Immune system

Introduction to Immunity

  • Immunity: The body's ability to resist or eliminate potentially harmful foreign materials or abnormal cells, including viruses, toxins, carcinogens, fungi, pollution, bacteria, germs, and parasites.

The Immune System

  • Nature of the Immune System: A functional system, not an organ system, consisting of various components:
    • Physical Barriers: Skin and lining of mucous membranes
    • Biochemical Barriers: Secretions like tears and mucus that are antimicrobial
    • Cells: White blood cells, including various types of lymphocytes
    • Organs: Bone marrow, spleen, thymus, lymphatic system, and resident immune cells in most tissues.

Types of Immunity

Innate Immunity
  • Definition: Natural immunity that acts as the first line of defense against environmental threats.
  • Components:
    • Physical Barriers: Prevent damage from substances.
    • Inflammatory Response: Rapid activation occurs if barriers are breached, leading to nonspecific responses.
Adaptive Immunity
  • Definition: A slower, specific process targeting particular microorganisms.
  • Key Feature: Has memory, allowing for a more rapid response upon subsequent exposures.

Differences Between Innate and Adaptive Immunity

  • Innate Immunity:
    • First line of defense against infection and tissue injury; always active.
    • Broadly specific; immediate response.
  • Adaptive Immunity:
    • Third line of defense initiated by signals from the innate system.
    • Slower response upon first exposure, rapid on subsequent exposure; highly specific.
    • Involves memory through T and B cells (antibodies).

Immune Cells Involved

  • Types of White Blood Cells (WBC):
    • Neutrophils: Most abundant, efficient phagocytes.
    • Macrophages: Phagocytose microbes and present antigens.
    • Natural Killer (NK) Cells: Eliminate virus-infected and tumor cells.

Inflammatory Response

  • Definition: A biological response to pathogens and irritants, characterized by:
    • Swelling and heat due to blood vessel dilation.
    • Increased capillary permeability leads to swelling and pain.

Mechanisms of Adaptive Immunity

  • Cell-mediated Response:
    • Involves T-lymphocytes (CD4+ and CD8+), targeting infected cells.
    • Helper T cells activate B cells and other immune cells.
    • Cytotoxic T cells destroy infected host cells.
  • Humoral Response:
    • B-lymphocytes produce antibodies targeting specific antigens.
    • B cells differentiate into memory cells or antibody-secreting plasma cells.

Failures of Immune Response

Hypersensitivity Reactions
  • Excessive immune response leading to:
    • Allergies (overreaction to environmental substances)
    • Autoimmunity (overreaction to self)
Immunodeficiency
  • Definition: Loss or inadequate function of immune components leading to increased infection risk.
  • Types:
    • Congenital: Genetic abnormalities affecting immune maturation.
    • Acquired: Resulting from infections or treatments affecting immune function, e.g., AIDS.

Summary of Key Points

  • The human defense mechanisms consist of:
    • Innate Immunity: Natural barriers and inflammatory responses.
    • Adaptive Immunity: Specific immune response with memory functions.
  • The inflammatory response includes physical barriers, signaling from innate immune cells, and activation of both T and B lymphocytes, resulting in a comprehensive immune defense strategy against pathogens.