BIOLOGY UNIT 3
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Nelson Biology 3&4, pg 172
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Any substance that triggers an immune
response is called an antigen.
Some responses are antigen-specific and
others are systemic – that is, they work
throughout the systems of the body, not
just at the site of infection.
Both of these lines of defence depend on
the ability of the immune system to
recognise self from non-self.
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Our Immune System
12 BIOLOGY, CH 6
Nelson Biology 3&4, pg 173
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The lymphatic system consists of the lymphoid
organs and transport vessels that carry a clear
fluid called lymph which bathes all body cells and
drains into lymph vessels.
Lymph vessels eventually join up with the
circulatory system and drain into the
bloodstream at the neck.
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The vessels have valves
that control one-way flow.
Unlike the blood circulatory
system, there is no pump,
and lymph relies on muscle
contraction for movement
through the lymph vessels.
Lymph vessels eventually
join up with the circulatory
system and drain into the
bloodstream at the neck.
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Nelson
Biology 3&4,
pg 174
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12 BIOLOGY, CH 6
Nelson Biology 3&4, pg 175
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A MACROPHAGE OVERCOMES AND EATS A CANCER CELL
FROM THE UPJOHN COMPANY, THE IMMUNE SYSTEM
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The Non-specific Immune Response
This topic is the subject of the Outcome
Assessment Task 4 and students will research it
and write a report.
OAT 4
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The adaptive immune response
The cells and processes are specific and can
detect and distinguish between different types of
invaders.
The adaptive immune response not only has
specificity but also memory.
The immune system can mount an enhanced
defence against a pathogen that infects the host
for a second time.
Lymphocytes are the key cells of the immune
system, the body’s specific, third line of defence.
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The B lymphocytes – humoral immunity
The humoral immune response is brought about
by B lymphocytes, or B cells, which produce an
amazing array of different types of proteins
(antibodies) that attack foreign antigens.
B cells mature in the bone marrow
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Antibodies
Antibodies combine
with specific antigens
and help remove them
from the body.
They consist of four
polypeptide chains
arranged in the shape
of a Y.
Nelson Biology 3&4, pg 183
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Antibodies
All antibodies are identical except for a region
at the two ends of the Y where there are two
identical binding sites that match up, or are
complementary, to a particular antigen.
It is believed that they work with a lock and
key system of identification similar to that
proposed for enzymes binding with their
substrate.
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Antibodies
Antibodies are also known as immunoglobulins
(Ig) and they occur in several different classes:
IgM antibodies are usually the first to be
secreted in an infection.
IgG are responsible for activating complement
proteins in the blood and can neutralise toxins
directly.
IgA antibodies neutralise pathogens in the
respiratory, digestive and reproductive tracts.
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Antibodies
IgE antibodies help initiate inflammation after a
pathogenic infection.
It is this type of antibody that also causes
allergic reactions to non-pathogenic agents
(eg. pollen).
At least 10 million different types of antibodies
are produced within our bodies!
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Nelson Biology 3&4, pg 184
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Recognition of a specific antigen triggers an
amazing response in the B cell, causing it to
divide rapidly, forming two types of B cells:
plasma and memory cells.
The plasma cells secrete up to 10 000
molecules of a specific antibody per second into
the body fluids.
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Memory B cells persist within the body for some
months or even years, not secreting antibodies
but still displaying them mounted on their
plasma membrane.
They are ready to ambush the antigen-specific
pathogen quickly should it reinvade the body of
the host.
Once activated by the revisiting antigen, the B
memory cells divide and rapidly produce large
quantities of antibody.
This is why most people only experience
chickenpox or measles once in their lives.
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Nelson Bology 3&4, pg 185
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Nelson Bology 3&4, pg 185
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T lymphocytes – the cell-mediated immune response
T lymphocytes also originate in the bone marrow
but mature in the Thymus gland, where they
become ‘programmed’ to recognise the antigen of
a specific pathogen.
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Nelson Bology 3&4, pg 187
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T lymphocytes do not produce antibodies.
T lymphocytes do not bind with antigens directly
but bind with the antigens presented on the MHC
markers.
It is the combination of antigen and MHC marker
that produces the binding site for T lymphocytes.
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T lymphocytes come in different forms, including
T-helper (TH), cytotoxic T (TC) and T-suppressor
cells.
T-helper cells help other cells of the immune
system by producing and secreting chemicals,
including lymphokines and interleukins, which
induce any activated B or T cell to divide and give
rise to large numbers of clones, some becoming
effector cells and others remaining as memory
cells.
Lymphokines can also stimulate macrophages to
engulf invading cells more readily.
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Cytotoxic T cells are killers which can eliminate
infected body cells or tumour cells by releasing
powerful cytotoxins when they ‘touch’ a cell that
carries an unrecognised antigen.
It is these cells that are chiefly responsible for
fighting off invading viruses by killing off infected
cells.
They can also cause problems for patients
requiring organ transplants as they destroy the
transplanted cells directly.
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T-suppressor cells play an important role in
regulating the action of lymphocytes.
They are also capable of suppressing the action
of phagocytes. In this way, they help prevent the
immune system overreacting to a stimulus.
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Nelson Bology 3&4, pg 189
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Nelson Bology 3&4, pg 190
Overview
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Review Question 27, pg 191
Reorganise the boxes into a flow chart that could act as a battle plan for defence
against an infection caused by Mycobacterium tuberculosis.
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Review Question 27, pg 191
Solution:
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Immunisation
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