non specific defence against pathogens

• Our bodies have many ways in which they try to defend themselves from invading pathogens -

  • cilia
  • skin
  • stomach acid
  • nose hairs
  • tears
  • pus
• Chemical defence – Chemicals or enzymes used to destroy pathogens before they enter the blood 
• Physical defence – Physical barriers that prevent pathogen entering the body
• Skin -

  • Barrier defence
  • Oily sebum production prevents pathogen growth
  • Natural flora outcompete other potential pathogens
• Lysozymes -

  • Found in tears
  • Enzymes which break down bacterial cell walls
  • Also help to prevent pathogen entry
• Mucous membranes -

  • These line most tracts within the human body
  • Examples include the airways- these contain cilia to help waft trapped microorganisms back up and out of the airway to be removed from the body.
  • They secrete mucus which:

  1. Contains lysozymes
  2. Contains specialised immunological cells called phagocytes
  3. Traps microorganisms
• Blood clots - Exposure of platelets with collagen in damaged skin or blood cell wall leads to clotting

  1. Platelets exposed to collagen
  2. Release Thromboplastin and serotonin
  3. Thromboplastin – enzymes cause cascade of reactions to clot blood
  4. Serotonin – cause smooth muscle to contract and narrow blood vessel
  5. Clot dries forming a scab while blood vessel and skin are repaired fully
• Inflammatory response - A localised response characterised by pain, heat, redness and swelling

  Mast cells in damaged tissue cause the release of :

  • Histamines

  1. Make blood vessels dilate
  2. Make blood cells leaky to form more tissue fluid leading to swelling
  3. Raise temperature

  • Cytokine

  1. Attract white blood cells to site so that phagocytosis can occur
• Expulsive reflexes - These are ways in which to eject or remove pathogens from the body

  • sneezing
  • diarrhoea and vomiting
  • coughing
• Plants contain receptors which respond to pathogens and cause signals to be sent to trigger responses in the plant.
• Callose - When plants get attacked they produce a Polysaccharide called Callose

  1. Callose is deposited next to the infected cell between the cell membrane and the cell wall. (BARRIER)
  2. This continues after initial infection and lignin is also added making a thicker, stronger barrier
  3. Callose blocks sieve plates in phloem cutting off infected area (PREVENT SPREAD)
  4. Callose blocks off plasmodesmata to seal off healthy cells  (PREVENT SPREAD)
• Plants can produce chemicals to repel insect vectors or to directly kill pathogens.

  Examples include:

  • insect repellents such as citronella
  • Insecticides such as pyrethrins, which are neurotoxins, and caffeine which is toxic to insects.
  • Antibacterial compounds such as lysosomes, defensins (disrupt cell membrane)
  • Antifungal compounds- examples include gossypol (cotton), saponins (affect the cell membrane of fungi) and chitinases (break down chitin in cell wall of fungi)
  • Anti-oomycetes- These are enzymes which break down polymers called Glucans in the cell wall of oomycetes.