Immune System

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Immune System

• Chapter 21

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Immune system

• Immunology study of the immune system
• Immunity - elaborate defense system of the human
  body
• Immune system functions
• protects the body from pathogens
• protects the body from all other foreign agents
  pollens (ragweed),toxins (bee stings), own cells
  that have gone astray (cancer cells)

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Classification of the Immune system

• Non-specific immunity -
• Specific immunity-

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Non-specific ImmunityBody does not need to
recognize the specific foreign agent

• First Line of Defense -
• Mechanical barriers - intact skin, mucous
  membranes...pathogens cant cross to enter body
• Chemical barriers - secretions of the mucous
  membranes assist in defensive function
• Ex. tears, sweat, saliva wash away
  microorganisms, tears establish hostile
  environment to preventing colonizing
• Certain reflexes -
• sneezing, coughing help remove pathogens
  from the respiratory tract
• vomiting, diarrhea help remove pathogens from the
  digestive tract

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Second Line of Defense

• Phagocytosis
• Inflammation
• Fever
• Protective Proteins
• Natural Killers

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Phagocytosis

• Phagocytose - eat, destroy pathogens
• Wandering phagocytes - neutrophils/monocytes are
  signaled by injured cells (chemotaxis)...neutrophi
  ls/monocytes travel through the blood to site of
  infection...then squeeze through gaps in the
  epithelial tissue (diapesis)
• Fixed phagocytes - monocytes deposit themselves
  in various organs (liver, spleen, lungs, lymph
  nodes)...give rise to macrophages, the big
  eaters

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Inflammation

• Bodies response to an irritant
• Irritant friction, heat, cold, radiations,
  chemicals, injuries
• when pathogens irritate the body...infection
• Characterized by redness, swelling, heat, pain
• Caused by Inflammatory response
• Injured cells release histamine, causes blood
  vessels to dilate, more blood flow to area (heat)
  (redness)
• Histamine also causes the leak fluid and
  dissolved substances into the tissue spaces
  (swelling)(pain)...

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Inflammatory Response
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Fever (pyrexia)

• Pyrogens - fever producing substances released by
  phagocytes as their perform their duty
• Pyrogens stimulate the hypothalamus to reset the
  body temperature...producing a fever
• Fevers are beneficial in two ways
• stimulates phagocytosis
• decreases the ability of certain pathogens to
  multiply

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Fever

• Elimination of the fever may do more harm than
  good..
• Studies show that the reduction of fever prolongs
  and infection however... high body temperatures
  may cause severe, irreversible brain damage.
  High fevers in children usually are accompanied
  by a seizure (febrile seizure).

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Protective Proteins

• 2 groups of protective proteins
• Interferons
• group of proteins secreted by the cells that are
  infected by the virus
• they interfere with viral replication
• activate the NK cells and macrophages ...boosting
  the immune system
• Compliment proteins
• circulate in the blood in an inactive form
• when activated...they swarm over the bacterium,
  attach to the bacterium's outer membrane, punch
  holes in the membrane allowing fluid and
  electrolytes to enter...burst...die
• activated compliments perform other functions
  that enhance phagocytosis and the inflammatory
  response

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Natural Killers (NK)
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Specific ImmunityThird Line of defense

• Specific immunity targets a foreign substance and
  provides protection against one specific
  substance... but no others
• 2 Cells that play a key role
• Lymphocytes (B lymphocytes, T lymphocytes)
• Macrophages
• Understand Antigens to understand Lymphocytes

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Antigen

• Antigen is a substance that stimulates the
  formation of antibodies
• Antigens are found on the surface of many
  substances...pathogens, red blood cells, pollens,
  food, toxins, and cancer cells
• Foreign substances that display antigens are
  described as antigenic
• Antigenic substances are attacked by lymphocytes!!

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• The key to a healthy immune system is its
  remarkable ability to distinguish between the
  bodys own cells (self) and foreign cells
  (non-self). The bodys immune defenses normally
  coexist peacefully with cells that carry
  distinctive "self" marker molecules. But when
  immune defenders encounter cells or organisms
  carrying markers that say "foreign," they quickly
  launch an attack.

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Lymphocytes

• T Lymphocytes (T Cells) - 50 of lymphocytes
  travel to the thymus gland to mature and
  differentiate...eventually they leave the thymus
  gland to lymphoid tissue (spleen, lymph nodes)
  and some circulate in the blood
• B Lymphocytes (B Cells) - differentiate in fetal
  liver and bone marrow...take up residence in
  lymphoid tissue
• Both T cells and B cells attack antigens ...in
  different ways
• T cells attack antigens directly (cell-to-cell
  contact)
• B cells interact with the antigen
  indirectly...through the secretion of antibodies
  called antibody-mediated immunity

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Antibodies

• Antibodies are proteins secreted by the B Cells
  called Immunoglobulins
• Immunoglobulins are found primarily in the plasma
• 3 most abundant (total 5)
• IgG (immunoglobulin G)
• IgA (immunoglobulin A)
• IgM (immunoglobulin M)

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What do antibodies do?

• Antibodies destroy pathogens in 2 ways...
• Directly bind to antigens (antibody-antigen
  reaction)
• Agglutination (clumping together) occurs making
  it easier for the phagocytic cells to destroy the
  cells
• Indirectly activation of the compliment proteins
• cause a variety of effects
• chemotaxis (chemical attraction of more
  phagocytes)
• promotes agglutination...more phagocytosis
• encourages lysis (rupture of the pathogen)

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Primary and Secondary response

• Primary response - initial response to an antigen
• when the B cells produce many plasma cells and
  memory cells --remember plasma cells secrete
  antibodies
• associated with low levels of plasma antibodies
• Secondary response - when exposed to the same
  antigen for a second time...
• immune system responds quickly and produces a
  larger amount of antibodies

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Secondary response benefits

• Secondary response means you are immune!
• Example... if you had measles as a child, you
  already developed antibodies and many memory
  cells...if exposed again, memory cells quickly
  call to action the antibody secreting plasma
  cells
• Level of antibodies in your blood is called an
  antibody titer

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Types of Immunity

• Genetic
• Acquired
• Naturally acquired (active)
• Passive
• Artificially acquired
• Vaccine
• Immune globulin
• Antitoxins, Antivenoms

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Allergic Reactions
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Autoimmune Disease
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Meet Your Immune System

• Germs are awful things that get inside your
  bodies through the nose, mouth, scrapes, and any
  other way they can get in.   Although the fevers
  mean your immune system is fighting against
  germs, you probably wish there were other ways to
  show that they are fighting.
• The first immune fighters at the site are the
  phagocytes.  Some release a chemical that
  causes a fever.  That heat is another way of
  killing some germs, because they prefer a
  temperature of 98.6 degrees.
• White blood cells are first on the spot along
  with the phagocytes and lymphocytes.  They help
  destroy the germs, but also they warn the rest of
  your body that germs have invaded.
• Helper T-cells are in the command.  They control
  the entire immune T-cell system and give orders
  about how to destroy the germ.

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• Then the Killer T-cells arrive.  T-cells are made
  in the marrow of our bones.  They stay there
  until they are needed.  Then they go to the
  thymus to get circulated into the blood searching
  for germs.  When they find germs, the Killer
  T-cell helps the phagocytes kill the germ.
• When Helper T-cells call for the B-cells they
  come out of the bone marrow.  B-cells are made in
  the marrow of your bones.  They stay there until
  T-cells call for them. 
• Each germ has proteins called antigens on its
  surface.  Antibodies are proteins that attach to
  the germ's antigens.  Think of it like a boat
  dock.   If one boat docks, another cannot fill
  the same space.  Antibodies fill the germ's dock
  so it can not attach to a cell and infect it. 
  Antibodies are made by the B-cells. 
• Suppressor T-cells get there when the battle is
  over and it looks safe. They tell the Killer
  T-cells to stop fighting. Inhibitors!
• Memory T-cells are sent after the Suppressor
  T-cells.  They patrol the area and watch for the
  germ's return.   If the germ returns, they alert
  the system which already has a strategy for
  fighting this germ.