Lymphatic System and Non-Specific Defense  The Lymphatic System Anatomy of the Lymphatic System Lymphatic Vessels and Flow Lymph Nodes Other Lymphoid Organs

The Lymphatic System  Consists of two semi-independent parts Lymphatic vessels Lymphoid tissues and organs  Lymphatic system functions Transport fluids back to the blood Play essential roles in body defense and resistance to disease

Parts of the Lymphatic System Lymphatic vessel or duct One way system toward the heart No pump One-way valves restrict flow Made of overlapping endothelial cells; very permeable Lymph moves toward the heart through milking action of skeletal muscle and rhythmic contraction of smooth muscle in vessel walls

Lymphatic Vessels  Lymph Capillaries Walls overlap to form flap-like mini-valves Fluid leaks into lymph capillaries Capillaries are anchored to connective tissue by filaments Higher pressure on the inside closes mini-valves

Lymphatic Vessels  Lymphatic collecting vessels Collects lymph from lymph capillaries Carries lymph to and away from lymph nodes Returns fluid to circulatory veins near the heart Thinner walls,more valves Lymphatic ducts Return to venous circulation Right lymphatic duct Thoracic duct

Lymph Fluid  Materials returned to the blood Water Blood cells Proteins  Harmful materials that enter lymph vessels Bacteria Viruses Cancer cells Cell debris

Lymph Nodes: Where Are They? Figure 12.3

Lymph Nodes: Function, Structure, & Flow  Filtering of lymph before it is returned to the blood  Structure Mostly kidney shaped, < 1 inch long Outer Cortex contains follicles – collections of lymphocytes that respond to antigens, intense B cell reproduction centers Inner Medulla contains phagocytic macrophages that engulf and destroy foreign substances  Lymph Flow Lymph enters the convex side through afferent lymphatic vessels Lymph flows through a number of sinuses inside the node Lymph exits through efferent lymphatic vessels Fewer efferent than afferent vessels causes flow to be slowed

Other Lymphoid Organs  Spleen: Filtering and removal of old red blood cells; blood reservoir. Site of lymphocyte proliferation and immune surveillance and response.  Thymus: Hormone production (thymosin) and maturation and "education" of T lymphocytes.  Tonsils: Trap and remove bacteria and particulate matter; tonsilitis is bacterial inflammation (Part of MALT)  Peyer’s patches: Capture and destroy bacteria in intestine, preventing them from breaching the intestinal wall (Part of MALT). Generates “memory” lymphocytes Figure 12.5 * MALT: Mucosa-Associated Lymphatic Tissue

Cells of the Lymph: Lymphocytes  Types of Lymphocytes T cells (cell-mediated and cytotoxic immunity) oManage the immune response oAttack and destroy foreign cells B cells (blood based or humoral immunity) oProduce plasma cells, which secrete antibodies  Functions of Lymphocytes T cells and B cells protect against antigens oAnything the body perceives as foreign  Bacteria and their toxins; viruses  Mismatched RBCs or cancer cells

Other Lymphoid Cells  Macrophages phagocytize foreign substances and help activate T cells  Dendritic cells capture antigens and deliver them to lymph nodes  Reticular cells produce stroma that supports other cells in lymphoid organs