Download Defence against infections Immunisation

Defence against infections
Antigen
Antibody
-
foreign protein
substance produced by white blood cells to stop/combat the antigen
1.
Skin
mechanical barrier preventing the access of bacteria
2.
Stomach acid
kills most of the harmful bacteria entering with food
3.
Blood:
i.
Clotting
platelets clump to block cuts in small capillaries.
Platelets are stimulated by damage (exposure to air), which produce a
substance, which, via a series of enzyme reactions, convert soluble
fibrinogen into insoluble fibrin. Fibrin forms a network to trap red
blood cells and form a clot. The clot prevents access to harmful
bacteria.
ii.
White blood cells
(a)
Phagocytes
Ingest harmful bacteria at the site of the wound and stop them
from entering the circulation. White blood cells can squeeze out
of the blood through capillaries to attack bacteria.
(b)
Lymphocytes
Produce proteins called antibodies, which attack specific
antigens or foreign proteins that invade the body. The antibody
attaches to the surface of the antigens making the antigens
clump together which may now be ingested by the phagocytes.
Immunisation
Edward Jenner
(1749 – 1823)
He trained in London as an army surgeon for a period. His major discovery was
vaccination after the Latin word “vacca” meaning cow. Jenner saw that cowpox victims
became immune from smallpox (discovered in 1796). He was ridiculed when he though of
possible relationships between swinepox, smallpox and cowpox. (Smallpox could kill
whereas cowpox was not as bad).
Jenner injected cowpox into James Phipps and later injected him with smallpox to see if he
was immune: he was.
However, sometimes the vaccinations were too infected and the patients died. In 1840, the
British government made it free for all infants and in 1853, it was made compulsory.
Immunity
If someone is immune to something, they cannot catch that disease as their body knows how
to deal with the disease.
Immunity is the way in which white blood cells and antibodies enable the body to combat
infection.
Natural acquired immunity
If someone catches a disease, their body produces antibodies to defend itself from the
disease. The lymphocytes, which produce these antibodies, remain in circulation for some
time – just in case the body is infected again. Sometimes, babies inherit the antibody from
their mother’s milk. This is called innate immunity.
Naturally acquired immunity builds up in recovery from a disease. The immunity remains in
the body forever.
Innate immunity
This is when a person is born with a specific immunity. This can either be acquired from the
mother’s milk (a clear advantage of breast feeding) or via the placenta (during pregnancy).
The immunity is acquired from the mother for infections, which the mother has recently
combated. Antibodies are only present in the milk for the first four days.
Artificial acquired immunity
When someone is vaccinated against a disease, a harmless form of the bacteria (or virus) is
introduced into the body so that the body produces the antibodies to deal with it.
Artificial immunity produced by a vaccine has different forms:
1. May have harmless form of the disease. This stimulates unspecialised antibodies to
produce clone cells capable of producing antibodies against the disease.
2. May be the killed form of the disease
3. May have ready-made antibodies
4. May have toxoid – to neutralise poison from disease
However, the problem with these is that they need to be repeated as they only last a short
period of time.
Penicillin
1922
-
Alexander Fleming, by chance, saw bacteria on an agar plate.
However, he noticed that where a mould of penicillin was present,
there was no bacteria near it.
Penicillin mould
zone of inhibition –
where no bacteria
grows
agar plate with
bacteria
This penicillin mould was producing a substance, which diffused through the agar and
prevented the growth of the bacteria.
Penicillin does this in different ways:
1. Bacteriostatic
-
stops cell wall synthesis. If the bacteria can not synthesise
cell walls, they can not reproduce.
2. Bacteriocidal
-
Kills bacteria
There is a danger if penicillin is overused. Resistant strains can occur. This is when, due to
natural selection, certain bacteria, which happened to have mutated (randomly) survive as
they are resistant (i.e. are unaffected) by the penicillin. These, then reproduce and continue
to do so as they are unaffected by the penicillin. The penicillin is now useless against this
form of bacteria and another antibiotic must be created.
Difference between Antibiotics and Drugs:
Antibiotics are organic chemicals produced by microorganisms (e.g. bacteria or fungi),
which suppress the growth of other microorganisms.
Antibiotics can either act as:
Bacteriostatic
stop bacteria reproducing
Bacteriocidal
will kill bacteria
Antibiotics have no effect of viruses.