Nonspecific Defenses

Lesson Objectives

• Describe barriers preventing pathogens from entering the body.
• Explain the inflammatory response and the role of nonspecific leukocytes in fighting pathogens.

Vocabulary

• Inflammatory response
• Leukocyte
• Mucous membrane
• Mucus
• Pathogen
• Phagocytosis

Introduction

• The immune system acts like a medieval castle with a series of defenses.
• Three lines of defense:
  • The first and second lines are nonspecific.
  • The third line is specific to pathogens.

First Line of Defense

Pathogens

• Disease-causing agents like bacteria and viruses.

Mechanical Barriers

• Skin: Tough outer layer, primary defense.
• Mucous membranes: Provide barriers in body openings, secretes mucus, and have cilia.
  • Cilia sweep pathogens out through sneezing or coughing.
  • Tears and urine also help remove pathogens.

Chemical Barriers

• Sweat, mucus, tears, saliva have enzymes that kill pathogens.
• Urine and semen create inhospitable environments for pathogens.
• Stomach acid kills pathogens entering through the GI tract.

Biological Barriers

• Harmless bacteria on skin and in GI tract prevent harmful bacteria growth.

Second Line of Defense

Inflammatory Response

• Triggered by chemicals (cytokines and histamines) released during tissue damage or infection.
• Causes redness, warmth, and swelling at site of injury.

Leukocytes

• White blood cells attracted to infection site.
• Role:
  • Nonspecific defense: Phagocytosis, where leukocytes engulf pathogens.
  • Specific defense explained in a subsequent lesson.

Summary

• First line: Mechanical, chemical, and biological barriers.
• Second line: Inflammatory response and phagocytosis.

Review Questions

1. Identify and give examples of three barrier types.
2. Describe the second line of defense and its activation.
3. Explain the role of nonspecific leukocytes.
4. Explain how phagocytosis defends the body.
5. Define nonspecific defense.
6. Explain the signs of infection using an example.
7. Describe how the inflammatory response fights infection.

Points to Consider

• First and second lines of defense are nonspecific.
• Third line of defense is pathogen-specific.
• Consider how the immune system identifies specific pathogens and the mechanisms of specific defenses.