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| ==Lymph Nodes==
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| ===Lymph Node Anatomy===
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| {|
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| ! Lymph Node Anatomy
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| |-
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| | [[File:Thymus cartoon.jpg|400px]]
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| | [[File:Gray1178.jpg|400px]]
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| |-
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| | adult thymus - bilobed, superior mediastinum, anterior to heart
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| | infant thymus - large
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| |}
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| {|
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| ! Thymus Involution
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| |-
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| | [[File:Fetal thymus weight growth graph.jpg|400px]]
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| | valign=top|'''Overall Size Changes with age'''
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| * birth 10-15 g
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| * puberty 30-40 g
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| * after puberty - involution
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| ** replaced by adipose tissue
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| * middle-aged 10 g
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| |}
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| ===Lymph Node Functions===
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| {| class="wikitable mw-collapsible mw-collapsed"
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| ! colspan=2|Lymph Node Functions
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| |-
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| | valogn=top|
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| * specialised thymus microenvironments allow the production of self-tolerant T-cells (T lymphocytes) from immature precursors.
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| ** immature precursors enter the thymus
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| ** differentiate and undergo selection by thymic epithelial cell (TEC) subtypes
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| ** mature release into circulation of these cells
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| * destruction of cells that recognise self antigens
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| * T-cells kill infected and oncogenic cells
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| '''T Cells maturation within the thymus'''
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| # '''T cell progenitors''' enter the thymus at the cortex/medulla border via post–capillary venules
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| # '''migrate''' toward the capsule in response to chemokine signalling.
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| # '''cortex''' - thymocytes undergo positive selection by cTECs then migrate to the medulla
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| # '''medulla''' - thymocytes are screened for reactivity to tissue-restricted self antigens expressed by mTECs.
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| # '''Mature T cells''' exit the thymus via blood or lymphatic vessels in response to a sphingosine-1-phosphate (S1P) gradient.
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| | [[File:Thymus structure and function cartoon01.jpg|600px]]
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| |-
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| | [[File:Mouse adult thymus 11.jpg|200px]]
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| Macrophages phagocytosis of T cells
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| {{Thymus Movie 1}}
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| | [[File:T and B lymphocytes EM09.jpg|400px]]
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| EM - T and B lymphocytes (look the same)
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| |}
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| ===Lymph Node Structure===
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| {| class="wikitable mw-collapsible mw-collapsed"
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| ! Lymph Node Structure
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| | '''Structure Overview'''
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| [[File:Thymus histology 06.jpg|400px|right]]
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| * Connective tissue capsule (thin) with numerous trabeculae (septa)
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| ** major blood vessels run in CT
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| * Lobules containing '''cortex''' and '''medulla''' regions
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| ** medullary regions are continuous (connected together)
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| * NOT supplied by afferent lymph vessels
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| '''Blood-Thymic Barrier'''
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| * Blood vessels are separated from thymus cortex by epithelioreticular cells.
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| * impermeable to most macromolecules.
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| * Barrier layers: capillary endothelium - endothelial basal lamina- perivascular CT sheath - basal lamina of epithelioreticular cells - epithelioreticular cell sheath
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| {|
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| |-bgcolor="F5FAFF"
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| ! Thymus Epithelioreticular cells (TEC)
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| ! Macrophages
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| ! Lymphocytes
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| |-
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| * Abundant, eosinophilic, large, ovoid and light nucleus 1-2 nucleoli
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| * sheathe cortical capillaries
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| * form an epitheloid layer
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| * maintain microenvironment for development of T-lymphocytes in cortex (thymic epitheliocytes)
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| * cortex and medulla
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| * difficult to distinguish from reticular cells in {{HE}}
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| * remove auto-reactive T-lymphocytes
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| * located in cortex and medulla
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| * more numerous (denser) in cortex
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| * majority are developing T-lymphocytes (= thymic lymphocytes or thymocytes)
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| |}
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| |}
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| ===Lymph Node Histology===
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| {| class="wikitable mw-collapsible mw-collapsed"
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| ! Lymph Node Histology
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| |-
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| * Capsule (thin) with trabecular or septa (dense connective tissue)
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| [[File:Thymus histology 01.jpg|600px]]
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| [[File:Thymus histology 06.jpg|600px]]
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| Infant thymus
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| {|
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| ! Fetal thymus
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| ! Young medulla
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| ! Young cortex
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| |-
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| | [[File:Fetal thymus.jpg|300px]]
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| | [[File:Thymus - young 01.jpg|300px]]
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| | [[File:Thymus - young 02.jpg|300px]]
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| |}
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| {|
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| ! Adult Thymus
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| |-
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| | [[File:Thymus adult.jpg|300px]]
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| * Cortical lymphoid tissue is replaced by adipose tissue (involution)
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| * Increase in size of thymic corpuscles
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| * '''Thymic corpuscle''' - (Hassall’s corpuscle) mass of concentric epithelioreticular cells.
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| |}
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| {{Thymus Histology}}
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| |}
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| ==Lymph Nodes==
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| [[File:Lymphatic-system-overview.jpg]]
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| * Location throughout the entire body - Concentrated in axilla, groin, mesenteries
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| * Encapsulated organ (1 mm - 2 cm)
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| * Antigen transformed lymphocytes from the blood
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| * In lymph vessel pathways “filter”
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| * Afferent- towards node
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| * Efferent- away from node
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| Lymph flow
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| * enters the node through '''afferent vessels'''
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| * filters through the '''sinuses'''
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| * leaves through '''efferent vessels'''
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| ===Lymph Node Structure===
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| [[File:Lymph_node_cartoon_01.jpg|Lymph_node_cartoon_01.jpg]]
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| Connective Tissue
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| * '''Capsule''' - dense connective tissue (irregular CT, some adipocytes))
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| * '''Trabeculae''' - dense connective tissue
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| * '''Reticular Tissue''' - Reticular cells and fibers, supporting meshwork (collagen type III)
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| ** Reticular cell produces reticular fibers ('''collagen type III''') and surrounds the fibers with its cytoplasm
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| ** reticular fibbers can also be produced by fibroblasts
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| <gallery>
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| File:Lymph node cartoon 03.jpg|Cartoon with histology features
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| File:Lymph node histology 01.jpg|Subcapsular Sinus (marginal sinus, continuation of trabecular sinus)
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| File:Lymph node histology 02.jpg|Follicle
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| File:Lymph node histology 03.jpg|Germinal Centre
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| File:Lymph node histology 04.jpg|Medullary Cords and Sinuses
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| File:Lymph node histology 05.jpg|High Endothelial Venules
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| File:Lymph_node_histology_06.jpg|Macrophages
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| </gallery>
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| {|
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| ===Lymphocyte (T and B) Traffic===
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| # Enter from high endothelial venules (HEVs also called post-capillary venules)
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| # Spend 8 to 24 h in the lymph node interstitium.
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| # Enter a network of medullary sinuses.
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| # Drain from sinuses into efferent lymphatic vessels.
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| '''Important -''' Please note that the lymphocytes exit from the node by efferent lymphatic vessels.
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| [http://www.ncbi.nlm.nih.gov/books/NBK27092/figure/A47 See Figure]
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| See also [[:File:Lymph node cartoon 02.jpg|Image - Cell Trafficking into and out of Lymph Nodes]].
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| | {{Lymph Node Movie 7}}
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| T and B motility
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| {{Lymph Node Movie 8}}
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| T and B interaction
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| |[[File:Lymph node histology 05.jpg|200px]]
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| High Endothelial Venules
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| See also [[:File:Lymph node - high endothelial venule.jpg|Lymphocyte Migration at High Endothelial Venule Model]]
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| |}
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| '''Links:''' [http://www.ncbi.nlm.nih.gov/books/NBK27092/figure/A47 Immunobiology - Figure 1.8. Organization of a lymph node]
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