View source for Lymph Nodes - Anatomy & Physiology

{{toplink
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|linkpage =Lymphatic System - Anatomy & Physiology
|linktext =LYMPHATIC SYSTEM
|tablelink = Lymphatic System (Table) - Anatomy & Physiology
|maplink = Lymphatic System (Content Map) - Anatomy & Physiology
|sublink1 =Secondary Lymphoid Tissue - Anatomy & Physiology
|subtext1 =SECONDARY LYMPHOID TISSUE
|sublink2 =Adaptive Immune System - WikiBlood
|subtext2 =ADAPTIVE IMMUNE SYSTEM
|pagetype =Anatomy
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[[Image:Lymph Node positions.jpg|thumb|right|150px|Positions of the lymph nodes (dog) - Copyright B.Catchpole RVC]]
==Introduction==
''For haemolymph nodes click [[Haemolymph Nodes - Anatomy & Physiology|here]]''
[[Image:LH Lymph Node Diagram.jpg|thumb|150px|right|<p>'''Diagram'''</p>]]
<p>Part of the [[Lymphatic System - Anatomy & Physiology|lymphatic system]], the body contains hundreds of lymph nodes of varying size (1-20mm) and these are located along the routes of [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessels]]. They are found throughout the body but are more concentrated in the axilla, groin and mesenteries. Lymph nodes act as a filter for the lymph removing antigens and releasing immune-competent cells and immunoglobulins.</p>
==Development==
<p>Lymph nodes develop from lateral plate mesoderm in paired sacs from [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessels]]. These sacs undergo remodelling, and endothelial and mesenchymal outgrowths form the meshwork of channels and spaces that produces the cortex-medulla structure. Lymphocytes then populate the cortex and medulla. The sub-capular sinus is a remainder of the [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessel]].</p>

==Structure==
[[Image:LH_Lymph_Node_Follicles_Histology.jpg|thumb|150px|right|<p>'''Primary & secondary follicles'''</p><sup>©Nottingham Uni 2008</sup>]]
[[Image:LH_Lymph_Node_Follicle_Histology.jpg|thumb|150px|right|<p>'''Secondary Follicle'''</p><sup>©RVC 2008</sup>]]
===General===
<p>Grossly the lymph nodes are round or bean shaped and have an outer cortex and an inner medulla. Microscopically the nodes have a follicles, paracortical zones and medullary cords and sinuses. At the hilum the medulla is present on the outer part of the node. Lymph nodes are located in series with [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessels]] and afferent vessels enter the node on its convex side and efferent vessels exit on its concave side.</p>
===Capsule and reticular framework===
<p> The nodes are surrounded in a fibrous capsule that extends into the node as trabeculae, which provide an overall framework. Below the capsule is the sub-capsular sinus. The nodes parenchyma contain a fine network of reticular fibres and reticular cells. Reticular cells provide "scaffolding" for other cells as well as expressing surface complexes and substance to attract [[Lymphocytes - WikiBlood#T cells|T cells]], [[Lymphocytes - WikiBlood#B cells|B cells]] and [[T cell differentiation - WikiBlood#Dendritic Cells|dendritic cells]]. 
The cortex has aggregations of [[Lymphocytes - WikiBlood#B cells|B cells]] (in the follicles) in its outer region and a paracortex consisting of a rim of [[Lymphocytes - WikiBlood#T cells|T cells]] surrounding these follicles. [[T cell differentiation - WikiBlood#Dendritic Cells|Dendritic cells]] are also found in close association with the [[Lymphocytes - WikiBlood#T cells|T cells]].  The medulla contains medullary cords of cells ([[Lymphocytes - WikiBlood#B cells|B cells]], plasma cells and some [[Macrophages - WikiBlood|macrophages]]) and between these cords is the medullary sinus lined with endothelial cells and [[Macrophages - WikiBlood|macrophages]].</p>

===Sinuses===
<p>Three sinuses are present:
*Subcapsular/cortical
**Where afferent vessels drain
*Trabecular
**Drain lymph from subcapsular to medullary sinuses
*Medullary
Antigens and transformed cells that pass through the sinuses are filtered by [[Macrophages - WikiBlood|macrophages]] and removed from the lymph.</p>
==Follicles==
<p>Lymph nodes have two types of follicles primary and secondary. Secondary follicles contain germinal centres (sites of B-cell proliferation) and have three layers. 
*The central dark zone contains a high density of dividing centroblasts, [[Lymphocytes - WikiBlood#B cells|B cells]] without surface Ig. These centroblasts migrate to the Basal light zone.
*In the basal light zone the [[Lymphocytes - WikiBlood#B cells|B cells]] express surface Ig and become exposed to the follicular dendritic cells.
**Here there is a high rate of apoptosis but surviving cells migrate to the apical light zone.
*Apical light zone (mantle zone) which contains cells which are destined to become B memory (lymphoblasts) or plasma cells (plasmablasts). </p>
<p>Follicles in the cortex of a stimulated node are larger and have a pale germinal centre. Activated [[Lymphocytes - WikiBlood#B cells|B cells]] differentiate into plasma and memory cells and plasma cells migrate migrate to the medullary cords and produce immunoglobulins.</p>
==High endothelial venules==
<p> High endothelial venules (HEV)are composed of cuboidal/columnar epithelium and are the major route for lymphocytes to enter the node. HEV contain a large number of aquaporin-1 channels allowing for a large uptake of water which in turn drives lymph flow through the cortex, this fluid is returned direct to the bloodstream. The venules are the source of most of the nodes [[Lymphocytes - WikiBlood#T cells|T cells]] and [[Lymphocytes - WikiBlood#B cells|B cells]] and express selectins (receptors for lymphocytes primed with antigens).</p>
<p>HEV express CD34 and GlyCAM-1 which bind to L-selectin on naive lymphocytes. This allows circulating [[Lymphocytes - WikiBlood|lymphocytes]] to recognise when they have reached a [[Secondary Lymphoid Tissue - Anatomy & Physiology|secondary lymphoid organ]] and they leave the bloodstream, entering the lymphatic tissue.</P>

==Function==
See [[Adaptive Immune System - WikiBlood#Antigen Processing and Presentation|here]]

==Pig Lymph Node==
''As well as dolphins, hippopotamuses and rhinoceroses''
<p> The structure of the pig lymph node is inverted compared with that of most mammals.
* Most follicles are found deep in the paracortex
** The paracortex is surrounded by loose medullary tissue
* Afferent lymphatics enter at the hilus
** Connect with para-trabecular sinuses and exit from efferent lymphatics on the node surface.
* [[Blood Vessels - WikiBlood|Blood vessels]] enter and leave at the hilus</p>
==Histology==
<gallery perrow="4" >
Image:LH Lymph Node Gross Histology.jpg|<p>'''Gross view'''</p><sup>©Nottingham Uni 2008</sup>
Image:LH_Lymph_Node_Gross_2_Histology.jpg|<p>'''Gross view'''</p><sup>©RVC 2008</sup>
Image:LH_Lymph_Node_Gross_3_Histology.jpg|<p>'''Gross view'''</p><sup>©RVC 2008</sup>
Image:LH_Lymph_Node_Capsule_Histology.jpg|<p>'''Capsule'''</p><sup>©RVC 2008</sup>
Image:LH_Lymph_Node_Medullary_Histology.jpg|<p>'''Medullary sinus'''</p><sup>©RVC 2008</sup>
Image:LH_Lymph_Node_Trabecular_Histology.jpg|<p>'''Trabecular sinus'''</p><sup>©RVC 2008</sup>
Image:LH_Lymph_Node_Follicular_layers_Histology.jpg|<p>'''Follicular layers'''</p><sup>©RVC 2008</sup>
Image:LH_Lymph_Node_HEV_Histology.jpg|<p>'''High endothelial venule'''</p><sup>©Nottingham Uni 2008</sup></gallery>

==Functions==
<p>The lymph nodes are [[Secondary Lymphoid Tissue - Anatomy & Physiology|secondary lymphoid tissue]], and as the [[Spleen - Anatomy & Physiology|spleen]] removes antigens from the blood, lymph nodes remove antigens from tissue/lymph. Antigen presenting cells ([[Lymphocytes - WikiBlood#B cells|B cells]] and [[Lymphocytes - WikiBlood#T cells|T cells]]) migrate from peripheral tissue via afferent [[Lymphatic Vessels - Anatomy & Physiology|lymphatic vessels]] to the lymph nodes where they present their antigen to lymphocytes. [[Lymphocytes - WikiBlood#B cells|B cells]] and [[Lymphocytes - WikiBlood#T cells|T cells]] enter via the high endothelial venules by diapedesis and [[Lymphocytes - WikiBlood#B cells|B cells]] migrate to the cortex while [[Lymphocytes - WikiBlood#T cells|T cells]] to the deep cortex.</p>
<p>Antibodies and immunologically competent cells leave the lymph nodes via the efferent lymphatics.</p>

==Links==
[[Lymph Nodes - Pathology|Lymph Node Pathology]]