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Your Body’s Immunity
Section 11 – Science 24
Your body’s physical defences
• We are surrounded by billions of bacteria and
viruses. To many of them, a human being is like
a walking smorgasbord, offering nearly limitless
resources that they can use for energy and
reproduction.
• Luckily for us, getting into the human body is not
an easy task!
• From the point of view of these tiny organisms, a
human is a bit like a fortress
• The skin is thick and very hard to
penetrate. In addition, the skin also
produces a variety of substances
that are harmful to invaders.
• Openings such as the eyes, nose,
and mouth are protected by fluids
or sticky mucus that capture
harmful attackers.
• The respiratory tract also has
mechanical defenses in the form of
cilia, tiny hairs that remove
particles.
• Intruders that get as far as the
stomach are up against a sea of
stomach acid that kills most of
them.
BODY’S DEFENCES
Inflammatory Response
If pathogens get past the physical barrier created by the
skin, the blood vessels surrounding the injury swell and
the area becomes red and warm as more blood arrives
The body will send white blood cells (macrophages) to
repel the invader
Your body’s physical defences and the inflammatory
responses are called…
GENERAL DEFENCES
…because the body reacts in the same way
regardless of what kind of pathogen is invading
Your third line of defence is the formation of
antibodies in the immune system. This line of
defense targets specific pathogens as you will see..
Immunity – How does it work?
• Your body recognizes antigens that are not part of
itself
• Antigens are specifically structures that are attached
to pathogens. All living tissues such as viruses,
bacteria, fungi, transfused blood, transplanted organs
and cancer cells contain antigens.
How does your immune system
respond to the antigens it encounters?
• White blood cells make and release Y-shaped
protein compounds called antibodies
• Antibodies bind to specific antigens making it
easier for white blood cells to destroy them
• Each antibody has a shape that matches a specific antigen.
This means that an antibody produced against a cold virus,
for example, would not fit with an HIV antigen.
• So how do we have immunity from things like chicken pox?
• When you first contracted chicken pox your body didn’t have
antibodies against the chicken pox antigen. But your body
immediately started producing them.
• Now, if you contract it again, your body does have the
antibodies so your immune system will recognize and
destroy the antigen whenever it shows up again.
Immune System Response
1) When bacteria enter the body, an
inflammatory response occurs. Macrophages
surround and destroy some of the bacteria.
2) Antigens from the dead bacteria protrude from the
macrophages that engulfed the bacteria
3) White blood cells called “Helper T Cells” identify the
antigens on the macrophages.
Once activated, helper T cells start to divide and to
produce proteins that activate B and T cells.
4) White blood cells called B cells are the ones responsible
for making and releasing antibodies. But they wait until they
are activated by a Helper T cell – to inform them that there is
a current invasion
The B cell makes 2 types of cells:
1) Plasma cell
2) Memory cell
5) The plasma cell makes antibodies which attach to the
antigens on the bacteria
6) This makes them more noticeable to macrophages so they
come and eat them.
7) Memory cells store information about the antigen of the
invader, making it easier to destroy if it shows up again.
IMMUNE SYSTEM GAME
http://nobelprize.org/educational_games/medicine/immunity/index.html
• During your computer class tomorrow, you will be
training to become a Macrophage Commander.
Video