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Lymphatic System Chapter 12 Introduction Components Lymph is the fluid Vessels – lymphatics Structures & organs Functions Return tissue fluid to the bloodstream Transport fats from the digestive tract to the bloodstream Surveillance & defense The Lymphatic System Lymphatics Originate as lymph capillaries Capillaries unite to form larger vessels Resemble veins in structure Connect to lymph nodes at various intervals Lymphatics ultimately deliver lymph into 2 main channels Empty into large veins just before they join the superior vena cava Lymph Capillaries Lymphatic Vessels Main Channels of Lymphatics Major Lymphatic Vessels of the Trunk Lymph Tissue 3 types Diffuse lymphatic tissue Lymphatic nodules Some are found singly Some are found in clusters in specific areas Eg. Tonsils; appendix Lymphatic organs Lymph Nodules Lymph Nodes Oval structures located along lymphatics Enclosed by a fibrous capsule Divided into compartments Sinuses Produce lymphocytes Lymph enters nodes through afferent lymphatics, flows through sinuses, exits through efferent lymphatic Lymph Node Tonsils Multiple groups of large lymphatic nodules Location – mucous membrane of the oral and pharyngeal cavities Palatine tonsils Posterior-lateral walls of the oropharynx Pharyngeal tonsil Posterior wall of nasopharynx Lingual tonsils Base of tongue Tonsils Spleen Largest lymphatic organ Located between the stomach & diaphragm Structure is similar to a node Capsule present But no afferent vessels or sinuses Contains Lymphatic tissue Red blood cells Lymphocytes (plasma cells) Other leucocytes Functions Filters blood Stores blood Spleen Thymus Gland Location – behind the sternum The capsule divides it into 2 lobes Development Infant – conspicuous Puberty – maximum size Maturity – decreases in size Function Differentiation and maturation of T cells Thymus Gland Function of the Lymphatic System Defense against harmful organisms and chemicals Nonspecific resistance Inherited Wide variety of body reactions against a wide range of pathogens Specific resistance Resistance to a specific disease-causing microorganism Nonspecific Resistance Skin 1st line of defense Mechanical and chemical factors that fight disease Tears Saliva Flow of urine Gastric juice Nonspecific Resistance (cont’d) Interferon (IFN) Produced by body cells infected with viruses Then released by the infected cells Inhibits viral replication in neighboring cells Decreases disease-producing power of many viruses Phagocytosis Inflammation Fever Specific Resistance = Immunity Involves the production of a specific cell or molecule (antibody) to destroy a specific disease-causing organism or its toxin (antigen). Innate Immunity Inborn immunity Acquired Immunity Immunity acquired during organisms’ lifetime Characteristics of the Immune Response Specificity Involves the production of a specific cell or antibody to destroy a particular antigen Memory Acquired ability to detect and eliminate foreign substances Self vs. non-self recognition MHC Involves antibody-mediated and cell-mediated immunity Lymphocytes Initiate the Immune Response Types of lymphocytes T cells 80% of circulating lymphocytes B cells 10 – 15% of circulating lymphocytes NK cells 5 – 10% of circulating lymphocytes Derivation and Distribution of Lymphocytes Distribution and Life Span of Lymphocytes Ratio of B cells to T cells varies Depends on the tissue or organ considered Lymphocytes continually move throughout the body (wanderers) Lymphocytes have relatively long life spans Lymphocytes and the Immune Response 2 components Cell-mediated immunity Direct attack by T cells Virus & bacterial infected host cells, fungi, parasites, transplanted tissues, tumors, etc. Antibody-mediated immunity Attack by circulating antibodies Released by plasma cells derived from activated B lymphocytes Lymphocytes and the Immune Response What is an antigen? Antigen = “antibody generating” molecule any chemical substance that, when introduced into the body, causes the body to produce specific antibodies that can react with the antigen Properties of antigens: Foreign proteins or polysaccharides Examples: Cell membranes, flagella, viruses, toxins, enzymes, pollen, transplanted tissues & organs, markers on red blood cells Cell-mediated Immunity Characteristics of the Cell Mediated Immune System Upon interaction with specific antigens, specific T cells produce cytokines Proteins that activate both B & T cells Do not secrete antibodies Found in lymphoid tissue (nodes, blood, spleen) Act primarily on intracellular parasites (viruses, some bacteria), fungi & worms, cancer cells & transplanted tissues T Cells and Immunity 1000s of different types of T cells When an antigen enters the body, only the particular T cell programmed to react with the antigen becomes activated Macrophages phagocytize the antigen Macrophages present it to the T cell T cells increase in size, divide, differentiate Cytotoxic T cells Helper T cells Memory T cells Delayed hypersensitivity T cells Suppressor T cells Duality of the Immune System Cytotoxic T Cells (TC) Migrate to the site of invasion Attach to the invading cell Secrete substances that lyse the infected cell. Secrete interferon A TC Cell Lyses an Infected Cell Helper T Cells (TH Cells) Assist in the regulation and coordination of he immune response Steps of regulation 1. Processing Macrophage phagocytizes antigen, presents it on its surface 2. Recognition Appropriate TH cell binds to the macrophage 3. Stimulation Macrophage stimulates TH cell to form a clone of TH cells Cloned cells produce cytokines Stimulate B cells and TC cells 4. Response TC cells kill infected cells, B cells produce antibodies The Role of Helper T Cells as Mediators of Immune Responses Memory T Cells Recognize original invading organism if the pathogen invades later Swifter reaction than during the 1st invasion Pathogen is usually destroyed before any symptoms appear Other T Cells Delayed hypersensitivity T cells (TD) Key factor in allergy responses and transplant tissue rejection Suppressor T cells (TS) Turn off the immune response Additional Cell Components Macrophages Present antigen to TH cells, eliminate viral & bacterial infected cells, attack cancer cells, activated by antigen and cytokines from TH cells Natural Killer Cells Attack and lyse foreign cells, normal cells infected with viruses, and cancer cells Non-specific in action Antibody-Mediated Immunity B Cells 1000s of different kinds of B cells Each type responds to a specific antigen When an antigen enters the blood B cells are activated Become plasma cells Circulate in blood and lymph to reach site of invasion B cells become memory B cells Respond more rapidly and forcefully should a 2nd invasion occur What does an antigen do? Antigen with its antigenic determinant stimulates the formation of specific antibodies The antigenic determinant, a portion of the antigen, reacts with an antibody to form an antigen-antibody complex The formation of the antigen-antibody complex ultimately leads to inactivation and removal of the antigen Antigenic Determinants on an Antigen What is an antibody? Large Proteins Basic subunit has minimum of two binding sites at which it combines with antigens Also known as “immunoglobulins” Antibody Configuration 2 Methods of Antibody Production T cell independent production B cells differentiate without the interaction of TH cells T cell dependent production B cells differentiate with the interaction of TH cells T cell Independent Antigens T cell Dependent Antigens & Antibody Production Outcome of Antibody Production by B cells Disorders of the Immune System Allergy Person is overly reactive to an antigen Autoimmune diseases Body has difficulty in discriminating between its own antigens and foreign antigens Severe Combined Immunodeficiency (SCID) Both T cells and B cells are absent or inactive Acquired Immune Deficiency Syndrome (AIDS) Human immunodeficiency virus (HIV) Primarily attacks helper T cells