Lymph node
Lymph node | |
---|---|
Details | |
System | Lymphatic system, part of the immune system |
Identifiers | |
Latin | nodus lymphaticus (singular); nodi lymphatici (plural) |
MeSH | D008198 |
TA98 | A13.2.03.001 |
TA2 | 5192 |
FMA | 5034 |
Anatomical terminology |
A lymph node, or lymph gland,
In the lymphatic system, a lymph node is a secondary lymphoid organ. A lymph node is enclosed in a fibrous capsule and is made up of an outer cortex and an inner medulla.
Lymph nodes become
Structure
Lymph nodes are kidney or oval shaped and range in size from 2 mm to 25 mm on their long axis, with an average of 15 mm.[2]
Each lymph node is surrounded by a fibrous capsule, which extends inside a lymph node to form trabeculae.[3] The substance of a lymph node is divided into the outer cortex and the inner medulla.[3] These are rich with cells.[4] The hilum is an indent on the concave surface of the lymph node where lymphatic vessels leave and blood vessels enter and leave.[4]
Lymph enters the convex side of a lymph node through multiple afferent lymphatic vessels and from there flows into a series of sinuses.[3] After entering the lymph node from afferent lymphatic vessels, lymph flows into a space underneath the capsule called the subcapsular sinus, then into cortical sinuses.[3] After passing through the cortex, lymph then collects in medullary sinuses.[3] All of these sinuses drain into the efferent lymph vessels to exit the node at the hilum on the concave side.[3]
Location
Lymph nodes are present throughout the body, are more concentrated near and within the trunk, and are divided into groups.
There are no lymph nodes in the
Size
Generally | 10 mm[8][9] |
Inguinal | 10[10] – 20 mm[11] |
Pelvis | 10 mm for ovoid lymph nodes, 8 mm for rounded[10] |
Neck | |
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Generally (non-retropharyngeal) | 10 mm[10][12] |
Jugulodigastric lymph nodes | 11mm[10] or 15 mm[12] |
Retropharyngeal | 8 mm[12]
|
Mediastinum | |
Mediastinum, generally | 10 mm[10] |
Superior mediastinum and high paratracheal | 7mm[13] |
Low paratracheal and subcarinal | 11 mm[13] |
Upper abdominal | |
Retrocrural space | 6 mm[14] |
Paracardiac | 8 mm[14] |
Gastrohepatic ligament | 8 mm[14] |
Upper paraaortic region | 9 mm[14] |
Portacaval space | 10 mm[14] |
Porta hepatis | 7 mm[14] |
Lower paraaortic region | 11 mm[14] |
Subdivisions
A lymph node is divided into compartments called nodules (or lobules), each consisting of a region of cortex with combined follicle B cells, a paracortex of T cells, and a part of the nodule in the medulla.
The medulla contains large blood vessels, sinuses and medullary cords that contain antibody-secreting plasma cells. There are fewer cells in the medulla.[4]
The medullary cords are cords of lymphatic tissue, and include plasma cells, macrophages, and B cells.
Cells
In the lymphatic system a lymph node is a
There are fewer cells in the medulla than the cortex.[4] The medulla contains plasma cells, as well as macrophages which are present within the medullary sinuses.[17]
As part of the reticular network, there are
Lymph flow
Lymph enters the convex side of a lymph node through multiple afferent lymphatic vessels, which form a network of lymphatic vessels (
These are channels within the node lined by endothelial cells along with fibroblastic reticular cells, allowing for the smooth flow of lymph. The endothelium of the subcapsular sinus is continuous with that of the afferent lymph vessel and also with that of the similar sinuses flanking the trabeculae and within the cortex. These vessels are smaller and do not allow the passage of macrophages so that they remain contained to function within a lymph node. In the course of the lymph, lymphocytes may be activated as part of the adaptive immune response.
There is usually only one efferent vessel though sometimes there may be two.[19] Medullary sinuses contain histiocytes (immobile macrophages) and reticular cells.
A lymph node contains lymphoid tissue, i.e., a meshwork or fibers called reticulum with white blood cells enmeshed in it. The regions where there are few cells within the meshwork are known as lymph sinus. It is lined by reticular cells, fibroblasts and fixed macrophages.[20]
Capsule
Thin reticular fibers (reticulin) of reticular connective tissue form a supporting meshwork inside the node.[4] The lymph node capsule is composed of dense irregular connective tissue with some plain collagenous fibers, and a number of membranous processes or trabeculae extend from its internal surface. The trabeculae pass inward, radiating toward the center of the node, for about one-third or one-fourth of the space between the circumference and the center of the node. In some animals they are sufficiently well-marked to divide the peripheral or cortical portion of the node into a number of compartments (nodules), but in humans this arrangement is not obvious. The larger trabeculae springing from the capsule break up into finer bands, and these interlace to form a mesh-work in the central or medullary portion of the node. These trabecular spaces formed by the interlacing trabeculae contain the proper lymph node substance or lymphoid tissue. The node pulp does not, however, completely fill the spaces, but leaves between its outer margin and the enclosing trabeculae a channel or space of uniform width throughout. This is termed the subcapsular sinus (lymph path or lymph sinus). Running across it are a number of finer trabeculae of reticular fibers, mostly covered by ramifying cells.
Function
In the lymphatic system a lymph node is a secondary lymphoid organ.[4]
The primary function of lymph nodes is the filtering of lymph to identify and fight infection. In order to do this, lymph nodes contain lymphocytes, a type of white blood cell, which includes B cells and T cells. These circulate through the bloodstream and enter and reside in lymph nodes.[21] B cells produce antibodies. Each antibody has a single predetermined target, an antigen, that it can bind to. These circulate throughout the bloodstream and if they find this target, the antibodies bind to it and stimulate an immune response. Each B cell produces different antibodies, and this process is driven in lymph nodes. B cells enter the bloodstream as "naive" cells produced in bone marrow. After entering a lymph node, they then enter a lymphoid follicle, where they multiply and divide, each producing a different antibody. If a cell is stimulated, it will go on to produce more antibodies (a plasma cell) or act as a memory cell to help the body fight future infection.[22] If a cell is not stimulated, it will undergo apoptosis and die.[22]
B cells acquire antigen directly from the afferent lymph. If a B cell binds its cognate antigen it will be activated. Some B cells will immediately develop into antibody secreting plasma cells, and secrete IgM. Other B cells will internalize the antigen and present it to follicular helper T cells on the B and T cell zone interface. If a cognate FTh cell is found it will upregulate CD40L and promote somatic hypermutation and isotype class switching of the B cell, increasing its antigen binding affinity and changing its effector function. Proliferation of cells within a lymph node will make the node expand.
Lymph is present throughout the body, and circulates through
- The B cells migrate to the nodular cortex and medulla.
- The T cells migrate to the deep cortex. This is a region of a lymph node called the paracortex that immediately surrounds the medulla. Because both naive T cells and chemotactic factors, increasing the chance of T cell activation. Both B and T lymphocytes enter lymph nodes from circulating blood through specialized high endothelial venulesfound in the paracortex.
Clinical significance
Swelling
Lymph node enlargement or swelling is known as
Enlarged lymph nodes might be felt as part of a
In addition to a
Cancer
Lymph nodes can be affected by both primary
Local cancer in many parts of the body can cause lymph nodes to enlarge because of tumorous cells that have
Lymphedema
Lymphedema is the condition of swelling (edema) of tissue relating to insufficient clearance by the lymphatic system.[31] It can be congenital as a result usually of undeveloped or absent lymph nodes, and is known as primary lymphedema. Lymphedema most commonly arises in the arms or legs, but can also occur in the chest wall, genitals, neck, and abdomen.[32] Secondary lymphedema usually results from the removal of lymph nodes during breast cancer surgery or from other damaging treatments such as radiation. It can also be caused by some parasitic infections. Affected tissues are at a great risk of infection.[citation needed] Management of lymphedema may include advice to lose weight, exercise, keep the affected limb moist, and compress the affected area.[31] Sometimes surgical management is also considered.[31]
Similar lymphoid organs
The spleen and the tonsils are the larger secondary lymphoid organs that serve somewhat similar functions to lymph nodes, though the spleen filters blood cells rather than lymph. The tonsils are sometimes erroneously referred to as lymph nodes. Although the tonsils and lymph nodes do share certain characteristics, there are also many important differences between them, such as their location, structure and size.[33] Furthermore, the tonsils filter tissue fluid whereas lymph nodes filter lymph.[33]
The appendix contains lymphoid tissue and is therefore believed to play a role not only in the digestive system, but also in the immune system.[34]
See also
References
- ^ "Swollen glands NHS inform". www.nhsinform.scot. Retrieved 4 April 2020.
- ISBN 9780397508075. Retrieved 17 October 2022.
- ^ ISBN 9780702047473.
- ^ )
- ^ Themes, U. F. O. (6 January 2018). "Lymphatic Anatomy and Clinical Implications". Ento Key. Retrieved 21 September 2020.
- ^ Pan, Wei-Ren; Wang, De-Guang (2013). "Historical review of lymphatic studies in the head and neck" (PDF). Journal of Lymphoedema. 8. WoundsGroup. Archived from the original (PDF) on 30 July 2021. Retrieved 21 September 2020.
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- ^ PMID 15347718.
- ^ "Assessment of lymphadenopathy". BMJ Best Practice. Retrieved 4 March 2017. Last updated: Last updated: Feb 16, 2017
- ^ ISBN 9781482216202.
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- ^ a b Davidson's 2018, p. 67.
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- ^ Warwick R, Williams PL (1973) [1858]. "Angiology (Chapter 6)". Gray's anatomy. illustrated by Richard E. M. Moo re (Thirty-fifth ed.). London: Longman. pp. 588–785.
- ^ Hoffbrand's 2016, p. 103,110.
- ^ a b c Hoffbrand's 2016, p. 111.
- ^ Hoffbrand's 2016, p. 109.
- ^ a b c d e f g h i Davidson's 2018, p. 927.
- ^ Hoffbrand's 2016, p. 114.
- ^ Davidson's 2018, p. 1326.
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- ^ Davidson's 2018, p. 913.
- ^ a b c Davidson's 2018, p. 961.
- ^ Davidson's 2018, p. 1324.
- ^ PMID 25241097.
- ^ "Lymphedema". MayoClinic.org. 18 September 2019. Retrieved 17 November 2022.
- ^ a b Lakna (31 January 2019). "What is the Difference Between Tonsils and Lymph Nodes". Pediaa.Com. Retrieved 14 December 2019.
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Bibliography
- Ralston SH, Penman ID, Strachan MW, Hobson RP (2018). Davidson's principles and practice of medicine (23rd ed.). Elsevier. ISBN 978-0-7020-7028-0.
- Hoffbrand V, Moss PA (2016). Hoffbrand's essential haematology (7th ed.). West Sussex: Wiley Blackwell. ISBN 978-1-1184-0867-4.
External links
- Histology image: 07101loa – Histology Learning System at Boston University
- Lymph Nodes
- Lymph Nodes Drainage
- An overview of Normal Lymph Nodes and Swollen lymph nodes and their evaluation