4.1.1 Communicable Diseases

• What is a Pathogen?

  A pathogen is a microorganism that causes disease in its host.
• Pathogens live by taking nutrition from the hosts whilst causing considerable damage in the process
• The 4 types of Pathogens are?

  Bacteria , Virus , Fungi , Protocista
• Specific Human defense systems are designed to get rid of specific diseases such as antibodies
• Non-specific human defence systems are generalised immunity like the skin and stomach acid that are designed to protect the body and eliminate most diseases
• How does Bacteria cause disease?

  It produces toxins / toxic waste and damages cells
• How do Viruses cause disease?

  They invade host cells and take over genetic material and other organelles . They cause cells to manufacture more copies of the virus. Eventually the host cell bursts and releases many new virus particles
• How do Fungi cause disease?

  They live on the surface skin of animals where Fungal Hyphae form mycelium (network of fungal roots) . They send out reproductive Hyphae to skin surface which causes redness and releases spores
• How do Protists cause disease?

  They enter the host cells and feed on the contents as they grow. Immature forms of Malarial Parasite feeds on Haemoglobin
• Direct Transmission is directly from one organism to an other organism through direct contact.
• Direct Transmission Vertically is touching, kissing, sneezing
• Direct Transmission Horizontally is through the Placenta and Breast Milk from mother to child
• Indirect Transmission is from one organism to another via an intermediate (like a vector)
• Indirect Transmission Vertical Borne is through the Air, Dust , Water , Food
• Indirect Transmission Vector Borne is through insects bites , fungal diseases , another organism
• In plants and animals , defences can be categorised into 2 group: Passive or Active
• Passive Plant/Animal response are Barriers to pathogens entering the organism or to prevent spreading within the organism
• Active plant/animal response is An action done only in response to the presence of the pathogen
• Necrosis is deliberate cell suicide.

  It’s when a few cells are sacrificed to save the rest of the plant. Sacrificing cells limits the pathogens access to the plants nutrition and water
• Non-specific Animal defences are initial defences that happen in a human to stop pathogens getting in. Mammals have 2 lines of defences against the invasion of pathogens
• Mammals have 2 lines of defences:

  Primary - Non-Specific , Keep pathogens out the body and are always present

  Secondary - Non-Specific , Adapts to prevent growth of pathogens if they get in the body , only present after pathogen has entered
• What are the 8 key responses?

  1. Skin
  2. Lysozymes
  3. Mucus Membrane
  4. Expulsive Reflexes
  5. Blood Clotting and Wound Repair
  6. Fevers
  7. Inflammatory Response
  8. Phagocytosis
• Body cells recognise the proteins (on the surface of cells)as ?

  Self or Foreign
• Foreign Antigens trigger an immune response which involve the production of antibodies

  • This involves the specific immune system and can take up to 14 days to respond to a pathogen invasion
  • However Immune Memory Cells mean that it will react very quickly to a second invasion by the same pathogen
• What are the 2 main types of specific response to pathogens?

  Cell Mediated and Humoral
• Cell Mediated involves highly specialised cells that target pathogens inside cells
• Humoral. targets pathogens in body fluids with antibodies
• Lymphocytes are:

  • Smaller than pathogens
  • Have a large nucleus that fills most of the cell
• T-Cells - Mature in the Thymus Gland and respond to antigens present by APC’s

  
• What is an APC?

  Antigen Presenting Cell
• B-cells mature in the Bone Marrow and Make Antibodies

  
• In Cell Mediated Immunity:

  • T Lymphocytes respond to the own cells of an organism that have been changed in some way (like viral infection or mutations)
• T-Cells will make more of themselves and differentiate into different types of T-Cells to directly destroy these altered cells and kill the pathogen
• In Cell-Mediated Immunity:

  1. In the non-specific immune response , Macrophages engulf and digest pathogens by Phagocytosis
  2. They present the antigens on their surface to become a Antigen Presenting Cell
  3. Complimentary receptors on specific T-Helper Cells bind to antigens on APC
  4. T-Helper cells will activate and become interleukins which stimulates more T-Cells to divide rapidly by Mitosis

  
• Clones T Cells can :

  • Become T Memory cells
  • Become specific to the presented antigen and destroy infected cells
  • Produce interleukins to stimulate Phagocytosis
  • Product interleukins to stimulate B cells to divide
• Interleukins are what?

  Cell-Signalling molecules
• Colonal Selection is when a specific T or B lymphocyte is selected to divide if they have complimentary antibiodies
• Colonal expansion is when once the correct T or B lymphocytes has been activated it must increase in numbers by mitosis or differentiation
• Memory cells are long lived cells that remain in circulation so that if the same pathogen enters again, memory cells can quickly respond with an effective immune response