Chapter 11: Immunity

Introduction to Immunity

• Definition: No single definition; generally, immunity is your body's ability to fight off pathogens.
• Pathogens: Constantly surround us, both externally and internally (skin, table, within body).
  • Pathogens aim to enter the body and use resources, causing damage.
• Immunity: Prevents constant illness even amidst pathogen exposure.

Types of Defense Systems

External Defense System

1. Skin: Primary External Defense

   • Acts as a waterproof barrier to pathogens.
   • Produces acid (pH ~5.5) to inhibit bacterial growth.
   • Sweat contains chemicals inhibiting bacteria.

2. Stomach:

   • Considers external (exposed to outside via food ingestion).
   • Produces hydrochloric acid to denature and kill bacteria.

3. Airways and Lungs:

   • Also considered external (exposed via inhaled air).
   • Mucus: Traps pathogens (produced by goblet cells).
   • Ciliated Cells: Use cilia to push mucus upwards, protecting lungs.

Internal Defense System

• Activated when pathogens breach external defenses (e.g., into blood vessels).
• Immune System: Comprises primarily white blood cells.
  • White Blood Cells: Main players in internal defense.

White Blood Cells in Immune Response

• Complexity: Immune system is highly intricate beyond simple white blood cell involvement.
• A-Level Focus:
  • Two Types of White Blood Cells:
    • Phagocytes
    • Lymphocytes
  • Note: True immune response includes many more factors and cells.

Additional Notes

• Complexity in Education:
  • At A-levels, only a basic understanding is required.
  • Further education reveals deeper complexities (e.g., university level).

Summary

• Immunity involves both external and internal defenses to protect against pathogens.
• Understanding basic functions of skin, stomach, airways, and white blood cells is crucial for exams.
• The immune system is far more complex than initial A-level study might suggest.