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

• 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

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