鎖骨下リンパ節 (sakotsukalinpasetsu); T lymphocyte: Tリンパ球 (T linpakyuu); thoracic duct: 胸管 (kyoukan); thymus: 胸腺 (kyousen)

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