Anatomy & Physiology: Immune System Overview

Introduction

• Focus on cell-mediated (cellular) immune response.
• Defense mechanisms when skin, mucous membranes, and humoral immune response fail.

T Lymphocytes (T Cells)

• Main role: attack body cells hijacked by pathogens or cancerous.
• Functions:
  • Cause inflammation.
  • Activate macrophages.
  • Regulate immune response.

Types of T Cells

• Helper T Cells:
  • Activate other immune cells.
  • Cannot kill but regulate adaptive immune response.
• Cytotoxic T Cells:
  • Directly kill compromised cells by inducing apoptosis.
  • Recognize cells displaying abnormal proteins via Class I MHC.

Major Histocompatibility Complex (MHC)

• Class I MHC: Present on all nucleated cells, signals health or distress.
• Class II MHC: Present on immune cells (macrophages, dendritic cells, B cells), displaying engulfed pathogen fragments.
• Role in antigen presentation and immune activation.

Antigen Presentation

• Professional Antigen-Presenting Cells: Include macrophages and dendritic cells.
• Amateur Antigen-Presenting: All nucleated cells with MHC-I.
• Process of displaying pathogen parts via MHC to signal immune response.

Activation of T Cells

• Helper T Activation:
  • Binds to specific antigen-MHC II complex.
  • Releases cytokines to enhance immune response.
• Cytotoxic T Cell Activation:
  • Targets cells presenting abnormal proteins via MHC I.

Cytokines

• Chemical messengers that activate and regulate immune responses.
• Released by Helper Ts to trigger B cells and Cytotoxic T cells.

B Cells and Immune Regulation

• Naive B Cells: Require activation by Helper Ts to become memory or effector cells.
• Importance of checks and balances to prevent autoimmunity.

Autoimmune Diseases

• Caused by hyperactive immune responses attacking body's own cells.
• Examples: Multiple sclerosis, Type 1 diabetes.

Conclusion

• Balance and cooperation within the immune system are crucial for maintaining health.
• Importance of a regulated immune response to prevent diseases.

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Credits

• Episode produced by Crash Course staff and supported by Patreon.
• Filming and production team credits.