Transcript Microbes and Disease - Miss Hanson's Biology Resources

Microbes and Disease
WJEC Biology
Module 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:
The skin acts
as a barrier
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
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
You’re going
down
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
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