LYMPHATIC SYSTEM
Marieb - Chapter 20
Lymphatic System
•
•
•
•
•
capillaries
ducts
nodes
lymphoid organs
diffuse cell pockets
Lymphatic capillaries
• extremely permeable
• present throughout body
intermingle with blood
capillaries
– not in CNS or mineralized
tissues
Lymphatic
Ducts
• Trunks
–
–
–
–
–
Lumbar
Bronchomediastinal
Subclavian
Jugular
Intestinal
• Trunks anastomose &
enter veinous return at
junction of subclavian
& jugular veins
Lymph Vessel Structure
• much like veins
• more valves
• more frequent
anastomoses
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.
Lymphoid
organs
Lymph Nodes
• Encapsulated by
dense fibrous
connective tissue
• Trabeculae capsule extends
inward form
compartments
Lymph Nodes
• Clusters at junctions
of vessels into
trunks
Lymph node
structure
• Cortex
Figure 20.4a
– 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
Lymphoid Organs
Spleen
Spleen
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
Thymus
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
Tonsils
Tonsils
• not encapsulated
• blind pouches – crypts
– bacteria can enter
– induced immune response
Peyer’s Patches
Peyer’s Patches