SNAB Biology - Topic 6

  • Created by: Bambih369
  • Created on: 23-06-19 09:58
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  • Topic 6 - Immunity, Infection and Forensics
    • Forensics
      • Forensic entomology
        • Determine type of species on the body
          • Find the age of larvae on the body and determine the succession of species
      • Body Temperature
        • Body begins to cool after death for 1-2 days
        • It depends on the body position, clothing, Body size, humidity and surrounding temperature
      • Extent of decomposition
        • Enzymes in the gut break down the wall of the gut and surrounding area
          • As cells die they release enzymes which break down other tissues
            • Discoloration of skin and gas formation allow time of death to be determined
      • Rigor Mortis
        • Muscles stiffen and become fixed 6-9hrs after death
          • This is because contraction relies on ATP
          • It wears off after 36hrs
    • Antibiotics
      • Bactericidal
        • Kills bacteria by destroying cell wall
      • Bacteriostatic
        • Prevents bacteria from diving by inhibiting protein sythesis
      • Bacterial growth in cultures
        • Sterilize petri dishes using hot agar
          • Dip all instruments including forceps, inoculating loop into ethanol and run through the Bunsen burner
            • Keep a  Bunsen burner on near to the area of experiment to remove all extraneous bacteria
              • Dip the loop into bacteria and run through the agar in a zig-zag pattern
                • Add in antibacterial coated discs, lifting the lid as little as possible and then tape on three areas
    • DNA profiling
      • Forensic Technique for identifying genetic relationships
    • Immunity
      • Herd immunity
        • Enough people vaccinated to stop transmission e.g 90%
      • Types of immunity
        • Active
          • E.g vaccinations
        • Natural
          • E.g Body's natural response to infection
        • Artificial
          • E.g Anti serums such as antivenom
        • Passive
          • E.g antibodies being passed from mother to baby
      • Secondary infection
        • Shorter lag time
        • Greater production of antibodies produced
        • Much more rapid response
      • RNA splicing
        • Between the process of transcription and translation often mRNA is edited with some sections removed
          • Non-coding introns are removed
          • Exons remain and are expressed
            • This means several proteins can be made from one length of mRNA
    • Non- specific Responses
      • First line of defence
        • Skin
          • Physical barrier
          • Skin flora produce sebum which destroys microbes and out competes other bacteria for space
        • Lysozymes
          • Enzyme in tears, sweat and mucus
        • Stomach
          • Stomach acid to break down pathogens
          • Gut flora
        • Mucus
          • Traps pathogens which are broken down when we swallow in the stomach
      • Second line of defence
        • Lysozymes
          • An enzyme that kills bacteria by breaking down the cell wall
          • Found in nasal secretions, sweat and tears
        • Inflammation
          • When tissue is damaged mast cells and damaged WBC release histamines
            • These cause arterioles to dilate which causes heat and redness
            • It makes the walls of the capillaries permeable, forcing plasma, WBC and antibodies out of the capillary to cause swelling
        • Interferons
          • When cells are invaded they produce a chemical called interferons
            • This diffuses from the cell to surrounding cells where is binds to the receptors on the surface of uninfected cells
              • This prevents viral replication
        • Phagocytosis
          • The phagocyte produces a pseudopodia which grabs the microbes
            • These microbes go inside a vesicle called the phagosome
              • This vesicle fuses with the lysosome to produce the phagolysosome
                • The enzyme inside called the lysozyme breaks down the microbes and any piece too large leaves via exocytosis
    • Bacteria vs Viruses
      • Viruses
        • Dependent on host cell
        • No cell bound organelles
        • Nucleus
        • HIV
          • Symptoms include fever, diarrhea and secondary infections
          • Treated with anti retroviral drugs
          • Spread by sharing infected bodily fluids
    • Specific responses
      • Cell-mediated response
        • The pathogen invades the host cell which then displays the antigens on its MHC- becomming an APC
          • T killer cells with complementary receptor (CD4) binds to the APC
            • The T killer cell divides into active and memory cells
              • Cytokines secreted by T helper cells to stimulate the divide
              • Actuve T killer cells bind to the infected cell which releases chemicals causing pores to form in the cell which causes it to fill with water and burst via lysis
      • Humoral response
        • Bacterium engulfed by macrophage which presents antigens on the surface (APC)
          • APC binds to T helper cell with CD4 receptors which activates the T helper cells
            • T helper cells divide into active T helper cells and clones of T memory cells
              • Antigen binds to the B cell with CD4 receptor (APC)
                • Activated T helper cell binds to B cell with CD4 receptors and produces cytokines to stimulate B cell division
                  • B cells divide into B memory cells and B effector cells
                    • B effector cells differentiate into plasma cells which secrete antibodies which bind to antigens- identifying them for easier destruction
    • Hospital code of practise
      • Take full course and don't oversubscribe
        • Reduces selection pressure on organisms and destroys all bacteria causing infection
      • Hygiene
        • Prevents spread of infection and cuts down the number of places for infection
      • Isolating patients and resistant diseases
        • Prevents transmission of resistant bacteria between pts
      • Screening of pts coming into hospitals
        • Person may be infected without showing symptoms so detected and isolated and treated

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