Non- specific animal defences

• • skin provides a barrier- produces sebum, inhibits growth of pathogens.
  • acid in stomach
  • enzymes in tears
  • airways lined with cilia- goblet cells produce mucus
• Blood clotting

  = prevents lost of blood being lost

  1. damaged blood vessel releases thromboplastin which converts to prothrombin and thrombin
  2. fibrinogen converts to fibrin= forms a network of fibres that traps platelets and blood cells, platelets plug (scab forms)
  3. underneath the scab- epidermal cells below start to grow, sealing the wound permanently, while damaged blood vessels regrow.
  4. collagen fibres are deposited to give the new tissue strength.
• mast cells 


  = are activated in damaged tissues and release chemicals called histamines and cytokines.
• histamines

  = make blood vessels dialate, causing localised heat and redness- raised temperature prevents pathogens reproducing.

  • make blood vessel walls more leaky so white blood cell can get out.
• cytokines

  = signalling molecule attract white blood cells- phagocytes

  • interleukins
• antigens

  =molecule on surface of a cell that can trigger an immune response.
• fevers

  -normal body temp 37 is maintained by hypothalamus

  • pathogen invades body, cytokines stimulate hypothalamus to reset thermostat and your temp rises.
  • most pathogens reproduce best at or below 37 so a higher temp inhibits pathogen reproduction.
  • specific immune system works faster at higher temperatures.
• neutrophill

  • lobed nucleus

  
• macrophage

  • undefined shape

  
• phagocytosis in neutrophils

  1 phagocyte attracted by chemicals produced by pathogen.

  2. phagocyte recognises pathogen as non-self and binds to it.

  3. phagocyte engulfs the pathogen, pseudopodia forms around pathogen to form a phagosome

  4. lysosomes move towards phagosome and combines with it forming phagolysosome.

  5. In phagolysosomes, digestive enzymes from lysosome break down the pathogen.
• Macrophages

  -when it has digested the pathogen, it combines antigens from the pathogen surface membrane with glycoproteins in cytoplasm called major histocompatibility complex (MHC)

  -moves pathogen antigens to macrophages cell surface- membrane so it then becomes an antigen presenting cell

  -these antigens stimulate other cells to help.
• opsonins 


  = tags, chemicals that bind to pathogens and 'tag' them so they can be more easily recognised by phagocytes. Phagocytes have receptors on cell membranes that bind to opsonins and the phagocyte then engulfs the pathogen.