The Immune System: Innate Defense

Introduction

• The body is constantly under attack by various microorganisms like staph, strep, and E. coli.
• The immune system is responsible for protecting the body against these invaders.
• Unlike other systems, the immune system is not limited to specific organs but involves various tissues, organ systems, and specialized cells.

Components of the Immune System

• Innate (Nonspecific) Defense System
  • Acts as the first line of defense, akin to frontline soldiers.
  • Includes external barriers like skin and mucous membranes, and internal defenses like phagocytes and antimicrobial proteins.
  • Provides immediate response to threats.
• Adaptive (Specific) Defense System
  • Specialized response to specific pathogens, acting like "Seal Team Six."
  • Includes mechanisms to remember specific pathogens for future defense.
• Focus of the lecture is on the innate immune system.

Innate Defense System

Physical and Chemical Barriers

• Skin
  • Provides a physical barrier against pathogens unless damaged.
• Mucous Membranes
  • Line cavities exposed to the outside world: respiratory, digestive, urinary, reproductive tracts.
• Chemical Barriers
  • Stomach acid, sticky mucus in nasal passages, bacteria-fighting enzymes in saliva and eye fluid.
  • Defensins in skin and membranes deter bacteria and fungi.

Internal Innate Defenses

• Phagocytes
  • Cells that "eat" pathogens.
  • Neutrophils: Most abundant white blood cells, self-destruct after devouring pathogens.
  • Macrophages: Larger phagocytes that can consume pathogens multiple times.
• Natural Killer (NK) Cells
  • Unique cells that can destroy the body’s own infected or cancerous cells by inducing apoptosis.

Inflammatory Response

• Triggered when physical barriers are breached.
• Histamines
  • Released by mast cells, causing vasodilation and increased permeability of blood vessels.
  • Leads to redness, heat, swelling, and pain which are signs of healing.
• Leukocytosis
  • Release of neutrophils from bone marrow in response to infection.
  • Neutrophils and macrophages attack pathogens and clean up cell debris.

Fever

• Systemic response to overwhelming infections.
• Pyrogens
  • Chemicals that induce fever by affecting the hypothalamus.
  • Increase metabolism to speed up healing.
  • Restrict iron and zinc availability to pathogens.

Conclusion

• Innate immune responses include barriers like skin and mucous membranes, phagocytes, NK cells, and inflammation.
• In case of severe infections, fever acts as a systemic defense.
• For a more detailed study on adaptive defenses, further sessions are needed.

Credits

• Mention of contributors and supporters who make educational content possible.