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Lymphatic System and Immunity [11] Pathogens – Organisms that cause harm to the body Virus – particles not considered to be living that attack and multiply within cells Bacteria – prokaryotes that live in tissue fluid in tissues and produce toxins that damage cells Fungi – surface of the body and interstitial fluid Parasites – burrow into organs or live between tissues Parts of the lymphatic system 1. lymph – fluid 2. lymphatic vessels 3. lymphocytes – specialized WBC 4. lymphoid tissues and organs (glands) Lymphocytes (specific defense) respond to Invading pathogens Abnormal cells – cancer cells or cells containing viruses Foreign proteins – toxins Immunity – ability to resist infection and disease through activation of specific defenses Other systems involved with the immune system include: integumentary system, cardiovascular, respiratory system, digestive syst. Functions of the lymphatic system include: 1. Production, maintenance, and distribution of lymphocytes 2. Return of fluid and solutes from the peripheral tissues 3. Distribution of hormones, nutrients, and waste products from tissues of origin to general circulation. Lymphatic vessels begin with capillaries which 1. originate as blind pockets 2. larger that blood capillaries 3. very thin walls 4. have a flattened or irregular outline Larger lymphatic vessels have very thin walls that periodically have valves similar to the veins. The lymphatic vessels merge and empty into the right subclavian vein. Lymphocytes are specialized WBC 1. T (Thymus dependent cells) a. Cytotoxic T cells – direct attack on invaders b.Helper T cells – stimulate activation and function of B cells and T cells c. Suppressor T cells – inhibit activation and function of B cells and T cells 2. B cells become plasma cells which produce and secrete antibodies which react with specific proteins called antigens 3. NK cells – natural killer cells – attack foreign cells, cells infected with viruses and cancer cells Lymphocytes are formed in the bone marrow, but some migrate to the thymus where they mature into T cells. Some examples of lymphoid tissues include: 1. Pharyngeal tonsils 2. Palatine tonsils and 3. Lingual tonsils 4. MALT in the digestive tract (mucosaassociated lymphoid tissue) Lymphoid Organs include 1. Lymph nodes – a. Location- scattered throughout the body, b.Function – filtering lymph for antigens, stimulation of macophages to initiate immune response. 2. Thymus – a. Location – mediastinum just above the heart b.Function secretion of hormones that stimulate stem cell divisions, site for maturation of T-cells 3. Spleen a. Location - Along the curve of the stomach b.Function – Removal of abnormal blood cells Storage of iron from recycled RBC Initiation of B and T cells in response to antigens in blood Other cells that participate in Tissue Defense Table 22-3 (copy from the book) pg.787