Yr9 Biology - Infectious Diseases (GCSE AQA B1.1.2)

Microogranisms that cause infectious disease are called pathogens and they get inside our bodies through:
1. DROPLET INFECTION - cilia cells push up the pathogen with mucus. Cough, sneeze or talk contaminate droplets of mucus/breath. E.g. cold, flu, measles, chicken pox, TB
2. THROUGH CONTACT - skin has oil on it for sanitation
3. THROUGH BREAKS IN THE SKIN - our body forms a scab
4. THROUGH CONTAMINATED FOOD & DRINK - hydrochloric acid in stomach reacts to pathogen
5. PATHOGEN - microorganism that can infect our bodies
6. NATURAL BARRIER - what our body creates to fight infection
7. MICROORGANISM - small organism that can only be seen through a microscope
Bacteria and viruses may reproduce rapidly inside the body and may produce poisons (toxins) that makes us feel ill. Viruses damage the cells in which they reproduce
The immune system of the body produces specific antibodies to kill a particular pathogen. This leads to immunity from that pathogen. In some cases, dead or inactivated pathogens stimulate antibody production (called a vaccine). If a large proportion of the population is immune to a pathogen, the spread of the pathogen is reduced massively.
Semmelweis recognised the importance of hand-washing in the prevention of spreading some infectious diseases in May 1847. By insisting that doctors washed their hands before examining patients, he greatly reduced the number of deaths from infectious diseases in his hospital.
1. Handwashing removes/+kills pathogens on hands so that you do not transfer bacteria directly/indirectly
Some medicines, including painkillers, help to relieve the symptoms of infectious disease, but do not kill the pathogen
Antibiotics, incl. penicillin, are medicines that help to cure bacterial disease by killing infectious bacteria inside the body. Antibiotics cannot be used to kill viral pathogens, which live and reproduce inside cells. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from infectious diseases.
Strains of bacteria, incl. MRSA, have developed resistance to antibiotics as a result of natural selection. To prevent further resistance arising it is important to avoid over-use of antibiotics.
Mutations of pathogens produce new strains. Antibiotics and vaccinations may no longer be effective against a new resistant strain of the pathogen. New strain will spread rapidly because people are not immune to it and there is no effective treatment.
People can be immunised against a disease by introducing small quantities of dead or inactive forms of the pathogen into the body (vaccination). Vaccines stimulate the white blood cells to produce antibodies that destroy the pathogen, artificially creating primary immune response. This makes the person immune to future infections by the microorganism. The body can respond by rapidly making the correct antibody, in the same way as if the person had previously had the disease.
Immune System
1. The body has different ways of protecting itself against pathogens
2. White blood cells
  1. produced in bone marrow
  2. Two main types
    1. phagocytes
      1. sends out projections called pseudopodia (this surrounds pathogen, digests it and gets rid of it)
      2. PHAGOCYTOSIS - when a pathogen enters the body, white blood find the bacteria using chemotaxis (detecting toxins bacteria releases) and sends out toxins to engulf the pathogen
        STAGES: moves to site of injury --> detects pathogen using chemotaxis --> adheres to pathogen --> sends out pseudopodia --> engulfs pathogen --> digests pathogen --> destroys pathogen
    2. lymphocytes
  3. when pathogens are in body, WBCs squeeze through epithelials (blood vessel walls) to absorb pathogens, releasing enzymes and sending out messages to bring other WBCs to affected area
Antitoxins & Antibodies
1. Pathogens harms bodies by attacking cells by taking over them and preventing them from taking out functions and causing cell damage by breaking it open and killing it faster that the body can fight against it.
2. Bacteria releases toxins
3. Viruses cause cell damage
4. 1. White blood cells secrete antitoxins and release them into blood stream. 2. Antitoxins neutralise toxins by binding to them
  1. 1895 - American started to produce antitoxins to treat dipitheria (a bacterial disease)
5. Antibodies are produced by white blood cells and destroy antigens on the outside of pathogens
  1. 1. Body recognises pathogens as foreign (due to differently shaped antigens from our body cells) and white blood cells come to affected area
  2. 2. WBC, specifically LYMPHOCYTES, release antibodies shaped specifically to bind to the antigens of the pathogen
  3. Functions are: to clump together, destroy and label pathogens for destruction.
Memory cells
1. body remembers pathogens through white blood cells which become 'memory cells'
2. have a long longjevity
3. remember foreign cells so if infected again, white blood cell response is quicker
4. one particular memory cell remember one particular pathogen
MMR Vaccine
1. stops us from getting viral diseases: measles, mumps, and rubella. Contain weak form of each virus
2. Measles = highly contagious infectious disease characterized by a high fever, a rash and generally feeling unwell. 430 deaths from measles occur daily. Potentially fatal and childhood disease.
3. MMR = combined vaccine against measles, mumps and rubella. Introduced in the UK in 1988
4. People were worried about it because in 1998, a study published in The Lancet raised the possibility that the jab may be linked to autism and bowel disease
  1. not tested so not certain
  2. just observation, no scientific evidence
5. Issues with Wakefield's study
  1. 12 people - not enough tested
  2. only included those infected (lack of a control)
  3. Lawyers may choose cases - not random and introduces bias
  4. Observations carried out by non-professionals (parents)
  5. Wakefield paid and had obsession with autism (conflict of interest)

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Yr9 Biology - Infectious Diseases (GCSE AQA B1.1.2)

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