UNIT 6 Immunity (Chapter 21)

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UNIT 6 Immunity (Chapter 21)

• Immune System Overview
• Innate Host Defenses
• Adaptive Defenses

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NOTE The following information is based on the
Immune System Interactive Physiology tutorials I
highly recommend that you view the interactive
tutorials along with the lecture outline (at the
same time) the following outline is a blending
of the textbook and Interactive Physiology
tutorials
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Immune System Overview (view the Interactive
Physiology tutorial Immune System Immune System
Overview)

• There are two major functions of the immune
  system
• destroy pathogens
• detect and kill abnormal cells, such as cancerous
  cells
• Pathogens are classified according to their size
  and where they are located in the body there are
  5 types of pathogens
• 1. parasitic worms
• 2. fungi
• 3. protozoa
• 4. bacteria
• 5. viruses
• viruses are always intracellular (must
  reproduce inside cells), whereas the others are
  usually extracellular parasitic worms are
  macroscopic organisms, whereas the others are
  microorganisms, meaning that they can only be
  seen with a microscope

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Immune System Overview

• Line of Defense (fig. 21.1)
• INNATE DEFENSES (nonspecific defenses)
• innate external defenses - these are surface
  barriers, such as the skin and mucous membranes
  if the innate external defenses are penetrated
  then the next line of defense is the innate
  internal defenses
• innate internal defenses - these include cells
  and chemicals in body fluids (e.g. phagocytes and
  NK cells), fever, and inflammation internal
  defenses identify enemies by recognizing markers
  that are unique to the pathogens when they are
  overwhelmed, they secrete chemical messengers to
  mobilize adaptive defenses

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Immune System Overview

• Line of Defense (fig. 21.1)
• ADAPTIVE DEFENSES (specific defenses)
• differ from innate defenses
• they are specific (directed against an
  identifiable enemy)
• they involve B and T lymphocytes
• they have memory they will recognize an enemy if
  it attacks the body again in the future
• they are systemic (can act anywhere in the body)
• B and T lymphocytes recognize pathogens by
  binding to them they recognize antigens of the
  pathogen by shape, also known as the antigenic
  determinant
• specific B cells called plasma cells secrete
  antibodies, which bind to the antigens

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Immune System Overview

• Humoral (antibody-mediated) vs. Cellular
  (cell-mediated) Immunity
• humoral, or antibody-mediated, immunity is
  directed against pathogens in extracellular
  fluid this immunity involves B lymphocytes and
  antibodies
• cellular, or cell-mediated, immunity is directed
  against pathogens within the cells this immunity
  involves T lymphocytes for example T cells would
  be activated if a cell has become cancerous or
  attacked by a virus, or if a cell has been
  transplanted from another individual

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Innate Host Defenses (view the Interactive
Physiology tutorial Immune System Innate Host
Defenses) innate defenses are present at birth
and are genetically determined

• Innate External Defense System - first line of
  defense
• surface barriers include the skin and mucous
  membranes of the respiratory, digestive, urinary,
  and reproductive tracts
• characteristics of skin that help it to resist
  invasion
• water-resistant and tough keratin outer layer
• intercellular junctions hold skin cells tightly
  together
• skin secrections are acidic and have chemicals
  that make the skin inhospitable to pathogens
  e.g. lysozyme destroys cell walls of certain
  bacteria
• mucous membranes not only provide a barrier, but
  also produce a variety of protective chemicals
  (e.g. lysozyme) and acidic secretions
• the stomach secretes digestive enzymes and has a
  very low pH
• the digestive and respiratory pathways are lined
  with sticky mucous that traps pathogens

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Innate Host Defenses

• Innate Internal Defense System - second line of
  defense attempts to limit the spread of
  pathogens this system is fast-acting and
  nonspecific
• the internal defense system has 5 components
• phagocytic cells (e.g. neutrophils and
  monocytes/macrophages)
• NK cells (natural killer cells)
• antimicrobial proteins (complement and
  interferon)
• inflammation
• fever

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Innate Host Defenses

• Innate Internal Defense System - second line of
  defense attempts to limit the spread of
  pathogens this system is fast-acting and
  nonspecific
• phagocytes (fig. 21.2)
• neutrophils are the first cells to leave the
  blood and enter tissues at the sites of infection
  or trauma these cells are short-lived
• monocytes follow the influx of neutrophils into
  the affected tissue once in the tissue, they
  transform into macrophages they phagocytize many
  more pathogens than neutrophils
• phagocytes use special membrane receptors to
  recognize and bind molecules that are found on
  pathogens, but not on normal body cells
• when a phagocyte recognizes a pathogen it
• - ingests the pathogen
• - releases chemical alarm signals that mobilize
  other cells of innate and adaptive immunity
• OPSONIZATION - some bacteria have capsules that
  make it difficult for phagocytes to grab them
  the immune system makes molecules that coat the
  bacteria and enhance phagocytosis this is called
  opsonization both complement and antibodies can
  act as opsonins

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Innate Host Defenses

• Innate Internal Defense System - second line of
  defense attempts to limit the spread of
  pathogens this system is fast-acting and
  nonspecific
• NK cells (natural killer cells)
• type of lymphocyte involved in innate immunity
• attack body cells that have been invaded by
  pathogens (e.g. viruses) or cancer they will
  also attack the cells of transplanted tissues
• NK cells are larger than B and T cells, and
  unlike B and T cells, do not have antigen
  receptors
• both NK cells and T cells are involved in IMMUNE
  SURVEILLANCE (they continually scan our cells for
  abnormalities)

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Innate Host Defenses

• Innate Internal Defense System - second line of
  defense attempts to limit the spread of
  pathogens this system is fast-acting and
  nonspecific
• antimicrobial proteins
• interferons (fig. 21.5)- interfere with viral
  replication and activate immune cells cells that
  have been attacked by a virus release interferon
  to help protect neighboring cells that have not
  yet been affected
• complement (complement system) (fig. 21.6) - it
  complements or enhances other components of
  both innate and adaptive defenses it can mark
  cells for phagocytosis, promote inflammation, and
  kill some bacteria

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Innate Host Defenses

• Innate Internal Defense System - second line of
  defense attempts to limit the spread of
  pathogens this system is fast-acting and
  nonspecific
• inflammation
• when the body is injured (e.g. a cut, abrasion,
  or bruise) a sequence of events called
  inflammation is initiated
• tonsillitis, tendonitis, and laryngitis are
  examples of short-lived, or acute, inflammation
  arthritis is an example of long-term, or chronic,
  inflammation
• there are 4 cardinal signs of inflammation pain,
  swelling, redness, and heat
• the purpose of inflammation is to bring white
  blood cells and plasma proteins into an injured
  area inflammatory mediators (e.g. histamine from
  basophils and mast cells) cause vasodilation
  (increasing blood flow to the area) and an
  increase in vascular permeability (allowing
  phagocytes and plasma proteins to enter the
  tissue)
• plasma proteins and more fluid than usual leak
  into the injured area causing EDEMA (increased
  interstitial fluid) edema causes swelling, which
  can contribute to the sensation of pain

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Innate Host Defenses

• Innate Internal Defense System - second line of
  defense attempts to limit the spread of
  pathogens this system is fast-acting and
  nonspecific
• fever
• generalized increase in body temperature
• PYROGENS - chemicals secreted by leukocytes and
  macrophages that have been exposed to foreign
  substances in the body they cause the bodys
  thermostat (located in the hypothalamus) to set
  its temperature higher
• higher body temperatures enhance phagocytosis and
  cause the liver and spleen to sequester iron and
  zinc (making these essential elements less
  available to bacteria) pathogens also do not
  grow very well at higher temperatures

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Adaptive Defenses - the bodys third line of
defense (view the Interactive Physiology tutorial
Immune System Common Characteristics of B and T
Lymphocytes)

• Adaptive Defenses are Specific, Systemic, and
  have Memory they include Humoral Immunity
  (antibody-mediated) and Cellular Immunity
  (cell-meditated)
• B and T Lymphocytes are key players in adaptive
  immunity
• Antigens (fig. 21.7)
• have multiple antigenic determinants (based on
  shapes)
• self-antigens are the shapes that lymphocytes
  expect to find in the body (thus lymphocytes do
  not normally attack them)
• antigen receptors are specific and diverse

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Adaptive Defenses

• Education of Lymphocytes
• immunocompetence - the lymphocyte is able to
  recognize its one specific antigen by binding to
  it
• self-tolerance - the lymphocyte is unresponsive
  to self-antigens, so that it does not attack the
  bodys own cells
• T cells become immunocompetent and self-tolerant
  in the thymus, whereas for B cells this occurs in
  the bone marrow
• Autoimmune Diseases - lymphocytes attack the
  bodys own cells e.g. Type 1 Diabetes mellitus,
  Graves disease, and Multiple sclerosis
• Memory Cells - are created in large numbers
  during a primary immune response (exposed to
  antigen for first time) memory cells create a
  larger number of effector cells during a
  secondary immune response (exposed to antigen
  again) thus, the response to the second attack
  will be much greater

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