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Transcript
Immune System Continue reading Chapter 13 and Supp 14 Learning objectives • What is a pathogen? What kinds of life forms can be pathogens? • What is meant by “3 lines of defense” against pathogens? • Explain how the first line of defense prevents entry of pathogens. How does each work? • Explain how the 2nd line is a general system that is always ready, to respond to general threats. • Explain how the 3rd line is very specific to the threat, but takes time to respond. • How are infectious diseases spread? Pathogens Virus Helminths Bacteria Fungi Protozoa Ectoparasites Major Players in the Immune System • Skin • White Blood Cells • Lymphatic System 3 Lines of Defense 1. Surface barriers – Skin and body linings 2. Innate immune system – Immediate but generalized response 3. Adaptive immune system – Threatspecific response, create “memory” 1st Line of Defense: Surface Barriers • Skin: Acts as barrier, secretes antimicrobial substances • Tears, saliva, mucous: Contain lysozyme • “Friendly Bacteria”: Take space & resources, produce acids 2nd Line of Defense: Innate Immune system • Rapid response to infection • Increased blood flow to infection site • Neutrophils and Macrophages (types of WBC) – Engulf pathogens • Natural killer cells (WBC) – Kill virus-infected and cancer cells • WBCs release proteins that attract more WBCs Chemical Signals Released by WBCs • Complement proteins: kill invaders or flag them for macrophages • Cytokines: carry signals among cells Pathogens have ANTIGENS that identify them as ‘non-self’ 3rd Line of Defense: Acquired immunity • Specificity: B and T cells (WBC) make receptors for one type of antigen • Diversity: Collectively, B and T cells have receptors for at least a billion threats rd 3 Line of Defense: Adaptive Immunity • Memory: Some B and T cells held in reserve Defining Features for future infections Specificity: Each B or T cell makes receptors for only one type of antigen Diversity: Collectively, B and T cells have Antigen is recognized • B and T cells divide rapidly – Effector cells go for immediate attack – Memory cells set aside for future threats • B and T cells produce lots of antibodies – Mark invaders as non-self and allow other cells to destroy them. Memory cells • • • • Live long after infection heals Keep body ‘primed’ to fight infection Can mount very quick response Kill pathogens before they have a chance to reproduce much. Lymphatic System Thymus Gland: T cells specialize to combat specific antigens Spleen: Antibody production; holding site for lymphocytes, RBCs, and macrophages Lymph Nodes: WBCs accumulate; Filter pathogens from lymph Cytotoxic T cells cause rejection in organ transplants • Markers on cells must match very closely or they are recognized as antigens • Immunosuppressant drugs are necessary Infectious Diseases Modes of Transmission • • • • Direct contact Indirect contact Inhaling pathogens Contact with a vector (something that carries a pathogen from infected person to new host) Patterns of Infectious Diseases • Sporadic: irregular, affects few • Endemic: more or less continuous • Epidemic: disease rate above expected • Pandemic: epidemic in several countries