The Immune System: Innate Defenses 💪🦠

Introduction

• Our body constantly battles a variety of bacteria and pathogens.
• These microorganisms exploit the body for resources to feed, shelter, and reproduce.
• The body has developed a three-part strategy to combat these invaders executed by the immune system.

The Immune System

• Unique compared to other systems as it doesn’t consist of specific organs or tissues.
• Comprises various tissues, organs, and specialized defensive cells distributed widely.
• These components work together to perform defense functions, keeping the body alive in a germ-filled world.

First Line of Defense: Innate or Non-Specific Defense

• Ready to attack any suspicious entity, similar to a frontline soldier.
• Includes exterior barriers like skin and mucous membranes.
• Internal defenses: phagocytes, antimicrobial proteins, and other attack cells.

Physical Barriers

1. Skin:
   • Acts like a wall around a castle.
   • Keeps out various germs.
   • Keratinized epithelial membrane is effective unless damaged.
2. Mucous Membranes:
   • Line cavities exposed to germs, including respiratory, digestive, urinary, and reproductive tracts.
   • Provide physical protection.

Chemical Defenses

1. **Stomach Acid: **
   • Kills ingested pathogens.
2. **Nasal Mucus: **
   • Traps and expels invaders.
3. **Enzymes in Saliva and Tears: **
   • Combat bacteria.
4. **Antimicrobial Peptides: **
   • In skin and membranes to prevent the gathering of bacteria and fungi.

Second Line of Defense: Internal Innate Defenses

Phagocytic Cells

1. **Neutrophils: **
   • Most abundant white blood cells.
   • Self-destructive after attacking invaders (pus formation).
2. Macrophages:
   • Derived from monocytes.
   • Can roam the tissues or be fixed.
   • Engulf and digest pathogens repeatedly.

Natural Killer Cells (NK Cells)

• Roam the blood and lymph looking for abnormal cells.
• Kill infected or cancerous cells by inducing apoptosis (programmed cell death).
• Recognize unhealthy cells by the absence of MHC I protein.

The Inflammatory Response

• Triggered by tissue damage or infection.
• Mast cells release histamine, causing vasodilation.
• Redness, swelling, heat, and pain are signs of healing.

1. **Vasodilation: **
   • Increases blood flow and heat.
   • Helps with faster metabolism and repair.
2. **Increased Permeability: **
   • Allows fluids rich in proteins to flow out.
   • Helps clot formation and supports lymphatic system in cleaning up.
3. **Influx of Phagocytes: **
   • Neutrophils and macrophages clean up the infection site.
   • Neutrophils are the first responders, followed by macrophages for thorough cleaning.

Fever

• Triggered when phagocytes release pyrogens.
• Increases body metabolism, which speeds up healing.
• Liver and spleen retain iron and zinc to hinder bacterial growth.

Conclusion

• The immune responses start with physical barriers and escalate to internal defenses if needed.
• Further specialized defenses (adaptive immunity) come into play when innate defenses are overwhelmed.
• Detailed explanation to follow in the next lesson.

Appreciation

• Thanks to enthusiast supporters and patrons on Patreon.
• Special mention to all who made the production possible, including educational advisers, writers, editors, and the graphic design team.