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Published by norzamilazamri, 2022-04-19 21:12:11

Human Body Encyclopedia

Human Body Encyclopedia

HumanBody
Encyclopedia

A DORLING KINDERSLEY BOOK

LONDON, NEW YORK, MUNICH, Contents
MELBOURNE, and DELHI
Human body
Senior editor Penny Smith
Senior art editor Cheryl Telfer 4-5 Your amazing body
6-7 What makes you you?
Editors Ben Morgan, Zahavit Shalev 8-9 Building blocks
Additional design Jacqueline Gooden, 10-11 Organizing the body
Tory Gordon-Harris, Claire Patane, Laura Roberts
Skeleton and bones
Illustrator Peter Bull
Digital illustrator Pilar Morales 12-13 Skeleton
14-15 Head case
Consultants Dr Penny Preston, Dr Frances Williams 16-17 Bendy backbone
18-19 Living bone
Publishing manager Sue Leonard 20-21 Bone and cartilage
Managing art editor Clare Shedden 22-23 Moving joints

Jacket design Victoria Harvey Moving muscles
Picture researchers Marie Ortu, Rob Nunn
24-25 The body’s muscles
Production controller Shivani Pandey 26-27 How muscles work
DTP designer Almudena Díaz 28-29 Muscle power

First published in Great Britain in 2005 by Brain and senses
Dorling Kindersley Limited
30-31 Headquarters
80 Strand, London WC2R 0RL 32-33 Network of nerves
34-35 Touchy feely
A Penguin Company 36-37 Taste and smell
38-39 Look out!
2 4 6 8 10 9 7 5 3 1 40-41 How we see
42-43 Eye to brain
Copyright © 2005 Dorling Kindersley Limited, London 44-45 Listen here
46-47 Balancing act
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

written permission of the copyright owner.

A catalogue record for this book
is available from the British Library.

ISBN 1-4053-0848-6

Colour reproduction by Colourscan, Singapore
Printed and bound in China by Toppan

Discover more at

www.dk.com

2 Test yourself with the questions at the bottom of each page...

Heart and blood Reproduction and growth

48-49 Blood flow 94-95 Making a baby

50-51 Boom boom 96-97 Growing in the womb

52-53 All about blood 98-99 Double trouble

54-55 Blood cells Life cycle
56-57 Bumps and cuts
58-59 Hormones 100-101 The early years
102-103 Growing up
Lungs and breathing 104-105 Growing older

60-61 Air bags Keeping healthy
62-63 Air and oxygen
64-65 Making sounds 106-107 What’s in food?
66-67 Ah-choo! 108-109 Sleep
110-111 Doctors and dentists
Skin, nails, and hair
Communication
68-69 All wrapped up
70-71 At your fingertips 112-113 Body language
72-73 Fairly hairy 114-115 Use your hands
116-117 Express yourself
Fighting disease
Reference section
74-75 Germs
76-77 Body defences 118-119 Amazing facts about YOU!
78-79 Fighting germs 120-121 Through the ages
80-81 Allergies 122-123 Glossary
124-127 Index
Digestive system 128 Acknowledgements

82-83 Digestive system

84-85 Chew it over Coloured discs contain
facts about special topics,
86-87 From mouth to stomach Circles show such as taste.
88-89 Inside the intestines close-up images
Brain and senses Taste and smell
you might not
Taste and smell Runny nose
Urinary system otherwise be able Different tastes When you have a cold, tiny Your nose
to see. We need to eat and drink to There are five types of tastes hairs in your nose get clogged and mouth
survive, but taste and smell – bitter, sour, salty, sweet, with mucus. This stops them a re linked at
are what make these everyday and umami. wafting smell particles deep into the throat.
activities so enjoyable. your nose and makes it difficult
Bitter foods, such as to smell – and taste – things.
Taste detector coffee can be bad for you.
90-91 Waterworks Your tongue is a big muscle covered Most poisons are bitter. Sensitive nose
in clusters of taste buds. Each cluster
92-93 The stretchy bladder recognizes a particular kind of taste. Sour foods include lemon Much of what we
and vinegar. Food that think of as taste is
has “gone off” tastes sour.
actually smell.
Salt detecting taste buds The back of your
can be found on the lips
as well as on the tongue. nose is linked to
your mouth so
“Get into it” activity Sweet foods naturally you can smell
attract us. Our first food your food as
– milk – is sweet. you chew it.

buttons show you how Bitter Umami is the savoury ome noses can recogniz
Sour Sour taste of foods like soy
you can try things Salt
sauce and mushrooms.

buds are crammed
out for yourself. 10,000 taste e 10,000 different sme
ngue.
Sweet Salt
S
get into it Taste buds lls.
Saliva in your
Try putting mouth dissolves onto your to Smell receptors
sugar on different places your food. The food Special cells deep inside your nose
on your tongue. It tastes washes over tiny taste
sweeter in some places buds between the bumps recognize scent particles floating
in the air. These cells link
than others. Now try on your tongue. Taste buds directly to your brain.
salt, lemon juice, recognize different flavours.
and coffee. 37

36 1000-1500 millilitres.
How much saliva does an average person produce in a day?

About this book
This book has special features that will
show you how to get your hands on as
much information as possible! Use the
“become an expert” buttons to find out
more about a subject on other pages.

3
You will always find the answers here!

Human body Become
an expert...
Your amazing body
on the skeleton,
The greatest machine you’ll ever own is pages 12-13
your body. It’s more complicated
than any computer, it on digestion,
lasts for a lifetime, and pages 82-83
it’s yours for free.

Body parts Hair

Your body is made up Forehead
of hundreds of different
parts. You probably know Ears Inside your body
the names of the bits you Cheeks
Eyebrows Doctors can see
can see, but there are
many more hidden inside your body
deep inside you.
with special cameras.

Nose Eyes X-ray cameras take

pictures of hard body

Lips parts like bones. Other
Teeth cameras, called scanners,
can see soft body parts.

ands Fingers

Two of everything H

Body parts often come Wrists
in pairs. You have

two feet, two eyes,

two ears, two lungs,

and so on. This

means you have

a handy spare in

case one of them

gets damaged. A chest X-ray shows the bones in
your chest. The white shape in the
middle is the heart.

4 What do we call the study of the human body?

Water, water Your amazing body
Water is the most
important chemical Curiosity quiz
in your body. About
two-thirds of your Take a look at the first
few pages in this book
weight is water.
and see if you can
find these pictures.

The ingredients

Your body is made of just
a few simple chemicals,
plus water.

Carbon is the chemical
in diamonds and coal.
A fifth of you is carbon.

Iron makes your blood
red. You have enough to
make one small iron nail.

Robot Phosphorus is in the
tips of matches, as well
No substitute as your bones and teeth.
The human body is too
complicated for robots to Sodium and chlorine
copy. Robots can copy the make salt. Blood is one-
way we walk, but they third as salty as sea water.
can’t think or feel like we do.
Potassium is used in
some types of soap. It’s
also in your body fluids.

Nitrogen is important in
muscles. It’s also the main
ingredient in air.

Chimps have Compared to chimps, Being human
hands like ours. our bodies look almost
Although we look different to
hairless.
animals, our bodies are similar

Chimpanzee on the inside. Our closest

animal relatives are

chimpanzees. 5

Anatomy.

Human body

What makes you you?

All human bodies work the same way, but everyone
is different. Nobody looks, sounds, or thinks exactly
like you. You’re different because of the way your
genes and experience shape you as you grow up.

Fair skin

Green eyes

Curly hair

Black hair

Unique

The shape of your face,

the colour of your hair,

and many other things

Freckles make you unique –
different from

everyone else.
6 How many genes are there in the human body?

What makes you you?

In the genes

Genes are instructions that
build your body and tell it

how to work. Your genes
control many of the things

that make you unique,
like the colour of
your eyes or how
tall you’ll be.

There’s e This girl has a gene that allows get into it
her to roll up her tongue. The
DNA boy doesn’t have the gene, Look in a
Your genes so he can’t roll his tongue. mirror and see if you
are stored in can roll your tongue. Don’t
a chemical called DNA inside you to cheat by squeezing it with
DNA, which looks like a un a
twisted ladder with four stretc your lips. Test your
different types of rung.
The rungs make up a nough family to see who
four-letter alphabet that
spells out your genes, h to the S has the gene.
like letters in a book.
DNA can nd back 400 times.
split and
copy itself.

In the family Learning to ride
Your genes came from your parents. a bike changes your
Half come from your mother and brain and your
half come from your father. If
you look like your parents, it’s body.
because you share the same genes.
Changing body
Genes don’t control
everything – experience

also shapes you.
If you exercise a
lot, for instance,
your body gets
stronger.

7
About 30,000.

Human body

Building blocks

Every part of your body is made of
tiny building blocks called cells, which
fit together like bricks in a wall. Cells
are so small that hundreds could fit
on the point of a pin.

The nucleus DNA is
controls the rest stored in
of the cell. the cell
nucleus.
The inside of NA
a cell is packed D The skin on your
with a kind of fingertips is made
living jelly called of lots of small
cytoplasm. ridges.

Inside a cell

In the middle of a cell
is its control centre – the
nucleus. The nucleus sends
instructions to the rest of
the cell, telling the cell
what chemicals to make.

Before a cell divides,
the nucleus splits to
make two nuclei.

The outer skin, or Tiny generators
membrane, stops provide cells with
things leaking out. power.

Making new cells The new cells pull apart
A cell makes new cells by dividing. and separate, but they
The two new cells are half the size,
but they soon grow back. Millions of usually stay close
your cells die every second, but millions neighbours.

of others divide to replace them.

8 How many cells are there in the human body?

How big are cells? Building blocks

Cells are too small to see with the More than 2000 dead skin cells f
naked eye, but scientists can ell off you while you read this sentence.
photograph them through
powerful microscopes.
The cells on your skin
are about a hundredth
of a millimetre wide.

A microscope can The cells on
zoom in to see the the surface of
tiny, flaky cells on the your skin are tough
ridges of and flat. They overlap to
a person’s fingerprint. form layer of armour that
protects the softer cells below.

Fat cells are Many blood cells Nerve cells are thin Bone cells make Cells make tissue
bubble shaped. are red. They carry and wiry. They your bones hard. Your body contains
They store fat oxygen around the carry electrical They live in tiny hundreds of different
under your skin. signals. holes in bones. types of cells that do
body. different jobs. Cells of
the same type usually
About 100 trillion. group together to form
tissue. Fat, muscle,
bone, and nerves are
types of tissue. Blood
is a liquid tissue.

9

Human body Systems

Organizing Organs and
the body tissues work in
teams to carry out
Your cells and tissues are major tasks, like
organized into larger body transporting blood
parts called organs. In turn, or processing food.
your organs work together These teams are
to form body systems. called systems.

Kidney The heart is the largest
organ in
Heart the blood system.
It pumps blood around
Brain the body.

Organs The tubes that carry
blood away from the
An organ is a body part that heart are called
does a specific job. Your heart’s arteries (shown in
job, for instance is to pump red).
blood. Kidneys clean blood.
The tubes that
carry blood back to
the heart are called
veins (shown in
blue).

Organ transplant Heart and blood
If a vital organ stops working, doctors Your heart, blood, and
may replace it with an organ from another blood vessels make up
the blood system. It
person. This is called a transplant. transports vital supplies
around your body.
10 Which body system makes your
stomach rumble?

Muscles Muscles change Organizing the body
Your muscle system is made the position of your Other systems
of tissues that move parts skeleton by pulling
of your body by pulling different bones. Some of your other
on them or squeezing important systems
them. Your biggest are shown in this list.
muscles all pull
on bones. Breathing system: the
main organs are your
Your fingers lungs, which take in air.
are moved by
muscles in Hormone system: this
your arm. uses powerful chemicals to
control your body and mood.
The most powerful
muscles are Skin, hair, and nails:
in your legs. these form your body’s
protective covering.
Skeleton
Immune system: this
Bones and seeks and destroys germs
that get into your body.
joints make
Urinary system: this
up the skeletal cleans blood and gets
rid of waste chemicals.
system, an
Reproductive system:
inner frame these are the organs that
make babies.
that supports
Digestive system
the body. A quarter of Your digestive
your bones are organs break
Nerves in your feet. down food to
provide your
Your nervous system carries body with energy
and raw materials.
electrical signals around
Your mouth is the first
your body. You need part of the digestive

Signals shoot this system to see, system.
along nerves to
muscles, hear, think, A long, twisting tube
telling them makes up your
when to pull. and react. intestines, where
digested food is
Senses, such as Your brain is the
touch, rely on nervous system’s absorbed.
nerve cells that control centre.
send signals to 11
your brain.

The digestive system.

12 How many ribs have you got? Skeleton Skull Smallest bone Skeleton and bones
Jaw bone Around the same length
Your bones all join up to as a grain of rice, this
make a frame for your body is one of the smallest
called the skeleton. This bones in your body. It
protects your insides, and
helps you move about. lies deep inside your ear.

Shoulder A giraffe’s long
blade neck helps it to
eat leaves
Each finger off tall trees.
has three bones,
except for your
thumb, which
has two.

You have eight
small bones in
each wrist.

206 bones There are Rib Neck bones
24 bones in Pelvis Did you know that you
There are 206 bones your spine. have seven bones in your
in an adult skeleton. neck, the same number
Over half of these are found in as a giraffe? The top one
the hands and feet – the parts allows you to move your
of your body that perform the head up and down, the
most complicated movements. second lets you rotate it
from side to side.

24, unless you are one of the rare people born with 26. The thigh bone is the biggest and strongest in the body. Your tail bone is Frogs have very short
at the very spines to withstand the
13 bottom of your strain of the huge leaps
spine. they take.

Long lasting Thigh bone Snakes are A fish’s
Bone is a very hard incredibly bendy spine allows it
material and one of the last Shin bone thanks to many to bend its body from
parts to rot away when a identical side to side so it can
body is buried. This woman Your ankle has vertebrae forming swim smoothly.
lived in the Stone Age, 5000 three larger their long spines.
years ago, but her bones bones and four
have survived until today. smaller ones. Other skeletons Skeleton

Become There are 54 Most animals have a
an expert... bones in your backbone and are called
hands, and 52 “vertebrates”. Animals
on bone and cartilage, in your feet. with no spine, like spiders
pages 20-21
on teeth, and bugs, are called
pages 84-85 “invertebrates”.

Skeleton and bones

Head case The frontal bone forms

your forehead.

The most complex part of the is the domed part of your
skeleton is the skull. It is cranium
made of many bones Helmet
that fit together sk
tightly, to protect The upper part of the skull
the brain and The is like a helmet that protects ull.

support the face. the brain. The lower part

forms a structure for your

Eye sockets are facial features to attach to.
made up of seven

different bones.

The brain fills The front of the
most of the nose has no
cranium. bones.

Label

Facial features Teeth are set
This image shows the relationship into the
between your skull and face. There upper and
are no bones shaping the front part lower jaws.
of your nose, your lips, or your ears.

Your nose and ears are

14 shaped by cartilage.
Why does a baby have spaces between its cranial bones?

The spinal cord Head case
goes through a
large hole in the k of the
Bac head
skull.

Blood vessels
pass through
small holes in the

skull.

There are two Upper jaw The lower
parts to the jaw is not
upper jaw. shown here.

The lower jaw is Jigsaw Hole in the head
hinged. It is the only
The skull From underneath you can
skull bone that can bones fit clearly see the big hole at the
move. together like the bottom of this skull. The spinal
pieces of a jigsaw. cord – which runs down your
back – meets your brain here.

All but one of the

bones are locked in

place. This makes

the skull very strong.

Meet the relatives Face from the past
Chimpanzees and humans share a common ancestor. Scientists can work out what a
However, chimps have smaller brains than humans so dead person’s face looked like
their craniums are smaller. Chimps also have a large from their skull alone. They
ridge above their eyes, and a jutting jaw. examine the facial bones and
build up artificial cartilage,
muscle, and skin over them.

15
So its head could withstand being squashed while it was being born.

Skeleton and bones

Bendy backbone

Your spine is a length of bones
running down the back of your
body. Without it you couldn’t hold
up your head and body, or make
any sort of movement.

ont of spinThe first sevenStack of bonesThe thoracic
Back of spinebones are in your vertebrae form
neck. They are Your spine contains 24
Your spine curves gently, a bit like the letter “s”.known as theseparate bones calledjoints with
cervical vertebrae. vertebrae. At the bottom the ribs.
are nine more vertebrae.
The next 12 They are much smaller A straight
are called the and are fused together. back is
thoracic actually quite
vertebrae. curvy.

The five lumbar Fr The fused
vertebrae bear bones of the
most of your sacrum and
weight. coccyx don’t
allow much
movement.

The five sacral e
vertebrae are
fused together. The spinal cord goes
through this hole.

Segments of the spine

The coccyx Each vertebra has a strong, stubby
consists of four section that supports the weight of
fused vertebrae. your body, and a hole for the spinal

cord to pass through.

16 What is a slipped disc?

Shock absorbers Bendy backbone
You twist and bend your spine
almost every time you move. Ribcage
Sandwiched between the vertebrae Your thoracic vertebrae
are pads of cartilage to stop them connect to your ribs.
banging and rubbing against each Together they form a
other and getting worn out. cage around your heart
and lungs. Rib bones
Space for Pad of are curved. They are
spinal cord cartilage also thinner and more
bendy than the bones
in your spine.

The pads give A woman’s
pelvis is shaped
you a little bit differently to a
man’s. A baby can
Vertebra of movement pass through it

in all when she
gives birth.
could be this directions.
Pelvis
Yo u bendy...... Reproductive organs and some
digestive organs rest in the
The way the bowl-shaped hollow of your
back curves pelvis. The sacral vertebrae
means we can’t
bend as far and coccyx form
back as we can the bottom
forwards. of the bowl.

Bendy backbone geBtenidnotvoer. i ...with a lot of practice!

The amount of Gently feel the t
movement between bones of your spine
each vertebra and its with your fingertips.

neighbours is actually Can you follow
very small, but added them from neck
together they allow for
a large range of to waist?
movement.
17
It’s when one of the pads between the vertebrae gets damaged.

Skeleton and bones Marrow can be found
in the spine, skull,
Living bone and the main leg and
arm bones.
Their outer surface may be hard
and dry but that doesn’t mean
your bones aren’t alive. Bones
are always growing and
repairing themselves.

What’s inside our bones?

Bone accounts for one
sixth of your body’s
weight. Its clever
structure means
it’s often
lighter than
it looks.

Spongy bone Bone marrow
Parts of some bones have a A jellyish substance
honeycomb structure with lots of called marrow fills
spaces. This makes them weigh less the centre of many of
than if they were solid right through. your larger bones. It
supplies your body
Compact bone with red blood cells
The hardest and most at a rate of 3 million
dense part of the bones is cells per second.
the outer layer. It is made
of calcium, a substance
we get from our food. Teeth
are made of calcium too.

18 What are the most commonly broken bones?

Broken bone Living bone
Bones are strong and
flexible enough to cope Curiosity quiz
with a lot of pressure,
Take a look through
but, as this X-ray the skeleton and bones
shows, they sometimes
pages and see if you
break. Luckily they can identify where these
can heal themselves.
bony bits come from.

If the broken bone Become
ends have slipped an expert...
apart they must
be repositioned on the skeleton,
by a doctor before pages 12-13
healing begins.
on skin and nails,
On the mend pages 70-71
New cells form at each end of
the broken bone, closing the
gap between them. It takes
about 6 weeks for this
to happen.

iloyneosura lreatsetitlleens. Padded clothes
gYroowurinbg unt help protect
bones from
sudden impact.

Looking after
your bones
Calcium from
milk and cheese
is needed to build
strong bones.
Weight-bearing exercise
like walking, climbing,
or skating helps to
strengthen bones.

Fingers, wrists, and arms. 19

Skeleton and bones Baby’s
hand
Bone and cartilage

When you were a baby, you were tiny.
Slowly, as you get older and bigger,
your bones do a clever trick. Not only
do they grow, but they also change.

Making bones More, less

Babies’ bones are made out You’ve got more bones
of a soft and bendy material than your mum or dad!
called cartilage. Slowly this
hardens and turns into bone. You were born with over 300 “soft”
bones, but as you get older, many fuse
Baby bones are entirely
made of soft, growing together. By the time you’re 25 you’ll
cartilage. have 206 fully formed bones.

Adolescent bones are Cross-section of an
mostly bone, with a small ear – the cartilage sits
amount of cartilage. between two layers of
skin.
Adult bones have
stopped growing. Most no
longer contain cartilage.

Stick out your ears!
Your ears are made of
cartilage, not bone. They
are strong, but much
more bendy than
your bony bits.

20 Which foods are rich in calcium, the mineral you need to grow healthy bones?

Child’s Bone and cartilage
hand
Adult’s
hand

Bone shows up as purple in
these X-rays. The difference
between the amount of bone
can clearly be seen.

Taller, shorter
Between each bone
in your spine are small
disks of cartilage. During the day
these get squashed, and when you
rest at night they spread out again.
This means you’re a little bit taller
in the morning than in the evening.

Cartilage coats Smooth coated joints
the ends of these The ends of neighbouring
bones are covered in
bones. smooth cartilage. That
way, they can glide against
The pads of each other when you move.
cartilage get
squashed from
standing up and
stretch back out
while you’re lying
down.

Milk, cheese, yogurt and ice-cream. 21

Skeleton and bones

Moving joints

Joints are the places where
bones meet. Different kinds
of joints allow you to move
in different ways.

Hinge joint Fixed joints
The bones that make up
Your knee can bend your skull start to join up
in the middle but soon after you are born.
it can’t swing from Once they have fused,
side to side. This none of them allow
joint has a hinge movement except the
like the one that hinged jaw joint.
allows you to
open and Knee joint
close a door.

Have you ever used
a joystick? That’s a ball

and socket joint!

Ball and socket

Your hips are ball and socket joints.
They allow you to move your legs in

There are 19 moveable joints in

all directions and even to turn them. your hand – not counting the ones
in your wrist!

22
What is tennis elbow?

Moving joints

Bendy bits Your hand is a terrif ic feat of engineering!

Different sorts of joints get into it
all over your body keep
you moving. Tape your Thank your thumbs
thumb to your first Your thumb is the most
Neck bones feature a flexible of your fingers.
pivot joint that allows finger. See how You rely on your thumbs
your head to turn. difficult it is to open a whenever you handle
notebook, pick up a delicate objects.
Wrists have a joint that
allows them to turn but pen, and write This woman has
not to go right round. your name. stretchy muscles and
ligaments that
Ankles contain different Hip hooray allow her spine
joints for up and down Joints, particularly to bend
and side to side movement. knee and hip joints, further than
sometimes wear out in most people
old age. When this can manage.
happens, doctors can
remove the worn-out
joint and replace it
with an artificial one.

Ligaments Fabulously
flexible
Bands of tissue called ligaments act People whose
like elastic. They hold your joints are
bones together yet particularly
still allow you flexible are
to move. called “double-
jointed”. The condition
Ligament can run in families, but
people who are double-
Your elbows Bone jointed must practise if
have a hinge they want to keep their
joint for bending ligaments stretchy.
and a pivot joint so
they can turn.

The name for sore elbow tendons caused by overuse. 23

Moving muscles

The body’s muscles

Every time you move, you use Pulling strings
muscles. Muscles make you walk,
blink, and smile. Some muscles About 650 of your muscles are
work without you thinking about
them, but others need to be told to wrapped around the bones of
move. They all work by shrinking, your skeleton. They move your
which makes them pull or squeeze.
body by pulling on the bones.

Together

they form

the muscle

Smooth muscle The pectoralis system.
This type of muscle muscle swings
makes things move your arm.
inside your body. It
mixes food in your The biceps muscle
stomach and pushes bends your arm.

Smooth muscle cells food through
are short your intestines.
with pointed ends.

Heart muscle cells Heart muscle Your longest muscle
are stripy with When you put your is the sartorius. It
oval blobs. hand on your chest, helps cross your
you can feel your legs.
Skeletal muscle cells are heart beating. Your
long and heart is a strong The tibialis muscle
threadlike. muscle that squeezes bends your foot.
blood around your body.
24
Skeletal muscle
Skeletal muscles pull on
bones to change the shape
of your skeleton and
move your body. These
muscles are voluntary,
which means you can use
thought to control them.

What weighs more: all your bones or all your muscles?

The body’s muscles

Muscle magic Who’s in charge?

Muscles have hundreds You use hundreds of muscles when
of uses. They make up
about a third of your you run and jump. Your brain
body weight.
controls them all, a bit like Become
Largest muscle: you use a conductor controlling an an expert ...
the muscle in your buttock orchestra. It sends signals
for sitting and walking. along nerves to every on making sounds,
pages 64-65
Fastest muscle: this one
makes you blink. It works muscle, saying on how intestines
up to 5 times a second. exactly when push food,
to work and
Ear wiggling: a few pages 88-89
people can control the
muscles around their ears. when to rest.

Smile: a fake smile uses Hundreds of muscles
different muscles from a work in a carefully
real, involuntary smile. controlled sequence
when you jump in the
air.

Tongue twister
Your tongue is a bundle of
lots of muscles that make it

super flexible. It can reach
anywhere in your mouth
to pull and push bits

of food. Its acrobatic
movements are also
vital to speech.

at
le. at
leYmaosuatrk1te4oindtgiafufmeeraceoznintntmgaliuynssfclleexsitbh
Your muscles. 25

Moving muscles

How muscles work

Muscles work by contracting, which means
they shorten. As a muscle contracts, it pulls.
The larger the muscle, the more powerfully
it pulls.

When the bicep Working in pairs
muscle contracts, it
pulls your forearm Muscles can pull but
and bends your not push. They work
arm. in pairs that pull in
opposite directions.
When one muscle
pulls, its partner
relaxes.

When the triceps Your forearm
muscle contracts, it contains pairs
straightens your of muscles that
arm. move your hand
and fingers back
and forth.

Fibres in fibres
Skeletal muscles
are made of cells
called muscle fibres.
Inside these are even finer
fibres called myofibrils, which
contract to make a muscle shorten.

A typical
muscle

Bundle of One muscle cell Myofibrils inside

muscle cells a muscle cell
26 Where is the body’s smallest muscle?

Try raising your Tendons How muscles work
ring finger with Muscles are fastened
your hand in this to bones by tough bands Making faces
position. called tendons. When you
It’s stuck because wiggle your fingers, you Muscles in your face are
it’s joined to the attached to skin as well
same tendon can see the tendons as bone. They pull the
as the middle move on the back skin when you change
finger. of your hand. your expression. You
use about 17 muscles
when you smile.

Middle finger

Ring finger

A floppy start
A newborn baby has little
control over his head or neck

muscles. It takes about a
month before it can hold up
its head, and six months for
strong, steady head control.

No rest
Muscles work all the time. They hold
you upright - without them you would
flop on the floor. Muscles also work
when you are asleep, keeping your body
firm and toned.

Getting a stitch 27

If you run a lot, you may get a
pain in your side. This is a stitch.
Scientists aren’t sure exactly why
it happens but it might be because
the muscles and ligaments in your
abdomen are working too hard.

In the ear.

Moving muscles Stamina
If you have stamina, you
Muscle power can keep going for a long
time without getting tired.
The more you use your muscles,the Exercise that makes you feel
better they get. Active games and out of breath, like running,
exercise make your muscles larger, improves your stamina.
stronger, and more flexible. They also
help you keep going without tiring.

Flexibility
When you’re flexible,
your joints and muscles can
move freely and your body
can bend and straighten
easily. Exercise that
stretches your body, such
as gymnastics or dancing,
improves your flexibility.

This contortionist has made her body Strength
more flexible by doing exercises that Pushing, pulling, and lifting make
stretch her back. your muscles bigger and stronger.
Bodybuilders lift heavy weights over
and over again until their muscles
are enormous.

You need strong muscles
to win a tug-of-war.

Become
an expert ...

on how your heart
works, pages 50-51

on healthy food,
pages 106-107

28 What happens to muscles if you don’t exercise?

Muscle food Muscle power
Ways to keep fit
To build strong muscles,
you need a type of food Exercise is very good for
called protein. Meat, your health. As well as
fish, beans, milk, and making your muscles
eggs are rich in protein. bigger, it strengthens
your heart and lungs.
Most vegetables
don’t contain much Walking to school, or
protein. going out for walks, builds
strength and stamina.
Body heat Chicken Milk
This picture shows the Fish Egg Football is great for
heat of a man’s body. improving your flexibility
Muscles make heat when Beans and strength.
they work hard, which is
why exercise makes you Fish is a very Swimming strengthens
hot. On cold good source of your heart muscle and
days, your protein. builds stamina.
muscles try
to warm Cycling strengthens your
you up by leg muscles and builds
shivering. up stamina.

Dancing keeps your
body supple and helps
build strength.

They get small and weak. 29

Brain and senses Sense signals
The cerebrum is
Headquarters the main part
of your brain.
The brain is the body’s control It gets and stores
centre. It is a complicated organ sense information
that works very quickly,
a bit like a brilliant, and also controls
living computer. your movements.

Cerebrum

Clever calculator Cerebellum ain stem
The cerebrum is
also responsible for Br
thinking, speaking,
and complicated Your brain stem
tasks such as sums. works at the same
rate whether you’re
awake or asleep.

Muscle control 24 hours a day
Your cerebellum helps you Whatever else you do,
to balance and move your the brain stem makes
muscles. You use this bit of
your brain when you dance. sure your heart and
breathing never stop.

30 Does your brain hurt when you have a headache?

Headquarters

Skull In relation to the size Curiosity quiz
of our bodies, humans have
Brain the biggest brains of any Take a look through the
brain and senses pages
animal. and see if you can spot

Brain box

Your skull is a bony shell where these come from.

that fits together like a jigsaw

around your brain. Shock-

absorbing liquid fills the space

between the brain and skull.

Learning

When you
learn to do
something
you create
connections between
cells in your brain.
Next time you do it the
connections are already
there so it is easier.

Short-term memory
Your short-term memory only
holds information for about a
minute. You use it to compare
prices when you go shopping,
or to remember a name when
you meet someone new.

Long-term memory
Your name, phone numbers
you know by heart, and skills
such as riding a bike can be
kept for many years in your
long-term memory.

No, your brain can’t feel pain but the muscles around your head can. 31

32 Which is the longest nerve in your body? Network of nerves Brain and senses

All of the body contains nerve cells. These

link up to form the network of nerves

we call the nervous system. It Brain

transports messages between A good night’s sleep
Your body and brain slow down when
the body and the brain. you sleep, but they don’t stop working.
Your brain needs sleep to sort out the
Quick as a flash events of the previous day.

Nerve cells lie next to one Cross your Your knee jumps
legs and tap forwards even
another forming long chains. just below the though your brain
knee. hasn’t
They pass messages to their told it to move.
neighbours – rather like a
Spinal cord –
speedy relay race – to and the centre of
the network
from the brain.

Brain cells viewed
through a
microscope.

No need to think
You do some things without
needing to think about them.
These are called reflex actions
and include blinking, coughing,

and the knee-jerk reflex.

The one running from your big toe to the base of your spine. Messages You’ve got 150,000 km Pain-killers
(93,200 miles) of nerves When you get a filling,
Messages travel faster than a high-speed train.Your brain in your body. the dentist gives you an
controls your body. anaesthetic. This drug
It receives messages
from all parts of stops nerves passing
your body and on pain messages for
decides what
to do. a short time.

33 Walking is the result of Pins and needles Network of nerves
your brain telling your Sitting cross-legged for a long time
leg muscles to move. squashes the nerves in your legs. When
you stand up, the nerves start to work
Hunger is your stomach again, producing a tingling feeling.
telling your brain that it’s
empty and you must eat.

Needing to urinate is
a response to the message
that your bladder is full.

Itching is an irritating
feeling. Your body reacts
by making you scratch.

Pain gets a very quick
response. You move away
from what’s hurting you.

Blinking happens
without you needing
to think about it.

Breathing is automatic
too. It carries on even
when you are asleep.

Brain and senses Merkel’s disk responds to
light touch and
Touchy feely
is sensitive to the texture of
Your skin is in immediate contact with things.
the world. Using your sense of touch
allows you to tell if something is
hot or cold, dull or sharp, rough
or smooth, or wet or dry.

Things we can feel Not worth noticing Meissner’s
Although your brain receives messages all corpuscle senses
Skin is packed with
many sense receptors. the time, it filters out the less important light touch.
Each sort responds to ones. That’s why you’re not constantly
different sensations. aware of the clothes against your skin.

Warmth is detected by It feels slimy!....
nerve endings quite close
to the surface of the skin.

Cold is felt by different
sensors to heat. Extreme
cold registers as pain.

Deep touch sensors This girl quickly Ouch!
enable you to grip moves her finger
things tightly. The body has
away from the its own system of
Light touch sensors lie thorn to stop alarm bells. Pain
at the root of hairs on the pain. receptors warn us
your arms and legs. when a part of the
body has been
Vibrations from an hurt or is about
electric drill trigger
vibration sensors. to be harmed.

Tickly feelings result
from a light and
unexpected touch.

Sensitive fingertips full
of receptors are able to
tell coins apart.

34 How many touch receptors are in a fingertip?

Touchy feely

Free nerve endings
respond to heat, cold,
and pain.

Surface of skin The Ruffini ending
Dermis responds to firm or
Fat continuous touch.

Under the skin

Dead cells form the surface
of your skin. Below that lie
sweat glands, hair follicles,
and different types of
sensory receptors.

The Pacinian corpuscle

responds to firm pressure and

vibration. message shoots off to the brain....

.... the

Sensitive bits Reading by touch Braille was
Braille is a system that invented over 150
Skin contains more touch uses raised dots to represent
receptors than any other letters and numbers. It was years ago.
part of the body. But invented so that people with
some areas are more bad eyesight would be able B I RD
sensitive than others. to read by feeling the page
with their fingertips instead get into it
Fingertips are packed of looking at words.
with sensors, especially Put one finger
light pressure receptors. in cold water, one in hot,
then put both in warm water.
Lips have very thin skin The water feels cold to the
which is good at detecting hot-water finger and hot
heat and cold. to the cold-water finger.

Toes are very sensitive, 35
but thick skin makes the
heel less sensitive.

About 3,000. That’s roughly the same as on the whole of the trunk of your body.

Brain and senses Different tastes

Taste and smell There are five types of tastes
– bitter, sour, salty, sweet,
We need to eat and drink to and umami.
survive, but taste and smell
are what make these everyday Bitter foods, such as
activities so enjoyable. coffee can be bad for you.
Most poisons are bitter.
Taste detector
Sour foods include lemon
Your tongue is a big muscle covered and vinegar. Food that
in clusters of taste buds. Each cluster has “gone off” tastes sour.
recognizes a particular kind of taste.
Salt detecting taste buds
can be found on the lips
as well as on the tongue.

Bitter Sweet foods naturally
Sour attract us. Our first food
Salt – milk – is sweet.

Umami is the savoury
Sour taste of foods like soy

sauce and mushrooms.

buds are crammed
10,000 taste
Sweet Salt ngue.

get into it Taste buds onto your to
Saliva in your
Try putting mouth dissolves
sugar on different places your food. The food
on your tongue. It tastes washes over tiny taste
sweeter in some places buds between the bumps

than others. Now try on your tongue. Taste buds
salt, lemon juice, recognize different flavours.
and coffee.

36
How much saliva does an average person produce in a day?

Taste and smell

Runny nose Your nose and
When you have a cold, tiny mouth are
hairs in your nose get clogged
with mucus. This stops them linked at the
wafting smell particles deep into throat.
your nose and makes it difficult
to smell – and taste – things.

Sensitive nose

Much of what we
think of as taste is

actually smell.
The back of your

nose is linked to
your mouth so
you can smell
your food as
you chew it.

ome noses can recogniz
S e 10,000 different sme

lls.

1000-1500 millilitres (35-53 fl oz). Smell receptors
Special cells deep inside your nose

recognize scent particles floating
in the air. These cells link
directly to your brain.

37

Brain and senses Wandering eyes

Look out! Six muscles control each eye.
You use both eyes when you
Sight is the body’s main sense and look at something, so your
the main way we learn about our eyes move together.
surroundings. Two-thirds of the
information we take in comes Sclera (or white
from our eyes. of the eye)

Iris

Pupil

The muscles The middle of the
surrounding your eyeball is filled
eyeball make precise with fluid.
movements so you can
smoothly track moving iqureint
objects.
At n 1.6 km (1 mile) away.
ight, our eyes could d Aansiraisfiinsgaesrpun
Pupil Eyelid

Sc lera Hidden away
Iris Most of your
eye nestles
etect a lighted candle safely in its
socket and is
protected by pads of
fat. On the outside,
you can see the iris,

pupil, and some
of the sclera.

38 What is the sleep that collects in our eyes?

Tears are made behind Safekeeping Look out!
each eyelid.
Your eyes are fragile, Eye colour
The iris is the coloured
squidgy balls made of part of the eye. All eye
colours are produced by
watery jelly so they need one substance, melanin.
Lots of melanin results
Tears drain into tear ducts. to be well protected. in brown eyes, less
These link to your nose, means a lighter shade.
which is why your nose runs Bone in your skull
when you cry. surrounds your brain
and the backs of the eyes.
Crying

Tear glands behind your eyes Eyebrows sit above your
produce drops of salty fluid. eyes and prevent sweat
When you blink, your eyelids dripping into them.
sweep this fluid over your eyes

to keep them clean. If something Eyelids and lashes stop
gets into your eye, or you feel dust entering the eyes and
strong emotions, the drops turn then sweep it well away.

into floods of tears. Your pupils change size automatically.

Either it’s dark or this 39
person has seen
something they
like.

Pupil size
The pupil is the
opening that
controls how
much light
enters your
eye. It’s smaller
in bright light to
protect the nerve
cells in your eye,
and bigger in dim
light to let more light
in. It also gets bigger
when you see something
or someone you like.

Dust and mucus washed from our eyes as we sleep.

Brain and sensesLight re

How we see

Inside your eye is a lens like the lens
of a camera. Its job is to focus light
on the back of your eye so you can
see things clearly.

flects off an object and enters your eye.

The eye is filled with a
semi-solid jelly.

Optic The lens is clear and An object
nerve flexible. It focuses on
The pupil is a hole
The retina things by changing that lets light into
contains cells shape. the eye.
that sense
light.

How your eye works

Light from an object enters your eye Seeing in colour
through the pupil. It passes through Your eyes contain millions
the lens, and makes an upside down of cells. Cone cells give you
image on the retina at the back of
your eye. Cells in your eye send colour vision but don’t
messages down the optic nerve work well in dim light.
to your brain. Your brain Rod cells work well
flips the image back the in dim light but
see everything
right way round. in shades
of grey.

40 What is an eye specialist who tests eyesight called?

Blurry vision Can you see a nu How we see

Sometimes an eyeball is the wrong shape. mber? If not, you m
The lens cannot focus light on the retina and ay be colour blind
everything is blurry. Glasses make the light
focus in the right place to make things clear.

Short eyeball
If you have a short
eyeball you will have
difficulty seeing things
close up. This is called
long sightedness.
An optician.
Long eyeball Colour blindness
It is difficult to see .
objects that are far away Some people cannot tell certain
when your eyeball is too colours apart, especially red
long. This is known as and green. This is called colour
short sightedness. blindness. It is more common
in men than women.

get into it Glasses bend
the light entering
Close one eye Contact lenses
and hold a finger in front These work like your eye so it
of your nose. Open that eye mini glasses and focuses on the
and close the other one. sit directly in
front of the retina.
The finger appears to eye. They’re a
move! Each eye sees bit fiddly, but

things differently.

once they’re in you

can’t feel them at all.

Contact lenses are
made of very thin
plastic.

41

Brain and senses What can you see?

Eye to brain The dark blue in these
pictures shows how much
Your brain works out what you’re animals can see clearly.
seeing by comparing the images it gets Light blue shows what
from your eyes to things you have seen they can see less well.
in the past. Sometimes it can be fooled!
Humans have to move
ain combines images from bo their heads to see clearly
Your br th eyes. to the sides or look back.

Tigers see well to the
front to help them find
and catch their prey.

Zebras keep a look out for
movements to the sides so
they can avoid attack.

Ducks can see all the
way behind them, even
while facing forwards.

Chameleons see small
areas clearly. They swivel
their eyes to see all around.

The yellow areas are the parts of
your brain that deal with
information from your eyes.

Optic nerve

To the brain

Our eyes swivel around constantly,
taking in sights and adjusting to
focus on different things. The
information they collect travels
to the brain through the optic
nerve at the back of the eyes.

Eyeball

Your blind spot is the part of the eye that
can’t see anything. It is where the optic nerve
leaves the back of your eye.

42 What is it called when you look at something and think it’s something else?

Tallest tower Eye to brain
Does the green tower
look taller than the Finding your blind spot
others? That’s because Close your right eye and look
it’s further along the directly at the star. Slowly
track and we expect bring the book to your left eye.
objects further away You reach your blind spot
from us to look smaller. when the circle disappears.
The colours of the towers
also affect the size they
seem to be. In fact, all
the towers are exactly
the same size.

Recognizing objects

Your brain is very clever – it can
recognize this car from different
points of view. A computer would
have to be taught that both these
pictures are of the same object.

Certain
patterns trick your

eyes into seeing
movement where there is

none.

Do you believe your eyes?
Your brain helps your eyes to understand
what they see. Sometimes you see things
that aren’t actually there...

You see a heart
even though the
edge of the shape

isn’t there
because your
brain uses the

information
it has to fill

in the gaps.

An optical illusion. 43

Brain and senses How well can
you hear?
Listen here
Your hearing range is from
When you shout you send out the highest to the lowest
invisible sound waves through notes that you can hear.
the air. Your ears pick up
the waves and transmit Adults have quite a
the sound to your brain. small range compared
to other animals.
The speed of sound
Children hear higher
We don’t notice the slight notes than adults. Your
delay between someone’s range shrinks with age.

lips moving and Cats, dogs, and rabbits
the sound actually can hear much higher
reaching our ears. notes than people.
It’s too fast!
Bats have excellent
hearing. Their range is
five times as large as ours.

Sound travels through the

Headphones feed
different sounds
into each ear so
you feel as if
you’re surrounded
by instruments.

Why two ears?
Sounds normally reach one ear
first and then the other. This
helps our brains work out
where sounds are coming from
and how far away they are.

44 Why do we have ear wax?

Outer ear Listen here

What we call the ear is A little help
really just the part that Partially deaf
we can see. Sounds are people may use
hearing aids.
collected here, and These make the
funnelled inwards. sounds entering
the ear louder
and easier to
hear.

Middle ear

Sounds arriving here from the
outer ear cause the eardrum to
vibrate and set off movements
in three tiny little bones.

MiBonesCochlea
Outer
Ear canal

ear ddle ear r ear

air to your ear. Ear drum

Inne

Inner ear Tiny hairs are
moved by sounds.
The bones moving cause
vibrations in the liquid Signals travel
deep inside the ear. along these nerves
Tiny hairs in your to the brain.
inner ear pick up these
vibrations in the liquid
around them. The hairs
are attached to nerves,
which connect to your brain.

To protect the skin lining the ear canal, trap dust, and repel insects. 45

Brain and senses

Balancing act

As well as hearing, ears

help you balance. Sensors

in your ears work with The three
those in your eyes, semi-circular
muscles, joints, and feet canals deal with

balance.

to let your brain know Ear hole
your body’s position.

Keeping track

Deep inside your ear are three
tiny tubes filled with fluid. They
detect the movements your body
is making and let your brain
know about them.

One tube is for forward and Watch your step!
backward movements, another
for up and down, and the Keeping your balance
third for side to side while walking along
movements. a narrow wall takes
a lot of concentration.
A jelly-like knob floats in You are responding
each tube. Inside it are to information coming
from your eyes,
sensitive hairs that detect muscles, and ears
movement. at the same time.

46 The movements travel
along the hairs, through
a nerve, to the brain.

Can astronauts learn to balance in space?

Balancing act

The more you practise the better you will be at balancing. Basically, your Motion sickness
Travelling in a car,
boat, or plane can
make you feel ill. Your
eyes tell your brain
that you’re staying
still in the vehicle, but
your body says it can
feel movement. This

confusion is what
causes motion
sickness.

brain is the boss.

Muscle messages
When you move, sensors in your
muscles send messages to your
brain. If a movement isn’t going
right, your brain will make you
do things differently.

The brain

get into it

First make
sure there is nothing
unsafe nearby for you
to crash into. Then spin

round and round
and make yourself

feel dizzy.

Why do you feel dizzy? 47

The liquid in the tubes of your ear is like water in a cup.
When you spin, it continues to slosh around for a while
even after you’ve stopped. Your brain gets confused about
which way round you are, and you feel dizzy as a result.

Yes, but it can take a couple of days to learn how.

48 When you cut yourself, what kind of blood vessel does the blood usually come from? Blood flow Tube transport Heart and blood

Blood is the body’s Blood leaves the heart in
transport system. large blood vessels called
Pumped by the heart, arteries, and it returns
it travels around the in vessels called veins.
body in tubes called Between the arteries
blood vessels, delivering and veins are tiny
vital supplies to keep vessels called
your cells alive. capillaries.

Blood picks up Lung Lung Artery
oxygen from the
lungs and carries it Each major organ
around the rest of has an artery
the body. bringing fresh blood
and a vein carrying
Around the body away used blood.

Blood travels round Liver The aorta is the biggest Vein
your body, passing Stomach blood vessel in your
through organs on body. It is as thick as
the way. It picks your thumb. A blue
up oxygen in the whale’s aorta is wide
lungs and food in enough to swim through!
the liver, then
gets rid of waste Kidney Kidney
in the kidneys.
The vena cava is your Capillary
biggest vein.

body. Capillaries

km Arteries split into
in your smaller and smaller
branches. Eventually
Become (60,00T0hemrileesa)reofabbloouotd1v0e0s,s0e0ls0 Artery they turn into capillaries,
an expert... Vein which are finer than hairs.
Capillaries lead into veins,
on breathing in which join together and get
and out, pages 60-61 bigger on the way back to
the heart.
on air and oxygen,
A capillary. pages 62-63 Capillaries

From red to blue Arteries Blood flow
Veins
The colour of blood
49 depends on how much
oxygen it contains.

Oxygen-rich blood in
arteries is brilliant red.

Oxygen-poor blood in
veins is dark, purplish red
(shown blue on the diagram).

Heart and blood Double pump

Boom boom Your heart is really two pumps in
one. One half pumps blood through
Your heart is a pump that your lungs, and the other half pumps
pushes blood around your blood around the rest of your body.
whole body. Each time your
heart beats, it squirts out a Blood from most of Blood goes out to
small cupful of blood and the body enters the body through the
refills for the next beat. through the vena aorta.
cava.

Where is it? Blood goes
Your heart is in the middle of out to the
your chest, squeezed between lungs.
the two lungs. You can feel its
beat just left of the bone in One side pumps blood to the lungs...
the middle of your chest.

Blood comes
in from the
lungs

Vena cava
Aorta

Blood comes Blood goes out
from the body. to the body.

50 How many times does your heart beat in a year?

One-way system Boom boom

To keep blood flowing one way only, your Curiosity quiz
heart and most veins contain valves. Your
heartbeat is the sound of valves shutting Take a look through the
when your heart squeezes. heart and blood pages
and see if you can spot

any of the cells and
tissues below.

Blood goes out to Valves stop blood
the lungs. flowing
backwards.

he other pumps blood everywhere else.Blood
comes
in from
the lungs.

Beating faster
Muscles need extra
blood when you’re active,
so your heart speeds up.
It beats about 70 times a
minute if you’re resting
but up to 200 times a
minute if you’re running.

...and t get into it

Find your
pulse by pressing two
fingers on your wrist.
You should be able to feel
a gentle throb as your

heart pumps blood
around your body.

About 40 million times. 51

Heart and blood

All about blood

Blood is a warm, soupy mixture
of liquid and cells. The cells
carry oxygen and fight germs,
and the liquid carries nutrients to
body cells and takes away waste.

Main ingredients
Blood contains three types of cells –
red blood cells, white blood cells, and
platelets. They float in a yellowish
liquid called plasma.

One drop of Lots of White blood
blood contains plasma cells seek

5 million red blood cells, Yellow plasma out and kill
half a million platelet cells, makes up more germs. They
also eat up the
7,000 white blood cells, than half of dead cells that
water, sugar, salt, your blood.
hormones, vitamins, they meet.
fat, and protein.

White blood Red blood cells make blood red.

cells and

Become platelets.

an expert...

on fighting germs,

pages 78-79

on air and oxygen,

pages 62-63 Red blood cells

transport oxygen

from your lungs to

52 the rest of your body.

How long does a red blood cell live for?

All about blood

Your blood type

There are four main types of blood,
called blood groups. Your blood group
affects who you can donate blood to.

People with blood group People with blood group

A A can give blood only to O O can donate blood to
people with A or AB. almost anyone.
Blood bank
One in ten people People with blood group People with blood group
who go to hospital need extra
blood, so hospitals keep a store AB AB can only give blood B B can give blood only to
of blood in a “blood bank”. The to others with AB blood. people with B or AB.
blood is divided into separate
supplies of cells and plasma. How much blood?

White blood cells The average adult has about
10 pints (5.7 litres) of blood,
and platelets fight d but a newborn baby
has only a cupful.

The amount of blood
in your body grows
with you. By age 10
you have up to 4 pints
(2 litres).

Platelets are About four months.
cells that become
sticky to make blood isease.
clot and form scabs.

By a year old a
baby has more
than
1 pint (half a
litre) of blood.


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