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Immunity
- Resistance to disease
- Immune system = Two intrinsic systems
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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
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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
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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)
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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
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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]
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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
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Cardinal signs of acute inflammation
- 1. Redness
- 2. Heat
- 3. Swelling
- 4. Pain
- (5. Impairment of function)
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Leukocytosis
Neutrophils enter blood from bone marrow
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Margination
Neutrophils cling to capillary wall
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Diapedesis
Neutrophils flatten and squeeze out of capillaries
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Chemotaxis
Neutrophils follow chemical trail
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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
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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
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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
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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
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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
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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
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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
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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
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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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