Chapter 13: Lymphatic and Immune Systems

CHAPTER 13: LYMPHATIC AND IMMUNE SYSTEMS

LECTURE OUTLINE 13.1 The Lymphatic System The lymphatic system consists of lymphatic vessels and the lymphoid organs. It is closely associated with the cardiovascular system. Lymphatic Vessels Lymphatic vessels form a one-way system that begins with lymphatic capillaries that take up excess tissue fluid. The fluid inside lymphatic vessels is called lymph. Lymphoid Organs The primary lymphoid organs are red bone marrow and the thymus gland. The secondary lymphoid organs are the spleen and lymph nodes. Primary Lymphoid Organs Red bone marrow is the site of stem cells that are ever capable of dividing and producing blood cells. The thymus gland is largest in children and shrinks as we get older. Immature T cells migrate from the bone marrow through the blood stream to the thymus, where they mature. Secondary Lymphoid Organs Lymphocytes migrate to the secondary lymphoid organs. Here they encounter foreign molecules or cells, after which they proliferate and become activated. The spleen filters the blood. Lymph nodes are packed with B and T cells.

13.2 Innate and Acquired Immunity Immunity is the body’s capability of removing or killing foreign substances, pathogens, and cancer cells. Mechanisms of innate immunity are fully functional without previous exposure to these substances, while acquired immunity is enhanced by exposure to specific antigens. An antigen is any molecule that stimulates an immune response. Innate Immunity The four types of innate immunity include physical and chemical barriers, inflammation, phagocytes and natural killer cells, and protective proteins. Physical and Chemical Barriers Skin and mucous membranes lining the respiratory, digestive, and urinary tracts serve as mechanical barriers to entry of pathogens. The secretions of oil glands in the skin contain chemicals that weaken or kill certain bacteria on the skin. The stomach has an acid pH, which kills many types of bacteria or inhibits their growth. Inflammation An inflamed area has four signs: redness, heat, swelling, and pain. Phagocytes and Natural Killer Cells Neutrophils and macrophages migrate to the area of tissue damage where they engulf pathogens. Natural killer cells kill abnormal cells by cell-to-cell contact. Protective Proteins The complement system is composed of a number of blood plasma proteins that form a membrane attack complex to destroy invading bacteria. Interferons are proteins produced by virus-infected cells as a warning to noninfected cells. Acquired Immunity In acquired immunity, the body is able to distinguish “self” from “nonself”. Acquired defenses primarily depend on the action of lymphocytes, which differentiate as either B cells or T cells. B Cells and Antibody-Mediated Immunity When a B cell is activated by binding to a specific antigen, it is activated and makes many copies of itself. Activated B cells become plasma cells that produce antibodies. Structure of an Antibody Antibodies are also called immunoglobulins. They are typically Y-shaped molecules with two binding sites for foreign antigens. Types of Antibodies There are five major classes of antibodies: IgG, IgM, IgA, IgD, and IgE. T Cells and Cell-Mediated Immunity T cells can only recognize an antigen when it is displayed to them by an antigen- presenting cell in conjunction with an MHC (major histocompatibility complex) protein. There are two major types of T cells: helper T cells and cytotoxic T cells. Helper T cells secrete various cytokines while cytotoxic T cells destroy the target cell.

13.3 Active vs. Passive Immunity In active immunity, the individual alone produces an immune response against an antigen; in passive immunity, the individual is given prepared antibodies or cells via an injection. Active Immunity Active immunity usually develops naturally after a person is infected with a pathogen. Immunization involves the use of vaccines to initiate immunity. Passive Immunity Passive immunity occurs when an individual is given prepared antibodies or immune cells to combat a disease. This occurs naturally from mother to fetus. Immune Therapies Cytokines and Immunity Cytokines are chemical messengers produced by T cells, macrophages, and other cells. They regulate white blood cell formation and/or function. They may be used as immunotherapeutic drugs in the future. Monoclonal Antibodies Monoclonal antibodies can be produced in vitro. Currently these are being used for quick and certain diagnosis of various conditions. These may be used to treat cancer. 13.4 Adverse Effects of Immune Responses Allergies Allergies are hypersensitivities to substances, such as pollen, food, or animal hair, that ordinarily would do no harm to the body. An immediate allergic response can occur within seconds of contact with the antigen and may result in anaphylactic shock, a life- threatening problem. A delayed allergic response is initiated by memory T cells. Blood-Type Reactions The ABO blood system is the most important of the blood typing systems. ABO System The presence or absence of type A and type B antigens on red blood cells determine a person’s blood type. Transfusion with the wrong type blood can be fatal. Rh System Another important antigen in matching blood types is the Rh factor. A mismatch can be fatal.

Tissue Rejection The immune system is responsible for rejection of transplanted tissue. Organ rejection can be controlled by administering immunosuppressive drugs.

13.5 Disorders of the Immune System When a person has an autoimmune disease, cytotoxic T cells or antibodies mistakenly attack the body’s own cells. Examples include myasthenia gravis, multiple sclerosis, and systemic lupus erythematosus. In an immune deficiency, the immune system is unable to protect the body against disease. Examples include AIDS and severe combined immunodeficiency disease (SCID).