The Human Body
Immune System
Defences against pathogens
To understand the power of your immune system, all
you have to do is look at what happens to something
once it dies.
That sounds gross, but it does show you something
very important about your immune system. When
something dies, its immune system (along with
everything else) shuts down. In a matter of hours, the
body is invaded by all sorts of bacteria, microbes and
parasites. None of these things are able to get in when
your immune system is working, but the moment your
immune system stops the door is wide open. Once you
die it only takes a few weeks for these organisms to
completely dismantle your body and carry it away, until
all that's left is a skeleton. Obviously your immune
system is doing something amazing to keep all of that
dismantling from happening when you are alive.
Marshall Brain – www.health.howstuffworks.com
• The immune system is made up of specialised
cells and organs designed to keep us healthy.
• It protects us against microscopic germs that
can cause infection and disease.
• Some common disease causing microorganisms are viruses, fungi, prions, protozoa,
bacteria and macro-organisms.
• These organisms that cause infectious diseases
are commonly called pathogens.
• Pathogens can enter the body through
openings such as
– the eyes, nose and mouth, etc
– cuts and grazes
• The human immune system maintains a
number of lines of defence to protect us
from pathogen invaders.
3 lines of defence
• Your body has 3 lines of defence.
– The first acts as a barrier to entry of disease
causing organisms
– The second operates once the invading
bodies have been successful in entering the
blood stream
– The third is where antibodies that the white
blood cells produce will destroy antigens that
are recognised from previous infection, along
with our lymphatic system
Specific and Non-specific
• The first and second lines of defence are
non-specific (they function regardless of
the type of invader)
• The third line of defence acts in a specific
way depending on the invader
View clips the clip and brainstorm jot down
dot points of how the bodies first line of
defence acts to prevent disease
The first line of defence
1. Skin
2. Bodily Secretions
3. Hair (cilia)
The first line of defence
1.The skin
– Is the most important defence against
– Forms a protective physical barrier
– Skin contains an antibacterial agent
– A break in the skin, (eg.a cut or graze) can
give pathogens access to body tissue. If this
happens blood clots form a scab until new
skin seals the wound.
The first line of defence
2. Bodily Secretions
– Tears
• Wash away germs
• Contain antibacterial agents and lyzosymes that breakdown
bacteria cell walls
– Mucus
• The mucus traps the pathogen and enzymes in the mucus
destroy it.
– Sweat (changes pH and contains antibacterial agents)
– Internally, the stomach acid and bile means produce a pH which
destroys or inhibits the growth of many pathogens.
– Other secretions like acidic urine to flush out the urinary tract and
microflora (healthy bacteria) that produce a pH that prevents the
growth of fungi and bacteria
The first line of defence
3. Mucous Membranes and Hair (Cilia)
– Your excretory, respiratory, digestive and reproductive systems
have a mucous membrane which traps bacteria and pathogens
– Fluids like tears and saliva can contain lysozymes
– Small hairs (cilia) can trap invading particles and microbes and
beat to move the trapped particles towards the bodies exits
The Second Line Of Defence
If pathogens break through the first line of defence
and enter the blood or deep tissue there are
internal defences that operate.
• The damaged cells release chemicals that make
blood flow rapidly to the damaged area.
• This affected area may swell and become tender
and red.
The Second Line Of Defence
• Within the blood there are red and white
blood cells.
• White blood cells
– Detect foreign invading microbes and gobble
them up
– Some phagocytic cells are free to move after
– Alert the rest of the immune cells that an
invasion has occurred.
The Third Line Of Defence
Lymphatic system
– The lymphatic system filters foreign
substances from the blood and produces
white blood cells known as lymphocytes.
These are called T lymphocytes and B
– This system is a vast network of vessels,
lymph nodes and organs such as the tonsils,
thymus and spleen.
Lymphatic System
Body’s first line of defence:
skin, mucous membranes, hairs and
cilia, coughing, sneezing, tears,
saliva, urine, gastric juices,
temperature and enzymes
Body’s second line of defence:
(white blood cells)
Invasion by
Body’s third line of defence:
Antibodies of the
Immune System Review
Lymph Nodes
White Blood Cells
Respiratory System
Stomach & Intestines
Our immune system is very important and all of
these factors work together to help us fight disease.
It is important to keep your immune system strong
by getting rest, eating a balanced diet and doing
physical activity so it can continue to protect you
throughout your life.
The End
Skin Picture - http://en.wikipedia.org/wiki/Skin
Nose blow - www.healingdaily.com/conditions/colostrum.htm
Phagocytosis - J.A. Sullivan www.cellsalive.com
Phagocytosis – www.cellsalive.com
Lymphatic System - Ultimate Human Body (1994) Dorling Kindersley multimedia.
T-Cell – Dennis Kunkel, http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookIMMUN.html
B-Cell - www.evidencesofcreation.com/immune07.htm
Comics – MEDMYST, Mission Three: Nemesis in Neuropolis Available at:
Immune System Review - http://www.humanillnesses.com/General-Information-and-InfectiousDiseases-A-Co/Body-Defenses.html
Infomational Content - Books
– M. Ash, J. Buchanan, G. Lofts, M. Evergreen (1999) Jacaranda Science book 3. Published:
Milton, Qld : John Wiley & Sons Australia Ltd
– M. Haire, E. Kennedy, G. Lofts, M. Evergreen, (1999) Core Science, Jacaranda Wiley: Qld.
Infomational Content – Websites
– Wikipedia Online Encyclopaedia
• http://en.wikipedia.org/wiki/T_cell
• http://en.wikipedia.org/wiki/Immune_system\
– M.J. Farabee (2001) Lymphatic System and Immunity. Avaialable online:
– M. Brain (2006) How your Immune System Works Available online:
– N. Bess (2002) Immune System Website, Avaialble online:
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