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Lymphatic system

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"Lymphatic drainage" redirects here. For the massage technique, see Manual lymphatic drainage.
Lymphatic System
Human lymphatic system
Details
Identifiers
Latinsystema lymphoideum
MeSHD008208
TA98A13.0.00.000
TA25149
FMA7162 74594, 7162
Anatomical terminology

</ref> Eventually, the lymph vessels empty into the lymphatic ducts, which drain into one of the two subclavian veins, near their junction with the internal jugular veins.

Structure

Lymphatic system

The lymphatic system consists of lymphatic organs, a conducting network of lymphatic vessels, and the circulating lymph.

The primary or central lymphoid organs generate lymphocytes from immature progenitor cells.

The thymus and the bone marrow constitute the primary lymphoid organs involved in the production and early clonal selection of lymphocyte tissues. Bone marrow is responsible for both the creation of T cells and the production and maturation

Other lymphoid tissue

Regional lymph nodes

Lymphoid tissue associated with the lymphatic system is concerned with immune functions in defending the body against infections and the spread of tumors. It consists of connective tissue formed of reticular fibers, with various types of leukocytes, (white blood cells), mostly lymphocytes enmeshed in it, through which the lymph passes.[1] Regions of the lymphoid tissue that are densely packed with lymphocytes are known as lymphoid follicles. Lymphoid tissue can either be structurally well organized as lymph nodes or may consist of loosely organized lymphoid follicles known as the mucosa-associated lymphoid tissue.

The central nervous system also has lymphatic vessels, as discovered by University of Virginia Researchers. The search for T-cell gateways into and out of the meninges uncovered functional lymphatic vessels lining the dural sinuses, anatomically integrated into the membrane surrounding the brain.[2]

Lymphatics

Main article: Lymphatic vessel
Lymph capillaries in the tissue spaces

The lymphatic vessels, also called lymph vessels, conduct lymph between different parts of the body. They include the tubular vessels of the lymph capillaries, and the larger collecting vessels–the right lymphatic duct and the thoracic duct (the left lymphatic duct). The lymph capillaries are mainly responsible for the absorption of interstitial fluid from the tissues, while lymph vessels propel the absorbed fluid forward into the larger collecting ducts, where it ultimately returns to the bloodstream via one of the subclavian veins. These vessels are also called the lymphatic channels or simply lymphatics.[3]

The lymphatics are responsible for maintaining the balance of the body fluids. Its network of capillaries and collecting lymphatic vessels work to efficiently drain and transport extravasated fluid, along with proteins and antigens, back to the circulatory system. Numerous intraluminal valves in the vessels ensure a unidirectional flow of lymph without reflux.[4] Two valve systems are used to achieve this one directional flow—a primary and a secondary valve system.[5] The capillaries are blind-ended, and the valves at the ends of capillaries use specialised junctions together with anchoring filaments to allow a unidirectional flow to the primary vessels. The collecting lymphatics, however, act to propel the lymph by the combined actions of the intraluminal valves and lymphatic muscle cells.[6]

Development

Lymphatic tissues begin to develop by the end of the fifth week of embryonic development. Lymphatic vessels develop from lymph sacs that arise from developing veins, which are derived from mesoderm.

The first lymph sacs to appear are the paired jugular lymph sacs at the junction of the internal jugular and subclavian veins. From the jugular lymph sacs, lymphatic capillary plexuses spread to the thorax, upper limbs, neck and head. Some of the plexuses enlarge and form lymphatic vessels in their respective regions. Each jugular lymph sac retains at least one connection with its jugular vein, the left one developing into the superior portion of the thoracic duct.

The next lymph sac to appear is the unpaired retroperitoneal lymph sac at the root of the mesentery of the intestine. It develops from the primitive vena cava and mesonephric veins. Capillary plexuses and lymphatic vessels spread from the retroperitoneal lymph sac to the abdominal viscera and diaphragm. The sac establishes connections with the cisterna chyli but loses its connections with neighboring veins.

The last of the lymph sacs, the paired posterior lymph sacs, develop from the iliac veins. The posterior lymph sacs produce capillary plexuses and lymphatic vessels of the abdominal wall, pelvic region, and lower limbs. The posterior lymph sacs join the cisterna chyli and lose their connections with adjacent veins.

With the exception of the anterior part of the sac from which the cisterna chyli develops, all lymph sacs become invaded by mesenchymal cells and are converted into groups of lymph nodes.

The spleen develops from mesenchymal cells between layers of the dorsal mesentery of the stomach. The thymus arises as an outgrowth of the third pharyngeal pouch.

Function

The lymphatic system has multiple interrelated functions:[7]

Function of the fatty acid transport system

Lymph vessels called lacteals are present in the lining of the gastrointestinal tract, predominantly in the small intestine. While most other nutrients absorbed by the small intestine are passed on to the portal venous system to drain via the portal vein into the liver for processing, fats (lipids) are passed on to the lymphatic system to be transported to the blood circulation via the thoracic duct. (There are exceptions, for example medium-chain triglycerides are fatty acid esters of glycerol that passively diffuse from the GI tract to the portal system.) The enriched lymph originating in the lymphatics of the small intestine is called chyle. The nutrients that are released to the circulatory system are processed by the liver, having passed through the systemic circulation.

Immune function

Further information: Immune system

The lymphatic system plays a major role in body's immune system, as the primary site for cells relating to adaptive immune system including T-cells and B-cells. Cells in the lymphatic system react to antigens presented or found by the cells directly or by other dendritic cells. When an antigen is recognized, an immunological cascade begins involving the activation and recruitment of more and more cells, the production of antibodies and cytokines and the recruitment of other immunological cells such as macrophages.

Clinical significance

Main article: Lymphatic disease

The study of lymphatic drainage of various organs is important in the diagnosis, prognosis, and treatment of cancer. The lymphatic system, because of its closeness to many tissues of the body, is responsible for carrying cancerous cells between the various parts of the body in a process called metastasis. The intervening lymph nodes can trap the cancer cells. If they are not successful in destroying the cancer cells the nodes may become sites of secondary tumors.

Lymphadenopathy

Main article: Lymphadenopathy

Lymphadenopathy refers to one or more enlarged lymph nodes. Small groups or individually enlarged lymph nodes are generally reactive in response to infection or inflammation. This is called local lymphadenopathy. When many lymph nodes in different areas of the body are involved, this is called generalised lymphadenopathy. Generalised lymphadenopathy may be caused by infections such as infectious mononucleosis, tuberculosis and HIV, connective tissue diseases such as SLE and rheumatoid arthritis, and cancers, including both cancers of tissue within lymph nodes, discussed below, and metastasis of cancerous cells from other parts of the body, that have arrived via the lymphatic system.[8]

Lymphedema

Main article: Lymphedema

Lymphedema is the swelling caused by the accumulation of lymph, which may occur if the lymphatic system is damaged or has malformations. It usually affects limbs, though the face, neck and abdomen may also be affected. In an extreme state, called elephantiasis, the edema progresses to the extent that the skin becomes thick with an appearance similar to the skin on elephant limbs.[9]

Causes are unknown in most cases, but sometimes there is a previous history of severe infection, usually caused by a parasitic disease, such as lymphatic filariasis.

Lymphangiomatosis is a disease involving multiple cysts or lesions formed from lymphatic vessels.

Lymphedema can also occur after surgical removal of lymph nodes in the armpit (causing the arm to swell due to poor lymphatic drainage) or groin (causing swelling of the leg). Treatment is by massage, and is not permanent.[clarification needed]

Cancer

Reed–Sternberg cells.
Main article: Lymphoma

Cancer of the lymphatic system can be primary or secondary. Lymphoma refers to cancer that arises from lymphatic tissue. Lymphoid leukemias and lymphomas are now considered to be tumors of the same type of cell lineage. They are called "leukemia" when in the blood or marrow and "lymphoma" when in lymphatic tissue. They are grouped together under the name "lymphoid malignancy".[10]

Lymphoma is generally considered as either Hodgkin lymphoma or non-Hodgkin lymphoma. Hodgkin lymphoma is characterised by a particular type of cell, called a Reed–Sternberg cell, visible under microscope. It is associated with past infection with the Epstein-Barr Virus, and generally causes a painless "rubbery" lymphadenopathy. It is staged, using Ann Arbor staging. Chemotherapy generally involves the ABVD and may also involve radiotherapy.[11] Non-Hodgkin lymphoma is a cancer characterised by increased proliferation of B-cells or T-cells, generally occurs in an older age group than Hodgkin lymphoma. It is treated according to whether it is high-grade or low-grade, and carries a poorer prognosis than Hodgkin lymphoma.[11]

Lymphangiosarcoma is a malignant soft tissue tumor, whereas lymphangioma is a benign tumor occurring frequently in association with Turner syndrome. Lymphangioleiomyomatosis is a benign tumor of the smooth muscles of the lymphatics that occurs in the lungs.

Lymphoid leukemia is another form of cancer where the host is devoid of different lymphatic cells.

Other

History

Hippocrates, in 5th century BC, was one of the first people to mention the lymphatic system. In his work On Joints, he briefly mentioned the lymph nodes in one sentence. Rufus of Ephesus, a Roman physician, identified the axillary, inguinal and mesenteric lymph nodes as well as the thymus during the 1st to 2nd century AD.[12] The first mention of lymphatic vessels was in 3rd century BC by Herophilos, a Greek anatomist living in Alexandria, who incorrectly concluded that the "absorptive veins of the lymphatics," by which he meant the lacteals (lymph vessels of the intestines), drained into the hepatic portal veins, and thus into the liver.[12] The findings of Ruphus and Herophilos were further propagated by the Greek physician Galen, who described the lacteals and mesenteric lymph nodes which he observed in his dissection of apes and pigs in the 2nd century AD.[12][13]

In the mid 16th century, Gabriele Falloppio (discoverer of the fallopian tubes), described what are now known as the lacteals as "coursing over the intestines full of yellow matter."[12] In about 1563 Bartolomeo Eustachi, a professor of anatomy, described the thoracic duct in horses as vena alba thoracis.[12] The next breakthrough came when in 1622 a physician, Gaspare Aselli, identified lymphatic vessels of the intestines in dogs and termed them venae alba et lacteae, which is now known as simply the lacteals. The lacteals were termed the fourth kind of vessels (the other three being the artery, vein and nerve, which was then believed to be a type of vessel), and disproved Galen's assertion that chyle was carried by the veins. But, he still believed that the lacteals carried the chyle to the liver (as taught by Galen).[14] He also identified the thoracic duct but failed to notice its connection with the lacteals.[12] This connection was established by Jean Pecquet in 1651, who found a white fluid mixing with blood in a dog's heart. He suspected that fluid to be chyle as its flow increased when abdominal pressure was applied. He traced this fluid to the thoracic duct, which he then followed to a chyle-filled sac he called the chyli receptaculum, which is now known as the cisternae chyli; further investigations led him to find that lacteals' contents enter the venous system via the thoracic duct.[12][14] Thus, it was proven convincingly that the lacteals did not terminate in the liver, thus disproving Galen's second idea: that the chyle flowed to the liver.[14] Johann Veslingius drew the earliest sketches of the lacteals in humans in 1647.[13]

The idea that blood recirculates through the body rather than being produced anew by the liver and the heart was first accepted as a result of works of William Harvey—a work he published in 1628. In 1652, Olaus Rudbeck (1630–1702), a Swede, discovered certain transparent vessels in the liver that contained clear fluid (and not white), and thus named them hepatico-aqueous vessels. He also learned that they emptied into the thoracic duct, and that they had valves.[14] He announced his findings in the court of Queen Christina of Sweden, but did not publish his findings for a year,[15] and in the interim similar findings were published by Thomas Bartholin, who additionally published that such vessels are present everywhere in the body, not just in the liver. He is also the one to have named them "lymphatic vessels."[14] This had resulted in a bitter dispute between one of Bartholin's pupils, Martin Bogdan,[16] and Rudbeck, whom he accused of plagiarism.[15]

Galen's ideas prevailed in medicine until the 17th century. It was believed that blood was produced by the liver from chyle contaminated with ailments by the intestine and stomach, to which various spirits were added by other organs, and that this blood was consumed by all the organs of the body. This theory required that the blood be consumed and produced many times over. Even in the 17th century, his ideas were defended by some physicians.[13]

Alexander Monro, of the University of Edinburgh Medical School, was the first to describe the function of the lymphatic system in detail.[17]

Etymology

Lymph originates in the Classical Latin word lympha "water",[18] which is also the source of the English word limpid. The spelling with y and ph was influenced by folk etymology with Greek νύμϕη (nýmphē) "nymph".[19]

The adjective used for the lymph-transporting system is lymphatic. The adjective used for the tissues where lymphocytes are formed is lymphoid. Lymphatic comes from the Latin word lymphaticus, meaning "connected to water."

See also

References

  1. ^ "lymphoid tissue" at Dorland's Medical Dictionary
  2. ^ Louveau, Antoine; Smirnov, Igor; Keyes, Timothy J; Eccles, Jacob D; Rouhani, Sherin J; Peske, J David; Derecki, Noel C; Castle, David; Mandell, James W; Lee, Kevin S; Harris, Tajie H; Kipnis, Jonathan (2015). "Structural and functional features of central nervous system lymphatic vessels". Nature. 523 (7560): 337–41. doi:10.1038/nature14432. PMC 4506234. PMID 26030524. we discovered functional lymphatic vessels lining the dural sinuses. These structures express all of the molecular hallmarks of lymphatic endothelial cells, are able to carry both fluid and immune cells from the cerebrospinal fluid, and are connected to the deep cervical lymph nodes. The unique location of these vessels may have impeded their discovery to date, thereby contributing to the long-held concept of the absence of lymphatic vasculature in the central nervous system. The discovery of the central nervous system lymphatic system may call for a reassessment of basic assumptions in neuroimmunology and sheds new light on the aetiology of neuroinflammatory and neurodegenerative diseases associated with immune system dysfunction. {{cite journal}}: Unknown parameter |laysummary= ignored (help)
  3. ^ "Definition of lymphatics". Webster's New World Medical Dictionary. medicineNet.com. Retrieved 2008-07-06.
  4. ^ Vittet, D. "Lymphatic collecting vessel maturation and valve morphogenesis". Microvasc Res. 96: 31–7. doi:10.1016/j.mvr.2014.07.001. PMID 25020266.
  5. ^ Heppell C1, Richardson G; Roose, T. "A model for fluid drainage by the lymphatic system". Journal. 75 (1): 49–81. doi:10.1007/s11538-012-9793-2. PMID 23161129.{{cite journal}}: CS1 maint: numeric names: authors list (link)
  6. ^ Bazigou, E; Wilson, J; Moore, JE (2014). "Primary and secondary lymphatic valve development: Molecular, functional and mechanical insights". Microvasc Res. 96: 38–45. doi:10.1016/j.mvr.2014.07.008. PMC 4490164. PMID 25086182.
  7. ^ "The functions of the Lymphatic System". Retrieved Feb 25, 2011.
  8. ^ Britton, the editors Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston ; illustrated by Robert (2010). Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. p. 1001. ISBN 978-0-7020-3085-7. {{cite book}}: |first= has generic name (help)CS1 maint: multiple names: authors list (link)
  9. ^ "Lymphedema".
  10. ^ Anthony S. Fauci; Eugene Braunwald; Dennis Kasper; Stephen Hauser; Dan L. Longo (19 March 2009). Harrison's Manual of Medicine. McGraw Hill Professional. pp. 352–. ISBN 978-0-07-147743-7. Retrieved 12 November 2010.
  11. ^ a b Britton, the editors Nicki R. Colledge, Brian R. Walker, Stuart H. Ralston ; illustrated by Robert (2010). Davidson's principles and practice of medicine (21st ed.). Edinburgh: Churchill Livingstone/Elsevier. pp. 1001, 1037–1040. ISBN 978-0-7020-3085-7. {{cite book}}: |first= has generic name (help)CS1 maint: multiple names: authors list (link)
  12. ^ a b c d e f g Ambrose, C. (2006). "Immunology's first priority dispute—An account of the 17th-century Rudbeck–Bartholin feud". Cellular Immunology. 242 (1): 1–8. doi:10.1016/j.cellimm.2006.09.004. PMID 17083923.
  13. ^ a b c Fanous, Medhat YZ; Anthony J Phillips; John A Windsor (2007). "Mesenteric Lymph: The Bridge to Future Management of Critical Illness". Journal of the Pancreas. 8 (4). Department of Internal Medicine and Gastroenterology ALMA MATER STUDIORUM - UNIVERSITY OF BOLOGNA: 374–399. PMID 17625290. Retrieved 2008-07-11.
  14. ^ a b c d e Flourens, P. (1859). "ASELLI, PECQUET, RUDBECK, BARTHOLIN (Chapter 3)". A History of the Discovery of the Circulation of the Blood. Rickey, Mallory & company. pp. 67–99. Retrieved 2008-07-11.
  15. ^ a b Eriksson, G. (2004). "Olaus Rudbeck as scientist and professor of medicine (Original article in Swedish)". Svensk Medicinhistorisk Tidskrift (in Swedish). 8 (1): 39–44. PMID 16025602.
  16. ^ "Disputatio anatomica, de circulatione sanguinis". Account of Rudbeck's work on lymphatic system and dispute with Bartholin. The International League of Antiquarian Booksellers. Retrieved 2008-07-11. [dead link‍]
  17. ^ Turner, A. Logan (1937). Story of a Great Hospital: The Royal Infirmary of Edinburgh 1729-1929. Oliver and Boyd. p. 360.
  18. ^ lympha. Charlton T. Lewis and Charles Short. A Latin Dictionary on Perseus Project.
  19. ^ "lymph". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
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