Infection & Response

• Pathogens


  organisms that enter the body and cause disease
• Communicable diseases

  illnesses that are easily passed from one person to another
• Types of pathogens

  viruses, bacteria, protists, fungi
• Viruses

  - tiny particles, smaller than bacteria and other pathogens that invade your body and reproduce rapidly.

  
  

  - they live inside cells and replicate themselves using the cell's machinery to make many copies of themselves

  
  

  - cell will burst, releasing all the new viruses

  
  

  - cell damage is what makes you feel

  ill
• Bacteria


  single-celled organisms that reproduce rapidly inside your body and produce toxins which makes us ill and damages our cells and tissue.
• Protists


  A eukaryotic organism that cannot be classified as an animal, plant, or fungus.
• Fungi


  eukaryotic organisms that include microorganisms such as yeasts, moulds and mushrooms
• How are pathogens spread?

  Water, air and direct contact
• Measles

  - Measles is a serious viral disease that is spread by droplets from an infected person's sneeze or cough

  
  

  - Shows symptoms of a red skin rash and a fever

  
  

  - It can be very serious or fatal if complications arise.

  
  

  - For this reason, most people are vaccinated against measles when they are younger.
• HIV

  - HIV is a virus that is spread by sexual contact or by exchanging bodily fluids e.g blood. This can happen when people share needles when taking drugs. The virus can attack the body's immune cells

  
  

  - It initially causes flu-like symptoms for a few weeks.

  
  

  - Usually the infected don't experience any symptoms for several years

  
  

  - During this time, HIV can be controlled with antiretroviral drugs, which stops the virus replicating the body.

  
  

  - If the body's immune system is badly damaged, it can't deal with other infections/cancers

  
  

  - At this stage. the virus is known as AIDS
• TMV

  - TMV is a widespread plant pathogen that infects tobacco plants and many others species of plants

  
  

  - It can cause a mosaic pattern on the leaves of the plant, which leaves the leaves discoloured

  
  

  - This means that the plant can't carry out photosynthesis, the virus affects the growth of the plant.
• Rose black spot


  - Fungus that causes purple/black spots to appear on leaves of rose plants - the leaves then turn yellow and fall off

  
  

  - Prevents the process of photosynthesis and growth

  
  

  - Spread via the environment e.g. water or wind

  
  

  - Can be treated by fungicides and stripping the plant of its affected leaves and then burning the leaves so the virus doesn't spread to other rose plants.
• Malaria


  - The malaria protists have a life cycle that includes the mosquitoes

  
  

  - It causes repeating episodes of fever and it can be fatal

  
  

  - The spread can be reduced by preventing the vectors (mosquitoes) from breeding, insecticides and mosquitoes nets
• Salmonella

  - Bacteria that causes food poisoning by producing toxins

  
  

  - Symptoms are fever, stomach cramps, vomiting and diarrhoea

  
  

  
  

  - Caused by eating food contaminated with salmonella e.g. uncooked chicken

  In the UK, most chickens are vaccinated against salmonella.

  
  

  - This controls the spread of the disease
• Gonnorohea

  - Is a STD that is passed on by sexual contact e.g having unprotected sex

  
  

  - Symptoms include, pain whilst urinating, thick yellow/green discharge from the vagina/penis

  
  

  - Caused by bacteria

  
  

  - Was originally treated with the antibiotic penicillin until resistant strains appeared

  
  

  - The spread can be controlled by barrier methods of contraception e.g condoms or other antibiotics
• Non-specific defense system


  responds immediately to protect the body from all foreign substances
• Nose


  Hairs and mucus in your nose trap particles that could contain pathogens
• Trachea and bronchi

  - The T+B secrete mucus to trap pathogens

  
  

  - They are also lined with cilia, which are hair-like structures which waft the mucus up to the back of the throat where it can be swallowed.
• Skin

  Acts as a barrier to pathogens and secretes antimicrobial substances which kill pathogens
• Stomach

  Produces hydrochloric acid which kills pathogens that make it that far from the mouth
• Immune system pathogens

  - The white blood cells in your immune system travel around the blood and crawl in every part

  of you, searching for microbes

  
  

  - When they come across an invading microbe, they have 3 lines of attack
• Phagocytosis


  the process by which white blood cells engulf foreign cells and digest them either as a defense mechanism or as a means to obtain food.
• Producing antibodies

  - Invading pathogens have unique molecules called antigens on its surface

  
  

  - When types of WBC come across a foreign antigen, they will start to produce proteins called antibodies to lock on the invading cells so they can be found + destroyed by other white blood cells

  
  

  - The antibodies produced are all specific to that type of antigen so they won't lock on to any others

  
  

  - Antibodies are then produced rapidly and carried around the body to find all similar bacteria

  
  

  - If that person is infected with the same pathogen again, the WBC will rapidly produce the antibodies to kill it. This means that the person becomes naturally immune to that pathogen and won't get ill
• Producing antitoxins

  These counteract toxins produced by the invading bacteria
• Vaccinations

  - Injecting small amounts of dead or inactive pathogens into a person's bloodstream, which carry antigens which causes your body to produce antibodies attack them, even though the pathogen is dead/harmless.
• Antibiotics

  - Drugs that block the growth and reproduction of bacteria e.g penicillin

  
  

  - Antibiotics don't destroy viruses as viruses reproduce using your body's cells, which makes it difficult to develop drugs that destroy the virus without killing the body's cells.

  
  

  - The use of antibiotics has reduced the number of deaths from communicable diseases caused by bacteria
• Painkillers


  Drugs that relieve pain. Although they don't actually tackle the cause of disease or kill pathogens, they just help to reduce the symptoms e.g aspirin for
• Origins of Drugs

  - Most drugs come from plants or are chemically derived from plants

  
  

  - Aspirin is used as a painkiller and to lower fever. It was developed from a chemical cure found in willow

  
  

  - Digtalis is used to treat heart conditions. It was developed from a chemical found in foxgloves

  
  

  - Penicillin was discovered by Alexander Fleming from

  the Penicillium mould
• 3 main stages of drug testing

  1. preclinical:

  drugs are tested on human cells and tissues in the lab.

  
  

  2. preclinical:

  drugs are tested on live animals. This is to test the efficacy, to find out its toxicity and to find the best dosage.

  
  

  3. clinical:

  if the drugs passes the test on animals, then it's tested on human volunteers. very low doses of drugs are tested on healthy volunteers. This is to make sure that it doesn't have any harmful side effects when the body is working normally.

  
  

  If the drug is found to be safe, further clinical trials are carried out to find the optimum does for the drug

  
  

  In double blind trials, one group is given a placebo drug and the other is given the new drug. This is so the doctor can see the actual difference the drug makes