Lymphatics and the Immune System

The Lymphatic System Protects us against disease Lymphatic system cells respond to: Environmental pathogens Toxins Abnormal body cells, such as cancers

Lymphatic System One way system: to the heart Return of collected excess tissue fluid Return of leaked protein “Lymph” is this fluid Edema results if system blocked or surgically removed

Lymphoid Organs Lymph nodes Spleen Thymus Tonsils Small intestine & appendix aggregated lymphoid nodules

Lymph capillaries Picks up bacteria and viruses as well as proteins, electrolytes and fluid (lymph nodes destroy most pathogens)

Specific Defenses Lymphocytes Part of the immune response and Identify, attack, and develop immunity to a specific pathogen

Organization of the Lymphatic System A fluid similar to plasma but does not have plasma proteins Lymphatic vessels (lymphatics) Carry lymph from peripheral tissues to the venous system Lymphoid tissues and lymphoid organs Lymphocytes, phagocytes, and other immune system cells Function of the Lymphatic System To produce, maintain, and distribute lymphocytes Lymphocyte Production Lymphocytes are produced In lymphoid tissues (e.g., tonsils) Lymphoid organs (e.g., spleen, thymus) In red bone marrow Lymphocyte distribution Detects problems Travels into site of injury or infection

Lymphatic collecting vessels Lymph capillaries Absent from bone, bone marrow, teeth, CNS Enter lymphatic collecting vessels Lymphatic collecting vessels Similar to blood vessels (3 layers), but thin & delicate Superficial ones in skin travel with superficial veins Deep ones of trunk and digestive viscera travel with deep arteries Very low pressure Drain into lymph nodes

Up to 1 inch in size Lymph nodes: Act as filter Removes: Purifies lymph before return to venous circulation Removes: Debris Pathogens 99% of antigens Up to 1 inch in size

Lymph Nodes * Superficial groups -Cervical -Axillary -Inguinal Deep groups -Tracheobronchial -Aortic -Iliac Drainage -Superior R 1/4 of body: R lymphatic duct (green) * -The rest: thoracic duct * *

Macrophages on reticular fibers consume pathogens and foreign particles Usually pathogen free lymph enters lymph trunks

Types of Lymphocytes T cells B cells NK cells Thymus-dependent Bone marrow–derived NK cells Natural killer cells

T Cells Make up 80% of circulating lymphocytes Main Types of T Cells Cytotoxic T (TC) cells: Attack cells infected by viruses. Produce cell-mediated immunity Memory T cells: Formed in response to foreign substance. Remain in body to give “immunity” Helper T (TH) cells: Stimulate function of T cells and B cells Suppressor T (TS) cells: Inhibit function of T cells and B cells B Cells Make up 10–15% of circulating lymphocytes Differentiate (change) into plasma cells Plasma cells. Produce and secrete antibodies (immunoglobulin proteins) Natural Killer (NK) Cells, Also called large granular lymphocytes Make up 5–10% of circulating lymphocytes Responsible for immunological surveillance Attack foreign cells, virus-infected cells, and cancer cells

The Immune System Recognizes specific foreign molecules Each exposure (to the same pathogen) increases the effectivity of the response Lymphoid organs Lymph nodes Spleen Thymus Tonsils Small intestine & appendix aggregated lymphoid nodules

Basic Immunology Forms of Immunity Innate Adaptive Active Passive Present at birth Adaptive After birth Active Antibodies develop after exposure to antigen Passive Antibodies are transferred from another source

Immunity Adaptive Immunity Innate Immunity Active Immunity Forms of Immunity Immunity Response to threats on an individualized basis Adaptive Immunity Innate Immunity Adaptive immunity is not present at birth; you acquire immunity to a specific antigen only when you have been exposed to that antigen or receive antibodies from another source. Genetically determinedno prior exposure or antibody production involved Active Immunity Passive Immunity Develops in response to antigen exposure Produced by transfer of antibodies from another source Naturally acquired active immunity Artificially induced active immunity Naturally acquired passive immunity Artificially induced passive immunity Develops after exposure to antigens in environment Develops after administration of an antigen to prevent disease Conferred by transfer of maternal antibodies across placenta or in breast milk Conferred by administration of antibodies to combat infection 17

Immune Disorders Autoimmune disorders: A malfunction of system that recognizes and ignores “normal” antigens, (Rheumatoid arthritis) Immunodeficiency disease: Problems with embryological development of lymphoid tissues Viral infections such as HIV Can result in AIDS Allergies: Inappropriate or excessive immune responses to antigens

Helpful Definitions The immune system Antigen Pathogen Tolerance Cells in our bone marrow, thymus, and the lymphatic system of ducts and nodes, spleen, and blood that function to protect us. Antigen Anything causing an immune response, usually foreign material but may be our own tissues. Pathogen Any disease causing micro-organism. Tolerance Non-reactivity of the immune system, usually refers to "self" but may include foreign tissue in organ transplants. Autoimmunity A failure of tolerance, the immune system reacts to self. Chemokines Molecules released by pathogens and infected tissues to attract cells of the immune system. Cytokines Signaling molecules released by one cell to cause a response in another. Signaling is extremely important in our immune response. Innate immunity Protection that is always present. Includes phagocytic (cells that eat other cells) macrophages and dendritic cells. Adaptive immunity Protection that arises by an immune response, including humoral immunity producing antibodies and cellular immunity.

Components of the immune system Innate immune system Response is non-specific Exposure leads to immediate maximal response Cell-mediated and humoral components No immunological memory Found in nearly all forms of life (plants & animals) Adaptive immune system Pathogen and antigen specific response Lag time between exposure and maximal response Cell-mediated and humoral components Exposure leads to immunologic memory Found only in jawed vertebrates

Innate immunity The dominant system of host defense in most organisms Inflammation is one of the first responses Redness, swelling, heat and pain Chemical and cellular response During the acute phase of inflammation, particularly as a result of bacterial infection, neutrophils migrate toward the site of inflammation in a process called chemotaxis

Innate immunity continued The innate leukocytes include the phagocytes (macrophages, neutrophils, and dendritic cells), mast cells, eosinophils, basophils, and natural killer cells These cells identify and eliminate pathogens, either by attacking larger pathogens through contact or by engulfing and then killing microorganisms Innate cells are also important mediators in the activation of the adaptive immune system

Adaptive immunity The adaptive immune system evolved in early vertebrates and allows for a stronger immune response as well as immunological memory, where each pathogen is "remembered" by its signature antigen Antigen specificity allows for the generation of responses that are tailored to specific pathogens or pathogen-infected cells The ability to mount these tailored responses is maintained in the body by "memory cells“ Should a pathogen infect the body more than once, these specific memory cells are used to quickly eliminate it