Human Body's Defense System

Overview

• The human body's defense system protects against pathogens.
• Divided into physical/chemical barriers and the immune system.

Physical and Chemical Barriers

Skin

• Acts as a physical barrier against pathogens.
• Secretes oils and antimicrobial substances to kill pathogens on its surface.

Nose

• Contains hairs and mucus to trap pathogens and particles.

Trachea and Lungs

• Trachea, bronchi, and bronchioles are lined with mucus to trap particles.
• Cilia move mucus and trapped particles up to the throat to be swallowed.

Stomach

• Produces hydrochloric acid which kills pathogens in ingested mucus and food.

Immune System

White Blood Cells

• Patrol the body via blood and tissues.
• Three main functions:
  1. Phagocytosis: Engulf and destroy pathogens.
  2. Antitoxin Production: Neutralize toxins produced by pathogens.
  3. Antibody Production:
  • Antibodies bind to specific antigens on pathogens.
  • Act as signals for white blood cells to destroy the pathogens.
  • Immune system remembers antibodies for faster future response.

Key Terms

• Antigens: Foreign substances detected by the immune system (e.g., bacterial cell walls, virus proteins).
• Antibodies: Proteins made by white blood cells that bind to antigens and signal for their destruction.

Immunity

• Once the immune system recognizes a pathogen, it produces antibodies rapidly upon future exposures.
• This rapid response prevents the pathogen from causing disease.

Conclusion

• The defense system helps us survive daily attacks from millions of pathogens.
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