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

Lymphatic Characteristics Lymph – excess tissue fluid carried by lymphatic vessels Pale white fluid, similar composition to blood plasma, but with more leukocytes, lymphocytes, and triglycerides

Lymphatic Vessels Lymphatic vessels Carry lymph towards the heart, never away No pump, moved by “milking” action of muscles

Lymphatic Vessels Lymphatic vessels Fluid leaks into lymphatic capillaries from body tissue Lymphatic collecting vessels collect it from lymph capillaries Carries lymph to and away from lymph nodes Figure 12.1

Lymphatic Vessels Figure 12.2

Lymphatic Vessels Lymphatic collecting vessels (continued) Returns fluid to circulatory veins near the heart Figure 12.1

Lymph As lymph seeps into lymph capillaries, harmful materials are carried with it: Bacteria Viruses Cancer cells Cell debris

Lymph Nodes Lymph nodes filter lymph before it is returned to the blood

Lymph Nodes Leukocyte defense cells within lymph nodes: Macrophages – engulf and destroy foreign substances Lymphocytes – provide immune response to antigens

Other Lymphoid Organs Several other organs contribute to lymphatic function Spleen Thymus Tonsils Peyer’s patches Figure 12.5

The Spleen Spleen: Filters out and destroys worn out blood cells Acts as a blood reservoir Synthesizes antibodies, filters antibody-coated cells from blood

The Thymus Thymus: Produces hormones (like thymosin) to program (“educate”) certain lymphocytes

Tonsils Tonsils: Small masses of lymphoid tissue around the pharynx Trap and remove bacteria and other foreign materials

Peyer’s Patches Peyer’s Patches: Found in the wall of the small intestine Capture and destroy bacteria in the intestine

Body Defenses The body is constantly in contact with bacteria, fungi, and viruses The body has two defense systems for foreign materials: nonspecific and specific

Body Defenses Nonspecific defense system Mechanisms protect against a variety of invaders Responds immediately to protect body from foreign materials Specific defense system Specific defense is required for each type of invader Also known as the immune system

Body Defenses Figure 12.6

Nonspecific Body Defenses First Line of Defense: Body surface coverings and their secretions Intact skin - physical barrier, acidic pH Mucous membranes - mucus, protein-digesting enzymes, HCl (in stomach)

Nonspecific Body Defenses Second Line of Defense: Non-specific defense cells Phagocytes (like macrophages) - engulf & digest foreign matter Natural killer (NK) cells - lyse & destroy cancerous or virus-infected cells Antimicrobial chemicals The inflammatory response Fever

Antimicrobial Chemicals Two kinds: Complement, Interferon Complement Plasma proteins Lyse microorganism, enhance phagocytosis Figure 12.10

Antimicrobial Chemicals Interferon Secreted proteins of virus-infected cells Bind to healthy cell surfaces to inhibit viruses binding

Inflammatory Response Inflammation: an increase in blood flow, tissue fluid, and clotting proteins in a specific area Prevents spread of foreign agents to neighboring tissues, disposes of pathogens & debris, promotes tissue repair, releases chemicals that attract immune cells Triggered when body tissues are injured Signs: redness, heat, swelling, pain

Steps in the Inflammatory Response Figure 12.8

Fever Abnormally high body temperature Hinders pathogens with temperature preferences Increases mobility of leukocytes, rate of phagocytosis, production rate of certain lymphocytes