B3 - Infection & Response

  • Created by: Benny52
  • Created on: 21-02-19 11:21

Communicable Disease

  • Pathogens - microorganisms that enter body & cause disease. Cause communicable diseases. 
    • Bacteria - very small cells that can reproduce rapidly in body, Makes you feel ill by producing toxins - damages cells & tissues.
    • Viruses - not cells. Tiny - smaller than bacteria. Reproduce rapidly in body. Live in cells & duplicate using cell's machinery to produce many copies. Cell bursts, releasing new viruses. Cell damage makes you feel ill.
    • Protists - single-celled eukaryotes. Some are parasites - live on or inside other organisms & causes damage. Often transferred to organism by vector.
    • Fungi - Some are single-celled. Others have body made up of hyphae - thread-like structures. Hyphae can grow & penetrate human skin & surface of plants - causes diseases. Can produce spores - can be spread.
  • Pathogens spread in many ways:
    • Water - Drinking or bathing in dirty water.
    • Air - Carried in air & can be breathed in. Some airborne pathogens carried in droplets produced when you cough/sneeze.
    • Direct contact - touching contaminated surfaces, like skin.
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Viral, Fungal & Protist Diseases

  • Viral:
    • Measles - Spread by droplets from infected person's sneeze/cough. Develop red skin rash, and show signs of fever. Can lead to pneumonia or encephalitis if there're complications. Most people vaccinated against it when young.
    • HIV - Spread by sexual contact, or in exchange of bodily fluids. Initially causes flu-like symptoms for few weeks. Usually, person doesn't then experience any for many yrs. Controlled with antiretrovial drugs - stops virus replicating. Virus attacks immune cells. If immune systhem is badly damaged, it can't cope with other infections or cancers - late stage HIV infection or AIDS.
    • Tobacco mosaic virus - Affects plants - tomatoes, ect. Causes mosaic pattern on leaves - parts of leaves - discoloured - plants can't carry out photosynthesis as well - affects growth.
  • Fungal: Rose black spot - causes purple or black spots on leaves of rose plants. Leaves can turn yellow & drop off - less photosynthesis - plant doesn't grow well. Spreads by water or wind. Fungicides used or plant stripped of affected leaves - need to be destroyed so fungus can't spread.
  • Protist: Malaria - Mosquitoes - vectors. Pick up malarial protist when feeding on infected animal. When mosquito feeds on another animal, it infects it by inserting protist into animal's blood vessels. Causes repeating episodes of fever. Can be fatal. Spread reduced by stopping mosquitoes breeding. People protected by using insecticides & mosquito nets.
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Bacterial Diseases & Preventing Disease

  • Bacterial:
    • Salmonella - Causes food poisoning. Suffer from fever, stomach cramps, vomiting & diarrhoea. Symptoms caused by toxins the bacteria produce. Caused by eating food contaminated with Salmonella. UK - most poultry given vaccination - controls spread.
    • Gonorrhoea - STD. Passed on by sexual contact. Caused by bacteria. Get pain when urinating & thick yellow or green discharge from vagina or penis. Originally treated with penicillin, but strains of bacterial have become resistant to it. People treated with antibiotics & should use barrier methods of contraception.
  • Spread of disease can be reduced or prevented:
    • Being hygienic - washing hands before preparing food or after sneezing.
    • Destroying vectors 
    • Isolating infected individuals
    • Vaccination 
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Fighting Disease

  • Skin - barrier to pathogens. Also secretes antimicrobial substances - kills pathogens.
  • Hairs & mucus in nose trap particles that could contain pathogens.
  • Trachea & bronchi secrete mucus to trap pathogens. Are also lined with cilia - hair-like structures that waft the mucus up to back of throat to be swallowed.
  • Stomach produces HCl - kills pathogens.
  • Immune system destroys pathogens - white blood cells. When they come across invading microbe, they can:
    • Consume them - engulf foreign cells & digest them - phagocytosis.
    • Producing antibodies - invading pathogens have unique molecules - antigens - on surface. When white blood cells come across foreign antigen, antibodies produced to lock on invading cells so they can be found & destroyed by other white blood cells. Antibodies produced rapidly & carried round body to find similar bacteria or viruses. If person is infected with same pathogen again white blood cells rapidly produce antibodies to kill it - person naturally immune.
    • Producing antitoxins - counteract toxins produced by invading bacteria.
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Fighting Disease - Vaccination

  • Involves injecting small amounts of dead or inactive pathogens - carry antigens, causing body to produce antibodies to attack them. If live pathogens of that type appear after, white bloodc cells can rapidly mass-produce antibodies to kill pathogen.
  • Pros:
    • Helped control lots of communicable diseases once common in UK.
    • Big outbreaks of disease - epidemics - prevented if large % of pop. is vaccinated. Less people able to pass it on.
  • Cons:
    • Don't always give you immunity
    • Can have bad reaction - rare.
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Fighting Disease - Drugs

  • Painkillers - relieve pain. Don't tackle cause of disease or kill pathogen. Other drugs do similar things - only reduce symtoms. Antibiotics - kill or prevent growth of bacteria. Don't destroy viruses - reproduce using body cells so difficult to develop drugs that destroy just virus.
  • Bacteria can mutate - become resistant to an antibiotic. When you treat infection, only non-resistant strains will be killed. Individual resistant bacteria will survive & reproduce & pop. of resistant strain - increase. Could cause serious infection that can't be treated by antibiotics. To slow rate of development of resistant strains, important for doctors not to over-prescribe antibiotics. Also important to finish whole course of antibiotics.
  • Plants produce variety of chemicals to defend themselves against pests & pathogens. Some used as drugs to treat human diseases or relieve symptoms - Aspirin - used as painkiller & to lower fever. Developed from chemical in willow. Digitalis - treats heart conditions. Developed from chemical in foxgloves.
  • Some drugs extracted from microorgansims - Alexander Fleming - clearing Petri dishes containing bacteria. Noticed that 1 had mould and area round mould - free of bacteria. Mould - producing substance that killed bacteria - penicillin.
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Developing Drugs

  • Stage 1: Preclinical testing - drugs tested on human cells & tissues in lab. Can't use this to test drugs effecting whole or multiple body systems.
  • Stage 2: Preclinical testing - live animals - to test efficacy - whether drug works - to find out about its toxicity, and to find best dosage. People think its cruel to test on animals, but others believe it's the safest way to ensure drug isn't dangerous.
  • Stage 3: Tested on human volunteers in clinical trial. First tested on healthy volunteers to ensure there are no harmful side effects when body is working normally. Can then be tested on people suffering from illness - optimum dose is found - most effective & few side effects.
    • To test how well drug works, patients randomly put in 2 groups. 1 is given new drug, other given placebo - like drug but doesn't do anything - allows doctor to see actual difference drug makes - allows for placebo effect - when patient expects treatment to work so feels better
    • Clinical tests double-blind - neither patient nor doctor doesn't know whether they're getting drug or placebo - ensures doctors monitoring patients & analysing results aren't subconsciously influenced.
    • Results aren't published until peer reviewed - prevents false claims.
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