Microbes and Disease

WJEC BiologyModule 3

Microbes and Disease

• How does the body defend itself against infectious disease?

• How does immunisation work?• What are antibiotics?• Are there problems with using

antibiotics?

Learning Outcomes

• know that some micro-organisms, called pathogens, cause diseases and intact skin forms a barrier against them. The body also defends itself by: blood clots to seal wounds; white cells in the blood ingest microbes, produce antibodies and antitoxins.

Defence against disease

• A Pathogen is a micro-organism capable of causing disease

• The body has a first line of defence against disease this includes– The skin– Blood clotting– Hydrochloric acid in the stomach

Microbes: our defence against them

Our bodies have four major defence mechanisms against invading microbes:

If our skin is cut platelets seal the wound by clotting

The breathing organs produce mucus to cover the lining of these organs and trap the microbes

The skin acts as a barrier

Our blood contains white blood cells

Immune System

• The immune system is the second line of defence– White blood cells help defend against

disease by:• They engulf and digest the microbe• They produce antibodies to neutralise the

microbe• They produce antitoxins to neutralise the

poisons produced by microbes

Phagocytosis

• Phagocytes can move out of the capillaries to the site of infection

• They engulf the infecting pathogens and kill them by digesting them.

Antibody Production

• Lymphocytes – are white blood cells formed in lymph

nodes.– Produce antibodies or anti-toxins in

response to a pathogen (antigens)– A different antibody is produced for each

antigen

Antibody Production

• Lymphocytes can memorise the antigens that the body has been exposed to.

• this allows antibodies to be produced faster if reinfected

• Some antibodies remain in the blood to give a long term protection

Producing antibodies

Step 1: The white blood cell “sees” the antigen (microbe)

Step 2: The cell produces antibodies to “fit” the antigen

Step 3: The antibodies fit onto the antigens and cause them to “clump”

Step 4: The antigens are “eaten” by the white blood cells

You’re going down

Learning Outcomes

• understand that immunisation can be used to protect humans from infectious disease although it raises dilemmas for individuals and for society.

• Evaluate the factors influencing parents in decisions about whether to have children vaccinated or not including the roles of scientific evidence and public opinion. This indicates a moral responsibility which may ultimately be outside the scope of science.

NATURAL IMMUNITY

• Active

• This is when antibodies are produced by a person when needed

• Passive

• passed from the mother to the infant whilst breast feeding

ARTIFICIAL IMMUNITY

• Can be done in two ways:– A vaccine with dead or

harmless microbes is injected – the body produces antibodies

ready for the real thing. • This is called ACTIVE IMMUNISATION

– The antibodies are injected directly into the body • This is called PASSIVE

IMMUNISATION.

Immunisation

• Introduction of a mild or dead form of the pathogen – Stimulates immune system to respond– Production of anti-bodies

Immunisation- Dilemmas  MMR: How safe do you think it is?

• The largest study to date of the MMR vaccine suggests that it is safe (May 2001)– Researchers in Finland, who followed two

million children for two years failed to find a link between the combined measles mumps and rubella jab with autism or bowel disease.

• However, a separate report claims that the MMR vaccine was not tested properly before being introduced.

• How safe do you think this vaccine is? • Do the benefits of the MMR vaccine

outweigh the perceived risks?

Pupil Activity

• Read through the sheet on the MMR vaccination– Make a list of the pros and cons– If you were faced with the decision

• would you vaccinate your child with the MMR vaccination?

• Would you recommend to a close friend / family to immunise a child with the MMR vaccination?

Learning Outcomes

• know that an antigen is a protein, foreign to an individual, that triggers a response by some white blood cells which secrete antibodies specific to the antigen that is present. Antibodies destroy the cells bearing the antigen.

• assess data showing how, after an antigen has been encountered, memory cells remain in the body and antibodies are produced very quickly if the same antigen is encountered a second time. This memory provides immunity following a natural infection and after vaccination. The response is highly specific to the antigen involved.

Antibodies and Antigens

• an antigen is a protein– foreign to an individual, – It triggers a response by some white blood

cells

• An Antibody is a protein– which are secreted by WBC– They are specific to the antigen that is

present. – Antibodies destroy the cells bearing the

antigen

immunological Memory

• after an antigen has been encountered, memory cells remain in the body – antibodies are produced very quickly if

the same antigen is encountered a second time.

• This memory provides immunity following a natural infection and after vaccination.

Learning Outcomes

• understand why most people suffer from measles only once, but suffer from common colds many times during their lives

• know that a vaccine contains antigens derived from a disease-causing organism which will protect against infection by that organism by stimulating the white blood cells to produce antibodies. The memory cells remain and, when the disease causing organism is encountered, the rapid response is triggered which makes a person immune. Vaccines may be produced against bacteria and viruses.

Viruses and Disease

• Measles is caused by one virus, if you catch measles you are unlikely to catch it again in your lifetime

• The common cold is caused by a variety of viruses, which have the ability to change and mutate. Each virus has the ability to cause the common cold, you build up an immunity to them one at a time.

Vaccines

• A vaccine contains antigens derived from a disease-causing organism.

• These antigens stimulate the white blood cells to produce antibodies.

• The memory cells remain in the blood• when the disease causing organism is

encountered, the rapid response is triggered which makes a person immune.

• Vaccines may be produced against bacteria and viruses.

Learning Outcomes

• understand the effect of penicillin on bacteria growing on agar plates. Antibiotics, including penicillin, are medicines produced by living organisms which help to cure bacterial disease by killing the infecting bacteria.

• know that antibiotics may kill some bacteria, but not viruses and understand that resistant bacteria such as MRSA can result from the over use of antibiotics. Discuss the issues surrounding increasing bacterial resistance to antibiotics.

Antibiotics

• Antibiotics are chemicals which kill infecting bacteria.– E.g. penicillin

• As viruses infect our own body cells, antibiotics are not effective against them.

• Some bacteria such as MRSA can develop resistance to antibiotics.

• An increase in antibiotic resistance has been seen due to the overuse of anti-biotics