non-specific animal defences against pathogens

• state all the seven non-specific defences for keeping pathogens out of the body

  • skin
  • mucous membranes
  • lysosomes in tears and urine
  • acid in stomach
  • coughing/sneezing/vomiting/diarrhoea
  • blood clotting and wound repair
  • inflammatory response
• how does skin act as a physical barrier to the entry of pathogens?

  • skin flora of healthy microorganisms that outcompete pathogens for space on the body's surface
  • produces oily sebum which inhibits pathogenic growth
• how do mucous membranes keep pathogens out of the body?

  • airways of gas exchange system and body's tracts lined with mucous membranes that secrete mucous
  • traps microorganisms and contains lysozymes which destroy bacterial and fungal cell walls
  • contains phagocytes which remove remaining pathogens
• how do lysozymes help keep pathogens out of the body?

  • in tears and urine
  • kill bacterial and fungal cell walls
• how does acid in stomach kill pathogens?

  low pH breaks down pathogenic cell walls
• how can pathogens be expelled from the body before they enter?

  • coughing/sneezing- ejects pathogen laden mucous
  • vomiting/diarrhoea- expel contents of the gut which might contain pathogens
• state how blood clotting works

  • platelets release thromboplastin- enzyme which triggers cascade of reactions
  • forms fibrin
  • this fibrin forms a network, which traps platelets and forms a clot
  • serotonin is also released by platelets- makes the smooth wall in the blood vessels contract so blood flowing to the area is restricted
• how does a wound form?

  • tough scab formed from clot which keeps pathogens out
  • epidermal cells below scab grow and seal the wound off to pathogens
  • collagen fibres deposited to give new tissue strength
  • scab sloughs off
• what are the characteristics of an inflammation?

  • pain
  • heat
  • swelling
  • redness of tissue
• what type of response is the inflammatory response to pathogens?

  a localised response
• what do histamines do in the inflammatory response?

  • make blood vessels dilate causing localised heat and redness
  • make blood vessel walls more leaky so blood plasma (tissue fluid) is forced out- causes swelling and pain
• what do cytokines do in the inflammatory response?

  attract white blood cells to the site, WBCs dispose the pathogen by phagocytosis
• state 2 non specific defences for getting rid of pathogens

  • fever
  • phagocytosis
• why do we get fevers?

  • higher temperatures inhibit pathogenic reproduction (optimum temp to do so is 37 degrees)
  • immune system works faster at higher temps
• what are the two main types of phagocytes?

  • neutrophils
  • macrophages
• state the stages of phagocytosis

  1. pathogens produce chemicals attracting phagocytes
  2. phagocytes recognise foreign antigens on the pathogen
  3. phagocyte engulfs pathogen and encloses it into vacuole called phagosome
  4. phagosome fuses with a lysosome to form phagolysosome
  5. enzymes from lysosome digest and destroy pathogen
  6. neutrophils stop here but macrophages combine antigens with MHC and present them on their cell membrane, becoming an APC
  7. these antigens stimulate cells involved in specific immune response

  
• what are opsonins?

  bind to pathogens and tag them so they are easier recognised by phagocytes
• what are cytokines?

  • cell signalling molecules that inform phagocytes that the body is under attack, stimulates them to move to the site of infection/inflammation
  • increase body temp and stimulate the specific immune system