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Transcript
The Immune System (Chapter 15) The Immune System • Immunity is the ability to react to antigens so that the body remains free of disease. – Disease is a state of homeostatic imbalance. • Can be due to infection or failure of the immune system. Primary Lymphatic Organs • Lymphatic organs contain large numbers of lymphocytes (White Blood cells). • Primary organs are:– Red Bone Marrow. • Site of stem cells. – Source of B lymphocytes. – Thymus Gland. Lymphocytes from bone marrow pass through to form T-lymphocytes • Produces thymic hormones (thymosin). • Aids in T lymphocyte maturation. Secondary Lymphatic Organs • Secondary lymphatic organs are places where lymphocytes encounter and bind with antigens. – – – – Spleen. Lymph nodes. Tonsils. Peyer’s patches. Lymphatic Organs Secondary Lymphatic Organs • Spleen – upper left of abdominal cavity behind stomach. Sectioned off by connective tissue- white pulp & red pulp. – White pulp – lymphocytes – Red pulp – filters blood. Blood entering the spleen passes through red pulp before it leaves (network of sinuses) – FRAGILE Secondary Lymphatic Organs • Lymph Nodes – occur along lymphatic vessels. Formed from connective tissue. – Packed full of Blymphocytes – As lymph courses through sinuses it is filtered by macrophages, which engulf pathogens and debris. – Also present- Tlymphocytes – fight infection and attack cancer cells Secondary Lymphatic Organs • Tonsils – patches of lymphatic tissue. • Perform the same function as lymph nodes – First line of defense • Peyer’s Patches – on the intestinal wall and appendix. Attack pathogens that ender the body by way of the intestinal tract. Nonspecific Defenses • Barriers to Entry. – Mucous membranes • Line respiratory, digestive, and urinary tract. – Oil gland secretions. • Chemicals that kill or weaken bacteria on skin – Ciliated cells. • Sweep mucus & particles into throat – Bacteria • Both in stomach and vagina, prevent pathogens from gaining a foot-hold. – Acid Innate Immunity • One important function of the immune system is to promote growth and repair after injury – Either via physical damage or microorganisms • The mobilization of innate immune cells to get rid of damaged cells or microorganisms is called inflammation • Small molecules called cytokines are also involved Innate Immunity • Inflammatory Reaction. – Tissue damage causes – tissue cells and mast cells to release chemical mediators. Innate Immunity • Inflammatory Reaction. • Histamine and kinins. – Capillaries dilate and become more permeable. » Skin reddens and becomes warm. – Proteins and fluids escape from tissue. Swelling occurs Innate Immunity • Inflammatory Reaction. – Proteins and fluids escape from tissue and cause swelling. » Swelling stimulates free nerve endings, causing the sensation of pain. Innate Immunity – Neutrophils and Monocytes migrate to site of injury. – Amoeboid – can change shape – squeeze through capillary walls and enter tissue fluid. – Neutrophils engulf pathogens –destroyed by hydrolytic enzymes when fused to a lysosome Innate Immunity • Macrophages: Monocytes change into these as they leave the blood and enter the tissues. – These are phagocytic cells – Can eat many (100’s) of pathogens and survive. – Eat old blood cells and bits of dead tissue – Stimulate the immune response. • Increase production of white blood cells in bone marrow Innate Immunity • Macrophages: Monocytes change into these as they leave the blood and enter the tissues. • Macrophages enter lymph vessels carring bacteria fragments to lymph nodes • This starts a specific immune response Protective protein system • Known as Complement proteins • Are activated when pathogens enter the body. • Complement certain immune responses. Protective protein system • Attract phagocytes. • Form holes in bacteria. • Interferon binds to receptors of non-infected cells causing them to prepare for possible attack Specific immunity • Antigen--shape on cell, allows recognition of self and detection of foreign cells. • Antibody--protein that recognizes and binds antigens. • Specific defenses respond to antigens. – Lymphocytes recognize an antigen due to antigen receptors whose shape allows them to combine with a specific antigen. • Immunity is primarily the result of the action of B lymphocytes and T lymphocytes. White blood cells • Granular Leukocytes – Neutrophils: Most abundant. Have multilobed nucleus. • They are the first to respond to infection, and engulf pathogens during phagocytosis. – Eosinophils: Have bilobed nucleus • Known to increase in number in the event of parasitic worm infection and during allergic reaction. – Basophils: U-shaped or lobed nucleus. • In connective tissues release histamines along with Mast Cells White Blood Cells • Agranular Leukocyles – Monocyles: Largest of the white blood cells. • Differentiate into even larger Macrophages • Phagocytize pathogens, old cells and debris • Stimulate production of other white blood cells – Lymphocytes: Two types: • T-lymphocytes – Destroy any cell with foreign antigens • B-lymphocytes – Produce antibodies that combine with antigens –Target pathogens for destruction Natural Killer Cells • Natural killer cells kill virus-infected cells and tumor cells by cell-to-cell contact. – Large, granular lymphocytes. T Cells • Provide cell-mediated immunity. • Produced in bone marrow, mature in thymus. • Antigen must be presented in groove of HLA molecule. • Cytotoxic T cells destroy non-self protein-bearing cells. • Helper T cells secrete cytokines that control the immune response. B Cells • Provide antibody-mediated immunity against bacteria. • Produced and mature in bone marrow. • Reside in spleen and lymph nodes. – Circulate in blood and lymph. • Directly recognize antigen and then undergo clonal selection. • Clonal expansion produces antibody-secreting plasma cells and memory B cells. Clonal selection Theory • The antigen selects which lymphocyte will undergo clonal expansion and produce more lymphocytes with the same type of antigen receptor. – Some become memory cells – long term immunity to the same infection. – B-cells become plasma cells – fight infection – Apoptosis – when danger of infection is over, all plasma cells undergo programmed cell death Specific Defenses – Antibodies are proteins shaped like an antigen receptor and capable of combining with, and neutralizing, a specific antigen. • Classes. – – – – – Antibodies IgG - Enhances phagocytosis. IgM - Activates complement proteins. IgA - Prevents attachment of pathogens. IgD - Antigen receptors on virgin B cells. IgE - Immediate allergic response. Induced Immunity • Active Immunity. – Immunization involves use of vaccines. – Contain an antigen to which the immune system responds. – Primary response. Secondary (booster) response. – Dependent upon the presence of memory B and T cells capable of responding to lower antigen doses. Induced Immunity • Passive immunity • occurs when an individual is given prepared antibodies. – Temporary. • No memory cells. • Primary and secondary injections Issue - Allergies • Occurs when your immune system reacts atypically to some antigens to which the host does not need protection. • Pollen, dust mites, cats, a hard days work! – Called Allergens • The atypical response produces a special antibody – IgE • A form of innate immunity Allergi esto mast cells. • IgE binds • When a person later encounters the same allergen, the allergen binds to the IgE on the mast cell • This triggers the explosive release of histamine • Capillaries dilate and become more permeable. • Skin reddens and becomes warm. Proteins and fluids escape from tissue. Swelling occurs – Allergi es • The large amounts of histamines released in an allergic reaction cause strong symptoms • Runny eyes, sneezing, or shortness of breath • Depends upon the tissue in which the mast cells were triggered Allergies • As allergy symptoms are caused by histamines, taking antihistamines stops the build up of histamines in the cells of blood vessels. • However, antihistamines do not stop the immune response or the release of histamines in mast cells • Other allergies are mediated by T-cells – Latex, poison ivy, dyes or chemicals in cosmetics or clothing – Antihistamines do not help in these allergic reactions Allergies • As each allergy is an antigen-specific immune response it shows memory and a greater response on the next exposure – This is why allergies get worse over time • Thousands of different substances can produce allergies in people – each triggered by a specific antigen-specific response – Why people are usually bothered by only a few • Appears to be inherited – Remember human genetics and meiosis!!!! The End. Any Questions?