Disease

• Microbes


  Organisms too small to be seen by the naked eye
• Microbes


  • Can enter the body through the mouth, nose and cuts or bites in the skin
  • Bacteria and viruses can cause diseases
• There are billions of microorganisms inside us and on our skin. Over 95% of those inside us right now are helpful - or at least harmless. The rest are not nice to have around - they may multiply rapidly inside our bodies and cause infectious illness; these nasty ones are called pathogens
• Pathogens


  Microbes that cause problems by either releasing toxins (poisons), or invading and damaging our cells (if they are viruses)
• Body's first line of defence


  • Thick skin, sticky mucus and cilia in the respiratory system, enzymes in tears, and acid in the stomach which kills most pathogens that enter our stomachs via our food
• Body's second line of defence


  • White blood cells attack the microbes in various ways and usually manage to destroy them, providing a scab for protection
• Vaccination


  Pathogens are introduced into the body in a weakened form, causing the body to produce enough white blood cells to protect itself against the pathogens, while not getting diseased
• Antibiotics


  Effective against bacteria but not viruses. Some strains of bacteria are resistant to antibiotics.
• Some diseases are not caused by pathogens and so are not infectious, such as scurvy, anaemia, diabetes and cancer
• Some disorders are inherited, such as red-green colour vision deficiency
• Cancer


  Happens when cells begin to divide out of control, forming tumours that can sometimes be felt as an unusual lump in the body. Diet and lifestyle can increase the risk of developing certain cancers.
• Tumours


  • Benign tumours grow slowly and are usually harmless, while malignant tumours often grow more quickly and may spread throughout the body
• Parasites


  Organisms that live on or in a host organism, benefiting from the arrangement but causing the host to suffer
• Malaria


  A disease caused by a protozoan, a type of single-celled organism, spread from person to person by mosquitoes (the vector)
• It is important to understand the life cycle of a pathogen and the way in which vectors spread the pathogen, as this knowledge gives scientists ideas about how the spread of a disease might be controlled
• Controlling the spread of malaria


  Avoiding contact with the vector (mosquitoes) by using mosquito netting, killing mosquitoes with insecticides, and giving infected people drugs to kill the parasite
• What white blood cells do


  • Engulf the microbe
  • Produce antibodies to neutralise the microbe
  • Produce antitoxins to neutralise the toxins released by the microbe
• Types of white blood cells


  • Lymphocytes
  • Phagocytes
• Lymphocytes


  Carry a specific type of antibody that neutralises a certain antigen
• How lymphocytes neutralise pathogens


  1. Lymphocyte with appropriate antibody meets antigen

  2. Lymphocyte reproduces quickly

  3. Makes many copies of antibody that neutralises pathogen
• Ways antibodies neutralise pathogens


  • Bind to pathogens and damage or destroy them
  • Coat pathogens, clumping them together so that they are easily ingested by phagocytes
  • Bind to pathogens and release chemical signals to attract more phagocytes
• Phagocytes


  • Can pass through blood vessel walls into surrounding tissue and move towards pathogens or toxins
  • Ingest and absorb pathogens or toxins
  • Release enzymes to destroy them
  • Send out chemical messages to help nearby lymphocytes identify the type of antibody needed
• Natural Killer Cells are the most aggressive white cells in the immune system
• Natural Killer Cells target tumor cells and protect against a wide variety of infectious microbes
• Immune Stimulation is the key to keeping the white blood cell count high and giving the Natural Killer Cells a chance to fight cancer and other diseases
• Vaccination


  Putting a small amount of an inactive or weakened form of a pathogen into the body to stimulate white blood cells to produce antibodies against the pathogen
• What vaccines can contain


  • Dead pathogens
  • Live pathogens treated to make them harmless
  • Harmless fragments of the pathogen
  • Toxins produced by pathogens
• Vaccines in early childhood can give protection against many serious diseases
• Vaccine boosters are needed because the immune response "memory" weakens over time
• Some bacteria and viruses mutate very quickly, making vaccines less effective
• Antibiotics kill bacteria or stop their growth, but do not work against viruses
• Penicillin was the first antibiotic, discovered in 1928 by Alexander Fleming
• Bacterial strains can develop resistance to antibiotics through natural selection
• MRSA is a very dangerous strain of bacterium that is resistant to most antibiotics
• Maintaining personal hygiene and keeping hospitals clean can reduce the risk of infection
• The body's defences against pathogens


  • Skin
  • Blood clotting
  • Mucus
  • Stomach acid
• Skin


  • Protects the body from physical damage, microbe infection and dehydration
  • Dry, dead outer cells are difficult for microbes to penetrate
  • Sebaceous glands produce oils that help kill microbes
• Blood clotting


  Platelets and fibrin form a scab to close a wound and prevent more microorganisms from entering
• Mucus


  Traps dust and microbes, which are then carried away by cilia (tiny hairs on cells lining the respiratory system)
• Stomach acid


  Kills harmful microorganisms in food and drink