under the microscope in your body

Sabrina Crewe
Consultant:
Professor Anne K. Camper,
Montana State University
Under the Microscope
In Your
Body
Copyright © 2010 by Infobase Publishing
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Library of Congress Cataloging-in-Publication Data
Crewe, Sabrina.
In your body / Sabrina Crewe ; consultant, Professor Anne K. Camper.
p. cm. (Under the microscope)
Includes index.
ISBN 978-1-60413-825-2 (hardcover)
ISBN 978-1-4381-3369-0 (e-book)
1. Microorganisms Juvenile literature. 2. Bacteria Juvenile literature. 3. Microscopy
Juvenile literature. 4. Human body Juvenile literature. 5. Microscopes Juvenile literature. I. Title.
QR57.C744 2010
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Text design by Sabine Beaupré
Illustrations by Stefan Chabluk
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Composition by Discovery Books
Cover printed by Bang Printing, Brainerd, MN
Book printed and bound by Bang Printing, Brainerd, MN
Date printed: May 2010
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Acknowledgments
We would like to thank the following for permission to reproduce photographs: © Bärbel Stecher and
Wolf-Dietrich Hardt, Institute of Microbiology, ETH Zurich/SNF/Stecher et al. PLoS Biol 5(10): e 244:
p. 27 top; Dennis Kunkel Microscopy, Inc.: pp. 7, 11, 19, 23, 26; Science Photo Library: pp. 5 (Ralph
Eagle), 8 (Power and Syred), 10 (A. B. Dowsett), 12 (David Scharf), 13 (Biophoto Associates), 14 (David
Scharf), 15 (Andrew Syred), 16 (P. Motta, University La Sapienza, Rome), 17 (David Scharf), 18 (Steve
Gschmeissner), 20 (P. Motta and F. M. Magliocca), 21 (F. Carpino and P. Motta, University La Sapienza,
Rome), 22 (M. A. Ansary), 25 (NIBSC), 27 bottom (P. Ferguson, ISM); Shutterstock Images: pp. 4 (Leah-
Anne Thompson), 9 (Philip Dyer), 24 (Axel Kock), 29 (Raia).
Contents
The World Inside You 4
Cells Under the Microscope 6
A Look at DNA and Genes 8
Bacteria in the Body 10
A Layer of Skin 12
Life on Your Head 14

Inside Your Mouth 16
Into the Bloodstream 18
Digesting Your Food 20
Worm Host 22
Invader Viruses 24
The Fight Against Microbes 26
Size and Scale 28
About Microscopes 28
Micro-Detective 29
Glossary 30
Explore These Web Sites 31
Index 32
Some words are bold the first time they appear
in the text. These words are explained in the
glossary at the back of this book.
4
The World
Inside You
Take a look in the mirror. You
are very familiar with what you
see there—your hair, your eyes,
and the shape of your body. But
you probably don’t spend much
time thinking about the inside of your
body. Nor do you put your body under the
microscope and look at it up close.
If you did, you would find that your body is
a world of its own. It is made up of trillions of
microscopic parts called cells.
Microscopic life

The cells are just the beginning, however. You
may think you are the only thing living in your
body, but you are not! An incredible number of
microscopic living things inhabit your
body along with you.
Organisms are living
things, and living things
too small to see with the
human eye are called
microorganisms. These
include microanimals so
tiny that they go unnoticed
on your skin. Even smaller
are the microorganisms
4
5
we call microbes. Microbes include
bacteria, protists, microfungi,
and viruses. We’ll find out about
all these things in this book.
Journey around
your body
We are going to take a tour
of the human body so you can
discover the world of living things
that make their homes inside you.
Before we do that, let’s take a look at
the cells you are made of and find out
how they make you what you are.
Micro-Fact

You are made of
about 100 trillion cells.
And for every single one
of those cells, there are
ten microbes in
your body!
When things
are magnified, you see
them in a different way.
This is part of an iris, the
colored part of a human
eye. The blue pool at the
bottom is the pupil, which
is the black circle in the
center of your eye
that is actually
a hole.
5
6
cell membrane
nucleus
cytoplasm
ribosomes
mitochondria
other
organelles
Cells Under
the Microscope
Cells are the units that all living things are made of.
We’ll be seeing a lot of cells as we travel around the

microworld of your body. That’s because all parts
of you—from your hair to your toes—
are a mass of microscopic cells.
Cell structure
Whether a cell is in a strand
of your hair or part of a toe
muscle, it has the same
basic structure. You can
see the basic cell parts
in this diagram.
The organelles
of this human cell
include the nucleus,
which controls the cell.
The ribosomes produce
protein, which cells are
made of. The mitochondria
process oxygen and
food to make energy
for their cell.
7
The membrane holds the
cell together and protects it.
It is filled with a substance
called cytoplasm, which
contains various smaller
parts, or organelles. Each
type of organelle has a
particular job to do to keep
the cell working properly.

The headquarters of the
cell is called the nucleus.
You’ll find out more about
the nucleus soon.
Life of a cell
Things are always changing in your body. Every second,
some cells are dying and others are being made. Where
do the new ones come from? Many cells reproduce
themselves simply by dividing. First the nucleus splits
in two. Then the cell stretches in the middle and splits,
with each nucleus becoming the center of a new cell.
Micro-Fact
Some human cells
live for just a day,
while others last
for years.
These are nerve
cells, or neurons—
the type of cells that
make up the nervous
system. The nervous system
carries messages around the
body. Messages travel through
strands that connect neurons
to each other and to other
parts of the body,
such as muscles.
8
A Look at DNA
and Genes

So how does a cell in your tongue know to look and act like
a tongue cell? Why doesn’t it become a piece of knee or
stomach? The answer lies inside the nucleus of every cell.
Let’s take a look under the microscope.
Nucleus in control
We read earlier that the nucleus
controls the cell. What does that
actually mean? It means the
nucleus directs the functions
of the other organelles. But
the nucleus also contains
instructions—a type of
recipe—that the cell follows
when it develops. It’s how the
cell “knows” what to be.
Chromosomes
and DNA
The packages in the
nucleus that hold this
vital information are
called chromosomes.
These are tightly coiled
strings of molecules of
These are human
chromosomes like the
ones inside all the cell
nuclei in your body. They have
been magnified about 10,000
times. Your cells contain two sets of
chromosomes, half of them from

your father and half from your
mother. The chromosomes
carry DNA arranged in the
patterns that form your
own special genes.
8
a substance
called DNA,
which is short for
deoxyribonucleic
acid. DNA is made
of several different
chemicals.
Genes
The way the
strings of DNA are
arranged is the key
to making a cell what
it is. In fact, DNA makes
you who you are. Stretches
of DNA molecules form patterns
called genes. Each gene, or pattern,
holds the information every cell needs
to develop and function. When new
cells form from existing cells, the
information is passed to the new
cell because the chromosomes
copy themselves.
How Small
Is Small?

Scientists believe that if you
stretched out a string of DNA
from just one chromosome, it
would be about 1.25 inches (about
6 centimeters) long. That may not
sound very long. But the string is
packed into a chromosome only
1 micrometer wide, and
1 centimeter is 10,000
micrometers!
Genes are
passed from
parents to children.
Because they have
similar gene patterns,
people in the same
family often
look alike.
9
10
Bacteria in the Body
We already read that there
are different kinds of
microorganisms that live
in and on your body:
microfungi, tiny animals,
and even tinier bacteria
and viruses. Let’s learn
about bacteria, because
we’re going to find them

everywhere!
What is a
bacterium?
A bacterium is a living
thing, like an animal. But
there are several important
differences. Bacteria have
only one cell, and it is
simpler than the human
one we looked at earlier.
Unlike plants and animals,
bacteria reproduce by
simply dividing in two!
Bacteria that live in or
on people absorb food from
whatever part of the body they
call home. This could be the oil on
your skin or the food in your stomach.
Escherichia coli
(E. coli for short) is a
bacterium that lives in
people’s intestines. It is
usually a good bacterium,
but some kinds of E. coli cause
food poisoning. You can see that
the bacterium in the center is
dividing, and it will soon separate
into two cells. These bacteria
have been magnified
about 26,000 times.

Good bacteria
Bacteria can be very useful as they
process their food—in fact, we
couldn’t live without them. Out in
the world, they digest waste, such
as dead plants, and turn it into
nutrients. Inside your body, many
bacteria help digest your food.
Groups of bacteria inside your
body and on your skin also help
fight off germs.
Bad bacteria
Some bacteria that live on our
bodies are harmful, however.
Microbes that make us sick
are what we call germs,
but scientists call them
pathogens. Several common
pathogens are bacteria that
find their way into or onto
our bodies. They may enter
in the food or water we
consume, or they may
be in our environment.
Pathogens release
chemicals that harm
us instead of help us.
These chemicals, or
toxins, can destroy cells
or cause food poisoning.

11
Micro-Fact
Some bacteria can
divide and multiply
several times in
just one hour.
This image shows
several kinds of bacteria,
most of which live on our
skin. Many bacteria are shaped
like a straight rod, while some
are twisted. Others are ball-shaped.
Some have flagella (little tails
that help them move around).
You can see that some of
the bacteria in this picture
are dividing to reproduce
themselves.
A Layer of Skin
It would be impossible for our bodies to
exist without the layer of skin that
covers us. Skin keeps our insides
in and protects them from the
outside world. It is a barrier
against hot and cold weather,
water, and the knocks and
bumps of daily life.
Defense and attack
Skin is also the first defense
your body has against pathogens

that attack you, such as bad
bacteria. Sweat contains
chemicals that help
fight off pathogens.
Our skin is
home to about
1,000 different
12
Micro-Fact
Every square inch of
skin contains 30 million
cells. Between 10,000 and
1 million microbes live
on each of those
square inches.
Staphylococcus
epidermidis bacteria
live on human skin.
They cluster together in
colonies like the ones you
see here. Staphylococci
measure about
1 micrometer across.
These have been
magnified
8,000 times.
13
Microfungi
When you see fungi growing
outside, they look like plants—

mushrooms are a fungi, for
example. But fungi are different
from plants. They spread
threads called hyphae across
the food source they live on.
Fungi with microscopic hyphae
are called microfungi. Some
microfungi, like this one, live on
human skin. This fungus causes
athlete’s foot. You can see the
hyphae (orange) spreading
among the flakes of skin.
types of bacteria. Most
are harmless, and
some help protect our
bodies. The bacterium
Staphylococcus
epidermidis, for
example, lives all
over the body. It can
protect us from a
similar bacterium,
Staphylococcus aureus,
which causes skin
infections and other
diseases.
Animals on
your skin
There are several
microanimals that can

live on you or feed on
your skin. These include
several types of mites.
The female scabies mite
actually digs into the
skin to make tunnels!
She lays her eggs as she
goes, and these eggs
soon hatch to produce
more mites. Scabies
mites cause a rash and
terrible itching.
14
Lice hold on
tight by wrapping
their claws around
your hair. You can see
that this louse has
already attached an
egg to the hair.
14
Life on Your Head
You probably know about lice, even though
you may not have seen one. Lice are very small
insects that like to live in our hair.
Dribbling lice
People with lice infestations have very itchy
scalps. The itch is caused by dribbling lice! To
get food, lice puncture the skin of the scalp with
their mouthparts and suck out blood. As they

feed, lice drool liquid, which is like
the saliva in your mouth. This louse
dribble irritates most people’s
skin and makes them itch.
15
Micro-Monster
Almost everyone has eyelash
mites living in the hair follicles
(tiny holes) from which their
eyelashes grow. The mites feed
on skin oils and the dead skin
around our eyes. This picture
shows the tails of eyelash mites
sticking out of a follicle next
to an eyelash (right). In real
life, eyelash mites are 0.25
millimeters long. These have
been magnified 139 times.
Sticky nits
Females lay eggs,
called nits, once a day.
They make sure the
nits stick to a person’s
hair by covering them
with glue. The eggs
look like tiny white
specks, and they are
just visible if you
look carefully. After
about a week, the

nits hatch, and out
come new lice.
Catching and
killing lice
It’s easy to pick up
lice from other kids
at school if you have
your heads close
together. The lice
simply crawl from
one head to another.
There are special
shampoos that can
kill lice. You need to
use a fine-tooth
comb to dislodge
the sticky nits.
16
Inside Your Mouth
Lots of stuff gets into your body through your mouth, and a
lot goes on there. It’s quite a center of microscopic activity!
Your tongue
It’s fun to take a close-up look at your
tongue. It looks pretty smooth until
you put it under the microscope. Then
you see that your tongue is covered
in small lumps called papillae. Some
contain rounded taste buds, which
you use to taste your food. Other
papillae are spiky and help hold onto

food and move it around. The papillae
also let you know if your food is too
hot or too cold.
Germ Barriers
Your mouth has
cells that are tightly
packed together,
which makes it hard
for the pathogens
you breathe in to
get through to cells
underneath. Your
saliva, like your sweat,
contains chemicals
that fight pathogens.
In this photo
of a person’s tongue,
you can see the larger,
rounded papillae that
contain tastebuds. In
between are the spiky
papillae that process
your food.
16
17
Biofilm on Your Teeth
Teeth are covered in hard material called enamel, which is
made of calcium and other minerals. Enamel is tough so you
can bite and chew food without breaking your teeth. You’ve
probably heard plenty of times how important it is to keep

your teeth clean. If you don’t, they get covered in plaque
and start to decay. Under the microscope, we discover that
plaque is actually a slimy substance, called biofilm, with
bacteria in it. Some of the bacteria produce this slime to
help them stick to your teeth. Some biofilm is a good thing—
it protects your teeth from pathogens. But if you let too much
plaque build up on your teeth, the bacteria will eat away
at the enamel and cause your teeth to decay.
18
Into the Bloodstream
We’re going to take a
look at the amazing
system called the
bloodstream. It is
a transportation
network running
through your
body, carrying
blood to every
part of you.
What is
blood
made of?
The liquid part
of blood, called
plasma, is mostly
water, but it also contains
nutrients. The main job of
plasma is to transport three types
of blood cells: platelets, red blood

cells, and white blood cells.
Platelets are useful when you bleed.
They thicken up, or clot, at the wound and
stop the bleeding. That’s how scabs form over cuts.
White blood cells are the body’s defenders against
infection and sickness. We’ll learn more in a while about
how they defend your body.
You can see
red blood cells and
white blood cells
traveling through
this blood vessel
in the liver. The
blood is carrying
nutrients and
oxygen.
19
How Small
Is Small?
A red blood cell measures
about 7 micrometers across.
A drop of blood 1 cubic
millimeter in size can hold
about 5 million red
blood cells.
Red blood cells
Most of your blood cells are
red blood cells, and they give
your blood its color. Their job is
to deliver oxygen and remove

waste. When blood travels to
the lungs, red blood cells pick
up oxygen from the air you
inhale. They travel around the
bloodstream, releasing oxygen
to all the cells that need it.
Red blood cells also pick up
waste from the cells in the form
of carbon dioxide. They carry
the carbon dioxide back to the
lungs, where you breathe it out
and get rid of it.
Protozoa
Sometimes, microbes
get into our blood. They
may belong to a group of
organisms called protozoa,
which are animal-like
protists. Most protozoa
catch or find food, but a few
are parasites, which means
they absorb food from a
host. If that host is you, the
protozoa are likely to make
you sick. Sleeping sickness,
dysentery, and malaria
are all illnesses caused
by parasitic protozoa.
The protozoa below, in
amongst red blood cells,

are called trypanosomes,
and they cause sleeping
sickness. The green threads
are their flagella.
Digesting
Your Food
If you’re looking for bacteria, you can be sure to find them in
your colon. The colon is also called the large intestine, and it
is home to more bacteria than any other part of your body.
Follow the food
After you swallow your food, it heads down a tube called the
esophagus to get to your stomach. Your food is churned up,
or digested, in the stomach and then processed further in
the small intestine. The small intestine extracts nutrients from
the food and passes them into the bloodstream.
20
Protozoa, such as
these Giardia lambia,
can live in the small
intestine. Giardia lock
onto the intestine wall with
suckers and feed there.
Unfortunately, they
can make you
very sick, too!
21
The colon gets the food next. By this
time, what’s left is a liquid containing
lumps of stuff your body can’t digest.
The colon absorbs the liquid for

your body to use. The rest will be
turned into waste that leaves your
body when you go to the bathroom.
But first, the good bacteria in your
colon will go to work.
Bacteria at work
These good bacteria are often called intestinal flora.
They digest food your stomach can’t handle. For example,
vegetables and fruits contain nutrients we need but can’t
process ourselves. The bacteria in our colon release the
nutrients for us as they feed on these foods.
Bacteria have other jobs in the colon, too. As they feed,
they produce acids and other substances that stop bad
bacteria multiplying. Intestinal flora even
make vitamins for your body!
Micro-Fact
About 30 percent of
your feces (poop)
consists of bacteria
from your colon.
A peek
into the colon
shows clusters of
bacteria (pink)
living on the
intestinal
wall.
21
22
Worm Host

As you read earlier,
parasites are organisms that
survive in or on a host by
feeding off it. Some parasites
in the human body are
animals. It’s hard to believe
that you might actually have
animals living inside you, but it’s
true! Scientists say half the people
in the world have worms living in them.
Roundworms
Some worms are microscopic when
they are larvae, or newly hatched
worms. They may stay microscopic,
such as the roundworms that live in
your blood. Others can grow very big,
such as the large roundworm. It lives
in the small intestine and grows to
be 1 foot (30 centimeters) long.
Pinworms
By the time you turn twelve,
it’s likely you’ll have had
some pinworms living in
you. They feed on bacteria
that live in digested food.
This is the stuff that has
How Small
Is Small?
Pinworms can be up to
0.5 inches (13 millimeters)

long. So when they come
out to lay their eggs, they
are visible to the
human eye.
The mass
of white-colored
roundworms above
was found in a section
of intestine. The larvae
of these worms can
leave the intestine
and travel around
the body, causing
sickness.
passed through the
colon and is ready to
leave your body. Yes,
pinworms are worms
that live in your poop.
The females wriggle
out at night to lay their
eggs on your skin.
They also deposit a
substance that makes
the skin itch, which
is usually how
people know they
have worms.
Hookworms
Most worms arrive

in your body in
food or water, but
a hookworm enters
by burrowing into
your skin as a larva.
They get into the
bloodstream, then
into the intestine.
The adult worm,
about 0.4 inches
(10 millimeters) long,
feeds by sucking
blood from the
intestinal wall.
Micro-Monster
Tapeworms are parasites that people
can get from dirty food or water or
from meat that is not fully cooked. This
tapeworm would grow by attaching
to your small intestine with the hooks
and suckers on its head. There, some
tapeworms grow to 20 feet (6 meters)
long! Some smaller tapeworms can
travel anywhere in the body through
the bloodstream. They can get into
muscles, eyes, and even the brain.
23
Invader Viruses
Viruses are unlike other microbes.
Instead of being made of

living cells, they are simply
a package of chemicals.
Scientists say that they are
not actually organisms,
because they can’t grow
or feed. Instead, they
reproduce themselves by
invading cells of a host. The
host could be a plant, animal,
protist, or even a bacterium.
How host cells make
more viruses
So how does this work?
You remember reading
about DNA in your
cells. A virus also
has DNA or similar
This is a
picture of what a
Swine flu virus would
look like if you opened
it up. The coiled stuff in
the center is the DNA
it injects into host
cells to make copies
of itself.
24
Micro-Scientist
Scientists who study
microorganisms and cells

are microbiologists. Some
microbiologists, called
virologists, study viruses
and how they damage cells
and make people sick.