1. Immune System Overview

  • The immune system protects the body from harmful pathogens like bacteria, viruses, fungi, and toxins.
  • It consists of cells, tissues, and organs that work together to defend the body.
  • Key components: White Blood Cells (WBCs), antibodies, lymphatic system, bone marrow, thymus, spleen.
  • The immune system is classified into innate immunity and adaptive immunity.

2. Types of Immunity

(A) Innate Immunity

  • Innate immunity is the body's first line of defense, present from birth.
  • It provides non-specific defense against all pathogens.
  • Composed of:
    • Physical barriers: Skin, mucous membranes.
    • Chemical barriers: Enzymes in saliva, stomach acid, tears.
    • Cellular barriers: Macrophages, neutrophils, natural killer (NK) cells.
    • Inflammatory response: Redness, swelling, fever to fight infections.

(B) Adaptive Immunity

  • Adaptive immunity (acquired immunity) develops after exposure to pathogens.
  • It provides a specific defense mechanism and retains memory of past infections.
  • Divided into:
    • Humoral immunity: Involves B cells that produce antibodies to neutralize pathogens.
    • Cell-mediated immunity: Involves T cells that destroy infected cells.
  • It is further divided into:
    • Active immunity: Developed by the body after infection or vaccination.
    • Passive immunity: Antibodies are received from another source (e.g., mother’s milk, antibody injections).

3. Immune Responses

(A) Primary Immune Response

  • Occurs when the body encounters a pathogen for the first time.
  • B cells recognize the antigen and produce antibodies after a few days.
  • Response is slow and weak but helps in developing memory cells.

(B) Secondary Immune Response

  • Occurs when the body encounters the same pathogen again.
  • Memory cells recognize the antigen and trigger a strong and quick response.
  • Prevents reinfection and provides long-term protection.

4. Components of the Immune System

  • White Blood Cells (WBCs): Also called leukocytes, they fight infections.
  • Lymphocytes: Include B cells and T cells, responsible for adaptive immunity.
  • Macrophages: Engulf and digest pathogens.
  • Antibodies: Proteins that neutralize pathogens.
  • Lymphatic System: Includes lymph nodes and lymph vessels that filter pathogens.
  • Thymus: Site of T cell maturation.
  • Spleen: Helps filter blood and remove infected cells.

5. Disorders of the Immune System

(A) Autoimmune Diseases

  • Occurs when the immune system attacks the body's own cells.
  • Examples: Rheumatoid arthritis, Type 1 diabetes, Lupus.

(B) Immunodeficiency Diseases

  • Occurs when the immune system is weakened or defective.
  • Examples: HIV/AIDS (Human Immunodeficiency Virus).

(C) Allergies

  • Overreaction of the immune system to harmless substances (allergens).
  • Common allergens: Pollen, dust, certain foods, insect stings.
  • Symptoms: Skin rash, sneezing, difficulty breathing, anaphylaxis.

6. Vaccination and Immunization

  • Vaccination introduces a weakened or dead pathogen to stimulate immunity.
  • Immunization is the process of developing resistance to a disease through vaccines.
  • Examples of vaccines: BCG (Tuberculosis), Polio, Hepatitis B, COVID-19.
  • Vaccines help in herd immunity, protecting the larger population.

7. Conclusion

  • The immune system is the body's defense mechanism against diseases.
  • Innate immunity provides general protection, while adaptive immunity offers specific and long-term protection.
  • Vaccines play a crucial role in preventing infectious diseases.
  • A balanced diet, exercise, and a healthy lifestyle help strengthen immune function.

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