Immune System Lecture Notes

Introduction

• The body is in a constant battle with microorganisms like staph, strep, E. coli.
• The immune system acts as the body's defense mechanism.
• Three-part policy: innate (nonspecific) and adaptive (specific) defense systems.
• Immune system involves multiple tissues, organ systems, and defense cells.

Innate Defense System

• First Line of Defense: Immediate response with existing physical and chemical barriers.

  • Physical Barriers:
    • Skin: Tough keratinized membrane, acts like a fortress wall.
    • Mucous membranes: Line cavities exposed to the outside, including respiratory, digestive, urinary, and reproductive tracts.
  • Chemical Barriers:
    • Stomach acid: Destroys harmful bacteria.
    • Mucus: Traps viruses and bacteria.
    • Enzymes in saliva and eye fluid: Fight bacteria.
    • Defensins: Prevent bacteria and fungi growth.

• Second Line of Defense: Activated when physical barriers are breached.

  • Internal Defenses:
    • Phagocytes: Cells that consume harmful entities.
      • Neutrophils: Abundant white blood cells, self-destruct after devouring pathogens.
      • Macrophages: Larger cells that can consume pathogens multiple times.
    • Natural Killer (NK) Cells: Target infected or cancerous cells by inducing apoptosis.
    • Fever: Raises body temperature to enhance healing and inhibit bacterial growth.

Inflammatory Response

• Triggered by injury or infection.
• Key Reactants:
  • Histamines: Cause vasodilation, increasing redness and heat.
  • Increased Permeability: Allows protein-rich fluids to leak, aiding in clotting and scab formation.
  • Phagocytes and Lymphocytes: Drawn to injury site to consume pathogens and clean up debris.
• Leukocytosis: Release of neutrophils from bone marrow to bloodstream in response to signals from injured cells.

Systemic Responses

• Fever:
  • Induced when local defenses are overrun.
  • Increases metabolism for faster healing.
  • Instructs liver and spleen to conserve iron and zinc to prevent bacterial growth.

Conclusion

• The innate immune system is the body's first defense line.
• Involves physical barriers, phagocytes, natural killer cells, and the inflammatory response.
• Adaptive immune defenses are called upon for more serious threats.

Credits

• Lecture by: Linnea Boyev
• Scriptwriter: Kathleen Yale
• Consultant: Dr. Brandon Jackson
• Production: Crash Course Team
• Supported by: Patreon contributors