Your body (whats your body made of and how it works?)

USBORNE HOTSHOTS
YOUR
BODY
USBORNE HOTSHOTS
YOUR
BODY
Written by Susan Meredith
Designed by Fiona Johnson
Illustrated by Kuo Kang Chen,
Colin King and Sue Stitt
Series editor: Judy Tatchell
Series designer: Ruth Russell
Additional illustrations by Chris Lyon,
Guy Smith, Annabel Spenceley
and Peter Wingham
CONTENTS
4 What is your body made of?
6 Where does your food go to?
8 Why do you breathe?
10 What is blood for?
12 Your skin
14 Messages from outside you
18 Inside your head
20 What makes you move?
22 How are babies made?
24 What makes you ill?
26 Looking after your body
29 Amazing facts about
your body
32 Index

What is your body made of?
Your body is made of more
than 50 million million
living units called cells.
Most cells are so small
that you can only see
them with a powerful
microscope. The cells
are about two-thirds
water. Food and oxygen
mix together inside them
to give you energy.
Different kinds of cells
Cells are different shapes and
sizes depending on the job
they have
to do.
This is a group
of skin cells,
magnified
many
times.
One cell
This part
controls
the way the
cell works.
It is called
the nucleus.
Nerve

cell
Nerve cells are
very long. Messages
travel along them.
Muscle cell
Nucleus
Muscle cells
are long and
thin. They
can shorten
their length
(contract) and
then relax,
which makes
you move.
Nucleus
Cells lining nose
Cells lining your nose and windpipe
have tiny hairs on them. These waft
germs and dust away from your lungs.
Nucleus
Chromosome
The cells' instructions
The nucleus in each cell contains special
threads called chromosomes. These carry the
instructions the cell needs to live and work.
You inherit your chromosomes from your parents.
Chromosomes are made of a chemical called DNA,
which looks a little like a twisted ladder.
Growing and repair

Until you are about 18, your body keeps
making more and more cells. This makes you
grow. Even when you are grown up, your body
continues making some new cells. These replace
the millions that die every second. A new cell is
made when an existing cell divides in two.
Part of a
chromosome.
The rungs
on the DNA
"ladder" form
the coded
instructions.
The cell takes in
goodness from food
and grows.
The nucleus
divides and the
cell starts to
narrow in
the middle.
The cell
splits in
two.
The rungs on the DNA
"ladder" are arranged in a
different order in different
people. This makes the
instructions different, and
makes everybody unique.

4
Where does your food go to?
Without food to use as fuel, your body would soon
stop working. Before your body can use it, the food
has to be broken down inside you. This process is
called digestion. The digested food goes into your
blood and is carried to every tiny cell in your body.
Digestion
Digestion takes place as your food
travels through a long tube winding
from your mouth to your bottom.
Your teeth bite and chew your food into
small pieces. Saliva (spit) moistens it and
makes it easier to swallow. Saliva has
a digestive juice in it which starts
breaking up the food. When
you swallow the food, it goes
down your oesophagus into
your stomach.
Look on the opposite
page to find out what
different parts of the
digestive tube do.
Small
intestine
Oesophagus
Stomach
Large
intestine
This picture shows

the position of your
digestive system.
Rectum
Anus
Moving along
Food does not just slide
through your digestive
tube. It is squeezed along
by muscles in the tube.
Muscles squeeze here. Food is
pushed
along.
Food
Stomach
In your stomach the
food is churned up and
mixed with stomach juice. It
becomes rather like soup.
Small intestine
Your stomach releases
food into your small intestine.
Juices finish digesting it. The
digested food seeps through
the thin walls of your small
intestine into your blood.
Large intestine
Water and any food
which cannot be digested
move into your large intestine.
Most of the water goes into

your blood through the walls
of your large intestine.
Rectum
Solid waste is stored at
the end of your large intestine
in your rectum. It is pushed
out through your anus when
you go to the toilet.
Teeth
The hardest substance in
your body is the enamel
coating on your teeth.
There are 32 teeth in a full
adult set and 20 in a set of
first or "milk" teeth. Your
teeth are anchored in your
jawbone by long roots.
Waste water
Any water that your body does not
need is turned into urine (pee) in
your kidneys. These are in your
back. Urine is stored in your
bladder until you go to the toilet.
7
6
Blood
vessel
Your lungs are in your chest.
The air you breathe is
sucked through your

nose or mouth, down
your windpipe and into the
branching tubes in your lungs.
At the ends of the tiniest tubes
are bunches of air sacs. These
fill up with air, like balloons.
You have about 300 million air
sacs in each lung.
The air sac walls are only one
cell thick. Oxygen seeps through
them into your blood. Your blood
carries it to all your body cells
and brings back carbon dioxide.
Why do you breathe?
Before your body can use the energy which is in your
food, the food has to be mixed with oxygen. This
is a gas in the air. When you breathe in, you
take oxygen into your body.
When food and oxygen are combined in
your cells, energy is released. At the
same time, a waste gas, called carbon
dioxide, is made. You get
rid of this when you
breathe out.
Your lungs
from air
sac.
Carbon dioxide
seeps out of
blood into

air sac.
How you breathe
Your breathing is controlled by muscles
between your ribs and by your
diaphragm muscle, which is
below your lungs.
Oxygen goes in.
Ribs move up and out,
expanding the space
in your lungs.
Diaphragm moves
downward.
Carbon dioxide
and water go out.
Ribs move down
and in, squeezing
air out.
Diaphragm
relaxes
upward.
Blood vessel
Voice box
The
lumpy
part at the
front of your
Your voice neck is your
box is here. voice box.
You have some stretchy
cords, called vocal cords, in

your voice box. When you
speak, you breathe out and
air passes between the cords.
It makes them vibrate and
produce sounds.
Vocal cord
High sounds
Low sounds
Muscles in your voice box
alter the shape of your vocal
cords to produce high or low
sounds.
8
Air in
and out
9
The main job of your blood is to carry food and
oxygen to your cells. It also collects up waste for
disposal. Your blood is pumped by your heart. It flows
around your body in tubes called blood vessels.
What is blood for?
Heart and blood vessels
Your heart is about the size of your fist
and is made of muscle. It keeps squeezing
so blood spurts out of it into your blood
vessels. There are three types of blood
vessels: arteries, capillaries and veins.
Arteries are blood vessels which
carry blood away from your
heart. Blood in your arteries is full of

oxygen and is bright red.
Capillaries are tiny blood
vessels. They pass between
all the cells of your body. Their
walls are so thin that substances
can pass in and out of them, to
and from your cells.
Veins are blood vessels which
carry blood back to your heart.
Blood in your veins is purplish-red
because the oxygen has been used up.
10
Blood
Blood consists of a mixture of cells
floating in a pale yellow liquid called
plasma. Digested food and waste
products are carried in your plasma.
White blood cell
help to fight off
illnesses. They
Platelets help cuts to surround and
stop bleeding. They destroy germs.
plug up the wound
by making a clot.
Heartbeat
Your heartbeat is the sound
made by two pairs of valves,
like gates, in your heart. They
slam shut after each surge of
blood has gone through. This

stops the blood from flowing
back. You have valves in your
veins,
Red blood cells pick up oxygen as
your blood passes through your
lungs. This turns them bright red.
Circulation
Your blood
always goes
in the same
direction
around your
body, as
shown here.
Pulse
Every time your heart pumps,
your arteries throb as blood
surges through them. You
can feel this throbbing, or
pulse, at your wrist.
Heart
Your skin
Your skin is not just a bag to hold your body together. It also
protects you from the outside world. It is about 2mm (0.08in)
thick over most of your body and is arranged in two main
layers: the outer epidermis and the inner dermis.
Your surface skin is dead. This strong protective
covering gradually gets worn away but new cells
from the bottom of the epidermis are
growing up all the time to take its place.

Dark or fair? Hair
Your skin produces
a dye called
melanin. The more
melanin you have, the darker
your skin.
In strong sunlight extra melanin
is produced as protection
against the sun's rays. This is
why peoples who originated
in hot, sunny climates
have dark skin.
Your hair grows out of pits
called follicles. Cells at the
root of the hair divide and
push it upward. As your hair
grows, the ends
get so far away
from your blood
that they die.
Having a hair cut is
painless, because
the hair is dead.
Hot or cold?
When you are hot, your blood
vessels widen so that more
blood can flow near the skin's
surface and be cooled by the
air. This makes
you look red.

When you are
cold, the blood
vessels narrow
to prevent heat
loss and you
look paler.
Waterproofing
Your skin is coated with oil
made in groups of cells called
sebaceous glands.
The oil helps to
keep your
skin and hair
waterproof
and supple.
Goose pimples
You get goose
pimples when
you are cold
because tiny
muscles
attached to
your hairs contract. This makes
the hair on your body stand on
end. This is not much use to
humans but in furry animals the
hairs trap air. This helps to
keep the animal warm.
Sweat
Sweat is mainly water and salt,

which pass into your sweat
glands from nearby blood
vessels. The sweat comes out
through holes called pores. The
air cools you as it
dries the sweat
on your skin.
Your eyelashes help
to keep dust and dirt
out of your eyes.
Lower eyelid
As this eye looks
at the rocket, the
light rays that come
from the rocket
cross each other
behind the lens, so
that the picture on the
retina is upside down.
The brain turns the picture
back the right way up.
Big or small pupils
When it is dark, your pupils
expand to let in as much light
as possible. In bright light they
shrink to prevent damage to
your retina.
Tears
Every time you blink, tears wash
over your eyes and clean them.

Right eye
This part of
your eye is
called the iris.
Muscles in the iris
change the size of
your pupils.
Tears are made
under your top
eyelids.
Tears drain into your
nose through the inside
corner of your eye.
You can watch your pupils
changing size. Try looking at
them in a mirror, first in a
bright place, then in a dim one.
If you get something in your eye,
extra tears are made to wash it
away. Nobody knows why
people cry when they are upset.
Taste
Your tongue has tiny spots
called taste buds on it.
Receptor cells in the
taste buds sense four
different tastes:
sweet, sour, salty and bitter. Different
parts of your tongue pick up the
different tastes.

Smell
Receptor cells high in your nose
are sensitive to smells. They
sense subtle tastes too. This is
why you can't taste much if
your nose is blocked up.
15
Messages from outside you
Information from the outside world comes to you through
special nerve cells called receptors. When these are stimulated
by light or sound, for example, they produce tiny electrical
impulses, which travel along nerves to your brain. Your brain
sorts out what they mean.
How you see
Everything you see has rays of light
bouncing off it. The light goes into
your eyes through the pupil (the
black dot in the middle). Behind
the pupil is a lens. This bends
the light rays so that a clear
picture of what you are
looking at fits onto the back
of your eye (the retina).
Receptor cells which
react to light are in
your retina. They
send impulses
your brain.
The "whites" of
your eyes protect

the parts behind.
How you hear
Sound is really vibrations in the air. These affect
receptor cells right inside your ears.
The outside of your ears is like the big end of a
funnel. It collects sounds and directs them down
a tube, called the ear canal.
Where the sounds go
The sounds hit a
piece of thin,
tightly-stretched
skin called the ear
drum and make it
vibrate.
The vibrations pass Fluid in the cochlea
along a chain of
three tiny bones
and then to a
coiled tube called
the cochlea.
shakes around and
pulls on hairs in the
receptor cells. These
send electrical
impulses to the brain.
When you move your head,
fluid in the semi-circular canals
swirls around and pulls on
receptor hair cells. These send
impulses to your brain, which

tell it about your position.
If you spin around and then
stop, you may feel dizzy. This is
because the fluid in the canals
continues to swirl for a while,
even though your body is still.
This confuses your brain.
Loud noises
This chart shows the
approximate loudness of
certain sounds. Loudness is
measured in decibels (dB).
Repeated exposure to loud
noise, say through headphones,
can damage the receptors in
your ears and make you deaf.
Touching and feeling
You have pain
receptor cells
deep inside you
as well as in
your skin.
Pain helps to
protect you by
warning you
when something
is wrong.
16
Receptor cells in your skin respond to
different sensations such as heat, cold,

light touch, pressure, itch or pain. You
have lots and lots of receptor cells in your
mouth, fingers and the soles of your feet.
A tiny hurt in one of these places can feel
much worse than a hurt in a place with
fewer nerve endings.
17
A mouth ulcer can be
very painful because you
have so many receptor
cells in your mouth.
Balancing
Receptor cells in
your skin have
different shapes.
Inside your head
Your brain controls your body and makes sure that all the
different parts of you work together. It makes sense of what
happens to you and enables you to think, learn and feel. Rather
like a computer, your brain receives information, processes it
and decides what action to take.
Brain and nerves
Your brain is connected to all
parts of your body by nerves.
Messages go to and from
your brain along the
nerves in the form of
electrical impulses,
also called nervous
impulses.

3. Brain notices,
"That's an itch!"
2. Message goes along
nerve to brain from
nerve ending
(receptor)
in arm.
Follow the numbered
labels to see how a
message travels to and
from your brain.
4. Message goes
from brain to hand:
"Scratch itch."
The main
pathway for
your nerves
is inside your
backbone.
Parts of the brain
Different parts of
your brain have
different jobs to
do. There are
some parts that
nobody knows
much about. They
are probably to
do with thinking,
memory and

making decisions.
Funny bone
You can't
normally feel
the impulses as
they travel along
your nerves.
However, your
funny bone is
very close to a nerve and the
shooting pain you get when you
bang it is an electrical impulse.
Sleeping
Dreaming may be a
way of making sense
of what has
happened
to you
Your brain works even when
you are asleep. It makes sure
your heart keeps beating and
that you breathe and digest
your food.
Two halves of the brain Rapid reflexes
Each half of the brain controls
the opposite side of the
body. This is because
the nerves to the
two sides of your
body cross each

other as they leave
your brain.
The right side of
your brain controls
the movements of
your left hand.
If you prick your finger, you pull
your hand away immediately.
This automatic reaction is called
a reflex. It helps to
protect you from
danger.
To do this as fast
as possible, the
impulses bypass
your brain and go
from your spine
to your muscles.
19
What makes you move?
Your skull
protects
your brain.
Your ribs protect
your heart and
lungs.
You are able to move the different parts of
your body because of the way your muscles,
bones, brain and nerves all work together.
Your skeleton

Besides helping you to move, your skeleton
gives your body shape and stops it from
collapsing. It also protects parts of your body.
What's in a bone?
The outside of your bones is very hard but the
inside is softer and spongy. It is arranged in a
meshwork, which makes it light but strong.
Some bones contain a
substance called marrow.
Blood cells are made in
the marrow.
Joints
The place where two bones meet is
called a joint. Most joints are movable.
Here are just two types.
Ball and
socket joint -
at hips and
shoulders.
Your bones are held together by
strong threads called ligaments.
They are cushioned by
pads of a rubbery
substance called
cartilage and oiled
by a special fluid.
Without the cartilage
and fluid, your bones
would grind together.
20

Hinge
joint -
at knees
and
elbows.
Knee joint
Cartilage
Fluid
Ligament
Raising
your
eyebrows
uses over
30 muscles.
Your muscles
Many of your muscles are arranged in layers
over your skeleton. They are attached to your
bones by strong cords called tendons. You can
see and feel your biggest tendon, just above
your heel.
You can also see tendons
on the inside of your
wrist when you clench
your fist and at the
inside of your elbow
when you bend your arm
How muscles work
When you want to move part of your body,
your brain sends impulses along nerves to
your muscles, telling them to contract

(shorten). As they contract, they pull on
your bones and make them move.
Most of your muscles work in pairs.
While one muscle is contracting, its
partner relaxes.
21
How are babies made?
A baby starts to grow when a special cell from a woman, called
an ovum or egg cell, and one from a man, called a sperm cell,
meet and join together inside the woman's body.
Sperm cells Tube
Sperm cells are made in
a man's two testicles.
These are inside a bag of
skin, which hangs behind
his penis. Sperm can
travel from the testicles
along two tubes and out
of the end of the penis.
Egg cells
A woman's egg cells are stored in her
two ovaries. Once a month, an egg cell
travels from one of the ovaries down
one of the tubes leading to her womb.
Penis Testicle
Growing up
When you are
around I I years
old (girls) and 13
(boys), changes

start taking place
in your body as
you grow into an
adult. This time is
called puberty. The
main purpose of
the changes is to
enable you to have
children when you
are grown up.
22
A baby develops
Together, the egg and sperm make one new
cell. This cell divides to make two cells
exactly the same. These two cells then
divide to make four. The cells continue
dividing until a whole ball of cells is made.
The ball of cells settles down in the
lining of the woman's womb. There,
it gradually develops into a baby
until, after nine months, it is
ready to be born. A baby is born
through its mother's vagina.
The cell
divides.
Eye
A ball
of cells
A baby after one
month in the

womb.
Having a period
Every month, the lining of a woman's womb gets thick and soft
with blood, in case a baby starts to grow there. If this does not
happen, the lining and the egg cell, which has come from the
ovary, break up and trickle out of the woman's vagina with
some blood. This is called having a period.
23
When a man and woman have sex, the
man's penis gets stiffer and fits inside the
woman's vagina. Sperm come out of the
penis and swim up into the woman's
womb and tubes. If the sperm meet an egg,
one of them may join with it. This moment
is called conception or fertilization.
What makes you ill?
Most everyday illnesses are caused by germs and are called
infections. Germs are tiny living things, which are everywhere.
Not all of them are harmful. The symptoms of infection, such as
fever, are caused by germs damaging your cells and by your body
fighting back. The main types of germs are bacteria and viruses.
Bacteria
Bacteria are so tiny that
over a million could fit on
a pinhead. Some cause
illnesses such as ear and
skin infections.
Some bacteria attack your
cells by giving off poisons.
They can also spread

infection around your
body in your blood.
Medicines called antibiotics
can be used to kill bacteria
that cause illness.
No medicines can get rid of
viruses. Your body has to
fight them off by itself.
How germs spread
Most germs spread through the air. When you cough,
sneeze or just breathe out, you spray tiny droplets into the
air. This can spread illnesses such as colds and flu to other
people. Covering your mouth and nose when you cough
or sneeze helps stop germs from spreading.
Try not
to share
other
people's
towels,
if they
have an
infection.
Some skin
infections, such
as cold sores or
warts, can be
spread from one
person to another
by touching the
infected place.

A blood
vessel
magnified
many times.
Germ
Fighting back
When germs damage your cells, more
blood flows to the infected place. Some
of your white blood cells then devour the
germs (see page I I).
Other white blood cells kill germs using
chemicals known as antibodies. Antibodies
can recognize germs that have attacked
you before. They stay in your body to
stop the same germs from attacking
again. This means you only catch most
infections once. Being protected like this
is called being immune.
What is an allergy?
Allergies are not caused by germs. An
allergy is when white blood cells send
out antibodies to fight ordinary things
as if they were germs. An allergy to
pet hairs or feathers can cause the
wheezing and coughing of
asthma, or the sneezing
and itchy eyes of
hay fever.
24
Viruses

Viruses are over a million
times smaller than bacteria.
They cause many common
infections such as colds, sore
throats and stomach upsets.
Viruses
have
strange
shapes.
Viruses attack by getting inside
a cell. The cell then becomes a
kind of factory for making new
viruses.
Looking after your body
There are several things you can do to help
you stay healthy. Here are some of them.
Eating well
Different foods do different jobs in your body, so you need to
eat a good balance of all the different types. Eating the right
amount is important too: neither too much nor too little.
Protein foods make you
grow and help repair your
body. Meat, fish, eggs and
nuts contain
protein.
Carbohydrates give you
energy. Bread, cereals, rice,
pasta and potatoes are good
energy
foods.

Milk, cheese and yogurt
contain calcium, which
makes your bones and teeth
strong. They also
contain protein.
Fruit and vegetables contain
vitamins and minerals. You
need these to keep your
body working
efficiently.
Fibre is a carbohydrate that your body
cannot digest. It is good for your
digestive system, though. It
prevents constipation and may
protect against some serious
illnesses. Fibre is found in
wholemeal bread and pasta,
wholegrain cereals, brown
rice, fruit and vegetables.
26
Foods to cut down on
Sugar gives you energy but has no other
benefits; it rots your teeth and too
much of it makes you overweight.
Burgers and
French fries
are fatty.
Sweets and
fizzy drinks
are very

sugary.
Too much fat can make you overweight. Animal
fat, which is found in foods such as meat and
butter, contains a substance called cholesterol.
Over time, this can cause your arteries to get
blocked and lead to heart disease.
Some foods, for example milk shakes, ice
cream and biscuits are mostly fat and sugar.
Some people are allergic to additives, such as food dyes
and preservatives, which are put into many foods.
Keeping clean
You need to wash every day to get rid of
dirt, dead skin, oil and sweat. This helps to
prevent germs from growing and spreading
on your skin. Your hair needs to be washed
regularly for the same reasons. Brushing
your hair helps to keep headlice away.
Always wash your hands
after going to the toilet, and
before eating or handling
food. This helps to stop
many germs from spreading,
especially those that cause stomach upsets.
You have
lots of
sweat
glands
under
your
arms.

Your mouth contains bacteria which
feed on any tiny pieces of food and
drink left on your teeth. As they
feed, they produce acids which
make holes in your teeth. Cutting
down on sugary foods and drinks,
and brushing your teeth regularly
help to prevent tooth decay.
Food
Tooth decay leads
to toothache.
27
Exercise
Exercise is good for you in lots of ways.
1. It makes you strong
by making your muscles
bigger and stronger.
Without exercise,
muscles waste away
and turn to fat.
2. It strengthens your
bones and keeps your
joints supple, so they do
not stiffen up and give
you aches and pains.
3. It makes your heart
and lungs more
efficient so that they
can do more work
with less strain.

4. It makes you less
likely to pick up
infections and to
develop illnesses, such
as heart disease, later
on in your life.
5. It helps to keep you
slim.
6. It helps you to relax
and makes you feel good.
The best exercise for your
whole body is swimming.
You need to exercise regularly to
get fit, so it is important to do a
sport you enjoy. The best are those
which have as many of the benefits
listed on the left as possible. These
include swimming, soccer, energetic
dancing and cycling.
Smoking, alcohol and drugs
You may meet people who encourage you to
smoke cigarettes, drink alcohol or take drugs.
These can be habit-forming, so that once you
start using them it is hard to stop. They can be
extremely harmful.
28
Amazing facts about your body
Cell lifespans
Some of the cells in your body
live longer than others. For

example, cells in your small
intestine get worn away by
food and live for only a few
days, whereas some nerve and
brain cells last a lifetime.
Type of cell
Cells of small intestine
Taste bud cells
Skin cells
Red blood cells
Bone cells
Muscle cells
Nerve and brain cells
Average
lifespan
2-3 days
7 days
3 weeks
4 months
25-30 years
Most last a
lifetime
Some last a
lifetime
Small intestine?
Your small intestine is "small"
only because of its width: just
4cm (1.5in). It is actually very
long: about 4m (13ft) if it
were uncoiled.

Long slow journey
A meal stays in your stomach
for about three hours and can
take three days to travel all the
way through your digestive
tube.
Hic! Hic!
You get hiccups when the
diaphragm muscle in your chest
gets out of control, making your
in-breaths come in
short gasps. The
noise is caused by
your vocal cords
snapping shut.
Voice breaking
The longer your vocal cords, the
deeper your voice. In their early
teens, boys' voices get much
deeper or "break". This is
because their vocal cords grow
twice as fast as girls'.
Pumping blood
At rest, a child's heart beats
about 80 to 100 times a minute.
An adult's heart beats about 70
times. When you exercise, your
heart beats harder
and faster. An
average adult has

about 5 litres
(8.5 pints) of
blood in
their body.
Red blooded
You have about 30 million
million red blood cells, more
than any other type of cell. Red
cells are made in your large
bones, at a rate of about
three million a second.
These cells have
no nucleus.
29
Thin skinned?
Although your skin is about
2mm (0.08in) thick in most
places, it is only 0.5mm (0.02in)
thick on your eyelids and 6mm
(0.2in) thick on the soles of
your feet. A rhino's skin is
about ten times thicker than
your skin.
Colour blind
Some people have faulty
receptor cells in their eyes and
cannot see colours correctly.
About one in 20 people cannot
tell the difference between red
and green.

Colour
blind view
With normal
colour vision
A good sniff
Your smell receptor cells cover
an area about the size of a
postage stamp but they allow
you to detect over 3,000 smells.
Some dogs, however, can smell
about a million times better
than that.
Brainbox
The average human brain
weighs about 1.4kg (3lb). It is
thought that the brain can store
about as much information as a
20-volume encyclopedia.
Lightning reactions
When you are awake, about
three million nervous
impulses flash around your
body every second.
Some of these travel
at over 400kmph
(250mph), which
is faster than a
high-speed train.
Nervous tension
An adult has some 75km

(45 miles) of nerves in their
body, enough to stretch over
185 times around an Olympic
running track.
How many bones?
You have over 200
bones. Around half of
them are in your hands
and feet. Your thigh
bone is both the longest
and strongest bone in
your body.
How much muscle?
You have over 600
muscles. The
largest are in your
bottom but the
strongest are the
ones you use for
biting at each side
of your mouth.
Biggest and smallest cells
The biggest cells in the
human body are
female egg cells. Each
is about the size of
the dot over this
letter "i". The
smallest cells are
in your brain.

They are 100
times smaller
than egg cells.
Bacteria invasion
Your body is a warm damp
place with plenty of food, so
bacteria grow and spread
quickly inside you. Within
hours there can be millions in
one small part of your body.
Atchoo!
Sneezing sprays
millions of
germs into
the air. Some
of them may
shoot out
over 3m (I0ft)
away.
Common complaints
The two mo$t common
infections are colds and gum
disease. Scientists estimate that
about four out of five people
suffer from gum disease at
some time in their lives.
Water of life
You could live for several
weeks without food but only
for a few days without

water. There is
water not only
in drinks but
in food too.
Lettuce and
carrots, for
example,
are both
nine-tenths
water
How much energy?
The energy you get from food
is measured in kilojoules (kj)
or kilocalories (kcal). Different
foods have different
amounts
of kilocalories. Between the ages
of ten and fourteen you
need around 2,000 to
3,000 kilocalories a
day: about the same
as an adult. Apple
50kcal
30
31
Index
antibodies 25
arteries 10, I I, 27
balancing 16, 19
bladder 7

bones 20, 21,30
brain 18-19, 30
capillaries 10
cartilage 20
cells 4-5, 29, 31
cholesterol 27
chromosomes 5
circulation I I
conception 22
diaphragm 9, 29
digestion 6-7, 26, 29
DNA 5
dreaming 19
ears 16, 17
egg cells 22, 23, 31
energy 4, 8, 26, 27, 31
exercise 28, 29
eyes 14-15, 30
fat 12, 27, 28
fertilization 22
food 4, 6, 7, 8, 10, II,
26-27, 3 I
germs 11, 24-25, 27
growing 5, 26
hair 4, 12, 13, 27
hearing 16, 17, 19
heart 10, 11,20,28,29
hiccups 29
intestines 6, 7, 29
joints 20, 28

kidneys 7
ligaments 20
lungs 8-9, II, 20,28
marrow 20
melanin 12
muscles 4, 21, 28, 31
nerves 4, 14, 18, 19,
21,30
nose 4, 15, 16
oesophagus 6
ovaries 22, 23
ovum 22
oxygen 8, 9, 10, I I
penis 22
periods 23
plasma I I
platelets I I
pores 13
puberty 22
pulse I I
pupil 14, 15
receptors 14, 15, 16,
17, 18, 30
reflexes 19
retina 14, 15
ribs 9, 20
saliva 6
sight 14-15, 19, 30
skeleton 20, 21
skin 12-13, 17,29, 30

sleeping 19
smell 15, 19, 30
sperm 22, 23
stomach 6, 7, 29
sweat 13, 27
taste 15, 19, 29
teeth 6, 7, 26, 27
tendons 21
testicles 22
thinking 18, 19
touching 17, 19
urine 7
vagina 22, 23
veins 10, I I
vocal cords 9, 29
waste 7, 8, 10, I I
water 4, 7, 9, I 3, 31
windpipe 4, 8, 9
womb 22, 23
This book is based on material previously published in Usborne Starting Point Science: What's
Inside You?, Where do Babies Come From?, What Makes You IIP, Young Scientist: Human Body.
Facts and Lists: Body Facts.
First published in 1996 by Usborne Publishing Ltd, Usborne House, 83-85 Saffron Hill,
London ECIN 8RT, England.
Copyright © 1996, 1993, 1992, 1991, 1983 Usborne Publishing Ltd.
The name Usborne and the device are Trade Marks of Usborne Publishing Ltd. All rights
reserved. No part of this publication may be reproduced, stored in a retrieval system or
transmitted in any form or by any means, electronic, mechanical, photocopying, recording or
otherwise, without the prior permission of the publisher.
Printed in Italy.

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