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The Brain is BossPages 4–6

Look Here!Pages 7–9

What’s that Smell?Pages 10–12

Smile a While!Pages 13–15

Feeling Hairy?Pages 16–17

What an Earful!Pages 18–20

The SkeletonPages 21–22

Muscle PowerPages 23–25

The Skin You’re InPages 26–27

What a Nerve!Pages 28–30

Take a Deep BreathPages 31–33

CONTENTS

CONTENTSHard-working HeartPages 34–36

Red for Go!Pages 37–39

Fuelling the BodyPages 40–42

A New Life BeginsPages 53–55

Babies and ToddlersPages 56–57

Eat Well, Stay Fit!Pages 60–61

WastePages 43–44

Get a GripPages 45–47

Best Foot ForwardPages 48–49

Growing OlderPages 58–59

Expecting a BabyPages 50–52

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The brain may look like a blob of jelly, but it is one ofthe most extraordinary and amazing creations in theuniverse. It is home to a staggering one hundred billion nerve cells, or neurons! The brain is the site ofyour thoughts, memories and hopes. It monitors andregulates unconscious bodily processes like heart rateand breathing, and coordinates almost every movement you make.

Are human brains different toanimal brains

What is the brain

Human brains may not be the biggest or heaviestbrains in the animal kingdom, but they are certainlythe most complex. Tucked inside your head is a brainthat has evolved over millions of years to become themost advanced body part in the world!

Each neuron in your brain can make contact with tensof thousands of others, via tiny structures calledsynapses. Our brains form over one million newconnections every single second! These connectionsare constantly changing and no two brains are alike.

You should be proud to be human! That’s because human brains are morecomplex than anything else on Earth. Together with your spinal cord, yourbrain controls almost every process in your body, from breathing and blinkingto reading the latest Harry Potter book.

THE BRAIN IS BOSS

The average brain weighsas much as three cans ofbaked beans!

A newborn baby’s brain grows almost three times insize during the first year!

The brain never sleeps – in fact it’s always verybusy. Recordings of its tiny electrical nerve signals,or ‘brain waves’, show that the brain stays activeeven during sleep, and especially when dreaming.

FACT FILE

BakedBeans

BakedBeans

BakedBeans

Brain stem

Cerebrum

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What do different parts of the brain do

The lower part of the brain, the brain stem, deals withvital body processes we rarely think about, likebreathing, heartbeat and digesting food. The smaller,wrinkled part of the lower rear brain, the cerebellum,is mainly for controlling muscles and making skilled

and coordinated movements. The large upper part, thecerebrum, receives information from the eyes, earsand other senses, and carries out thinking andspeaking processes.

Parietal lobe –touch, pressure,temperatureand pain

Cerebellum – movement,pressure and posture

The human brain

Temporal lobe

Occipital lobe – vision

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What is a CT scan Why are some people left-handed

No one really knows why –but we do know that theright side of the braincontrols the left side of thebody, including the lefthand, while the brain's leftside controls the body'sright side.

In most people, one or theother of the brain's sides isin charge, or dominant. Inabout eleven people inevery 100, the brain's rightside is dominant so theyuse their left hand most.

It is a very detailed picture of the inside of the body. ACT scanner is an advanced type of x-ray machine. Ittakes lots of pictures of the body and then uses acomputer to put them all together, providing an image.

CT stands for ‘computerised tomography’. The picturestaken by CT scans are called tomograms. They allowdoctors to diagnose many serious conditions includingbrain tumours.

A CT scan of a female skull

Every part of the body is made up of microscopicparts called cells, and the brain has more than 500billion of them.

The sperm whale has the largest brain in the animalkingdom. It weighs a whopping 7,800 g – overseven times more than the average human brain!

On average, a slightly higher proportion of left-handed people are likely to be creative or artistic insome way, such as artists, painters or sculptors,compared to right-handed people.

FACT FILE

The brain hemispheresperform specific jobs

Iris

Blood vesselsat centre ofoptic nerve

Blood vesselsbranch out oversurface of retina

Eye-moving muscle

Pupil

Conjunctiva

Cornea

Sclera

Choroid

Lens

Optic nerve

Fovea (yellowspot, area ofmost detailedvision)

Retina

From the moment you wake up in the morning until the moment you go tosleep, your eyes are gathering information and sending it to your brain to beinterpreted. Your eyes are delicate and precious. They should be shielded fromsunlight and protected from harm during dangerous activities like sport.

LOOK HERE!

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The human eye

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Cone cell

Rod cell

Networkof nervecells

Nerve fibres to optic nerve

Close-up of the retina

How does the eye work

The retina is located at the back of the eye. It sendsinformation about the image we are looking at to thebrain to be interpreted.

The retina contains special light sensitive cells called‘cone cells’ and ‘rod cells’. Rod cells process light.Cone cells process colour, and are responsible for theclarity (pureness) of an image. Cone cells are mostplentiful at the back of the retina, in a place called thefovea. This is where our vision is best.

What does the retina do

As the light from an object that you are looking atpasses through the lens in your eye, the imagebecomes reversed (turned backwards) and inverted(turned upside-down). At the retina, light-sensitivenerve cells send electrical messages along the opticnerve to the brain where information about the imageis processed and understood.

How light interacts with the eye

Why can’t people see in the dark

When light fades, the cone cells of the retina (thoseresponsible for processing colour) are no longer ableto work effectively. At this time, rod cells (responsiblefor processing light) process any available light as

shades of grey (monochrome). In this way, the humaneye is less effective when it gets darker. The brainrecognises the shades of grey processed by the rodcells as ‘darkness’.

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What do our eyelids do

Eye colour is determined by the levels of a moleculecalled melanin present in the coloured tissue of the iris.The levels of melanin, in turn, are determined by genesinherited from parents. Brown is the most common eyecolour in the world. Blue eyes are rarer than any othereye colour, and often found in people from Europe.

The coloured ring of the eye, known as the iris,tightens and relaxes, letting the appropriate amount oflight pass through the hole in the centre, called thepupil. Inside, the brightness of the light is detected bythe retina, which sends messages to the brain so that itcan continually adjust the iris muscles.

Why are eyes coloured

Did you know that your optic nerve is so long that,should your eyeball fall out of its socket, it wouldtouch your chin?

Each day the eyeball makes more than 60,000movements as it looks around, up and down.

FACT FILE

Parents’ eye colour Proportion of eyecolour in children

Eyelids keep our eyesfrom drying out andprevent dirt from enteringand irritating them. The rims of the humaneyelid are lined with oil-producing glands. When the eye blinks, the oil from these glandsis spread across the eye, ensuring that itremains moist.

Meanwhile, eyelashesserve as ‘dust-catchers’,catching irritants beforethey enter the eye.

Why do pupils change in size

WHAT’S THAT SMELL?

Olfactory bulb

Olfactory nerve to brain

Tonsil

Backbones in neck

Tooth

Cartilage(gristle) of nose

Air space (sinus)in skull bone

Nostril

Palate (roofof mouth)

Lip

Tongue

Jaw bone

Hyoid bone

A beautiful cake fresh from the oven. Flowers during spring. A pile of dirtyclothes. How do you smell these smells and thousands more? It’s your nose ofcourse! Let’s be a little bit nosy and find out more about this incredible organ!

Inside the nose and mouth

Cilia

Air chamberinside nose

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Why is smell so important

Identifying smells is your brain's way of telling youabout (or helping you to make ‘scents’ of) yourenvironment. Have you ever smelt smoke from a fire?Instantly, your brain interpreted the smell as a sign ofdanger and you knew to check where the smell wascoming from. Your sense of smell can also warn younot to eat something that smells rotten, like sour milk ormouldy bread.

When you inhale air through your nostrils, it enters thenasal passages and travels into your nasal cavity. The nasal cavity contains special receptors, calledcilia, that are sensitive to odorous molecules in the air.There are at least 10 million cilia in your nose! Whenthey are stimulated, signals travel along the olfactorynerve to the olfactory bulb. Signals are then sent fromthe olfactory bulb to the brain to be interpreted assmells you may recognise, like chocolate or chips!

Cilia

The part of the brain that processes information fromthe nose is closely linked to the area of the brain thatdeals with emotions and memory. This partly explainswhy the smell of flowers often makes people feelhappy, or the smell of rotten food can make peoplefeel sick. Certain smells can remind people of specialoccasions. For example, the smell of mince pies mayremind some people of Christmas.

How is smell linked to emotion

The outer portion of the nose (the part you can see) is made from cartilage, a soft rubbery tissue thatgives it its shape; it's attached to your skull at thenasal bone.

FACT FILEAir flowsinto nose

Odorous particles

How do people smell things

MucusArea containingcilia

Olfactory bulb

Odorous particles interact with the cilia

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Hot foods give off morepowerful odours than cold foods

You may think of the tongue whenyou think about taste – but youcouldn't taste anything without somehelp from the nose! The ability tosmell and taste go together becauseodours from foods allow us to tastemore fully.

To understand how smell enhancesflavour, take a bite of food and seehow it tastes. Then pinch your noseand take another bite. You shouldnotice that without smell, food tastesmore bland. When you have a badcold you may temporarily lose yoursense of smell. Although your tastebuds continue to work, the food youeat will taste of very little.

As people age, the cilia inside the nasal cavitybecome fewer. This means that young people,generally, have a far better sense of smell than olderpeople. A similar thing happens with the taste buds inthe mouth. Younger people experience smell and tastemore strongly than older people do.

Smell centrein brain

More odorantparticles

The average person can distinguish more than8,000 smells and odours.

Our sense of smell is 20,000 times more responsivethan our sense of taste.

FACT FILE

How does smell affect the taste of food

Do children have a bettersense of smell

Orbicularis orismuscles of lips closeto keep in foodsand drinks

Masseter musclecloses jaws for chewing

Zygomaticusmuscle pullsmouth wideto smile

Incisor teeth

Canine tooth

Premolar tooth

Orbicularis oculimuscles in eyelidsmake them blink

Temporalis musclehelps toclose mouth when chewing

SMILE A WHILE!Your mouth is a remarkable thing. Your teeth tear up food, munching it into awet ball. Chemicals in your saliva moisten the food, releasing its wonderfulflavours. Your tongue pushes the ball of chewed food to the back of yourthroat, and then it is gone …

Frontalis muscle raisesyour eyebrows in surprise

What does the mouth do

Why do some foods taste bitter

The mouth is a very important part of the body. It playsa role in speech, eating, drinking, facial expressions,kissing and breathing. Bounded by the lips, the mouthlinks up with passages leading to the stomach and to

the lungs. During eating, the tongue’s main job is topush food to the teeth for chewing and to mould foodinto a ball for swallowing.

The taste buds on the tongue’stip sense sweet flavours best.Those along the front sidesdetect salty flavours,while sour flavours aredetected along the rearsides. The taste budsacross the back detectbitter flavourants.Therefore, we tastesomething bitter lastof all, usually as weswallow, or just after.

Bitter

Sour

SaltySweet

The tongue is almost all muscle, with a thin, taste-sensitive covering. In fact it’s the most flexible musclein the body, formed from six pairs of smaller musclesall joined and working together.

The enamel covering a tooth is the hardestsubstance in the body. A typical tooth bites andchews over 15 million times throughout its lifetime.

Each day, six parts around the mouth (calledsalivary glands) make about one-and-a-half litres ofsaliva, or spit, to make food soft, and easy to chewand swallow.

FACT FILE

Saliva-makingcells

Lumps(lobules)of gland

Saliva duct (tube) Salivarygland

Drops of saliva

How is the tongue involved with taste

The tongue is covered with about 10,000 taste buds.Most taste buds are located around the sides andacross the back of your tongue. They provideinformation about the taste of the food you eat. Whenyour taste buds come into contact with food, they sendnerve signals to the brain, where they may beinterpreted as tastes you may recognise.

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The tongue

More than 50 – but not all at once! A typical babyhas 20 baby, or milk, teeth which appear from front toback, from about the age of six months to three years.By about six years, these first teeth start to fall outnaturally and the 32 adult, or permanent, teeth beginto grow, again appearing from front to back. Thewisdom teeth come through at 16–20 years of age –but in some people, they never develop.

How many teeth do people have

Molars

Premolars

Incisors

Canine

Why are teeth shaped as they are

The teeth in your mouth are different sizes and shapes.This is because they perform specific jobs. At the frontof the mouth, there are teeth called incisors. They arestraight-edged and sharp, which enables them to biteoff and slice chunks of food. Next to them is a taller,more pointed canine, which is better for tearing andpulling. Then come two premolars and three molars,which are wide with broad tops, for powerful chewingand crushing.

Positions of teeth in the mouth

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Taste buds will only respond to liquids. Solid food ina dry mouth will produce no sensation of taste atall; it is essential for saliva to moisten solid foodbefore it can be tasted.

The first sign of the development of teeth occurswhen the foetus is only six weeks old.

Your mouth contains over 500 different kinds ofmicroorganisms, which eat the leftover food in your mouth.They create acid and sulphur molecules. The acid eats intoteeth and causes holes, or cavities. The sulphur gives breatha foul odour.

Toothpaste rubs away these microorganisms, and removesstains caused by foods. Toothpaste also contains asubstance called fluoride, which makes the teeth strongerand more resistant to acid attacks. Fluoride is the mostimportant ingredient in toothpaste.

How does toothpaste work

FACT FILE

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Humans are one of the hairiest creatures on Earth! Every part of your body –except for your lips, palms of your hands and soles of your feet – is coveredby hair. By adulthood, you're likely to have about 5 million hairs poking outof your skin – about the same number as a gorilla!

Why do we have hair

Hair keeps us warm, protects the body andhelps us to make sense of the worldaround us. When a person is coldor in danger, hair is likelyto stand on end, trappingheat and making us lookbigger. Hair can alsohelp keep dust out of theeyes, ears and nose.

FEELING HAIRY?

Generally, about 80 hairs are likely to fall outevery day!

Nails are made of keratin, the same stuff that'sfound in bird feathers, antlers, cat's claws and yourfingernails!

Fair hair grows more slowly than thick, dark hair.

FACT FILE

Sebaceous gland

Nerve endings

A hair follicle

Nerve endingswrappedaround hairfollicle

Sweat gland

Sweat duct(tube)

Erectormuscle pullshair upright

Subcutaneousfat

Sweat pore

Cross section of the skin

Hair shaftSebaceous gland

Nerveendings

Hairroot

Hairbulb

Hair follicle

Human hair is not smooth but ‘scaly’ at 900times magnification

How many hairs are on the head

Male hairiness is partly to do with genes and also withthe male hormone testosterone. Men can grow long,thick facial hair which forms a moustache and beard.Most women do have these hairs, and all the othersthat men have too, it’s just that their hairs are mostlytiny and hardly visible.

Older people tend to develop grey hair because thepigment in the hair disappears and the hair turnscolourless. The grey or white appearance of anindividual hair is the result of the absence ofsomething called melanin, the same stuff responsiblefor eye colour. A head of hair will appear grey as aresult of the combination of coloured and colourlesshair – not because it is actually grey.

Why does hair turn grey

The average human head has about 100,000 hairs.However, this number varies with age and hair colour.People with blonde hair have around 130,000 headhairs, brown haired people about 110,000 and redheads about 90,000. Older people usually have fewerhairs on their head than young adults do.

Why are men so hairy

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Why is some hair curly

Whether your hair is straight, wavy or curly dependson the shape of your hair shaft. A round hair shaftproduces very straight hair. When the hair shaft isoval it produces wavy or curly hair. Really curly hair isproduced by flattened or kidney-shaped hair shafts.The amount of moisture in the air can alter the curlinessof hair, when water is forced back into the hair fibre.

Semi-circular canals(for balance)

Eardrum

Eustachian tube to throat

Bony canal

Pinna

Bone of skull

Cartilage(gristle)inside ear

Malleus (hammer)

Incus (anvil)

Cochlea nerveto brain

Bone ofskull

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Not only is the ear the sense organ that detects sounds, it also plays a majorrole in the sense of balance and body position. The ear is a very complexorgan that is divided into three parts: the outer ear, middle ear and inner ear.

WHAT AN EARFUL!

The ear

Stapes (stirrup)

Cochlea

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How does the ear work

Sound waves travel down the ear tube, or canal, to asmall sheet of thin skin called the eardrum. Theeardrum vibrates as sound waves hit it. It passes itsvibrations along three tiny bones, or ossicles – themalleus (hammer), incus (anvil) and stapes (stirrup) –to a part of the ear shaped like a snail and as big asa grape. This is the cochlea, in the inner ear. It isdeep in the head, just behind the eye. The cochleaturns the vibrations into nerve signals and sends themalong the auditory nerve to the brain.

FACT FILE

The highest-pitched sounds which most people canhear are 20,000 vibrations per second – but a batcan hear sounds ten times higher.

The lowest-pitched sounds which most people canhear are 25–30 vibrations per second – but anelephant can hear sounds five times lower.

The lining of the ear canal continually makes small amounts of sticky wax called cerumen. This wax plays animportant role in the cleaning of the ear canal. It also helps prevent dirt, bacteria, fungi and tiny insects fromreaching and harming the eardrum. Hairs grow in the ear canal for the same reason, to keep things out. Excessear wax can press against the ear drum or block the bony canal, which causes hearing to become impaired.

Why do we get ear wax

The ear is one of several organs responsible formaintaining the body’s sense of balance. The ears,eyes, joints, skin and muscles all provide the brainwith the information it needs to keep the body uprightand balanced.

The parts of the ear responsible for balance arelocated in the inner ear – the utricle, the saccule andthe semi-circular canals. When the body moves, thefluid in these tubes interacts with hair-like cells, whichfire messages along nerves to the brain.

How do ears affect balance

Bats can hear very high-pitchedsounds. Elephants can hear very low-pitched sounds

What do we actually hear

We actually hear sound waves that are produced bythe vibrations of air molecules. The size of these wavesdetermines the loudness of the sound, which ismeasured in decibels (dB). The frequency of thesewaves determines the pitch of the sound, which ismeasured in hertz (Hz). In healthy adults, the ear ismost sensitive to sounds in the middle range of 500 to 4,000 Hz.

Why can’t old people hearas well as young people

As we get older, our earsbecome less able to detect soundwaves of a higher frequency.This means that older peoplecan’t hear short, high-pitchedsounds like ‘ssss’ and ‘t’ as wellas younger people can.

A hearing aid amplifies sound

The path sound vibrations take through the ear

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Designed to provide maximum strength and mobility, the skeleton is thesupport network of the body, giving you shape and protecting your organs.Each bone is shaped to do a specific job and, where more flexibility isrequired, cartilage, ligaments and joints perform important functions.

Why have we got a skeleton

The skeleton provides a cage to protect the delicateparts of the body, while still allowing us to move. The ribcage, for instance, protects the lungs, heart,liver and stomach, while allowingthe chest to expand and contractas we breathe.

The skeleton is also the stableframe on which the other parts ofthe body are hung and supported.

THE SKELETON

The brain

The skeleton

Most adults have 206 bones intheir body. However, one personin 20 has an extra pair of ribs (13pairs rather than 12). A newbornbaby actually has more bonesthan an adult – around 350 atbirth. Some of these bones fusetogether as the child grows older.

How many bones are in thehuman body

Toe bones(phalanges)

Ribcage

Collarbone(clavicle)

Breastbone(sternum)

Base of spine(sacrum)

Shinbone (tibia)

Kneecap(patella)

Ankle bones(tarsals)

Hinge joint

Upper armbone(humerus)

Ball-and-socketjoint

Spinal bones(backbones)

Hip bone(pelvis)

Lower jaw

Skull

Wristbones(carpals)

Thighbone(femur)

Foot bones(metatarsal)

Calf bone(fibula)

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The ribcage

How long do broken bones taketo heal

Which knee has an artificial joint?

Broken bones take a varying amount of time to heal,depending on the bone broken, the age of the personand the type of break. In children, small bones takeabout four weeks to heal. In adults, larger bones,such as the thigh bone (femur), can take up to threemonths. Complicated breaks take even longer to heal.

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Elbow joint

Hinge joint (synovial joint)

When two or more bones in your body meet, theymake a joint. Joints are divided into two types: mobile(synovial) and fixed (fibrous).

Synovial joints include knees, shoulders and elbows.Here, two bones are held together by ligaments, whichkeep them in place as the muscles make the jointmove. In fibrous joints, like the joints found in yourskull, are bones that are joined by tough, stringytissue, which allows very little or no movement.

How do joints work

Ball-and-socket joint (synovial joint)

Shoulder joint Rounded head fits ina cup-like cavity

Joint moves to and fro

A baby is born with gaps in its skull, calledfontanelles, which ensurethat the skull is flexibleenough to cope with birth.

A baby’s skull does not formcompletely for up to twoyears. It looks like a jigsawpuzzle that joins together.

FACT FILE

Baby

Fontanelle

Child

Pectoralis major

Bicep

Vastus

TibialisToe-curling muscles (flexors)

Toe-pointing muscles(extensors)

Abdominals hold in thesoft parts, especially theintestines (guts).

Sartorius

Gastrocnemius

Rectus femoris

Did you know that you have more than 600 muscles in your body? Theymake every movement in your body possible, from the blink of an eye to awave. You control some of your muscles and others, like your heart, do theirjobs without you thinking about them at all!

MUSCLE POWER

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A selection ofhuman muscles

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What does muscle do

Muscles move you! You have three different types ofmuscle in your body: skeletal muscle, smooth muscleand cardiac muscle. Skeletal muscle is attached toyour bones. It enables you to consciously control mostof your body, meaning that you can run, jump or walkas you choose.

Smooth muscle, however, is involuntary, which meansthat your brain tells it what to do without you eventhinking about it. It helps to move blood through yourblood vessels and food through your digestive system.

Cardiac muscle is found in the heart. This heartymuscle is responsible for pushing blood around your body.

Tricep

The bicep contracts and the tricep relaxesto bend the arm

Bicep

It all starts with orders from the brain. Special cellscalled neurons carry electrical messages from the brainthrough the nervous system to the muscles you want tomove. If you're walking, your brain tells your legs to move and your arms to swing.

Skeletal muscles work in pairs. When one musclecontracts (gets shorter) the other muscle must relax (get longer). For example, your bicep must relax andlengthen when your tricep contracts and shortens. If this relationship did not exist and both muscle groupswere to contract at the same time, your arm wouldlock and there would be no movement at all.

How do muscles actually work

When you exercise, muscle fibres grow and multiply.The more you exercise, the stronger and bigger yourmuscles get.

FACT FILE

The bicep relaxes and the tricep contractsto extend the arm

Bicep

Tricep

What are muscles made of

Tens of thousands of small fibresmake up each muscle. Eachfibre is made up of long thincells, called myofibril, which arepacked in bundles. Each musclehas lots of these bundles – thebigger the muscle the morebundles of fibres it has.

Skeletal muscles are made up offibres that have horizontalstripes when viewed under amicroscope. Smooth muscleconsists of more looselyarranged fibres. Cardiac muscleconsists of fibres arranged in aneat criss-cross pattern.

How many muscles does it taketo smile or frown

The face and head have morethan 100 muscles, and we usethem to make our vast rangeof facial expressions. It takesabout 20 muscles to smile,but twice as many to frown!Scientists believe that ourfaces are pre-programmedto smile. A smile is used as away of communicating withothers, as a display ofhappiness or embarrassment.

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Muscle sheath

Bundles ofmuscle fibre

Muscle fibre(myofibrils)

Muscle fibreis a bundleof myofibrils Blood vessels and nerves

inside muscle

Myofibril consists of actin and myosin

Muscle strains can happen when muscles arestretched too far. Some of the muscle fibres can betorn and there can be bruising inside the muscle.

If you exercise too long, you can get a build up of achemical called lactic acid in your muscles, and thiscauses them to tighten up.

Muscles get most of their energy from glucose.Glucose is made from several types of carbohydratessuch as sugar, lactose (from milk) or fructose (from fruits).

FACT FILE

Cross section of skeletal muscle

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Your skin is alive! The largest organ in the human body, it’s made up of manythin layers of cells in which you'll find nerves, blood vessels, hair follicles,glands and sensory receptors.

THE SKIN YOU’RE IN

Sweat duct

Nerve endings

Nerve fibres to mainnerve and brain

Nerve fibre

Subcutaneous fat

Sebaceous gland

Horny layer of dermis

Sweat pore

Middle layer of dermis

Germ layer of dermis

Nerve ending for heat,cold and pain

Hair shaft

Nerve ending forlight touch

Blood vessels

Erector muscle pullshair upright

Main blood vessels

Cross section of the skin

Sweat gland

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Sunburn is a burn to the skin produced by too muchexposure to ultraviolet (UV light), usually from the sun.It occurs when the melanin in the skin is not able tooffer enough protection against UV light. Some peoplehave lots of melanin and others have little. People withless melanin are more likely to become sunburnt.

Why do we have skin

Why do people blush

Your skin doesn’t just cover you. Itdoes much more. It offersprotection from the world aroundyou, including germs and dirt. Itkeeps unwanted water out andkeeps your body’s fluids and saltsin. The skin contains a variety ofnerve endings that react to temperature, touch,pressure, vibration and tissue damage. It also allowsthe body to keep cool through sweating and softensthe impact of all kinds of wear and tear.

Germ layerof epidermis

Horny layerUV rays get through UV rays blocked

Pigment formingcells (melanocytes)

Melanin

UV rays penetrate the layers of our skin

Why do some people get sunburntmore easily

What are goose bumps

When you are cold orscared, you sometimesdevelop goose bumps.Goose bumps aretemporary bumps onyour skin caused bythe muscles that pullhairs upright. The bodydoes this when it is cold, as it tries to insulate warmair between the hair, trapping any body heat.

Goose bumps serve a purpose in animals, fluffing upfur to make them warmer or make them look biggerand scarier.

Everyone blushes. It’s a normal reaction to feelingembarrassed, anxious or excited. It is caused by anincreased blood flow through the tiny vessels in theskin of your cheeks. Sometimes people may not blushvisibly, but may react differently, like tapping theirfingers. Blushing is associated more with youngpeople, rather than old people – and women blushmore often than men do.

Close-up of a sweatpore

Brain

Cervical (neck) nerves

Thoracic (chest) nerves

Ulnar nerve along arm Spinal cord

Radial nerve alongarm Lumbar (lower back) nerves

Sciatic nerve (thickestin the body)

Sacral nerves

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Made up of the brain, spinal cord and billions of long nerve cells, the body’snervous system is the most complex and important network in the body. It isessential to seeing, thinking, dreaming, breathing, moving, running, sleeping,laughing, remembering, pain, pleasure, writing … everything you do!

WHAT A NERVE

The nervous system spreadsthroughout the whole body

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What is the nervous system

If you lined up all of the neurons in your body, theywould stretch for an incredible 950 km!

Every second the nerves transmit nerve signals atspeeds of up to 300 km/h, all around the body.

There are more nerve cells in the human brain thanthere are stars in the Milky Way.

FACT FILE

Made up of your brain, your spinal cord and anenormous network of around 30,000 million nervesthat thread throughout your entire body, the centralnervous system is the control centre of your body. Yourbrain uses information it receives from your nerves tocoordinate all of your actions and reactions. Withoutit, life as you know it would be impossible.

Nerves, or neurons, are thin threads of cells that runthroughout your entire body, carrying messages.Sensory nerves send messages to the brain. Theygenerally connect to the brain through the spinal cordinside your spine. Motor nerves carry messages backfrom the brain to all the muscles in your body.

Some nerve signals travel faster than racing cars.

What is a nerve

7.25 km/h

362 km/h

257 km/h

241 km/h

Sports car

High-speedtrain

Fast nervesignal

Slow nervesignal

Cell body

Dendrites

Axon(fibre)

Dendrites

A nerve cell, or neuron

Nucleus

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Nerves are connected to sensory receptors in the skin.These receptors are able to collect information from theworld around us. There are different nerve endings:Ruffini endings are sensitive to stretching of the skin;Merkel’s discs send touch information to the brain;Krause end bulbs are sensitive to temperature.

You may get pins and needles if a nerve becomessquashed or has its blood supply cut off. When thishappens, the nerve cells can no longer send clearmessages to the brain. This can result in the sensationof numbness, tingling or pricking, otherwise known as‘pins and needles’. Move, stretch and rub the affectedarea to get rid of the funny feeling.

What are ‘pins and needles’ How do nerves collect informationfrom the world around us

Merkel

What is a reflex action

Reflex actions occur quickly and automatically to helpyour body avoid harm. An example of a reflex actionis when you touch something hot with your hand andyour hand quickly moves away. The response happensquickly because it is ordered by the spinal cord rather

than the brain. If the order wasto come from the brain,

the signals would haveto travel further andyour reaction would be slower. If the boyin the picture had torely on his brain

to relay reflexinformation to

his hand, hecould havehurt himself

when hegrabbed the

hot mug.Krause Ruffini

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The body can survive without water for several days and without food for aweek or two – but it can only survive for a few minutes without oxygen.Breathing is one of the body’s most vital actions, and we do it almost withoutthinking – over 20,000 times each day.

Why do people breathe

Breathing enables the body to extract the oxygenneeded for life and to rid the body of harmful carbondioxide. Oxygen that comes into the lungs arrives atthe alveoli, where it is transferred to the blood.Oxygen is used by the cells in your body to move,build, reproduce and turn food into energy. It is also atthe alveoli that carbon dioxide is released from theblood and exhaled from the body.

TAKE A DEEP BREATH

The alveoli

Fresh air insidealveolus

Bronchiole

Tiny blood vessels (capillaries)take up oxygen

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Windpipe(trachea) in neck

Left lung

Air chamberin nose

Right lung is largerthan left lung

Air in and out

Faster and deeper breathing supplies the body withthe increased level of oxygen it requires duringexercise. At the same time, when we exercise, ourbody produces more carbon dioxide. When we

breathe faster, the heart rate increases and carbondioxide can be moved more quickly out of the body.After carbon dioxide levels fall, our breathing returnsto normal.

Why does breathing speed up during exercise

1/2 litre

1 litre

0 litre

Each breath usuallycontains half a litre of air The respiratory organs

Yawning is associated with tiredness, overwork, stressor boredom. However, the specific purpose of yawningis still disputed by scientists.Some think that it coolsthe brain while otherssay that it deals withexcess carbondioxide and a lackof oxygen in thebody. It could be away of displayingtiredness or boredom toothers. Some scientiststhink that it is a wayof equalisingpressure inthe ears.

Why do people yawn

What causes hiccups

The diaphragm is a sheet of muscle in your chest,just below your ribcage. When your diaphragmtightens, your lungs expand and you breathe in air.When it loosens, your lungs contract and youbreathe out.

Hiccups occur when your diaphragm suddenly jerksand air rushes over a flap (epiglottis) at the top ofyour windpipe, causing it to snap shut. It is thesound of this flap snapping shut that produces the‘hiccup’ sound.

Air flows intothe lungsthrough thenose or mouth

The flap(epiglottis)snappingshut

FACT FILE

The hiccup

On average, during a night’s sleep a personbreathes in and out all of the air in a typical-sizedbedroom.

Plants are our perfect breathing partners! Webreathe in air, use the oxygen in it, and releasecarbon dioxide. Plants take in carbon dioxide andrelease oxygen.

The tiny alveoli in both lungs, all spread out flat,would cover the area of more than 100 single beds.

Pulmonaryartery to lungs

Pulmonary veinsfrom lungs

Main artery (aorta)

Main arteries tohead and arms

Inferior vena cava

Superior vena cava

Right ventricle

Left ventricle

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The heart, the blood and the blood vessels make up the human body’scardiovascular system. The heart is responsible for pumping nutrients andgases around the body. The arteries carry blood away from the heart to thebody, while the veins carry blood on its return journey back to the heart.

HARD-WORKING HEART

Cross section of the heart

Right atrium

Left atrium

The heart

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Blood returns from the lungs through the pulmonaryvein. It is delivered to the left atrium, which pushes theblood into the left ventricle. The left ventricle thenpushes the blood through the aorta to the rest of thebody. The blood returns to the heart through two largeveins called the superior and inferior vena cava. It isdelivered into the right atrium, which pushes it into theright ventricle. The right ventricle then sends the bloodthrough the pulmonary artery back to the lungs.

What does the heart do

How big is the heart

How does the heart work

The heart’s job is to pump blood around two separatecirculations. First it pumps blood rich in oxygen fromthe lungs around the arteries, delivering food andoxygen to the body. Having delivered its oxygen, theblood then returns to the heart via the veins where it ispumped on its second circuit, this time up to the lungsto pick up more oxygen. The heart is also involved incommunication, pumping chemical messages(hormones) around the body.

The heart is about as big as the clenched fist of itsowner. It weighs about 340 g, or about the same asone-and-a-half cans of baked beans. Although it isoften thought of as being on the left side of the body,the heart is actually positioned more centrally in thechest, behind the lower part of the breastbone, withthe larger part positioned to the left.

Heart’s leftside pumps

blood aroundbody

Heart’s right sidepumps blood to lungs

If all the bloodvessels in thebody could bejoined end toend, they wouldstretch around the world twice!

FACT FILE

36

Does the heart ever stop beating

Your heart beats about 30 million times a year! Whenyou are sitting quietly, your heart beats about 60–80times a minute. You can count how fast your heart isbeating by gently feeling your pulse in your wrist.When you exercise, your heart beats much faster –about 120 times or more per minute. This sends moreoxygen and energy to the hard-working muscles.

The heart may stop beating while the body is stillalive, but only for a very short time. When yousneeze, your lungs are put under great pressure by thesqueezing action of chest muscles. The heart is unableto beat properly under this pressure, so it pauses forjust a moment.

The thick-walled arteries and veins that carry bloodunder pressure to and from the heart are the thickestblood vessels in the body. At any moment, theycan contain half of the body’s blood. The aortais the largest artery in the body. It carries blood rich in oxygen from the heart to theother parts of the body. Capillariesare the body’s smallest blood vessels. They enable the interchange of water,oxygen, carbon dioxide, nutrients andvarious waste products between theblood and surrounding tissues.

Which are the thickest vessels

What do heart valves do

How often does the heart beat

Blood is pumped so quickly through theheart, you might think it would be easy forit to lose its way! But there are four small flaps,or valves, which make sure that the blood alwaystravels in the right direction, and cannot flow back.

Blood vessels

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Every day the heart pumps about 10,000 litres of blood around the body –that’s enough to fill 120 bath tubs! The average three-year-old has around 1 litre of blood in their body; the average adult at least five times more!

RED FOR GO!

Aorta (main arteryfrom heart)

Carotid artery andjugular vein in neck

Brachial artery andvein to arm

Hepatic vessels in liver

Pulmonary veinsfrom lungs

Pulmonary arteriesto lungs

Femoral artery andvein in thigh

Anterior tibial arteryand vein in front ofshin Pedal arteries and

veins in foot

Posterior tibial arteryand vein in back of shin

The circulatory system

Your blood is made up of many different cells. Most ofyour blood is a liquid called plasma. Red blood cellsdeliver oxygen to the cells in the body and carry backwaste gases in exchange. White blood cells are partof your body's defence against disease. Some attackand kill germs eating them up; others attack them withchemicals. Platelets are other cells that help your bodyrepair itself after injury.

What is blood

Because it contains red blood cells! So why are they red? They contain a red substance calledhaemoglobin, which carries vital oxygen from thelungs to be used all around the body. Blood that is richin oxygen is a brighter shade of red than blood thatcontains little oxygen. Veins appear blue through theskin due to the interaction of light with the skin and theway that our brain interprets colour.

Red blood cells are doughnut shaped

A drop of blood the size of a pinhead contains 5million red cells, 10,000 white cells and 250,000platelets. Red cells die off and are replaced in thebody at the rate of 2 million every second.

FACT FILE

How much blood is in the body

Blood makes up seven per cent of the body’s totalweight. The average adult has about five litres ofblood pumping around their circulatory system. Onaverage, men have slightly more blood than women,as women have slightly more adipose (fatty) tissues,which need very little blood supply.

Why is blood red

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Platelet

White blood cell

Red blood cell

Plasma

Make-up of the blood

Why do people give blood

Blood is given to help people who need it. People mayneed blood after an accident or during an operation.Before blood is given to people, it is usually split intofour parts: red cells, white cells, plasma or processedplasma and platelets. Processed plasma is often givento people with haemophilia, which is a condition thatstops blood from clotting properly. Haemophiliacs canlose lots of blood very quickly if they are cut, so theyoften require blood transfusions.

39

A doctor takes a patient’s blood pressure

Your blood group is something that is inherited fromyour parents. There are 29 blood groups that arefound in humans. A person’s blood group isdetermined by the presence of substances calledantigens on the surface of the red blood cells. Antigensare part of the body’s natural defence mechanism. If aperson needs a blood transfusion, blood of a suitablegroup must be chosen – the wrong type could bedeadly. Most people are blood type O. Next comes A,then B, with only one person in 20 being type AB.

What are blood groups?

Platelets are the smallest cells in the body. They haveone function only: to make blood clot when bleedinghas to be stopped! Platelets are small sticky cells thatare made in the bone marrow. They rush to the site ofa cut, stick to the vessel wall and to each other so thata plug is formed. After this, other substances in theblood work withplatelets to form afibrin, whichprovides a morepermanentsolution tobleeding, suchas a scab.

How does a cut heal itself

Blood clots tostop bleeding

The digestive system

Stomach

Pancreas (makesdigestive juices)

Coils and loopsof small intestine

Large intestine(colon)

Rectum

Liver

Gullet(oesophagus)

Gall bladder

The digestive system is made up of a variety of different organs andsubstances that work together to break down food into nutrients and energythat can be absorbed and used in the body’s tissues and cells.

FUELLING THE BODY

Why do people feel hungry

The body uses energy all the time, not only to moveabout, speak and eat, but also to make the heart beat,the lungs breathe and for cells to function. As stores ofenergy gradually decrease, the body signals the needfor more energy by making us feel hungry.

Stomach

Oesophagus

Swallowedlumps of food

Throat

After food has been chewed in the mouth, it travelsdown the oesophagus and into the stomach. Theoesophagus is a 25 cm long, muscular tube thatcontracts in waves to move swallowed food through it.The swallowing sound that can be heard during eatingis the sound of the oesophagus functioning.

How does food reach the stomach

The oesophagus leads to the stomach

This is a general name for the intestines and thestomach too. The stomach is a J-shaped bag whichreceives swallowed food and drink. It squeezes,mashes and mixes food with powerful juices, includingstrong acids and digestive enzymes. From the stomach,food passes into the very long, coiled small intestine,where the digested nutrients are taken into the body.

The leftovers go on, into the shorter but wider largeintestine, which takes in water and a few morenutrients. The whole process leaves faeces at the end,in the rectum, ready to be removed from the body.

What are the ‘guts’

Why do people vomit

The muscles of the oesophagus wall are so powerful, aperson could swallow while upside down. They workin reverse too, to remove bad or unwanted food fromthe stomach, up and out of the mouth – by vomiting!

The whole digestive tract is about 8–9 m long:Mouth and throat 20 cmOesophagus 25 cmStomach 25 cmSmall intestine 600 cmLarge intestine 150 cmRectum 15 cm

FACT FILE

41

What food takes the longest to be digested

The time for digestion depends on the type of food.Sugary and starchy foods like birthday cake breakdown quite quickly in the stomach and contain plenty

of energy. Fruits and vegetables need more chewingand mashing. Fatty meals, especially those with lots ofanimals fats, take the longest to digest.

Vitamins and mineralsare found in fruit and vegetables.

Carbohydrates includebread, pasta, cerealand rice.

Proteins include fish,eggs and red meat.

Fatty foodsinclude cheeseand full-fatmilk.

A diet should bevaried and healthy

42

43

The colour of faeces depends on the foods we eat.Lots of fatty foods make them pale. Plenty of iron-richfoods make them darker. If you don’t eat enough fruitsand vegetables, the faeces may be too small andhard. They may get stuck on the way out, which isknown as constipation.

Excretion is the process of ridding the body of waste products that must beremoved if the body is to remain healthy. The body relies on various organsfor waste removal, including the kidneys, the lungs, the liver, the bladder andthe intestines.

Why do people go to the toilet

Why are faeces different coloursThe kidneys receive more blood, for their size, thanany other body part – about 20 per cent of all theblood pumped out from the heart.

Each day the kidneys filter the body’s entire volumeof blood more than 300 times.

Food drying up in the large intestine can remainthere for 8 hours to two days!

FACT FILE

We go to the toilet to rid the body of unwanted wasteproducts. Faeces (poo!) is made up of undigested andleftover food, bits of old lining from the digestivesystem and old red blood cells from the liver. About75 per cent of its weight is water, and about 10 percent is dead gut bacteria. These bacteria live in theirmillions in the large intestine and help with digestion.

Produced by the kidneys, urine contains wasteproducts produced by the body’s billions of cells.

Broccoli and redmeat are rich iniron and makefaeces darker

WASTE

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What do the kidneys do

The kidneys collect and filter waste products from theblood. They also control the amount of water passed

out of the body, and maintain the body’s balanceof salt. From the kidneys, waste products and

excess water are passed in the form of urinedown to the bladder, before they are passedout of the body.

The kidneys filter about one litre of bloodevery minute. They produce urinecontinuously during the day and night. The body passes about two litres of urineevery single day!

The bladder

Pipe outof bladder(urethra) Muscular

walls ofbladder

Pipes intobladder fromkidneys (ureters)

Cross section of a kidney

Urine collects incentral area

Main part of kidneycontains over onemillion micro-filters

Pipe tobladder(ureter)

Renal artery and veinfor blood supply

45

Nerves run to skinof thumb tip

Distal phalanx boneof thumb

Tendons of finger musclesrun to fingertip

Ligaments criss-cross over tendons

Blood vessels run to skinand bone of fingertip

Abductor pollicis pullsthumb towards palm

Abductor minimi pullslittle finger over palm

Main ulnarnerve

Tendons run under carpalligament in wrist

Tendons from finger-curlingmuscles in forearm

The hand is one of the most useful parts of the human body. From gripping atennis racket to threading a needle, our hands are perfectly designed forperforming everyday activities in the world around us.

GET A GRIP

The hand

Distal phalanges

Intermediate phalanges

Proximal phalanges

How do the hands ‘talk’

How many bones are in the hand

We communicate with our hands and fingers in manyways. For example, the forefinger held to the lipsmeans, ‘Shhhh – keep quiet’. A fist clenched by thecheek, with the thumb to the ear and the little finger tothe lips, means ‘I’m on the telephone.’ Hands can ‘talk’in another way too – by sign language. This isespecially useful for people who cannot hear properly.

The hand has 27 bones. There are five in the palm,called metacarpals, two bones in the thumb and threein each finger, all known as phalanges. There are alsoeight small bones, called carpals, in the wrist, whichjoin the hand to the forearm bones.

How do the hands work

The hand is truly amazing. It allows us to grip, hold,clench and perform more delicate movements likewriting. It is operated by more than 50 muscles – thethumb alone has about ten muscles that move andbend it in almost every direction! Most of your hand-moving muscles are joined to bones by long, cord-liketendons that pass through the wrist. Clench your handand you can see these tendons moving in your wrist!

Carpal bonesin wrist

Metacarpalbone in palm

Distalphalanx

Digit 3 (middle finger)

Digit 1(thumb)

Middlephalanx

Proximalphalanx

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Some people have double-jointed fingers. This meansthe ligaments and tendons surrounding the joints areunusually flexible, enabling them to bend or rotatethem in ways other people can’t.

FACT FILE

The bones of the hand

Arch Tented arch

The pattern of small, curved ridges in the fingertipshelp fingers to grip. Smooth skin would grip muchmore poorly. The fingertip skin also has a thin film ofsweat to improve the grip further. It’s not exactly clearwhy everyone has different patterns, but as no print isthe same, they are helpful for identifying people.

Why do we have fingerprintsWhy is the thumb so useful

The power grip is used to grasp items tightly,like this tennis racket

During the Gallic wars, Julius Caesar ordered thethumbs of captured warriors to be cut off so thatwhen they returned to their country, they would beunable to bear arms again.

FACT FILE

Pocket loop Whorl

47

Because it can ‘oppose’ each finger, which means itcan touch and press against each finger in turn. Thisenables humans to perform several different types ofgrip: the ‘power grip’, where the fingers and thumbwrap around an object; the delicate ‘precision grip’,which involves the tip of the thumb and your fingertips.

Your feet are incredibly sturdy, strong and flexible. They are able to supportthe weight of your entire body and still perform delicate movements likewiggling your toes. Your toenails are designed to aid balance, and the skin onthe sole is the thickest of any on the human body.

How many bones are in the foot

There are 26 bones in the foot: five in the sole, two inthe big toe and three in each of the other four toes.There are also seven bones in the ankle. One of these,called the calcaneus, forms the rear of the foot and the heel.

Strangely, the knobbly parts we call the ankles, on theinside and outside of the ankle joint, are not anklebones – in fact, they are the lower ends of the longbones, called the tibia and fibula, inside the leg.

BEST FOOT FORWARD

Metatarsalbones

Tarsal bonesin ankle

Rear of calcaneusbone forms lowerback of heel

Distalphalanx

Digit 1(big toe)

Why do men have bigger feetthan women

Partly because, on average, men have larger bodiesthan women. However, that is not the only reason. The male hormone testosterone has an effect on bonegrowth and makes parts such as the nose, chin, handsand feet grow more during the teenage years in boys.No human being is perfectly symmetrical, and most ofus have one foot bigger than the other.

Some people wholose the use oftheir hands, forexample, in anaccident, canlearn to use theirfeet and toesinstead for manyactions – fromtyping on akeyboard topainting pictures.

Each foot is ableto take up to fivetimes your bodyweight whenrunning.

FACT FILE

48

Middlephalanx

Bones of the foot

Proximalphalanx

How much pressure does thefoot have to absorb

Mainshinbone(tibia)

Tendons oftoe-curlingshin muscles

Nervescontroltoemusclesandfeelingsfrom skin

Interosseimuscles connectbones of toes

Extensortendon pullingtoe up runs totip of big toe

Flexor hallucismuscle curlsbig toedownwards

Muscle sheathsaround musclesof big toe

Tendonsattach to toebones

Tendons rununder strap-liketarsal ligamentin front of ankle

Calf bone(fibula)

Outer ankle islower end offibula bone

Gastrocnemiusmuscle in calf

The muscles of the foot and ankle

With every step you take, your feet have to absorb apressure that is about one and a half times the weightof your body. If you run or jump, the force may bemany times your body weight. You can see how thepressure varies during slow walking, jogging andleaping; just look at the depth of the different parts ofa footprint in damp mud or sand.

Running will leave the deepest footprints

Walking Jogging Running

Some scientists think that toenails aid walking, bymaking the toes stronger and stiffer for a better gripon the ground. Long ago,when our distant ape-likeancestors lived in trees, theirtoes were as good at holdingand gripping branches astheir hands. Toenails mayalso be involved in balance and coordination.

Why do feet have toenails

Nails helped our ancestors grip more easilywith their toes

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Life begins with a fertilisedegg, or embryo. This involvesthe coming together of twocells. One is the egg cell,produced inside the mother’ssex organs, or ovaries. Eachmonth one of them becomeslarger and ripe, and an egg isreleased into the Fallopiantube (oviduct). Here it maymeet the other cell, a spermcell, which comes from thefather. Sperm are made in themale sex organs, or testes.When egg and sperm join, itis called fertilisation.

Everyone begins life in the same way – as a tiny fertilised egg, smaller thanthe full stop at the end of this sentence. The development of a baby in themother’s womb is one of the most amazing parts of the human life cycle.

How long does a baby spendin the womb

Throughout a woman’s lifetime, she will produce400–500 egg cells.

The human heart starts to beat 21 daysafter conception.

From fertilised egg to full-grown foetus, body weightincreases six billion (6,000,000,000) times!

FACT FILE

Even though a baby is thought of as ‘nought’ or ‘zero’when it is born, at birth it is already nine months old –this is the length of time spent developing in themother’s womb during pregnancy.

EXPECTING A BABY

Egg in tubeSperm in tube

Fallopian tubeWomb (uterus)

Endometrium(lining of womb)

Vagina

CervixOvary

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How does life begin

Sperm travel to meetthe female egg

6 weeks

12 weeks

16 weeks

20 weeks

28 weeks

38 weeks

Stages of growth

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What is an embryo

The embryo stage lasts from fertilisation to eight weekslater. The fertilised egg moves along the Fallopian tubeinto the womb, where it sinks into the blood-rich lining.All the time the embryo is dividing and re-dividing toform a small group of cells called the morula. By eightweeks this group of cells has developed to form themain parts of the human body, yet the curled-upembryo is hardly larger than a grape.

Smaller cells aroundthe embryo

The fertilised egg has divided into two cells

A two-cell embryo

After eight weeks,the embryo is calleda foetus. It continuesto grow fast assmaller details of itsbody form, likeeyelids andfingernails. By thetime of birth(depending on theparents’ size andethnic group) thebaby weighs about3–3.5 kg.Supply of nutrients from

the mother’s blood

Exchange ofoxygen andnutrients forwastes

Amniotic fluid

Umbilical cord

Placenta

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It can’t – it is surrounded by fluid in the womb! Thefoetus receives all the oxygen it needs from its mother.This vital exchange is carried out by the placenta, towhich the foetus is attached by the umbilical cord. At the placenta, the foetus’s blood vessels pass closelyto the mother’s blood vessels and the exchange ofoxygen, food and waste products takes place. Theplacenta also acts as a barrier to protect the foetusfrom harmful substances.

Umbilicalarteries

Umbilicalvein

What is a foetus

Umbilical arteries carry deoxygenated bloodfrom the baby; the umbilical vein carriesoxygen to the baby

How does a baby breathein the womb

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A baby spends about 38–40 weeks growing inside its mother’s womb(uterus), where it is warm, well fed and protected. The lights, sounds, actionsand fresh air of birth come as a big shock!

A NEW LIFE BEGINS

The baby’s head presses downon the cervix (womb opening)at the start of birth

Muscles in wallof womb

Cervix is readyto open

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On average, it takes 14–17 hours for a mother todeliver her first baby, much shorter for her secondbaby, even shorter for the third, and so on. The longestpart of birth is the first stage, when the womb musclesstart to contract. These muscle contractions can last fora number of days. The second stage, delivery, can lastfrom anywhere between 15 minutes and two hours.The placenta is usually delivered between 15 minutesand one hour after the baby’s birth.

Twins can occur in two ways. Firstly, when just oneegg is fertilised but within days it splits, each halfdeveloping into an identical baby. Secondly, when twoeggs are released at the same time and are fertilisedby separate sperm resulting in non-identical twins.

How is a baby born

The womb in which the baby grows has powerfulmuscles in its walls, and a narrow, pocket-likeopening called the cervix. At birth, the wombmuscles shorten or contract powerfully, and thecervix becomes much wider. The muscles push thebaby through the dilated cervix, along a tunnelcalled the vagina, or birth canal, and out of themother’s body.

The womb muscles contract

Moving into the birth canal

Cervix

Cervix dilates(widens)

Spinal cordSpine

Pubicbone

Womb

Birthcanal

Twins are two babies who share the same uterusduring a single pregnancy.

They can be identical or non-identical, either of thesame or opposite sex. Triplets are three babies andquadruplets, four!

FACT FILEHow do twins occur

How long does birth take

Through the months of the year, slightly more babiesthan normal are born during August, and slightlyfewer in April. The most common time of day for birthsis in the middle of the night, between 3 and 4 am. Theleast common time is twelve hours later, around 3 pmin the afternoon.

Nearly all babies have grey–blue eyes at birth. This isbecause the coloured part of the eye, the iris, has notyet developed its full set of microscopic cells whichproduce the colouring substance, or pigment. Theeventual colour develops over a few months.

A blue-eyed baby stares at the bright world

What colour are a baby’s eyes

What is a baby’s first food

For every 100 new baby girls, on average, thereare 105 new baby boys.

At the time of birth, the womb (uterus) contains themost powerful muscles in the human body – 40 timestheir size before pregnancy.

FACT FILE

55

When are most babies born

Mother’s milk is the perfect food for new babies. It contains all the nutrients, fluids and energy that thebaby needs, and it is clean,freshly made, and readilyavailable, straight from themother’s breast. Somemothers are unable tomake milk, or produce toolittle, or become ill. Forthese and other reasons,powder or formula milk is used.

A baby feeds

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Most babies and toddlers go through the stages ofdevelopment in the same order, but their age at eachstage can differ greatly. A typical baby can rollover at nine to ten weeks of age, sit up unaidedat eighteen to twenty weeks, stand up supportedfrom six or seven months and crawl at eightmonths. He or she may walk unaided at eleven totwelve months. Some babies don’t bother withcrawling. They learn to roll sideways or bottom-shuffle,and then go straight to walking.

During the first years of life, a child develops rapidly and learns a great dealabout social roles and behaviour. It is during this time that they learn to walkand talk. Young children are like little sponges, soaking up information aboutthe world around them.

When does a baby first smile

Can toddlers walk before they crawl

Babies usually start smiling from the age of six weeks.Smiling is an important part of communication. A smilecan indicate that a baby is happy and content, orwants attention of some kind. Long before the firstsmile, babies want to communicate with people. Theycommunicate by copying the facial expressions of theirparents, holding the gaze of others, widening theireyes or moving their tongue.

BABIES AND TODDLERS

Sitting and standing are important stages, or‘milestones’, of development

A baby grows fastest as a foetus and through the firsttwo years of life.

From the age of two, both boys and girls grow aboutseven or eight centimetres a year, with boys typicallybeing slightly taller.

FACT FILE

57

Why do toddlers like bland foods

The sense of taste helps to warn us of foods which arebad, rotten or poisonous – and these often taste sour

or bitter. A toddler follows theirin-built reactions, or instincts,and avoids these tastes.Gradually, as the toddler growsinto a child and experiencesmore flavours, he or shelearns to tell apart differenttastes and knows which

foods may be rotten orbad in some way.

Babies don’t eat food – they wear it!

Having spent monthssuspended in fluid in theirmother’s womb, babies feelat home in the water. Allbabies are born with a swimand dive reflex. This meansthat they automatically holdtheir breath under water andare able to swim for shortdistances. This reflex isstrongest when a baby isunder three months old. After this time babies candevelop a fear of the water – but they can easilylearn to swim properly when they are older.

Is it true that newborn babiescan swim

Molars

Lateral incisor

Canine

Central incisor

What does cutting teeth mean

Between seven and twelve months, teeth start to growand push through the baby‘s mouth. They come fromlittle tooth ’buds‘ which were formed while in thewomb. Usually, the first to appear are the ‘central’incisors, or front teeth, followed by the ’lateral‘incisors. The baby is likely to drool more, eat andsleep less and be generally uncomfortable – which isnot surprising!

Most babies have a full set of milk teeth at three years.By the time they are six, they start to lose them as theirpermanent teeth come through. The positions of milk teeth

The menstrual cycle is something that is necessary forreproduction. During the menstrual cycle, the ovaryreleases an egg in an event called ovulation. If the eggis not fertilised it will die and be absorbed by thewoman's body. After this, hormones cause the uterus toshed its lining in a process called menstruation.

Growing ‘up’ is not just getting taller, or even becoming bigger all over. Itmeans a whole host of changes inside the body, especially during the teenageyears. As many more years go by, things change again and bodily systemsstart to slow down.

What is puberty What is the menstrual cycle

Puberty is the timewhen the sexorgans(reproductive parts)become active andstart to function.This phase mainlyinvolves physicalgrowth anddevelopment.

Puberty is part of alonger periodcalled adolescence,which involvesmany mental andemotional changes,changes infriendships andsocial life, andincreasing independence from parents.

GROWING OLDER

Ovulation(egg releasedfrom ovary)

Egg maturesin ovary

Egg breaksdown

Womb lining is shed (menstruation)

Level of oestrogen

Level ofprogesterone

End ofmenstruation

1 day 7 days 14 days 21 days 28 days

The menstrual cycle lasts on average 28 days

Start of menstruation

Adolescent boy and girl

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The menstrual cycles of women usually stop around theage of 50–55 years. This stage of life is called themenopause, and it means that ripe eggs are no longerproduced by the ovaries.

However, with modern medical techniques such as IVF(in vitro fertilisation or ‘test tube babies’) it has becomepossible for women to conceive at a much later age.Most men carry on producing sperm for longer, intotheir 60s or even 70s, so they can still be fathers.

When do women stophaving babies

Skin contains tiny threads, or fibres, of the substanceelastin. Like millions of microscopic elastic bands,these make the skin spring back after it is stretched.With age, the amount of elastin becomes less so theskin becomes stretched and loose, and puckers intocreases and wrinkles.

Why does skin become wrinkly

On average, in most developed countries, pubertyhappens two years earlier than it did 100 years ago.

This is probably due to better foods with healthiernutrients which allow faster growth.

FACT FILE

The bodily changes of puberty involve extra growth ofthe voice box, or larynx, in the neck. The strip-likevocal folds (cords), which vibrate to make the sound ofthe voice, become thicker and stiffer. They vibratemore slowly, making the voice deeper. This happensmost noticeably in boys, whose voices ‘break’ or‘crack’ during puberty, but also to an extent in girls.

Thyroid cartilage

Hyoid bone

Epiglottis

Vocal cordsinside voice box

Cricoid cartilage Windpipe(trachea)

Why do voices ‘break’

The voice box(larynx)

Too many fatty foods can be bad for the body,especially foods with lots of animal fats such as fattymeats or full-fat cheeses. In particular, they affect theheart and blood vessels. Also, too much food in total isunhealthy. Being overweight increases the risk of manyproblems such as heart disease, high blood pressure,breathlessness, diabetes and breathing disorders.

The body benefits from moderate and regular exercise, two or three timesweekly, and also a wide range of food and drink. The body needs a well-balanced diet to provide it with the substances it requires for energy, growthand repair.

Which foods are healthy

The body can cope with most kinds of food. The mainproblem is too much of any one kind, whether it’scrisps or carrots. A varied diet is best. Fresh fruits andvegetables are especially healthy. People benefit fromfour or five portions of them daily – a portion being apiece of fruit or a helping of vegetables.

EAT WELL, STAY FIT!

Which foods are not healthy

Fresh fruits are very healthy

Fatty and fried foods can lead to seriousheart problems

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Regular exercise benefits the body

61

Why is smoking harmful

Smoking tobacco is a very bad idea. It is linked withdiseases such as heart disease and cancers of thelungs, throat, gullet, bladder and many other parts. Itcan cause breathlessness, wheezing and increasedrisk of infections such as bronchitis and pneumonia.Worldwide, there wereabout 100 milliontobacco deathsduring thetwentieth century alone.

Most people benefit from at least two exercise sessionseach week. These should be enough tocause faster breathing and a morerapid pulse rate, which shows thelungs and heart are getting aworkout. A bit of sweat isalso usually a good sign.

How often should we exercise

Which sport or exercise is best

Swimming is a great way to get fit

Smoking while pregnant can harm the unborn baby.

Cigarette smoke contains over 4,000 chemicals,including over 50 known carcinogens (causes ofcancer) and other poisons.

The type of exercise or activity does not matter toomuch, provided it is done in moderation. We are morelikely to continue with regular exercise if:

• we enjoy it and it’s good fun• it fits in with our daily or weekly routine• it doesn’t involve too much special equipment,

travel or money.

It could be a team game like football or hockey, asport such as tennis or squash, or swimming, cycling,jogging, horse riding … the choices are endless!

FACT FILE

Alveoli

Tiny air sacs in the lungsthat carry the oxygen fromthe air into the blood.

Canines

The taller, pointed teeth tothe sides of the incisors atthe front of the mouth, goodfor tearing tough food.

Capillary

Delicate, thin-walled bloodvessels, some of which arefiner than human hairs.

Carbohydrate

One of the main foodgroups, relatively high insugar and starch – includesbread and potatoes.

Carpals

The eight small bones ofthe wrist which join thehand to the forearm bones.

Cartilage

A tough, relatively flexibletissue that can be found inthe nose and ears and in

joints – most of the skeletonis made from harder bone.

Cell

The smallest unit of anorganism (living thing) thatcan function on its own.

Cerebellum

The part of the brain thatcoordinates movementand balance.

Cerumen

Ear wax that plays animportant role in cleaningthe ear canal.

Cilia

Tiny hairs on cells, suchas those in the nose that,when touched by odorousparticles, send messagesto the brain for our senseof smell.

Digestion

The process by whichfood is broken down inthe stomach and intestineinto substances that canbe absorbed into the body. EnamelThe hard, white substancethat covers each tooth.

Eustachian tubeA tube inside the earwhich acts as a pressuregauge, letting air both inand out.FertilisationThe point at which theman’s sperm joins with thewoman’s egg and the lifeof a baby starts. FibrinA protein formed whenblood clots, making anetwork that holds the redblood cells and plateletstogether.FibrousConsisting of, orresembling, fibres, as infibrous tissue.FoetusThe tiny, growing baby inthe womb, from the secondmonth of pregnancy.FontanelleA small gap in the top ofa baby’s skull which canappear as a soft spot.GenesInherited, genes carryinstructions for how thebody grows, develops and

carries out life processes.

Haemoglobin

A protein that gives thered colour to blood cells.

Hair follicle

A tiny cavity in the skinfrom which hair grows. Ithouses the only part of thehair which is alive.

Hormone

A chemical substance that carries a signal fromone cell to another.Produced in the endocrineglands, it is transported inthe blood.

Incisors

The chisel-edged teeth atthe front of the mouth.

IVFIn Vitro Fertilisation – If awoman is unable toconceive naturally, eggcells can be removed fromthe woman’s ovary andfertilised by the spermoutside the body, beforebeing implanted in herwomb (uterus) whenpregnancy proceeds in thenormal way.

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GLOSSARY

KeratinThe substance (a protein)from which nails and hairare made.

MelaninBlack or dark brownpigments in the hair, skinand eyes of humans.

MetacarpalsThe five bones that formthe palm of the hand.

MyofibrilMuscle fibre that consistsof actin and myosinproteins.

NerveA fibre in the body thattransmits messagesbetween the brain orspinal cord and otherparts of the body.

NutrientAny substance thatnourishes the body –repairing it when neededand keeping it in goodworking order.

Odorous particleA ‘smelly’ airborne particlethat floats into the air andinto our nose, touching

micro-hairs (cilia) whichgive us our sense of smell.

Oestrogen

A hormone whichproduces and maintainsfemale characteristics.

Olfactory

Relating to the sense of smell.

Ossicles

The three tiny bones of theinner ear, known as themalleus (hammer), incus(anvil) and stapes (stirrup).

Paresthesia

The medical term given to‘pins and needles’ – a lossof sensation in areaswhere the blood pressurehas been affected.

Phalanges

The two bones of eachthumb and three bones ofeach finger.

Pigment

A substance that is foundin animal or plant tissuethat produces thedominant colour.

Protein

Compounds that form partof the body tissues and animportant part of our diet.

Plasma

The yellowish fluid part ofthe blood.

Platelet

A minute particle in theblood which helps it to clot.

Receptor

A nerve ending whichresponds to touch andsends messages to thebrain, for example,touching a hot surfacewith our fingertips andthen moving them away quickly.

Retina

The light-sensitive lining atthe back of the eyeball.

Sebaceous gland

Small glands in the skinthat secrete sebum intothe hair follicles and overthe surface of the body –except the soles of thefeet and the palms ofthe hands.

Sound waves

Waves that enable soundto travel, as in the soundtravelling from the mouththrough the air to our ears.

Synovial fluid

A clear, lubricating fluidsecreted by the membranelining the joints, makingjoint movement smooth.

Testosterone

A very strong hormoneproduced by the testes inthe male.

Umbilical cord

The long, tube-shapedcord joining the foetus tothe placenta, along whichvital nutrients are passedfrom the mother andwaste is passed back.

UV rays

Ultra-violet rays from theSun which can causewrinkles and prematureaging as well as sunburn.

Vena cava

The two large veins thatcarry oxygen-depletedblood to the heart.

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GLOSSARY

64

abdominal muscles 23adolescence 58alveoli 31, 33anvil 18–19aorta 34–37arms 21–24arteries 34–39, 44, 52auditory nerve 19

bacteria 19, 43balance 19ball-and-socket joint 22birth 21–22, 50–55blink 9, 23bladder 43–44blood 27, 34–39, 43blushing 27bones 10–11 18–19,21–22, 45–46, 48–49brain 4–8, 11–12, 14,19, 21, 28–30, 33breathing 28, 31–33,61

capillaries 31, 36carpals 21, 46cells 6, 8, 14, 19,24–26, 29–31, 38–40,43, 50–51cerumen 19cervix 53–54chest 21, 28, 33childbirth 53–55cilia 10–12cochlea 18–19

dermis 26–27diaphragm 33digestion 40–43

ears 18–20eating 13–15, 40–43,60egg 50–51, 58–59embryo 50–52emotion 5, 11, 28exercise 24–25, 32, 36, 61eyebrows 13eyelashes 9eyes 7–9

faeces 41, 43feet 21, 23, 48–49femur (thighbone) 21–22fibula 21, 48–49fingers 45–47fingerprints 47fitness 60–61flavours (tongue) 14foetus 52follicle, hair 16–17fontanelle 22food 13–15, 40–43, 60

gall bladder 40genes 9germs 27, 38goose bumps 27grip 47, 49growth 51–52, 56–59gullet 40–41guts (intestine) 40–41

hair 16–17hands 45–47heart 34–37, 61hiccups 33hinge joint 21–22

hormones 35, 58

incisors 15, 57intestines 40–41iris 7, 9, 55

jaw 10, 13joints 21, 22, 46

keratin 16knee 21–22kidneys 43–44

large intestine 40–41, 43left-handed 6legs 23, 37life cycle 50–59liver 40, 43lungs 31–38, 41, 61

melanin 9, 17, 27menstrual cycle 58–59metacarpals 46metatarsal 21, 48milk teeth 57mouth 10, 13–15, 33,41, 57muscles 13–14, 22–26,33, 36, 41, 45–46, 49,53–55

nasal cavity 10–12neck 28, 37, 59nerves 4, 10–11, 14,19, 24–26, 28–30, 45,49nose 10–12nostrils 10–12nutrients 36, 41, 52

odorous particles 11–12oesophagus 40–41olfactory bulb 10–11ossicles 18–19ovaries 50, 58–59oxygen 31–33, 35–36,38, 52

pain 28pigment 55pins and needles 30placenta 52, 54plasma 38–39pregnancy 50–54puberty 58–59pulmonary artery 34–37pulmonary vein 34–37

rectum 40–41red blood cells 38–39reflex 30reproductive system 50,58respiratory system 31–33retina 7–9ribcage 21, 33

sacrum 21saliva 12–15sebaceous gland 16, 26senses 5, 7–12, 14, 16,18–20, 27, 28–30, 57shaft, hair 16–17shin 49sign language 46skeleton 21–22skin 26–27skull 6, 18, 22 smell 10–12

smile 13, 25smoking 61sneeze 36sound waves 19–20speech 5, 14sperm 50spinal cord 28–30, 54spine 21stomach 21, 40–42sweat 16, 26, 47sweat duct 16, 26

taste 12, 14, teeth 13–15, 57testosterone 17, 48throat 13, 41tibia 48–49toenails 49tongue 10, 13, 14, 56toothpaste 15touch 30

umbilical cord 52ureter 44urine 43–44uterus 50, 53–55UV rays 27

vagina 54veins 34–38, 45, 52vocal cords 59vomiting 41

waste 41, 43–44, 52womb 50–55, 58wrinkles 59

yawning 33

INDEX

Picture credits

Main illustrations by Meme Design and Stephen Sweet.Additional Photography and illustrations by Beehive Illustrations,

Sushumu Nishinaja and the Science Photo Library.

How does the eye work? What donerves do? Why do people yawn? Howmany bones are in the human body?

Bursting with bite-sized facts, illustrations anddiagrams, this engaging 64-page book containsanswers to all the questions you always wanted

to ask about the human body – and more!

No question is too tough, no answer toodifficult to explain – Focus On are the

ultimate in addictive reading.

Published by Top That! Publishing plcCopyright © 2010 Top That!Publishing plcTide Mill Way, Woodbridge,Suffolk, IP12 1AP, UKwww.topthatpublishing.comTop That! is a registered trademark of Top That! Publishing plcAll rights reserved.0 2 4 6 8 9 7 5 3 1