Immunology Non-specific Host Defenses

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ImmunologyNon-specific Host Defenses

• Non-specific means that the defenses that are
  used to protect the body act the same no matter
  what the infection is. Specific defenses are
  specific to the disease, such as antibodies made
  for each individual disease.

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Nonspecific Host Defenses

• Skin and mucous membranes provide a mechanical
  barrier to keep organisms from entering the body.
  They work only if there are no cracks or tears,
  etc.
• Additional aids to contribute to the defense
  provided by the skin and mucous membranes are
• Lacrimal secretions (tears) wash dirt and germs
  from the eyes
• Saliva washes food and germs off of the teeth
• Mucous in RT and GIT traps dirt and germs so
  they cant colonize the membrane surface

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• Ciliated cells move mucous, dirt and germs out
  of the body
• Urine washes dirt and germs out of the urethra
• Vaginal secretions helps maintain normal pH,
  washes out dirt and germs
• Chemical factors that aid in defense
• Sebum oil made by glands of the skin, trap dirt
  and germs
• Perspiration flush org. off skin and produce
  lysozyme (break down cell wall of G)
• Gastric juice destroys most bacteria and toxins
  due to pH and acids

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• Normal Microbiota
• Aid in preventing disease by
• competing for attachment sites.
• competing for nutrients.
• making and excreting antimicrobials.
• Genetics
• Some host are genetcially resistant to infection
  by some organisms. For example, many diseases
  are specific to humans and do not infect animals,
  or vice versa.
• Monkeypox infects monkeys but does not cause
  disease in humans

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Nonspecific Defenses in the Blood

• Phagocytes (White Blood Cells) 2nd line of
  defense.
• Neutrophils first responder to the scene of the
  accident. Neutrophils begin cleaning up invading
  microorganisms by phagocytosis.
• As the infection progresses, macrophages dominate
  the clean up process.
• They begin as monocytes. Monocytes are not
  active phagocytes while in the blood. Once they
  move out of the blood vessels and into the
  infected tissue, they mature into macrophages,
  active phagocytes.

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The process of phagocytosis

• See Fig. 14.19
• Recognition Pathogen recognized as foreign by
  phagocyte due to foreign proteins on the surface
  of the organism.
• Proteins on the surface of cells are used as
  markers to identify the good guys and the bad
  guys. The bodys cells have markers that tell
  the immune system that they belong there and not
  to attack while the bad guys have foreign markers
  that are not recognized and signal the immune
  system that it doesnt belong there.
• Adherence phagocyte binds to pathogen.
• Ingestion pseudopods are extended around the
  pathogen and the pathogen is engulfed into a sac
  inside the cell. This is called a phagosome.

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• Digestion lysosomes within the cell migrate to
  the phagosome and merge with it, creating a
  phagolysosome. Chemicals that are toxic to the
  pathogen are released inside the phagolysosome
  leading to its digestion.
• Release of Debris Once the pathogen has been
  digested into small particles, the cell releases
  the undigestible debris into the surrounding
  environment.

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Inflammation

• Triggered by damage to bodys tissues.
• 5 signs and symptoms
• Redness
• Pain
• Heat
• Swelling
• Sometimes loss of function

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• Purpose of Inflammation
• Destroy injurious agent and remove it if
  possible.
• Limit effects on body by walling off injurious
  agent and its by-products away from the rest of
  the body.
• Repair tissue damaged by the injurious agent or
  its by-products.

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• 3 stages of Inflammation
• Vasodilation and increased permeability of blood
  vessels
• Increase in blood flow to help get the immune
  cells to the injured site more quickly and dilute
  toxic substances.
• Allows defensive substances, such as phagocytes,
  to pass through the walls and enter the injured
  area.
• Phagocyte Migration and Phagocytosis
• Blood flow decreases, phagocytes begin to squeeze
  between endothelial cells to reach damaged area.
• Phagocytes begin destroying invading
  microorganisms.

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• Tissue repair
• Begins during inflammation but cannot be
  completed until all harmful substances have been
  removed or neutralized.
• Fever
• The benefits of fever as still being debated and
  proved.
• It was thought as recently as 5-10 years ago that
  the increased body temperature killed invading
  microorganisms by providing an atmosphere that
  was too hot for them to survive.
• That has since been shown to be mostly false.
  Most microorganisms require a much higher
  temperature change to be affected than that
  caused by a fever.

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• However, your textbook does mention a few
  organisms that seem to be sensitive to the small
  temperature change, such as the Polio virus and
  the Chickenpox virus.
• There is some evidence that fever impedes the
  nutrition of bacteria by reducing the available
  iron.
• And it increases metabolism and immune responses.
• In general, whether or not slight to moderate
  fevers should be treated is still being debated.

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Other Antimicrobial Substances In Blood

• Complement and Interferon
• Complement Has several different functions.
• 20 different proteins found in normal serum.
• Punch holes in membranes of pathogens, releasing
  cellular contents. Called the Membrane Attack
  Complex or MAC.
• Contribute to development of inflammation.
• Coat outside surface of pathogen which enhances
  phagocytosis.

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• Interferon chemical made and released by cells
  infected by viruses.
• When the interferon is released it binds to
  receptors on the outside of neighboring cells.
• It actually works to block the virus from being
  able to bind to neighboring cells. That means
  that the virus cant infect neighboring cells
  because the attachment sites are taken by
  interferon.
• It also signals the cell to make antiviral
  proteins that inhibit viral replication.
• It sounds like a great treatment for viral
  infections but generally it isnt very effective.
  It is thought that the reason is because the
  amount of interferon needed to actually coat the
  cells and keep them continually protected is too
  great to maintain.
• See Fig. 14.20
• No HW.