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THE LYMPHATIC SYSTEM The Lymphatic System Two Semi-Independent Parts Lymphatics (vessels) 1. Collects leaked plasma & proteins from bloodstream (lymph) One way flow toward heart Minivalves Lymphoid tissues & organs 2. Immune functions Lymph Nodes Contain macrophages to digest bacteria Contain lymphocytes B cells that generate plasma cells (antibodyreleasing cells) T cells that destroy tumor cells More afferent than efferent vessels Lymphoid Organs Spleen – filters worn erythrocytes, bacteria, viruses, & other debris Thymus – Releases hormone thymosin during childhood to help T lymphocytes mature Tonsils – Trap foreign pathogens entering throat Peyer’s patches – capture & destroy bacteria in the small intestine The Immune System Two Types of Resistance: Nonspecific Resistance 1. General protection against many pathogens Immediate Present since birth (inherited) Specific Resistance 2. Develops in response to contact with specific invaders First Line of Defense: Barriers Physical Barriers: Skin Hairs Mucous Membranes Digestive Respiratory Urinary Reproductive Cilia First Line of Defense: Barriers Chemical Barriers Acid secretions – skin, vagina, stomach; kill bacteria Sebum – oil of skin; toxic to bacteria Lysozyme – enzymes in tears, saliva, and urine that destroys bacteria Second Line of Defense: Cells Nonspecific; Attack pathogens but don’t “remember” for next time. Phagocytes – perform phagocytosis Neutrophils – first to enter infected tissues; kill bacteria Macrophages – slower; BIG eaters Second Line of Defense: Cells Natural Killer Cells (Killer T cells) – Kills cancer cells Kills virus-infected body cells Lyses cell with perforin Second Line of Defense: Inflammatory Response Triggered when tissues are injured Four Signs: Redness Heat Swelling Pain Second Line of Defense: Inflammatory Response First Step: Alarm Injured cells release histamine & kinins causing: – increases blood flow Leaky capillaries – causes edema Activated pain receptors – forces rest Chemotaxis – chemical gradient attracts phagocytes and other white blood cells Vasodilation Second Line of Defense: Inflammatory Response One hour later: Neutrophils perform diapedesis and start clean-up 8-12 hours later: Monocytes become macrophages! Second Line of Defense: Inflammatory Response Prevents the spread of infection Disposes of cell debris & pathogens Sets the stage for repair and healing Second Line of Defense: Antimicrobial Chemicals Interferon – protein released by virus-infected cells to prevent neighboring cells from reproducing new viruses Urine Second Line of Defense: Antimicrobial Chemicals Complement System At least twenty proteins always circulating Activated by foreign antigens Release chemicals: Vasodilators Chemotaxis – cause foreign cell membranes to become sticky (and yummy) Opsonization Second Line of Defense: Fever White blood cells secrete pyrogens Triggers hypothalamus to raise body temperature Inhibits bacterial growth Stimulates phagocytosis Causes liver & spleen to store iron, reducing availability for bacteria Third Line of Defense: The Immune System Two parts (working simultaneously): Immunity – (antibody-mediated), antibodies present in the body fluids Cellular Immunity – (cell-mediated), lymphocytes defend the body Humoral Specific Systemic Has memory Overview: Antigens Nonself antigens Self antigens – MHC (major histocompatibility) complex Overview: Antibodies AKA immunoglobulins (Igs) Bind to specific antigen Inactivates by: Activating complement proteins = cell lysis Binds to toxic secretions, rendering them harmless Agglutination Causes precipitation of soluble antigens Effects of Antibodies Cell Overview: Lymphocytes Formed from hemocytoblasts in bone marrow Mature by gaining immunocompetence (ability to respond to specific antigen) In Bone marrow = B cells In Thymus = T cells Cell Overview: Macrophages Antigen Presentation – present fragments of the antigens they’ve eaten on cell surface, for T cells to recognize Secrete monokines, that further activate T cells Primary Humoral Response Antigen binds to immature B lymphocyte causing clonal selection Helper T cells activate B cells B cell makes clones! Plasma Make cells (most) antibodies Memory cells (few) Remember invader for faster response in future Clonal Selection/T cell activation B cell cloning/Antibody Production Secondary Humoral Response Achieved by memory B Cells in response to the old antigen Faster More prolonged More effective Active Immunity Active immunity – activation of B Cells – bacterial or viral infection Artificially – vaccine Naturally Spared threat of the disease Still primes immune system for secondary response Passive Immunity Passive immunity – antibodies are transferred into the body\ – from mother to baby through placenta or breastmilk Artificially – antivenin (snake bites), antitoxin (botulism, rabies, tetanus) Naturally B cells are not challenged by antigen Immunological memory does not occur Cellular Immune Response: Helper T cells Recruit other immune cells to join fight Cannot recognize free-floating antigen Macrophages present antigens: double recognition (self & non-self) Cellular Immune Response: Helper T cells Activation of Helper T cells: Stimulates B cells & Killer T cells to grow/divide Attracts other white blood cells to area Enhances macrophage ability to eat & destroy Releases lymphokines – chemicals that help destroy antigens Cellular Immune Response: Other T cells Suppressor T Cells – slows or stops the activity of B and T cells once the infection has been conquered Memory T Cells – same as memory B cells Killer T Cells (cytotoxic T cells)