Non specific

• Vertebrate animals


  • Have developed complex mechanisms to defend themselves against the invasion of pathogens
• Methods of defence


  • Physical
  • Cellular
  • Chemical
  • Commensal organisms
• Physical defence


  Body tissues act as barriers, preventing the entry of pathogens
• Physical defences


  • Skin
  • Mucous membrane of the alimentary canal
• Cellular defence


  Cells detect and signal the presence of pathogens. Protective substances are secreted and the pathogens are ingested and digested
• Chemical defence


  Secreted substances generate an inhospitable environment for the growth of pathogens. These substances can trap pathogens, cause them to burst, or prevent them from entering cells and reproducing
• Commensal organisms


  The harmless bacteria and fungi present on and in the body compete with pathogens for nutrients
• First line of defence

  • Skin
  • Mucous membranes
  • Expulsive reflexes
  • Chemical secretions
• Skin


  • Outer layer of dry, dead, hardened cells filled with keratin
  • Secretions of sebum that contain fatty acids which have antimicrobial properties
  • Evaporation of sweat leaves behind a salt residue
  • Lack of moisture, low pH and high salinity creates an inhospitable environment for the growth of microorganisms
• Mucous membranes


  • Line the gut, airways and reproductive system
  • Consist of epithelial cells and mucus-secreting cells like goblet cells
  • Mucus contains lots of glycoproteins with long carbohydrate chains that make it sticky
  • Trap viruses, bacteria, pollen and dust
  • Cilia move mucus towards the back of the throat
• Expulsive reflexes


  Cough or sneeze that expels air containing secretions from the respiratory tract and foreign particles
• Chemical secretions


  • Lysozymes are antimicrobial enzymes that breakdown the cell wall of bacteria
  • Hydrochloric acid in the stomach creates a low pH that kills ingested bacteria
  • Mucus secreted by gut cells prevents damage from hydrochloric acid
• Commensal microorganisms


  • Bacteria like Candida albicans and E. coli that grow on the skin, in the mouth and intestines but do not cause disease
  • They compete with pathogenic microorganisms and prevent them from invading host tissue
• Second line of defence

  • Blood clotting
  • Inflammation
  • Wound repair
  • Phagocytosis
• Blood clotting


  1. Release of molecules that trigger a chemical cascade

  2. Fibrin is produced to seal the wound

  3. Prevents excess blood loss and entry of pathogens
• Inflammation


  1. Mast cells secrete histamine

  2. Vasodilation increases blood flow

  3. Capillaries become "leaky" allowing fluid entry and swelling

  4. Plasma proteins leave blood

  5. Phagocytes enter tissue

  6. Cells release cytokines that trigger immune response
• Wound repair


  1. Scab formation from blood clotting

  2. Stem cells divide to heal wound

  3. New blood vessels form

  4. Collagen is produced

  5. Granulation tissue fills wound

  6. Stem cells form epithelial cells

  7. Contractile cells cause wound contraction

  8. Unwanted cells die
• All of the above are examples of non-specific immune responses
• Non-specific defences are present in humans from birth. The rapid response is the same for every pathogen; they do not distinguish between pathogens
• Non-specific defences are not always effective