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Immune System

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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Immune System

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  1. Immune System

  2. 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)

  3. 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.

  4. 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

  5. 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.

  6. 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

  7. 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

  8. 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

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