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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. Structural Framework of Lymphatic Organs. Mass of lymphocytes in a bed of supporting reticular fibers
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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
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
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
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)
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
Tonsils • Believed to play a role in immunological development during pre-teen years • Might be involved in fighting off pharyngeal & upper respiratory tract infections
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
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)
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