Immunology

• Bacteria are typically 0.5 - 5 micrometres long.

  They are roughly shaped like a cylinder, although other shapes do occur.

  They do not have membrane-bound organelles, and so are prokaryotes.
• Many fungi are microscopic.

  Its average size is between 5 to 50 micrometres long.

  They have membrane-bound organelles, and therefore are eukaryotes.
• A protist is not an animal, plant or a fungus.

  Most protists are unicellular organisms.

  Protists are typically 1 micrometre to 2 milimetres long.

  Some protists are parasitic pathogens, such as Plasmodium, causing malaria.
• Viruses are acellular (not made of cells) and do not contain any organelles. They consist of genetic material surrounded by a protein coat.

  Viruses' size ranges from 20 to 350 nanometres, although some are as large as 1 micrometre.
• Bacteria

  Examples of disease:

  • chlamydia
  • gonorrhoea
  • tuberculosis

  Treated by antibiotics, but they are becoming increasingly resistant to them
• Viruses

  Examples of disease:

  • common cold
  • mumps
  • measles
• Fungi

  Example of disease:

  • yeast infection (thrush)

  Other fungal skin infections include toenail fungus and athlete's foot
• Prions

  Example of disease:

  • Creutzfeldt - Jakob disease

  These are non-living pathogenic proteins. The mutant form of prion protein, when ingested, can cause normal prion proteins to change shape. This causes damage to the nervous system and eventual death.
• Protists

  Example of disease:

  • malaria
• Parasites

  Example of disease:

  • toxoplasmosis

  This disease is caused by Toxoplasma gondii, a parasitic protist.
• What are the different ways in which pathogens may enter the body?

  Direct transmission

  • physical contact
  • sharing needles
  • transfusion of contaminated blood or blood products

  Airborne transmission

  • where the pathogen is carried by dust or droplets in the air

  Indirect transmission

  • vehicle transmission: when infected food or water is ingested, or infected blood or inanimate objects such as clothing or bedding
  • another form of this transmission is being bitten by an infected vector
  • faecal - oral transmission is the result of poor hand hygiene
• How can infectious disease spread among populations and communities?

  Inadequate sanitation:

  • a lack of access to clean water for washing and drinking
  • inadequate sewage disposal, increasing the risk of faecal - oral transmission
  • lack of accessible health promotion information
  • lack of social distancing due to dense population
• An antigen is a substance recognised by the body as self (the body's own cells) or non-self (foreign cells and pathogens) and stimulates an immune response. Antigens are found on pathogens and also on the surfaces of all body cells.
• An antibody is a blood protein that is produced in response to a specific antigen, binding specifically to an antigen in a similar way to an enzyme binding specifically to its substrate.
• Antigens are usually proteins or glycoproteins that act as chemical markers.

  Some antigens on the surface of body cells allow the immune system to distinguish between the body's own cells and foreign cells including pathogens, leading to the initiation of an immune response.
• What are physical and chemical barriers to protect our body against invasion from a foreign substance?

  Skin

  Mucous membranes from goblet cells

  Antimicrobial protiens and peptides

  Lysozyme

  • hydrolyses bonds in the cell wall components of some bacteria, weakening the cell wall and causing the cell to swell and burst
  • present in tears and breast milk
• What is inflammation doing to protect our body against invasion from a foreign substance?

  Response to injury and infection where the area becomes hot, swollen and red as a result of increased blood flow.

  Mast cells respond to tissue damage by secreting histamine. This cell signalling compound stimulates a range of responses including:

  • increased blood flow in capillaries
  • capillaries begin to leak more, allowing fluid to enter the tissues resulting in swelling
  • phagocytes leave the blood and enter the tissues where they can engulf foreign material
  • cells release cytokines
• What is phagocytosis doing to protect our body against invasion from a foreign substance?

  Chemicals released by pathogens into the blood attract phagocytes. Receptors on the surface of phagocytes bind to antigens on the surface of pathogens, leading to the phagocyte engulfing and digesting the pathogen.

  Macrophages do not completely digest the pathogen. Antigens from the partially digested pathogen are processed and then appear on the plasma membrane of the macrophage, then presenting the antigens to lyphocytes. This is why macrophages are known as APCs (antigen presenting cells).
• What are specific defenses to protect our body against invasion from a foreign substance?

  T cells and B cells are activated by foreign antigens on pathogens or other foreign cells.

  • activated T cells bind to foreign antigens on infected cells
  • activated T cells then destroy the infected cells, removing bacteria and viruses that replicate inside cells
  • activated T cells form memory cells
  • activated B cells produce antibodies
  • these are specific to the antigens on the pathogens that led to the activation of B cells