3.5

• Antibody


  A protein produced by the immune system in humans and other animals which attacks foreign organisms (antigens) that infiltrate the body
• Antigen


  Protein found on the surface of the pathogen and alert the body to an infection
• Bacteria


  Single-celled micro-organism, of which some can be pathogenic (harmful)
• Cilia


  Tiny hair-like projections from a cell that help sweep particles away from a cell (e.g. sweep dust away from the lungs)
• Ciliated cells


  Cells with tiny hair-like structures on their surface
• Cytokines


  Protein molecules that act as a signal to specific white blood cells causing them to accumulate at the site of infection
• Enzyme


  A protein which speeds up a chemical reaction
• Goblet cells


  Cells in the lining of the airways which produce mucus to trap dust and invading pathogens
• Immune system


  The body's defence system against invading pathogens and agents such as pollen grains. The role of the immune system is to prevent disease
• Lymphocytes


  White blood cells which produce antibodies to attack pathogens
• Lysosomes


  Organelle found in the cytoplasm of some cells which contains digestive enzymes
• Mucus


  Slimy white protein which lines the respiratory tract and gastrointestinal tract
• Pathogen


  A bacterium, virus or other organism that can cause disease
• Phagocytes


  Cells, such as white blood cells, which engulf and destroy harmful micro-organisms (pathogens), or other foreign bodies in the bloodstream and tissues by phagocytosis
• Phagocytosis


  Involves the engulfing of pathogens and their destruction by digestive enzymes contained in lysosomes
• Vasodilation


  The increase in diameter of the skin arterioles to increase blood flow and increase heat
• The body is constantly defending against attacks from pathogens
• The first line of defence against pathogens

  1. Non-specific (does not target certain types of pathogen)

  2. Physical OR chemical barriers
• Physical barriers against pathogens

  • Skin (Epithelial cells)
  • Nose
  • Mucus and ciliated cells
• Epithelial cells form a physical barrier
• The skin covers almost all parts of your body to prevent infection from pathogens
• If the skin is cut or grazed it immediately begins to heal itself, often by forming a scab
• The nose has internal hairs, which act as a physical barrier to infection
• Cells in the nose produce mucus. This traps pathogens before they can enter the lungs
• When the nose is blown, mucus is removed and any pathogens are trapped within it
• The cells that line the trachea also have hairs called cilia (ciliated cells)
• The ciliated cells beat and sweep mucus and pathogens upwards towards the throat where it is swallowed into your stomach
• Goblet cells create the mucus in order to trap pathogens. The production of mucus in your airways is a physical barrier
• Chemical barriers against pathogens

  • Tears and saliva
  • Stomach acid
  • Mucus
• Tears and saliva have enzymes (e.g. lysozymes) that destroy bacterial cells by breaking down their cell walls
• Hydrochloric acid, in the stomach, is strong enough to kill any pathogens that have been caught in mucus in the airways or consumed in food or water
• Mucus is a sticky substance secreted by goblet cells in the trachea. Foreign particles and pathogens are trapped by the mucus and cilia sweep the mucus away from the lungs
• The inflammatory response


  1. Physical injury or infection occurs

  2. Mast cells (immune cells) release chemical called histamine

  3. Histamine stimulates blood vessels to vasodilate and increases permeability of capillaries

  4. This causes an increased blood flow

  5. Phagocytes and clotting elements accumulate at the site of injury or infection
• Phagocytes (non-specific defence)


  Phagocytes recognise pathogens and destroy them by phagocytosis. Phagocytes release cytokines which attract more phagocytes to the site of infection