non specific body defences

• A pathogen is a bacterium, virus or other organism that can cause disease/harm.
• Antigens are molecules, often proteins located on the surface of cells that trigger an immune response.
• Physical:

  Closely packed epithelial cells are found in the skin and inner linings of the digestive and respiratory systems are physical defences.
• Chemical:

  Chemical defences include secretions such as tears, saliva, mucus and stomach acid.
• Histamine is released by mast cells causing vasodilation and increased capillary permeability. The increased blood flow leads to an accumulation of phagocytes and clotting elements at the site of infection.
• Phagocytes are white blood cells which recognise pathogens and destroy them by phagocytosis.
• Phagocytosis involves the engulfing of pathogens and their destruction by digestive enzymes contained in the lysosomes.
• Cytokines are protein molecules that act as a signal to specific white blood cells causing them to accumulate at the site of infection.
• The skin around a puncture wound often becomes red and swollen due to increased permeability of capillaries.