1. Divisions of the Lymphatic System System of vessels: draw fluid from extracellular space & return to venous system in the neck Various organs: help provide defense against disease

2. Structural Framework of Lymphatic Organs Mass of lymphocytes in a bed of supporting reticular fibers – Lymphocytes are a sub-category of leukocytes (WBCs) – Reticular fibers form a network structure of collagen

3. Lymph Vessel Structure 2 outer fibrous layers surround an inner epithelium Have valves similar to veins to allow propulsion of lymph via skeletal muscle contraction

4. Lymph Nodes Filtering stations; part of the bodies defense system Afferent vessels carry lymph into lymph nodes and efferent vessels carry lymph away Three palpable nodes: cervical (neck), axillary (armpit) & inguinal (groin)

5. Lymph & Circulatory Connection Cysterna chyli: large lymph sac on vertebral column at first lumbar Thoracic duct: ascends from cysterna chili, passes in front of vertebral column from abdominal cavity to upper thoracic cavity & behind heart to venous junction in the heart

6. Edema

7. Tonsils Believed to play a role in immunological development during pre-teen years Might be involved in fighting off pharyngeal & upper respiratory tract infections

8. Thymus Only known function is production & maturation/training of T-cells or “thymic” lymphocytes involved in cell-mediated immunity Largest and most active during neonatal & pre- adolescent periods; begins to atrophy in early teens 2 distinct lobes, composed of numerous lobules

9. Spleen Found in upper left quadrant of abdominal cavity Filters blood independent of lymph-filtering lymph nodes Also removes old RBCs, stores blood in case of hemorrhage (red pulp region) Stores and produces lymphocytes involved in antibody production & removal of microbes and debris from blood (white pulp region)

10. Immune Cells & Lymph Filtration Macrophages: enlarged WBCs; remove foreign material by phagocytosis T cells: directly attack foreign antigens they were programmed to destroy & secrete chemicals to attract macrophages and other lymphocytes to attack B cells: secrete chemical antibodies to inactivate or destroy foreign antigens