Immune System Overview

Introduction

• The immune system works continuously to maintain health.
• Key focus on human anatomy and physiology, specifically the immune system.

The Immune System

• Comprised of cells like macrophages, neutrophils, and eosinophils.
• Functions to defend against pathogens: viruses, bacteria, fungi, protozoa, and parasitic worms.

First Line of Defense: External Defenses

• Skin: Acts as a barrier to prevent pathogen entry.
• Mucous Membranes: Located in areas like the nose to block pathogens.
• Classified as non-specific defenses.

Second Line of Defense: Innate Immunity

• Inflammatory Responses: Triggered by injuries, e.g., a thorn prick.
  • Mass cells release histamine, causing blood vessels to dilate and become permeable.
  • Allows macrophages to engulf and digest pathogens.
• Complement System: Enhances immune functions by attracting more macrophages.
• Still a non-specific response.

Third Line of Defense: Adaptive Immunity

• Targets Specific Antigens that the body recognizes as foreign.

Types of Adaptive Immunity

1. Cell-Mediated Response:

   • Involves cytotoxic T-cells destroying infected cells through apoptosis.
   • Requires specific stimulation from infected cells presenting antigens.
   • Helper T-cells release chemical signals activating cytotoxic T-cells.

2. Humoral Response:

   • Macrophages present antigens to Helper T-cells, activating B-cells.
   • B-cells: Produce antibodies found in blood, mucus, saliva, etc.
   • Antibodies:
     • IgG: Most abundant, protects against bacterial and viral infections.
     • IgA: Found in mucous membranes, saliva, tears.
     • IgM: First response antibody, forms complexes with antigens.
     • IgE: Associated with allergies and parasitic infections.
     • IgD: Found on B-lymphocytes, initiates immune responses.
   • Antibodies neutralize pathogens and mark them for destruction by macrophages.

Memory Cells

• Memory B and T cells: Retain memory of antigens, initiating rapid response upon re-exposure.
  • Memory B cells: Lead to plasma B cells, producing antibodies.
  • Memory T cells: Activate cytotoxic T-cells.

Types of Immunity

Active Immunity

• Occurs when the immune system produces antibodies after exposure to pathogens.
• Acquired through natural infection or vaccinations.
• Long-lasting, often lifelong protection.

Passive Immunity

• Provided by antibodies from another source (e.g., mother to baby, antibody therapies).
• Immediate protection, but temporary, as antibodies do not last long.

Conclusion

• Understanding the immune system is key for exams and practical knowledge.
• Encourage questions and further resources are available for deeper study.