Talk:Draft 2016

Lymph Nodes

Lymph Node Anatomy

Lymph Node Anatomy
adult thymus - bilobed, superior mediastinum, anterior to heart	infant thymus - large

Thymus Involution
	Overall Size Changes with age birth 10-15 g puberty 30-40 g after puberty - involution replaced by adipose tissue middle-aged 10 g

Lymph Node Functions

Lymph Node Functions
specialised thymus microenvironments allow the production of self-tolerant T-cells (T lymphocytes) from immature precursors. immature precursors enter the thymus differentiate and undergo selection by thymic epithelial cell (TEC) subtypes mature release into circulation of these cells destruction of cells that recognise self antigens T-cells kill infected and oncogenic cells T Cells maturation within the thymus T cell progenitors enter the thymus at the cortex/medulla border via post–capillary venules migrate toward the capsule in response to chemokine signalling. cortex - thymocytes undergo positive selection by cTECs then migrate to the medulla medulla - thymocytes are screened for reactivity to tissue-restricted self antigens expressed by mTECs. Mature T cells exit the thymus via blood or lymphatic vessels in response to a sphingosine-1-phosphate (S1P) gradient.
Macrophages phagocytosis of T cells  ‎‎Thymus 1 Page | Play	EM - T and B lymphocytes (look the same)

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

• Location throughout the entire body - Concentrated in axilla, groin, mesenteries
• Encapsulated organ (1 mm - 2 cm)
• Antigen transformed lymphocytes from the blood
• In lymph vessel pathways “filter”
• Afferent- towards node
• Efferent- away from node

Lymph flow

• enters the node through afferent vessels
• filters through the sinuses
• leaves through efferent vessels

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