LYMPHATIC SYSTEM Marieb Chapter 20 Lymphatic System capillaries

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. 4 a – 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

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