Talk:Draft 2016

Lymph Nodes

Lymph Node Anatomy

Lymph Node Anatomy
Location throughout the entire body - concentrated in axilla, groin, lung, gastrointestinal tract mesenteries Small (1 mm - 2 cm) encapsulated organ (diffuse lymphoid tissue - no capsule) Antigen transformed lymphocytes from the blood In lymph vessel pathways “filter” lymph Afferent - towards node (A - arrives at the node) Efferent - away from node (E - exits the node) Mesenteric lymph nodes

Lymph Node Functions

Lymph Node Functions
In lymph vessel pathways “filter” lymph Immune - detect infections from peripheral tissues skin, respiratory tract, gastrointestinal tract, etc. secondary lymphoid organ return extracellular fluid to circulation

Lymph Node Structure

Lymph Node Structure

Structure Overview Connective tissue capsule (thin) with numerous trabeculae (septa) major blood vessels run in CT Lobules containing cortex and medulla regions medullary regions are continuous (connected together) NOT supplied by afferent lymph vessels Blood-Thymic Barrier Blood vessels are separated from thymus cortex by epithelioreticular cells. impermeable to most macromolecules. Barrier layers: capillary endothelium - endothelial basal lamina- perivascular CT sheath - basal lamina of epithelioreticular cells - epithelioreticular cell sheath Thymus Epithelioreticular cells (TEC) Macrophages Lymphocytes Abundant, eosinophilic, large, ovoid and light nucleus 1-2 nucleoli sheathe cortical capillaries form an epitheloid layer maintain microenvironment for development of T-lymphocytes in cortex (thymic epitheliocytes) cortex and medulla difficult to distinguish from reticular cells in (Stain - Haematoxylin Eosin) remove auto-reactive T-lymphocytes located in cortex and medulla more numerous (denser) in cortex majority are developing T-lymphocytes (= thymic lymphocytes or thymocytes)

Lymph Node Histology

Lymph Node Histology

Capsule (thin) with trabecular or septa (dense connective tissue) Infant thymus Fetal thymus Young medulla Young cortex Adult Thymus Cortical lymphoid tissue is replaced by adipose tissue (involution) Increase in size of thymic corpuscles Thymic corpuscle - (Hassall’s corpuscle) mass of concentric epithelioreticular cells. Thymus Histology: Fetal Thymus overview | Fetal Thymus Medulla | Fetal Thymus Cortex | Adult Thymus | unlabeled fetal overview | unlabeled fetal medulla |unlabeled fetal thymic corpuscle |unlabeled fetal cortex | unlabeled adult overview | Category:Thymus | Immune System Development

Lymph Nodes

Lymph Node Structure

Connective Tissue

• Capsule - dense connective tissue (irregular CT, some adipocytes))
• Trabeculae - dense connective tissue
• Reticular Tissue - Reticular cells and fibers, supporting meshwork (collagen type III)
  • Reticular cell produces reticular fibers (collagen type III) and surrounds the fibers with its cytoplasm
  • reticular fibbers can also be produced by fibroblasts

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  Cartoon with histology features

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  Subcapsular Sinus (marginal sinus, continuation of trabecular sinus)

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  Follicle

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  Germinal Centre

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  Medullary Cords and Sinuses

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  High Endothelial Venules

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  Macrophages

Lymphocyte (T and B) Traffic Enter from high endothelial venules (HEVs also called post-capillary venules) Spend 8 to 24 h in the lymph node interstitium. Enter a network of medullary sinuses. Drain from sinuses into efferent lymphatic vessels. Important - Please note that the lymphocytes exit from the node by efferent lymphatic vessels. See Figure See also Image - Cell Trafficking into and out of Lymph Nodes.

‎‎Lymph Node 7 Page | Play T and B motility

‎‎Lymph Node 8 Page | Play T and B interaction

High Endothelial Venules See also Lymphocyte Migration at High Endothelial Venule Model

Links: Immunobiology - Figure 1.8. Organization of a lymph node