Immune System: Innate Defense System

Overview

• The body continuously battles against pathogens such as staph, strep, and E. coli.
• The immune system is responsible for protecting the body, comprising various tissue groups, organ systems, and specialized defense cells.

Types of Defense Systems

• Innate Defense System (Nonspecific): The first line of immediate defense consisting of the skin, mucous membranes, phagocytes, and antimicrobial proteins.

  • Physical Barriers: Skin and mucous membranes act as barricades.
  • Chemical Defenses: Stomach acid, mucus, saliva enzymes, and defensins.

• Adaptive Defense System (Specific): Targets specific threats and retains memory for future responses (Seal Team Six comparison).

Key Functions of Innate Defense

• Physical Barriers

  • Skin serves as an effective barrier unless damaged.
  • Mucous membranes line cavities exposed to the outside world (respiratory, digestive, urinary, and reproductive tracts).

• Chemical Barriers

  • Stomach Acid: Neutralizes ingested pathogens.
  • Mucus: Traps airborne pathogens.
  • Enzymes in Saliva and Tears: Combat bacteria.
  • Defensins: Prevent bacteria and fungi around inflamed areas.

Internal Innate Defenses

• Phagocytes:

  • Neutrophils: Most abundant; self-destruct after consuming pathogens.
  • Macrophages: Derived from monocytes; engulf pathogens repeatedly.

• Natural Killer Cells (NK Cells):

  • Patrol blood and lymph; kill infected or cancerous cells by triggering apoptosis.
  • Detect cells missing MHC1 protein.

Inflammatory Response

• Initiated by injuries (e.g., scraping knees).

• Histamines & Chemical Signals:

  • Cause vasodilation, redness, and heat.
  • Increase blood vessel permeability for fluid, clotting, and pathogen removal.

• Phagocyte Attraction:

  • Neutrophils arrive first; die in pus formation.
  • Macrophages clean up pathogens and debris.

Fever and Systemic Response

• Fever:
  • Triggered when local defenses are overwhelmed.
  • Increases metabolic rate for healing; retains iron and zinc to inhibit bacterial growth.

Conclusion

• Physical and chemical barriers initiate immune responses.
• Involvement of phagocytes and NK cells is crucial.
• The inflammatory response helps contain and eliminate pathogens.
• For more formidable threats, the adaptive immune system is engaged.

Acknowledgments

• Headmaster of Learning: Linnea Boyev
• Crash Course Team and Patreon patrons.

This episode was produced in the Doctor Cheryl C. Kinney Crash Course Studio and involved contributions from various writers, directors, and designers.