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Guardians Within: Understanding the Body's Defenses Against Pathogens

Explore the body's powerful defenses against infections through physical and chemical barriers such as skin, tears, and fever, as well as the immune system's response to foreign invaders.

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Guardians Within: Understanding the Body's Defenses Against Pathogens

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  1. Lesson Overview 35.2 Defenses Against Infection

  2. THINK ABOUT IT: do not write • With pathogens all around us, it might seem amazing that most of us aren’t sick most of the time. • Why are we usually free from infections, and why do we usually recover from pathogens that do infect us? • One reason is that our bodies have an incredibly powerful and adaptable series of defenses that protect us against a wide range of pathogens.

  3. Nonspecific Defenses • The body’s first defense against pathogens is a combination of physical and chemical barriers. • skin • tears • secretions • inflammatory response • interferons • fever • These barriers are called nonspecific defenses because they act against a wide range of pathogens.

  4. First Line of Defense • The most widespread nonspecific defense is the skin. • Very few pathogens can penetrate the layers of dead cells that form the skin’s surface.

  5. Second Line of Defense • If pathogens make it into the body, through a cut in the skin, the body’s second line of defense swings into action. • These mechanisms include: • inflammatory response • interferons • fever

  6. Inflammatory Response • The inflammatory response causes infected areas to become red, painful, and inflamed. • Pathogens stimulate cells called mast cells to release chemicals -histamines. • Lymph nodes may become enlarged and swollen • Histamines increase the flow of blood and fluids to the affected area.

  7. Inflammatory Response • Fluid leaking from expanded blood vessels causes the area to swell. • White blood cells move from blood vessels into infected tissues.

  8. Inflammatory Response • Many of the white blood cells (phagocytes) engulf & destroy bacteria. • All this activity may cause a local rise in temperature. • That’s why a wounded area sometimes feels warm.

  9. Recognizing “Nonself” • The immune system recognizes foreign organisms as “nonself.” • Once the immune system recognizes “others,” it attacks • After encountering a specific invader, the immune system “remembers” the invader • This recognition, response, and memory -the immune response.

  10. Antigens • Antigen (Bad Guy) -a foreign substance that can stimulate an immune response. • Antigens are located on surfaces of bacteria, viruses, or parasites. • Immune system responds by making cells that attack the invaders or produce proteins • Made by plasma cells: antibodies (Good Guy)

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