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LYMPHATIC SYSTEM
Marieb - Chapter 20
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Lymphatic System
• capillaries• ducts• nodes• lymphoid organs
• diffuse cell pockets
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Lymphatic capillaries• extremely permeable
• present throughout body intermingle with blood capillaries– not in CNS or mineralized tissues
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Lymphatic Ducts
• Trunks – Lumbar– Bronchomediastinal
– Subclavian– Jugular – Intestinal
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• Trunks anastomose & enter veinous return at junction of subclavian & jugular veins
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Lymph Vessel Structure• much like veins
• more valves• more frequent anastomoses
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ELEPHANTIASIS
• A tropical disease caused by lymphatic obstruction. Victim is bitten by a mosquito infected with a roundworm known as a filarial worm.
• The resulting edema leads to fibrosis and elephant-like thickening of the skin.
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Lymphoid
organs
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Lymph Nodes
• Encapsulated by dense fibrous connective tissue
• Trabeculae - capsule extends inward form compartments
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Lymph Nodes
• Clusters at junctions of vessels into trunks
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• Cortex– dense follicles with germinal centers
• dividing B cells • Deep cortex (T cells)
• Medulla– inward extensions of cortical tissue (B, T and plasma
cells)• Sinuses
– lymph drainage– filtered by macrophages
• Circulation in the node: – afferent lymphatic vessel subcapsular sinus drain
through tissue hilus efferent vessels
Figure 20.4a
Lymph node structure
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Lymphoid Organs
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Spleen
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Spleen
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Thymus
• primary function is in early life– Secretes thymosin and thymopoietin which causes T lymphocytes to become immunocompetent
– Lacks B cells (no follicles)– Atrophies with age: prominent in newborns, stops growth by adolescence, degenerates by old age
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Thymus
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Lymphoid Follicle Aggregates
• MALT (mucosa associated lymphatic tissue) includes: – Peyer’s Patches in intestines– Appendix– Tonsils– Small bronchiolar follicles
• MALT are positioned well to:– Destroy bacteria that breach the mucosal membrane from outside
– Develop “memory” lymphocytes for long term immunity
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Tonsils
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Tonsils
• not encapsulated• blind pouches – crypts
– bacteria can enter – induced immune response
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Peyer’s Patches
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Peyer’s Patches