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Immune System. Means of Defense (3 categories). First two are Nonspecific A. Barriers Doesn’t distinguish between agents Helps Prevent Entry into the body Includes skin and mucous membranes which provide a mechanical and chemical barrier

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means of defense 3 categories
Means of Defense (3 categories)
  • First two are Nonspecific
  • A. Barriers
    • Doesn’t distinguish between agents
    • Helps Prevent Entry into the body
    • Includes skin and mucous membranes which provide a mechanical and chemical barrier
    • Oil and sweat glands give skin an acidic pH which discourages bacterial growth
    • Perspiration, tears, and saliva contain an enzyme lysozyme which breaks down the cell walls of bacteria.
    • Stomach acid kills bacteria
    • Nostril hairs-filter out particles and mucous traps microorganisms. (swept out by cilia)
means of defense 3 categories3
Means of Defense (3 categories)
  • B. Nonspecific Internal Defenses
    • 1. Phagocytic cells like neutrophils and monocytes attack microorganisms that get through the skin barriers. They engulf them and consume bacteria, viruses and cell debris in the interstitial fluid.
    • Neutrophils make up 60-70% of WBC’s. Short lived.
    • Monocytes become macrophages which live a long time.
    • Many wander but some are permanent residents in organs like the lung or brain
    • Can engulf 100+ bacteria
    • 2. Natural Killer Cells
    • Destroy the body’s own infected cells-especially those with viruses in them
    • Destroys cells which may be changing and could form tumors
    • Not phagocytic but lytic-breaks cell membranes.
means of defense 3 categories4
Means of Defense (3 categories)
  • 3. The Inflammatory Response
  • Triggered by damage to tissues by injury or microorganisms
  • Injured cells give off a substance that aids the inflammatory response
  • release histamine-which causes dilation of neighboring blood vessels and makes the capillaries more leaky (histamine is contained in WBC’s called basophils and in mast cells (in connective tissue)
  • Small blood vessels dilate and this increased blood flow causes the redness, heat and swelling associated with infection. Blood vessels also become leakier causing swelling due to increased fluid.
  • The increased blood flow enhances migration of phagocytic WBC’s from the blood to the interstitial fluid
  • neutrophils first
  • followed by monocytes that develop into macrophages
more inflammatory response
More Inflammatory Response
  • Pus- is mostly dead cells and accumulated fluid (will be absorbed)
  • Clotting proteins in plasma seal the area off and prevent the spread of infection.
  • Systemic Reactions
    • the number of WBC’s circulating is increased ( may be dramatic and within hours)
      • fever
      • toxins from the pathogens may trigger fever.
      • Some WBC’s release pyrogens which set the body thermostat higher
      • The higher temperature stimulates phagocytosis and inhibits the growth of microorganisms and may speed up repair.
still more non specific response
Still More Non-specific Response
  • 4. Antimicrobial Proteins- Some proteins attack microorganisms or negatively affect their reproduction.
    • A. Interferon- a substance produced by a virus infected cell that helps other cells resist the virus
    • -The virus turns on the interferon gene- can save the infected cell but diffuses to nearby cells and inhibits viral reproduction there
    • -Host specific-not virus specific
    • -Inteferon may act against cancer since some may be induced by viruses
    • one kind mobilizes natural killer cells-destroys tumor cells
    • may change malignant cell membranes- make them less likely to metastasize
    • activates macrophages
another antimicrobial protein
Another Antimicrobial Protein
  • B. Complement
    • many (at least 20) proteins that work with other defense mechanisms
    • They circulate in the blood in an inactive form
    • They are activated by the immune response or markers on microorganisms
    • They increase the inflammatory response- histamine release and attraction of phagocytes.
    • They coat microbes- this increases the rate of phagocytosis by opsonization (“making tasty”)
    • They team up to cause lysis of the microbial membrane
the third line of defense
The Third Line of Defense
  • C. Specific Immune Response
    • The immune system learnsto distinguish “self” from “non-self”
    • Detects “antigens”- foreign substances . These cause an increase in the cells that attack or produce antibodies. They may be things like molecules on surfaces of viruses and bacteria or marker molecules on transplanted organs.
    • The immune response must be activated by the presence of an antigen
    • The response is specific for a particular foreign substance or invader
    • The system remembers the antigens after the initial contact. There is a quick response the second time. This is memory.
    • Vaccination- immune response is prevented with a nonvirulent or weakened form of a pathogen-initiates long term capability to respond quickly to real infective agent.
    • -Active immunity- body produces antibodies
    • -Passive immunity- body acquires antibodies from other sources such as placenta, injection, immunity is temporary