Chapter 21: Immune System

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  1. Immunity
    • Resistance to disease
    • Immune system = Two intrinsic systems
  2. Innate Defenses
    • Surface barriers ward off invading pathogens (skin, mucous membranes, and their secretions)
    • Physical barrier to most microorganisms
    • Keratin resistant to weak acids and bases, bacterial enzymes, and toxins
    • Mucosae provide similar mechanical barriers
  3. Surface Barriers
    • Protective chemicals inhibit or destroy microorganisms (acidity of skin and secretions)
    • Enzymes - lysozyme of saliva, respiratory mucus, and lacrimal fluid
    • Respiratoy system modifications
    • Surface barriers breached by nicks or cuts - second line of defense must protect deeper tissues
  4. Internal Defense: Cells and Chemicals
    • Phagocytes
    • Natural killer (NK) cells
    • Antimicrobial proteins (interferons and complement proteins)
    • Fever
    • Inflammatory response (macrophages, mast cells, WBCs, and inflammatory chemicals)
  5. Phagocytosis
    • 1. Phagocyte adheres to pathogens or debris
    • 2. Phagocyte forms pseudopods that eventually engulf the particles, forming a phagosome
    • 3. Lysosome fuses with the phagocytic vesicle, forming a phagolysosome
    • 4. Lysosomal enzymes digest the particles, leaving a residual body
    • 5. Exocytosis of the vesicle removes indigestible and residual material
  6. Natural Killer (NK) Cells
    • Nonphagocytic lymphocytes
    • Attack cells that lack "self" cell-surface receptors (Induce apoptosis in cancer cells and virus-infected cells
    • Secrete potent chemicals that enhance inflammatory response
    • [T lymph cells]
  7. Inflammatory Response
    • Triggered whenever body tissues injured
    • Prevents spread of damaging agents
    • Disposes of cell debris and pathogens
    • Alerts adaptive immune system
    • Sets the stage for repair
  8. Cardinal signs of acute inflammation
    • 1. Redness
    • 2. Heat
    • 3. Swelling
    • 4. Pain
    • (5. Impairment of function)
  9. Leukocytosis
    Neutrophils enter blood from bone marrow
  10. Margination
    Neutrophils cling to capillary wall
  11. Diapedesis
    Neutrophils flatten and squeeze out of capillaries
  12. Chemotaxis
    Neutrophils follow chemical trail
  13. Fever
    • Abnormally high body temperature
    • Systemic response to invading microorganisms
    • Leukocytes and macrophages exposed to foreign substances secrete pyrogens
    • Pyrogens act on body termostat in hypothalamus, raising body temperature
  14. Adaptic Defenses
    • Specific - recognizes and targets specific antigens
    • Systemic - not restricted to initial site
    • Have memory - stronger attacks to "known" antigens
    • Two separate, overlapping arms - humoral (antibody-mediated) and cellular (cell-mediated) immunity
  15. Antigenic Determinants
    • Most naturally occurring antigens have numerous antigenic determinants that - mobilize several different lymphocyte populations / form different kinds of antibodies against it
    • Large, chemically simple molecules (e.g., plastics) have little or no immunogenicity
  16. Cell of the Adaptive Immune System (3 types)
    • Two types of lymphocytes (B cells - humoral)(T cells - cel-mediated)
    • Antigen-presenting cells (APCs) - do not respond to specific antigens - play essential auxiliary roles in immunity
  17. Proliferation and Differentiation
    • Activated lymphocyte proliferates exact clones
    • Most clones --> effector cells that fight infections
    • Few remain as memory cells - able to respond to same antigen more quickly second time
    • B and T memory cells and effector T cells circulate continuously
  18. Antigen-presenting Cells (APCs)
    • Engulf antigens
    • Present fragments of antigens to T cells for recognition
    • Major types - Dendritic cells (in connective tissues and epidermis) Macrophages (in connective tissues and lymphoid organs) B cells
  19. Adaptive Immunity: Summary
    • Uses lymphocytes, APCs, and specific molecules to identify and destroy nonself substances
    • Depends upon ability of its cells to - recognize antigens by binding them / communicate with one another so that whole system mounts specific response
  20. Immunological Memory
    Primary immune response
    • Cell proliferation and differentiation upon first antigen exposure
    • Lag period: three to six days
    • Peak levels of plasma antibody are reached in 10 days
    • Antibody levels then decline
  21. Immunlogical Memory
    Secondary immune response
    • Re-exposure to same antigen gives faster, more prolonged, more effective response
    • Sensitized memory cells respond within hours
    • Antibody levels peak in two or three days at much higher levels
    • Antibodies bind with greater affinity
    • Antibody level can remain high for weeks to months
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Chapter 21: Immune System
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