Changes

<p>Grossly the lymph nodes are round or bean shaped and have an outer cortex and an inner medulla. Microscopically the nodes have 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]]. Afferent vessels enter the node on its convex side and efferent vessels exit on its concave side.</p>

<p>Grossly the lymph nodes are round or bean shaped and have an outer cortex and an inner medulla. Microscopically the nodes have 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]]. Afferent vessels enter the node on its convex side and efferent vessels exit on its concave side.</p>

===Capsule and reticular framework===

===Capsule and reticular framework===

<p> The nodes are surrounded by a fibrous capsule that extends into the node as trabeculae, which provide an overall framework. Below the capsule is the subcapsular 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]].  

<p> The nodes are surrounded by a fibrous capsule that extends into the node as trabeculae, which provide an overall framework. Below the capsule is the subcapsular 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#T cells|T cells]], [[Lymphocytes#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>

The cortex has aggregations of [[Lymphocytes#B cells|B cells]] (in the follicles) in its outer region and a paracortex consisting of a rim of [[Lymphocytes#T cells|T cells]] surrounding these follicles. [[T cell differentiation - WikiBlood#Dendritic Cells|Dendritic cells]] are also found in close association with the [[Lymphocytes#T cells|T cells]].  The medulla contains medullary cords of cells ([[Lymphocytes#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===

===Sinuses===

==Follicles==

==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.  

<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.

*The central dark zone contains a high density of dividing centroblasts, [[Lymphocytes#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.

*In the basal light zone the [[Lymphocytes#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.

**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>

*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. Plasma cells migrate to the medullary cords and produce immunoglobulins.</p>

<p>Follicles in the cortex of a stimulated node are larger and have a pale germinal centre. Activated [[Lymphocytes#B cells|B cells]] differentiate into plasma and memory cells. Plasma cells migrate to the medullary cords and produce immunoglobulins.</p>

==High endothelial venules==

==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 then returned direct to the bloodstream. The venules are the source of most of the node's [[Lymphocytes - WikiBlood#T cells|T cells]] and [[Lymphocytes - WikiBlood#B cells|B cells]] and express selectins (receptors for lymphocytes primed with antigens).</p>

<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 then returned direct to the bloodstream. The venules are the source of most of the node's [[Lymphocytes#T cells|T cells]] and [[Lymphocytes#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>

<p>HEV express CD34 and GlyCAM-1 which bind to L-selectin on naive lymphocytes. This allows circulating [[Lymphocytes|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==

==Function==

==Functions==

==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>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#B cells|B cells]] and [[Lymphocytes#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#B cells|B cells]] and [[Lymphocytes#T cells|T cells]] enter via the high endothelial venules by diapedesis and [[Lymphocytes#B cells|B cells]] migrate to the cortex while [[Lymphocytes#T cells|T cells]] to the deep cortex.</p>

<p>Antibodies and immunologically competent cells leave the lymph nodes via the efferent lymphatics.</p>

<p>Antibodies and immunologically competent cells leave the lymph nodes via the efferent lymphatics.</p>

==Links==

==Links==

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

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