Infection and Response

• Pathogens


  Microorganisms that enter the body and cause communicable (infectious) disease. Plants and animals can be infected by them.
• Bacteria


  • Small cells that can reproduce very quickly in the body, produce toxins that make you feel ill, damaging your cells and tissues
• Viruses


  • Much smaller than bacteria, can also reproduce quickly in the body, live inside your cell where they replicate, then burst out of the cell, releasing new viruses
• Protists


  • Eukaryotes (multicellular), some are parasites which live on or inside other organisms, often carried by a vector
• Fungi


  • Sometimes single celled, others have hyphae that grow and penetrate human skin and the surface of plants, can produce spores which can spread to other plants
• Pathogens can be spread in many ways, for example: water, air, direct contact
• Ways to prevent the spread of pathogens: being hygienic, destroying vectors, isolation, vaccination
• Skin


  • Acts as a barrier to pathogens
• Nose


  • Hairs and mucus trap particles
• Trachea and bronchi


  • Secrete mucus to trap pathogens, have cilia which move backwards and forwards to transport the mucus towards the throat, trapping any pathogens, the mucus is usually swallowed
• Stomach


  • Contains hydrochloric acid to kill any pathogens that enter the body via the mouth
• Immune system


  • Kills any pathogens that enter the body
• Phagocytosis


  White blood cells engulf pathogens and then digest them
• Antitoxins


  Produced by white blood cells to neutralise the toxins
• Antibodies


  Produced by white blood cells, lock on to the antigen on the outside of the pathogen, white blood cells then destroy the pathogens, antibodies are specific to one antigen and will only work against that antigen
• Vaccination


  Involves an injection of a dead or weakened version of the pathogen, they carry antigens which cause your body to produce antibodies which will attack the pathogen, if you are infected again, the white blood cells can produce antibodies quickly
• Vaccinations have been developed to protect us from future infections
• Drug testing


  Pre-clinical testing (on cells, tissues, animals), clinical testing (on healthy human volunteers, placebo, blind trial, double-blind trial)
• Painkillers


  Relieve the pain and symptoms, but do not tackle the cause
• Antibiotics


  Kill the bacteria causing the problem, but do not work on viruses, viruses are very difficult to kill because they live inside the body cells
• Chemicals produced by plants to defend themselves can be used to treat human diseases or help with symptoms