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 Lymphocytes Lymphoid tissue Lymphatic nodule (follicle) with germinal center

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 Medulla Sinuses Circulation in the node: Figure 20.4a 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

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