The following presentation is brought to you by Discovery Channel School, a leading provider
of quality educational resources that help teachers bring the world to their students.
This is TLC Elementary School, a place where teachers of kindergarten through sixth grade
can find high quality documentary programs chosen to inform and delight students.
Use TLC Elementary School to complement your classroom lessons and to give students an
up close look at the world and the people around them.
On this edition of TLC Elementary School, watch closely as the human body defends itself
against bacteria, viruses, and an invader that causes an allergy.
First, see how the salmonella bacteria is passed from host to host.
Then follow the journey of the flu virus as it attacks the throat.
Finally, find out what happens when a wasp sting causes an extreme allergic reaction.
And watch for classroom activities right after each segment.
Segment 1, Bacteria.
This chicken is hiding a deadly secret.
Its intestines are a breeding ground for some of the smallest organisms on earth.
Neither plant nor animal, these single cell creatures exist almost anywhere, in extremely
high or low temperatures.
They've been around for billions of years and can even make their way into tonight's
dinner.
We call these hardy single cell organisms bacteria.
One type of bacteria living inside this chicken is salmonella.
It doesn't harm the chicken because chickens have adapted to living with this type of bacteria.
Because humans haven't adapted to living with salmonella, it can cause serious problems
if it enters the body.
Some bacteria are helpful to humans.
They live in the intestines and play a role in digestion.
Bacteria can enter the body through the nose or mouth or breaks in the skin.
In some cases, it's through the water we drink or the food we eat.
The high temperature of cooking kills most bacteria, but undercooked food is usually
the source of the salmonella bacteria.
Even though this chicken has been cooked, it's still teeming with life because it wasn't
cooked thoroughly.
So millions of salmonella have been able to survive.
In one mouthful of undercooked chicken, thousands of salmonella are carried down into the stomach.
Because our bodies aren't used to living with the bacteria salmonella, digestive acids
try to attack the foreign bacteria.
The stomach's digestive acids are not strong enough to fight off all the salmonella.
The remaining salmonella are swept into the intestines by contractions of the muscles.
In order to survive, the salmonella must invade healthy cells.
The moment the salmonella lands on a healthy cell, it begins to multiply.
Bacteria have two goals, to eat and to reproduce.
Only two hours after dinner and the salmonella has completely taken over the infected cell.
The new bacteria burst out of the host cell they have destroyed and spread to neighboring
cells.
Now they really begin to multiply.
Despite the commotion of all this spreading and breeding, this man has no idea there's
a battle waging inside him.
The body must defend itself against the attacking salmonella.
As each cell dies, it releases a chemical signal that alerts the body's immune system.
Defense cells, a type of white blood cell, are sent in to fight the bacteria.
But the mighty salmonella overpowers them.
As the bacteria destroy more and more cells, the body sends a distress signal in the form
of a physical reaction in the intestines.
The muscular contractions that should go one way switch into reverse.
This causes a feeling of extreme nausea.
This is the first sign that something isn't quite right.
His body prepares for a violent expulsion.
Food shoots back into his stomach.
The flap to his windpipe slams shut.
Another blocks off his nose.
His body gets rid of the bacteria by vomiting.
This powerful response only clears the top few inches of the intestines.
The contractions in the intestines get faster.
Fluid rushes through and builds up at the bottom of the intestine.
It causes a painful and unmistakable feeling.
Diarrhea.
Mike?
Is that you?
Mike?
Diarrhea feels terrible, but it's an effective way for the body to rid itself of harmful
bacteria.
Around five million salmonella are flushed from the intestines all at once.
And then again.
How are you feeling?
I'm fine.
Everywhere hurts, man.
My stomach feels like a washing machine.
Do you think it was the chicken?
His body has been fighting the salmonella invasion for 24 hours.
Along with vomiting and diarrhea, these bacteria can also cause severe cramps, body aches,
and headaches.
It's a serious matter.
And it's not over yet.
The bacteria invasion has picked up pace, and the body seems to be fighting a losing
battle.
Right.
Give me a nice big smile, please.
That's it.
As the salmonella spreads, it triggers another defense system.
This looks like a normal cell for the salmonella to attack, but actually it's a trap.
The salmonella passes through a gateway into a gland, where it comes into contact with
helper cells, immune cells that begin to multiply.
Now the body is ready to really fight back.
An army of helper cells is released from the gland to head toward the battle site.
They release a chemical that causes the body's defense cells to double in size.
The defense cells release a poison over the salmonella.
It's released so quickly that the salmonella doesn't have time to defend itself.
At last, the body's defense cells have become efficient killers.
Finally, the painful symptoms of a bacterial infection begin to go away.
Right.
Are we set?
Salmonella germs are usually carried through poultry, milk, and eggs, but it's easy to
prevent the spread.
Always cook chicken thoroughly and keep foods properly refrigerated.
The human body has adapted to using some types of bacteria, but unlike chickens, we still
aren't used to living with salmonella.
Try this activity to complement bacteria.
Work in small groups to make and illustrate a flowchart showing a salmonella invasion
into the body.
Show the body's responses to the invasion from the beginning to the destruction of the
bacteria.
Segment 2, Viruses.
Holly Jones is a healthy young woman, but her body is about to become a battlefield.
Can you hold the door, please?
The man standing next to her is sick with the common flu.
As he sneezes, the air explodes from his mouth and nose at 40 miles an hour, sweeping droplets
of mucus into every corner of the elevator.
Most of these droplets are harmless, but some of them carry microscopic particles called
viruses.
Viruses are lifeless by themselves, but when they invade a cell, they begin to multiply.
The virus that has entered Holly's nose is called influenza B. Many different viruses
can infect humans, but they all work in a similar way, by attacking certain cells in
the human body.
The cells that the influenza B virus attacks are in the nose, lungs, and throat.
This virus makes its way through the mucus protecting her throat and lands on a cell.
Spikes on the virus allow the cell to read it as a harmless protein.
The virus slips inside easily.
Once in, it takes control of the cell's machinery.
Instead of making proteins, the cell now begins to manufacture parts for thousands of new
influenza B viruses.
Each new virus will set out to take over another cell and turn it into a machine for making
viruses.
Holly's body starts to fight back.
White blood cells are patrolling her body all the time.
Their job is to protect the body from invaders.
When they find one, they spray a poison to destroy it.
In the process, many of Holly's own throat cells are destroyed.
Dead cells pile up in her throat.
If they aren't disposed of, she could choke as she sleeps.
But Holly's immune system has its own cleanup crew.
These cells, called macrophages, dispose of debris in a simple way.
They eat it.
It's been less than a day since the virus entered her body.
For the first time, Holly can feel the effects of the battle being waged beneath her skin.
Trying to contain the virus, her own immune system has destroyed thousands of throat cells.
Holly's throat has become raw, swollen, and sore.
Holly is getting the flu.
But what people often consider symptoms of the flu are actually the results of the body
fighting the flu virus.
The macrophages working in her throat release a chemical signal into her bloodstream, summoning
more white blood cells.
But this chemical makes Holly feel terrible.
Her nerves become so sensitive, the slightest movement causes her pain.
The pain has a purpose.
Holly's body is telling her to slow down.
She'll need extra energy to defeat the virus.
The chemical signals from the macrophages also tell her brain to heat up her body.
As a result, Holly gets a fever.
And as her temperature rises, the viruses slow down.
But her body speeds up.
The white blood cells divide and multiply faster than ever.
Holly's raised temperature makes the blood vessels around her brain swell.
The pressure gives her a throbbing headache.
But she will suffer as long as her immune system continues to fight the virus.
Her body has other weapons.
It launches thousands of special white blood cells called T cells.
They hone in on infected cells and destroy them.
The final battle has begun.
Her body also manufactures an antibody, a special protein made specifically to fight
this virus.
It attaches to the virus' spikes and makes them useless.
Because the viruses are paralyzed, they can no longer infect Holly's cells.
Only when her immune system scales down its efforts will she start to feel better.
It has taken a week for Holly's body to beat the virus.
On the battlefield, new throat cells are starting to grow.
Most of the T cells, their job done, shrivel and die.
But some, known as memory cells, will patrol her body for the rest of her life.
If this exact virus tries to invade again, the memory cells will instantly wipe it out.
But the influenza B virus can mutate.
If she's infected by the mutated virus, she may get the flu all over again.
There are ways to help stop the spread of the influenza virus.
Always cover your mouth when you sneeze or cough.
And always wash your hands before eating.
You never know when you may come in contact with influenza B.
Try this activity to complement viruses.
Diagram the path of a flu virus inhaled into the body.
Follow the virus as it colonizes healthy cells and replicates.
Show how the body's immune system, with the help of T cells and macrophages, takes action
against the virus.
Segment 3, allergies.
Every day, the human body is bombarded with foreign substances.
Dust, pollen, chemicals, even venom from bug stings can enter the body.
In people without allergies, the body's immune system successfully defends against these
substances.
In others, the body's defenses overreact, causing an allergic reaction.
Sting stung by an insect is no fun.
Most people try to avoid the flight paths of bees and wasps.
Phoebe has never been stung by a wasp before.
For people with or without an allergy, the sting starts out the same.
With pain.
Instantly, venom is pumped into the skin.
Within seconds, the venom kills skin cells, triggering nerve endings of pain receptors.
Immediately the immune system starts its routine plan of attack.
Mast cells, or special immune cells, react to the venom.
They release histamine, a chemical that makes tiny blood vessels expand.
This allows more blood to flow into the area.
The human bloodstream is full of antibodies, the immune system's most powerful weapon.
Our bodies make antibodies to fight against different invaders.
This antibody protected Phoebe against a virus she caught when she was three.
This antibody protected her against bacteria she encountered at ten.
In non-allergic people, or with someone who has not been stung before, the immune system
creates antibodies to keep the venom from invading, leaving only a tender bump for a
few days.
But for some people, including Phoebe, the body goes further and begins to make an antibody
against the venom.
These are called E antibodies, and they are made in large amounts.
Because Phoebe has an allergic tendency, which is most likely inherited, her body makes
these antibodies.
Twenty-four hours after the wasp stung her, Phoebe's body shows little sign of damage.
And E antibodies are attaching to mast cells all over her body.
E antibodies are the cause of most allergies.
If Phoebe is stung again, venom may attach to the many E antibodies on her mast cells,
causing an extreme allergic reaction.
Just like the first sting, wasp venom spreads through Phoebe's skin cells.
Her body begins to react the same way it did the first time she was stung.
But this time, her mast cells are covered with E antibodies, causing her body to overreact
to the venom.
Phoebe is about to experience a rare but extreme allergic reaction, anaphylactic shock.
The E antibodies cause mast cells to release more histamine, which opens up the blood vessels.
Venom surges through her bloodstream, and more E antibodies trigger more mast cells to release
histamine into her body, making it appear as though she's been stung all over.
Her body is feeling itchy.
Her blood pressure drops.
She starts to feel faint and cannot breathe properly.
Phoebe needs emergency medical care immediately.
High levels of histamine make her airways close down.
Her body releases adrenaline, a hormone that tries to fight the histamine, letting her
airways open up.
But venom is still in her blood, and E antibodies are still triggering new mast cells to make
histamines.
Her heart beats faster, trying to pump blood throughout her body.
But it's fighting a losing battle.
Phoebe is in serious trouble.
The doctor gives her a shot of adrenaline, 30 times stronger than her body produced minutes
earlier.
Again, adrenaline races through her bloodstream.
This time, there's enough to stop the effects of histamine for good.
Within minutes, Phoebe is awake.
Don't worry, Phoebe, you're in hospital.
You're going to be fine.
Because she is allergic to wasp stings, Phoebe must go see an allergist for treatment.
She will most likely take a series of injections, which will, in time, protect her from future
allergic reactions.
Phoebe will be able to enjoy the outdoors without the fear of an extreme allergic reaction.
Until then, she will have to carry doses of adrenaline with her wherever she goes.
Try this activity to complement allergies.
As a class, identify common allergens in and around your school, such as dust, mold, and
even wasp venom.
Create a poster to hang in the hallway, informing students about these potential allergens and
the human body's reactions to them.