Steve.parker.just.the.facts.human.body.2006.Retail.ebook Distribution

8/2/2019 Steve.parker.just.the.facts.human.body.2006.Retail.ebook Distribution

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INFORMATION AT YOUR FINGERTIPS


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HUMAN

BODY


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CONTENTS

s edition published in the United States in 2006 by School Specialty Publishing, a member of the School Specialty Family.

pyright ticktock Entertainment Ltd 2005 First published in Great Britain in 2005 by ticktock Media Ltd. Printed in China.

rights reserved. No part of this book may be reproduced, stored in a central retrieval system, or transmitted in any form or by

means,electronic, mechanical, photocopying, recording, or otherwise,withouth the prior written permission of the publisher.

tten by Steve Parker.

rary of Congress-in-Publication Data is on file with the publisher.

d all inquiries to:

ool Specialty Publishing

0 Orion Place

umbus, OH 43240-2111

N 0-7696- 4255-1

3 4 5 6 7 8 9 10 TTM 11 10 09 08 07 06

HOW TO USE THIS BOOK ....................................................................................4

BODY SYSTEMS................................................................................................................6 Integumentary Muscular Skeletal Nervous Sensory Respiratory Circulatory Digestive Urinary Reproductive Hormonal Lymphatic Immune

THE SKIN ..................................................................................................................................8 Sense of touch Fingertips Sweat Layers of the skin Microsensors Shed skin Skin thickness Main tasks of the skin Size of the skin

HAIR AND NAILS ....................................................................................10 Nail parts Growth of nails Hair thickness Structure of a hair Eyebrows Eyelashes Growth of hair Hair life cycle Why have hair? Why have nails?

MUSCLES & MOVEMENT ...................................................................................12 Types of muscle Muscle used for facial expressions Inside a muscle Power of muscles How muscles work

Muscle recordsTHE SKELETON ...............................................................................................................14

Size and variation The coccyx Cartilage Bone strength Tasks of the skeleton Number of bones

BONES AND JOINTS ...............................................................................................16 Parts of a bone What a bone contains Bone records Ligaments Synovial fluid The knee joint Different types of joint Head movements

THE NERVOUS SYSTEM ......................................................................................18 Parts of the nervous system Nerve cells Nerve signals Spinal cord Nerve lengths

THE BRAIN..........................................................................................................................20 The cortex Energy requirements Blood supply to the brain Brain parts Size of the brain Sleep Left and right Brain development through life

EYES AND SIGHT ........................................................................................................22 Parts of the eye How the eye sees Cones Blind spot Moving the eye Blinking

EARS AND HEARING ..............................................................................................24 How we hear Sections of the ear Bones in the ear Pitch Sense of balance Stereo hearing Ear measurements The loudness of sounds

NOSE AND TONGUE ................................................................................................26 How we smell Parts of the nose Parts of the tongue How we taste Other tasks of the tongue

TEETH AND JAW ..........................................................................................................28 Numbers of teeth Parts of a tooth Plaque When teeth grow Chewing Roof of the mouth Saliva

LUNGS AND BREATHING ..................................................................................30 Size and shape of the lungs Gases used Breathing rates Parts of the lungs The voicebox Speech

THE HEART .........................................................................................................................32 Parts of the heart Hearts blood supply Hearts job The pulse Changing pulse rate through life How the heart works Size and shape Typical day

CIRCULATORY SYSTEM .................................................................... Veins and arteries Using oxygen Types of blood vessels Size and length of blood vessels Journey times of blood Blood pressure in blood vessels

BLOOD ...................................................................................................................

Blood flow Amount of blood in the body Blood types Red blood cells What is in blood?

DIGESTION ........................................................................................................ The digestive tract Digestive juices Length of foods journey Faeces Stomach Appendix Small intestine Large intestine

FOOD AND NUTRIENTS ....................................................................

Food groups Daily needs Carbohydrates Fats and oils Proteins Fiber Fruit and vegetables Vitamins Mineral

LIVER AND PANCREAS .....................................................................

Tasks of the liver Gall bladder Bile Blood supply to the Liver of young children Jaundice Shape of the liver Shape of the pancreas

KIDNEYS AND URINARY SYSTEM ....................................... Size and shape of kidneys Parts of the kidney Nephrons Urinary parts Size of the bladder Male and female syste Filtering the blood

GENES..................................................................................................................... DNA Chromosomes Genes Inherited characteristics Genetic fingerprinting Clones

REPRODUCTION ..................................................................48 Size and shape of female reproductive parts Female parts Egg release cycle Eggs and sperm Male parts Size and shape of male reproductive parts

STAGES OF LIFE .....................................................50

Growth rates How an egg is fertilized Embryo Fetus New baby Puberty Aging

HORMONES ............................................................52 Thyroid Parathyroid Pituitary Pancreas Thymus Adrenals Adrenaline

Other hormone making partsLYMPH AND IMMUNESYSTEMS ................................................................54 Lymph nodes Lymph fluid Lymphocytes How the immune system works Types of immunity

DISEASES AND MEDICINES .......................56 Types of medicines Medical drugs Causes of illness and disease Bacteria Viruses Protists Microfungi Medical specialists

GLOSSARY ....................................................................58

INDEX .................................................................................60


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Your body cant digest food with just its digestive tract (passageway)

mouth, gullet, stomach and intestines. Also needed are two parts

called the liver and pancreas. These are next to the stomach and

they are digestive glands, which means they make powerful substancesto break down food in the intestines. Together with the digestive tract,

the liver and pancreas make up the whole digestive system.

Most body parts are supplied withblood flowing along one or a fewmain arteries.

The liver has a main artery, thehepatic artery.

The liver also has a second andmuch greater blood supply.

This comes along a vessel calledthe hepatic portal vein.

The hepatic portal vein is theonly main vein that does nottake blood straight back tothe heart.

It runs from the intestines tothe liver, bringing blood full ofnutrients from digestion.

W H A T I S T H E

L I V E R ?

The liver is the largestsingle part or organ insidethe body.

Wedge-shaped, dark red incolour.

Typical weight 1.5 kg.

Depth at widest part on right side15 cm.

Has a larger right lobe andsmaller left lobe.

Lobes separated by a stronglayer, the falciform ligament.

The gall bladder is asmall storage bag underthe liver.

It is 8 cm long and 3 cm wide.

Some of the bile fluid made inthe liver is stored in the gallbladder.

The gall bladder can hold upto 50 millilitres of bile.

After a meal, bile pours fromthe liver along the main bile

duct (tube), and from the gallbladder along the cystic duct,into the small intestine.

Bile helps to break apartor digest the fats and oilsin foods.

The liver makes up to onelitre of bile each day.

The liver has more than 500known tasks in the body and probably more thathavent yet been discovered.Some of the main ones are:

Breaking down nutrients andother substances from digestion,brought direct to the liver fromthe small intestine.

Storing vitamins for times whenthey may be lacking in food.

Making bile, a digestive juice.

Breaking apart old, dead, worn-out red blood cells.

Breaking down toxins orpossibly harmful substances,like alcohol and poisons.

Helping to control the amount ofwater in blood and body tissues.

If levels of blood sugar(glucose) are too high,hormones from the pancreas tellthe liver to change the glucoseinto glycogen and store it.

If levels of blood sugar(glucose) are too low,hormones from the pancreas tellthe liver to release the glycogenit has stored.

THE LIVERS TASKS

Most babies and youngchildren have bigtummies (abdomens).This is partly becausetheir liver is much larger,in proportion to thebodys overall size, thanthe liver of an adult.

An adult liver is usually

1

40thof total body weight.

A babys liver is nearer120th

of total body weight.

Pancreas has two main jobs.

One is to make hormones.

The other is to make digestivechemicals called pancreaticjuices.

These juices contain about 15powerful enzymes that breakapart many substances infoods, including proteins,carbohydrates and fats.

Pancreas makes about 1.5litres of digestive juices daily.

During a meal these passalongthe pancreaticduct tubesinto the small intestine, toattack and digest foods there.

HOW THEPANCREAS WORKS

The liver is so busy withchemical processes and tasksthat it makes lots of heat.

When the body is at rest and themuscles are still, the liver makes

up to one-fifth of the bodys totalwarmth.

The heat from the liver isntwasted. The blood spreads out theheat all around the body.

Fatty foods, such as chips,are broken apart by enzymes

made in the pancreas.

WARM LIVER

See pages34-35 for informationon the circulatory system.

LIVER & PANCREAS

Theliveris intheupperabdomen,behind

thelower right ribs.Thepancreas is in theupper left abdomen,behindthe stomach.

WHERE INTHE BODY?

W H A T I S T H E

PANCREAS?

The pancreas is a long,

slim, wedge- or triangular-shaped part.

It is soft, greyish-pink in colour. Typical weight 0.1 kg.

Typical length 15 cm.

Has three main parts: head(wide end), body (middle) andtail (tapering end).

See pages36-37forinformationon the blood.

By the time a babybecomes a toddler, theirliver isnt such a largeproportion of their totalbody weight.

See page 52forinformationon hormones.

One of the livers main functions is to break down nutrients forthe body. This means the liver has a unique blood supply.

A yellowish tinge to theskin and eyes is known as

jaundice, and it is often a signof liver trouble.

Usuallythe l iverbreaksdownoldred blood cellsand getsrid of the

colouringsubstance inbile fluid.

Ifsomethinggoeswrongthe colouring

substance buildsup inblood and skin

and causesjaundice.Hepatitis,aninfectionof the l iver,can

cause jaundice.

WHEN THINGSGO WRONG

Alcohol is a toxin whichthe liver breaks down andmakes harmless. Too much

alcohol can overload the liverand cause a serious disease

called cirrhosis.

GALL BLADDERAND BILE

BABY LIVER

UNUSUAL SUPPLY

liver

liver

pancreas

liver

pancreas

gall bladder

Mouth,teeth,throat,gullet,stomach,intestines,rectumandanusmakeupthedigestivepassagewayortract.

Liver,gallbladderandpancreasplusthetractmakeupthewholedigestivesystem.Breaksdownordigestsfoodintonutrientstinyenough

totakeintothebody.Getsrid ofleftoversassolid wastes(bowelmotions,faeces).Nutrientsprovide energyforalllife processesand raw

materialsforgrowth,maintenance and repairingeverydaywear-and-tear.

DIGESTIVE SYSTEM

About640skeletalmusclesalloverthe body,mostlyattached tobones(skeletalorvoluntary

muscle).Muscle layersinthe walls

ofinnerpartslike thestomachand intestines

(visceralorinvoluntarymuscle).

Muscle inthe wallsofthe heart(heart muscle ormyocardium).

Musclesgetshorterorcontracttoproduce allformsofbodily

movement.Sometimescombined withbonesand jointsasthe musculoskeletalsystem.

Nose,windpipe,mainchestairwaysand lungs.

Obtainsessentialoxygenfrom the airaround,and passesittothe blood fordistribution.

Getsrid ofwaste carbondioxide,whichwould be

poisonousifitbuiltupinthe blood.

Usefulextrafunction istheabilitytomake

vocalsoundsand speech.

Heart, blood vessels and blood. Heart provides pumping power to send blood all around

the body. Blood spreads vital oxygen, nutrients, hormones and

many other substances to all body parts. Blood collects wastes and unwanted

substances from all body parts. Blood clots to seal wounds

and cuts. Closely involved with the

immune system in self-defence and fightingdisease.

CIRCULATORY (CARDIOVASCULAR ) SYSTEM

Lymphvessels,lymphnodes(glands),lymphductsand lymphfluid.

Gathersgeneralbodyfluidsfrom betweencellsand tissues.

One-wayflowchannelsfluid throughlymphnetwork ofnodesand vessels.

Helpstodistribute nutrientsandcollectwastes.

Lymphfluid emptiesintoblood system.Closelylinked withimmune system.

Defends the body against invadingdangers such as bacteria, virusesand other microbes.

Gets rid of debris in tissues fromnormal wear-and-tear.

Helps recovery from diseaseand illness.

Helps repair of injury and normal wear-and-tear. Keeps watch for problems and disease processes arising

inside the body, such as malignant (cancerous) cells.

Onlysystem whichdifferssignificantlyinfemalesand males.Onlysystem whichisnotworkingatbirth,butstartstofunction

atpuberty.Male system producessperm cellscontinually,millionsperday.Female system producesripe eggcells,aboutone every28days,duringmenstrualcycle.

Ifeggcelljoinssperm cellto form anembryo,female systemnourishesthisasitgrowsintoa babyinside the womb.

The body is often divided into body systems,

each one of which performs a certain job.

Body systems are made from microscopic

building blocks called cells. A typical cell is only

0.03 mm across, and there are about 50 million

million cells in the body. There are many different

kinds of cells, like nerve cells, muscle cells and so on. Many

cells of the same kind form a tissue, such as nerve tissue or fat tissue.

Different kinds of tissue make up a main part of the body, known as

an organ, like the brain, stomach or kidney. Several

organs working together to carry out one major

task or function, like digesting food, are known

as a body system. About a dozen major systems

make up the whole human body.

Eyes, ears, nose, tongue and skinmake up the five main sets ofsense organs. Also sensors inside the body fortemperature, blood pressure,

oxygen levels, positions of joints, amountof stretch in muscles and many other changes.

Gravity and motion sensors in the inner earcontribute to the process of balance.

Sometimes included as part of the nervoussystem, since the main sense organs are ineffect the specialized endings of sensorynerves.

Kidneys,ureters,bladderand urethra.Filtersblood togetrid of unwanted substancesand wastes.Formsunwanted substancesand wastesinto

liquid waste orurine.Storesurine,thenreleasesitto

the outside.Controlsamount and concentration

ofblood and bodyfluids,waterbalance,byadjustingamountofwaterlostinurine.

About10mainpartscalled endocrine orhormone-makingglands.

Some organswithothermaintasks,like thestomachand heart,alsomake hormones.

Hormonesspread around the bodyinblood.Closelylinked tonervoussystem forcoordinated

controlofinnerbodyprocesses.Closelylinked withreproductive system and

controlsitbysexhormones.

Skin,hairand nails.Protectsoftinnerpartsfromphysicalwear

and knocks,dirt,water,sunsraysand

otherharm.Skinkeepsinessentialbodyfluids,

saltsand minerals.Helpstocontrolbodytemperature

bysweatingand flushingtoloseheat,orgoingpale withgoosebumps toretainheat.

Providessense oftouch(seeSensorysystem).

Getsrid ofsmallamountsofwastesubstances,insweat.

Brain,spinalcordandperipheralnerves.Controlsandcoordinatesallbodyprocesses,frombreathingandheartbeatto

makingmovements.Allowsmentalprocessessuchasthoughts,recallingmemoriesandmakingdecisions.Sensorynervesbringinformationfromthesenseorgansandothersensors.

Motornervescarryinstructionstomusclesaboutmovement,andtoglandsaboutreleasingtheirproducts.

Worksalongwiththehormonalsystem.

208bonesand the variouskindsofjointsbetweenthem.Givesphysicalsupporttoholdup the bodyssoft,floppyparts.Givesprotectiontocertain

bodypartslike the brain,eyes,heart,lungs.Pulled bymuscles,toallow movement.

Actsasa store orreservoirofvaluable mineralslike calcium,incase these are inshortsupplyinfood.

Sometimescombined withmusclesasthemusculoskeletalsystem.

RESPIRATORY SYSTEM

BODY SYSTEMSINTEGUMENTARY

SYSTEMSENSORY SYSTEM

URINARY SYSTEM

LYMPHATIC SYSTEMNERVOUS SYSTEM

HORMONAL (ENDOCRINE) SYSTEM

IMMUNE SYSTEM

REPRODUCTIVE SYSTEM

MUSCULAR SYSTEM

6 7

SKELETAL SYSTEM

medulla of the kidney, or theadrenal medulla of theadrenal gland.

MeningesThree thin layerscovering the brain and spinalcord, and also making andcontaining cerebrospinalfluid. They are known as thedura mater, arachnoid andpia mater.

MeiosisPart of special typeof cell division, when thechromosomes are not copiedand only one set (not adouble-set) moves intoeach resulting cell.

MetabolismAll of thebodys thousands of chemicalprocesses, changes andreactions, such as breakingapart blood sugar to releaseenergy, and building upamino acids into proteins.

MineralA simple chemicalsubstance, usually a metalsuch as iron or calcium, ora salt-type chemical such asphosphate, which the bodyneeds in small quantities infood to stay healthy.

MitosisPart of normalcell division, when thechromosomes have beencopied and one full double-set moves into each resultingcell.

Motor nerve A nerve thatcarries messages from thebrain to a muscle, telling itwhen to contract, or to agland, telling it when torelease its content.

MucusThickish, sticky, slimysubstance made by manybody parts, often forprotection and lubrication,such as inside the nose andwithin the stomach.

Myo- To do with muscles,such as myocardium or heartmuscle.

NephronMicroscopicfiltering unit in the kidney forcleaning the blood.

NeuronA nerve cell, thebasic unit of the nervoussystem.

OlfactoryTo do with thenose and smell.

Optic To do with the eye,especially the optic nervecarrying messages from theeye to the brain.

PapillaeSmall lumps,bumps or pimples on abody part such as thetongue.

Peripheral nerves Thebodywide network of nerves,excluding the central nervoussystem of brain and spinalcord.

PeristalsisWave-likecontractions of muscles in thewall of a body tube, such asthe small intestine, ureter(from kidney to bladder)or oviduct (from ovary towomb).

PulmonaryTo do with thelungs.

Renal To do with thekidneys.

SebumNatural waxy-oilysubstance made in sebaceousglands associated with hairfollicles that keeps skinsupple and fairly waterproof.

Sensory nerveA nervethat carries messages to thebrain from a sense organ orpart, such as the eye, theear, the tiny stretch sensors inmuscles and joints, and theblood pressure sensors inmain arteries.

SkeletalTo do with theskeleton, the 206 bones thatform the bodys supportinginner framework.

SystemIn the body, aset of major parts ororgans that all worktogether to fulfil onemain task, such asthe respiratorysystem, which

transfers oxygen from the airaround to the blood.

Tendon The string, fibrous,rope-like end of a muscle,where it tapers and joins to abone.

ThoracicTo do with thechest, which is also calledthe thorax.

ThrombosisThe process ofblood going lumpy to form aclot, which is also known asa thrombus.

TissueA group of verysimilar cells all doing thesame job, such as muscletissue, adipose or fat tissue,epithelial (covering or lining)tissue, connective tissue(joining and filling in gapsbetween other parts).

ValveA flap, pocket orsimilar part which allowsa substance to passone way but notthe other.

AbdomenThe lower partof the main body or torso,below the chest, whichcontains mainly digestive andexcretory (waste-disposal)parts, and in females,reproductive parts.

ArteryA blood vessel (tube)which conveys blood awayfrom the heart.

AxonThe verylong, thinpartofanerve cell or neuron,also calledanerve fibre.

BladderBag-like sac orcontainer for storing fluids.The body has several,including the urinarybladder (often just called thebladder) and gall bladder.

Blood sugar Also calledglucose, the bodys mainenergy source, used by allits microscopic cells to carryout their life processes andfunctions.

CapillaryThe smallest typeof blood vessels, usually lessthan one millimetre long andtoo thin to see except througha microscope.

CardiacTo do with theheart.

CartilageTough, light,slightly bendy andcompressible bodysubstance, often calledgristle, which forms partsof the skeleton such as theears and nose, and alsocovers the ends of bonesin joints.

Cell The basic microscopicbuilding block of the body,a single living unit, with mostcells being 0.01-0.05 mmacross. The body containsover 50 million million cells.

Central nervous systemThe brain and spinal cord.

CerebralTo do with thecerebrum, the largest partof the brain which forms itswrinkled domed shape.

Cerebrospinal fluid Liquidsurrounding the brain andspinal cord, to protect andcushion them as well as helpprovide nourishment andtake away wastes.

CiliumMicroscopic hair,usually sticking out fromthe surface ofa cell, which canwave or bend, andperhaps sensesubstances as in the

olfactory epithelium ofthe nose and in the tastebuds on the tongue. (Plural:cilia.)

CloneA living thing withexactly the same genes asanother living thing.

CollagenTiny, tough, strongfibres found in body partssuch as skin and bones.

CortexThe outer part orlayer of a body part, suchas the renal cortex of thekidney, or the cerebralcortex of the brain.

CraniumThe upper domedpart of the skull or braincase, which covers andprotects the brain.

Cermis The inner layer ofskin, under the epidermis(see below), which containsthe touch sensors, hairfollicles and sweat glands.

DNA De-oxyribonucleicacid, the chemical substancethat forms the geneticinformation or genes.

EmbryoThe name for adeveloping human body,from fertilization as asingle cell, to eight weekslater.

EndocrineTo do withhormones and the hormonalsystem (seehormone).

EnzymesSubstanceswhich alter the speed of achemical change or reaction,usually speeding it up, butwhich remain unchangedthemselves at the end ofthe reaction.

EpidermisThe protectiveouter layer of skin, which isalways being worn away butcontinually replacing itself.

ExcretoryTo do withremoving waste substancesfrom the body. The mainexcretory system is made upof the kidneys, bladder andtheir linking tubes.

FertilizationWhen an eggcell joins a sperm cell to startthe development of a newhuman body.

FetusA developing humanbody from eight weeks afterfertilization until birth.

FoveaThe small area in theretina of the eye where visionis most detailed and clearest,due to the great number ofcone cells.

GastricTo do with thestomach.

GlandA body part thatmakes a substance orproduct which it thenreleases, such as the tearglands which make tear fluidfor the eyes, and the sweatglands in the skin.

GlucoseSeeblood sugar.

GustatoryTo do with thetongue and taste.

HepaticTo do with the liver.

HormoneA naturalchemical messengers thatcirculates in the blood andaffects how certain bodyparts work, helping thenervous system to controland coordinate all bodyprocesses.

Humour Old word used todescribe various body fluids,still used in some cases, forexample, to describe thefluids inside the eye, thevitreous (glassy) humourand aqueous (watery)humour.

ImmunityProtection orresistance to microbialgerms and other harmfulsubstances.

IntegumentaryConcerning the skin andother coverings, includingnails and hair.

LigamentA stretchy, strap-like part that joins the bonesaround a joint, so the bonesdo not move too far apart.

Medulla The inner orcentral region of a bodypart, such as the renal

GLOSSARY

58

HOW TO USE THIS BOOK

JUST THE FACTS, HUMAN BODY is a quick and easy-to-use way to look up facts about the

systems that control how our bodies work. Every page is packed with cut-away diagrams, charts,

scientific terms and key pieces of information. For fast access to just the facts, follow the tips on

ese pages.

TWO QUICK WAYS

TO FIND A FACT:

Look at the detailed CONTENTS list onpage 3 to find your

topic of interest.

rn to the relevantge and use the BOX HEADINGS to find theormation box you need.

Turn to the INDEX that starts on page60 and search for key words relating toyour research.

he index will direct you to the correct page,nd where on the page to find the fact

you need.

GLOSSARY A GLOSSARY of words and termused in this book begins on page 5

The glossary words provideadditional information to suppleme

the facts on the main pages.

JUST THE FACTSEach topic box presents the facts youneed in short, quick-to-read bullet points.

WHERE IN THE BODY?An at-a-glance look at where thepart of the body can be found.

PICTURE CAPTIONSCaptions explain whatis in the pictures.

EXTRA INFORMATIONThe black box on the right handside of the page explains a newaspect of the main topic.

67 Body Systems 5859 Glossary

LINKS

Look for the purple links throughoutbook. Each link gives details of othepages where related or additional facan be found.

3

............................................................45

............................................................67

NervousSensoryary Reproductive

............................................................89

LayersoftheskinnessMain tasksoftheskin

............................................1011

cknessStructureofa hairHair lifecycle

......................................................12-13

expressionswmuscles work

.....................................................14-15

lageBonestrengthes

......................................................16-17

sBonerecords Ligamentsrent typesofjoint

......................................................18-19

sNerves ignals

.....................................................20-21

od supplytothebrainLeft and right

......................................................22-23

nes Blind spot

......................................................24-25

esin theear Pitchmeasurements

......................................................26-27

rtsofthetonguee

......................................................28-29queWhen teeth grow

....................................................3031

Breathing ratesech

....................................................3233

lyHeart sjob Thepulsewtheheart works

CIRCULATORY SYSTEM.............................................................................34-35Veinsand arteriesUsing oxygen Typesofblood vesselsSizeand length ofblood vesselsJourneytimesofbloodBlood pressurein blood vessels

BLOOD...........................................................................................................................36-37Blood flowAmount ofblood in thebodyBlood groupsRed blood cellsWhat is i n b lood?

DIGESTION ...............................................................................................................38-39Thedigestivetract DigestivejuicesLength offoodsjourneyFaecesStomachAppendix Small intestineLargeintestine

FOOD & NUTRIENTS ....................................................................................40-41Food groupsDailyneedsCarbohydratesFatsand oilsProteinsFibreFruit and vegetablesVitaminsMinerals

LIVER AND PANCREAS ..............................................................................42-43Tasksoftheliver Gall bladder BileBlood supplytotheliverLiver ofyoung children JaundiceShapeoftheliverShapeofthepancreas

KIDNEYS & URINARY SYSTEM .......................................................44-45Sizeand shapeofkidneysPartsof thekidneyNephronsUrinarypartsSizeof thebladder Maleand femalesystemsFiltering theblood

GENETICS ...................................................................................................................46-47DNAChromosomesGenes Inherited characteristicsGeneticfingerpri nting Clones

REPRODUCTION .......................................................48-49Sizeand shapeoffemalereproductivepartsFemalepartsEgg releasecycleEggsand sperm MalepartsSizeand shapeofmalereproductiveparts

STAGES OF LIFE...........................................50-51

Growth ratesHowan egg i sfertilizedEmbryoFetusNewbaby PubertyAgeing

HORMONES ..................................................52-53Thyroid ParathyroidPituitaryPancreasThymusAdrenalsAdrenalineOther hormonemaking parts

LYMPH & IMMUNESYSTEMS ......................................................54-55Lymph nodesLymph fluid LymphocytesHowtheimmunesystem worksTypesofimmunity

DISEASES & MEDICINES ...................5657Typesofmedici nesMedical drugsCausesofil lnessand diseaseBacteriaVirusesProtists Micro-fungiMedical specialists

GLOSSARY..........................................................58-59

INDEX......................................................................6064

CONTENTS

veu c es ourneyFaecesStomach

mall intestine Largeintestine

& NUTRIENTS ....................................................................................4od groups Dailyneeds CarbohydratesFats and oils

Proteins Fibre Fruit and vegetables VitaminsMinerals

LIVER AND PANCREAS..............................................................................42-43Tasksof theliver Gall bladder Bile Blood supplyto theliverLiver ofyoung children Jaundice Shape ofthe liverShapeofthepancreas

KIDNEYS & URINARY SYSTEM .......................................................44-45Sizeand shapeofkidneysPartsofthekidneyNephronsUrinaryparts Sizeofthebladder Maleand femalesystemsFiltering theblood

GENETICS...................................................................................................................46-47DNA Chromosomes Genes Inherited characteristics

Geneticfingerprinting Clones

RODUCTION.......................................................48-49nd shapeof femalereproductiveparts

arts Egg releasecyclem Maleparts

alereproductiveparts

ms apple 31dnine 46anoids (pharyngealnsils) 54a, 54c-d

enal glands 53c, 53denaline (epinephrine)6b, 52b-d, 53c, 53dng 51dhol 21d, 42a-csterone 53ces 47a-cgies 56b, 56c-doli 31a-cno acids 41amonia 44a-diotic fluid 50a-desthetics 56a, 57desthetist 57dgesics 56aes 15demetics 56bnflammatories 56b

biotic drugs 56b, 57abodies 37d, 54b,5a-c, 55dcoagluants 56bconvulsants 56bdepressants 56bdiuretic hormone (ADH)2c-dungal 56bgens 55a-c, 55dhistamine 56bpyretic 56bseptic 56btoxin 56bviral 56b

nus 6-7c, 38a, 39a-canvil bone (incus) 24aaorta 33d, 34a-b,

34c-daortic valve 33a-c,

33dappendix 38a,39d

aqueous humour23a-c

arms 15darteries 20a, 33a-c,

34, 35, 36a, 43b-c,44b-d

arterioles 35a-c, 35d,36b

artificial acquiredimmunity 55dscorbic acid (Vitamin

C) 40b, 41dasthma 56bastigmatism 23catlas vertebra 16c-datria, heart 33a-c, 33datriopeptin 53a-cauditory nerve 25a-cauricle (pinna) 24a

auricularis muscle 12a-dautoimmune problems56c-d

autonomic nerve system18b

axillary hair 10b-daxis 16c-daxons 18c-d, 19a-b, 19c,

20b-c

B

babies 14b-c, 15a-b, 50-1bacilli 57abackbone 15dbacteria 6-7c, 45a-c, 55a-

b, 55c, 56b, 57abacterial infections 57abalance 6-7c, 24a-dball-and-socket joint 17dbeta-blocker 56abile 42a-c, 42d, 43abladder 44b-d, 45a-cblastocyst 50b-dblinking 23cblood 15a-c, 16a, 34b-d,

36-7, 40a, 45dclotting 6-7b, 36c-d, 37d,

40a, 56a, 56bblood groups 36c-dblood pressure 21a-c, 35a-

c, 40c-d, 53a-c, 56ablood sugar (glucose) 12a,

20a, 30b-d, 37d, 40c-d,42a-c, 53

blood transfusions 36c-dblood vessels 34a, 34b- d,

36b-d, 53d, 56abody salts 37d, 53a-cbody systems 6-7

see alsonamed systemsbone marrow 15a-c, 16a,

37a-cbones 6-7a, 16-17, 40a,

41asee alsonamed bones

bowel motions 6-7c, 39b-cBowmans capsule 44a-dbrain 6-7a, 18a, 18b-d,

20-1, 24c-d, 37a-b,52b-d

breastbone 15dbreathing 21a-c, 30-1,

40c-d, 53dbronchi 31a-cbronchioles 31a-c, 56abronchodilator 56abuccinator muscle 12a-d

C

caecum 39dcalcaneal (Achilles) tendon

13dcalciferol (Vitamin D) 9d,

41dcalcitonin 52acalcium 15a-c, 16b-d, 40a,

40b, 41c, 52a, 52bcalcium carbonate 16b-dcalcium phosphate 16b-dcancers 56c-dcapillaries 35a-c, 35d,

36acarbohydrates 40, 43acarbon dioxide 6-7a,

31a-c, 37dcarbonate 16b-dcardiac muscle

(myocardium) 12b-d,32c-d, 33a-c

cardiologist 57dcardiovascular system

6-7b, 34-5carotene (Vitamin A) 41dcarotid artery 20acartilage 15a-b, 17a-c,

17dcells 6-7a, 40, 49a-c,

50b-dsee alsonamed types ofcell

cellulose 40b-dcerebellum 21a-ccerebral cortex 20b-c,

21a-ccerebral vessels 35a-ccerebrospinal fluid (CSF)

19a-b, 21a-bcerebrum 21a-ccervical vertebrae 15d,

16c-dcervix 48b, 48c-dchemosenses 26b-dchemotherapy 56achewing 29dchloride 40b

INDEX

A

abdomen 43b-caccidents 56c-dAchilles (calcaneal) tendon

13dids 39a-cuired immunity 55d

3a-cunity 55d

Adams apple 31d

adenine 46aadenoids (pharyngealtonsils) 54a, 54c-d

adrenal glands 53c, 53dadrenaline (epinephrine)

36b, 52b-d, 53c, 53dageing 51dalcohol 21d, 42a-caldosterone 53calleles 47a-callergies 56b, 56c-dalveoli 31a-camino acids 41aammonia 44a-damniotic fluid 50anaesthetics ,an

aaaaaa

Thelettersa, b,c, d,following

thepagenumberindicate thecolumn(letteringfromlefttoright)inwhich theinformationmaybefoundonthatpage.

I

INTRODUCTION TO TOPIC

BOX HEADINGSLook for heading words linked to yourresearch to guide you to the right fact box.

CUTAWAY DIAGRAMSClear, accurate diagrams show howthe parts of the body fit together.

See pages 3637 forinformation on the blood.


5/35

Mouth, teeth, throat, esophagus, stomach, intestines, rectum, and anus make up the digestivepassageway or tract.

Liver, gall bladder, and pancreas are also part of the digestive system. Digests food into nutrients tiny enough to take into the body. Gets rid of leftovers as solid wastes. Nutrients provide energy for all life processes and

raw materials for growth, maintenance, and repairingeveryday use.

DIGESTIVE SYSTEM

About 640 skeletal muscles all overthe body, mostly attached tobones (skeletal or voluntary

muscle). Muscle layers in the walls

of inner parts like thestomach and intestines

(visceral orinvoluntary muscle).

Muscle in the walls of the heart(heart muscle or myocardium).

Muscles contract to produce allforms of bodily movement.

Sometimes combined with bonesand joints as the musculoskeletal

system.

Includes the nose, windpipe, main chestairways, and lungs.

Obtains essential oxygen from the air aroundand passes it to the blood for distribution.

Gets rid of waste carbondioxide, which would be

poisonous if it built upin the blood.

Also provides theability to makevocal sounds

and speech.

The heart, blood vessels, and blood. The heart provides pumping power to sen

around the body. Blood spreads vital oxygen, nutrients, hor

and other substances to all body parts. Blood collects wastes and unwanted

substances from all body parts. Blood clots seal wounds

and cuts. Closely involved with the

immune system for fightingdisease.

CIRCULATORY (CARDIOVASCULAR

The lymph vessels, lymph nodes (glands), lymphducts, and lymph fluid.

Gathers general body fluids from betweencells and tissues.

One-way flow channels fluid through thelymph network of nodes and vessels.

Helps to distribute nutrients andcollect wastes.

Lymph fluid empties into blood system. Closely linked with to immune system.

Defends the body against invadingdangers such as bacteria, virusesand other microbes.

Gets rid of debris in tissues fromnormal use.

Helps the body recover fromdisease and illness.

Helps repair injuries and normal use. Keeps watch for problems and disease proces

inside the body, such as malignant (cancerous

The only system which differs significantly in females and males. The only system which is not working at birth, but starts to

function at puberty. The male system produces sperm cells continually,millions per day. The female system produces egg cells, about one every 28

days, during the menstrual cycle. If an egg cell joins a sperm cell to form an embryo, the female

system nourishes this as the egg grows into a baby inside the womb.

The body is often divided into body systems.

Each system, though performing specific

jobs, works together with the other syst ems.

Body systems are made from microscopic building

blocks, called cells. A typical cell is only 0.011 inches

across. There are about 10 trillion cells in the body.

There are many different kinds of cells, such as nerve cells

and muscle cells. Many cells of the same kind form tissue, such as nerve

and muscle tissue. Two or more different kinds of tissue create an organ,

like the brain, stomach, or kidney. Several organs working

together to carry out one major function, such as

digesting food, are known as a body system.

The eyes, ears, nose, tongue, andskin make up the five main sets ofsensory organs. Sensors inside the body monitorfor temperature, blood pressure,

oxygen levels, positions of joints, amountof stretch in muscles, and many other changes.

Gravity and motion sensors in the inner earcontribute to the process of balance.

Sometimes included as part of the nervoussystem, since the main sense organs are ineffect the specialized endings of sensorynerves.

The kidneys, ureters, bladder, and urethra. Filters blood to get rid of unwanted substances and

Forms unwanted substances and wastes intoliquid waste or urine.

Stores and releases urine. Controls amount and concentration

of blood and body fluids, calledwater balance, by adjusting amountof water lost in urine.

About ten main parts called endocrineor hormone-making glands.

Some organs with other main tasks, like thestomach and heart, also make hormones.

Hormones spread around the body in blood. Closely linked to the nervous system for

coordinated control of inner-body processes. Closely linked with reproductive system..

The skin, hair,and nails. Protectsinternal organs

from physicalwear, dirt, water,

suns rays, and harm. Skin keeps in essential body fluids,

salts and minerals. Helps to control body temperature

by sweating and flushing to loseheat, or going pale withgoosebumps to retain heat.

Provides sense of touch (seeSensory System).

Gets rid of small amounts of waste

substances in sweat.

The brain, spinal cord, and peripheral nerves. Controls and coordinates all body processes, from breathing and heartbeat, to

making movements. Allows mental processes, such as thoughts, recalling memories,and making decisions.

Sensory nerves bring information from the sense organs and other sensors. Motor nerves carry instructions to muscles about movement and to glands

about releasing their products. Works with the hormonal system.

208 bones and the variouskinds of joints between them. Gives physical support to holdup the bodys soft, floppy parts.

Gives protection to certainbody parts like the brain,

eyes, heart, lungs. Pulled by muscles,to allow movement.

Acts as a store or reservoirof valuable minerals like calcium,in case these are in short supplyin food.

Sometimes combined withmuscles as the

musculoskeletal system.

RESPIRATORY SYSTEM

BODY SYSTEMSINTEGUMENTARY

SYSTEMSENSORY SYSTEM

URINARY SYSTEM

LYMPHATIC SYSTEMNERVOUS SYSTEM

HORMONAL (ENDOCRINE) SY

IMMUNE SYSTEM

MUSCULAR SYSTEM SKELETAL SYSTEM

REPRODUCTIVE SYSTEM


6/35

Protection

Provides protectioand bumps.

Keeps out dirt, geliquids. like water

Shields the body fthe suns dangero(especially ultravioperhaps by going (suntan).

Keeps fluids in

Keeping in valuabfluids, minerals, a

Touch

Provides sense of

Temperature cont

Cools the body if too hot.

Keeps heat inside in cold conditions

Vitamin D

Produces an impovitami n D, that keehealthy.

Waste removal

Removes of some wproducts (through

Anti-germ layer

Produces germ-kilsubstances to formon skin.

MAIN TASKSS K

LAYERS OF THE SKIN

average patch of skin5 sq. in. (the size of a

gernail) contains:

5 million microscopic cells oft least 12 main kinds.

00 tiny holes, called pores, foreleasing sweat.

,000 micro-sensors of aboutix main shapes for detectingarious features of touch.

more than 100 hairs.

About 3.2 ft. of blood vessels.

About 20 in. of micronerves.

About 100 of the tiny glandshat make sebum, a natural

waxy-oily substance that

eeps skin supple and fairlywaterproof.

THE SKIN

When you look at yourself in the mirror, most of what you seeskin,

hair and nailsis not living. Just underneath this dead surface,

however, skin is very much alive, and very busy, tooas you know

if youre unlucky enough to scratch or cut yourself. Skin is the bodys largest

single organ. It has at least ten main tasks, which include providing your sense

of touch. It wears away every monthbut it replaces itself every month, too.

Your sense of touch or feelingis more complicated than itseems. It is not just a singlesense, detecting physical

contact. It is a multi-sensedetecting:

Light contact, such as a brushfrom a feather.

Heavy pressure, such as beingpushed or squeezed hard.

Cold, like an ice-cube.

Heat, such a hot water.

Movement, including tiny, fastvibrations. Your fingertip skin candetect vibrations that are toosmall for your eyes to see.

Surface texture, such as roughwood or smooth plastic.

Moisture content, from dry sandto wet mud.

Skin on the fingertips has morethan 465 microsensors per

square inch, to give themost sensitive touch.

It has more sweatglands that makea thin layer ofsweat on the skinthat helps you to gripbetter.

It also has tiny ridges or swirls togive even better grip. These formthe pattern of your fingerprints.

Every set of fingerprints for everyperson around the world is

differenteven betweenidentical twins.

The largest touch micro-sensorsare called Pacinian sensors.They have many layers like tinyonions and are up to 0.019 in.across. They detect hard pressure.

The smallest microsensors are 100times smaller and feel light touch.

MICROSENSORS

Area

A typical adul ts skin, taoff and ironed flat, wou6.5 sq. feetabout the

a single bed or a small

WeightThe weight of the skin6.68.8 lbs. for a typtwice as heavy as theorgan, the liver.

S I Z E O FS K

e skin is a tough but flexi bleayer that covers the entirebody. It helps to control

temperature and protectsternal organs from damage.

WHERE INTHE BODY?

al number of sweat glands 35 million

al length of tubes in all sweat glands stretched out

traight and joined end-to-end 31 miles

ount of sweat on average day 1017 fl. oz.

ount of sweat on a cold day 2.3 fl. oz.

SWEAT FACTS

Each minute about 50,000 tinyflakes of skin are rubbed off orfall from the body.

This loss is natural and is madeup by microscopic cells at thebase of the epidermis multiplyingrapidly.

This happens so fast that theepidermis replaces itself aboutevery month.

Over a lifetime the body shedsmore than 88 lbs. of skin.

Skin makes itself thicker where itis worn or rubbed more.On average:

Soles of feet - 0.2 in. or moreBack 0.10.15 in.Palms of hands - 0.080.15 in.Scalp on head - 0.06 in.Fingertips - 0.04 in.Average body 0.040.08 in.Eyelids - 0.019 in.

SKIN THICKNESS

epidermis

dermis

A thin layer ofsweat on the

fingertips helpsyou grip objects better.

Lowest layer - hypodermis

Contains mainly body fat, whichworks as a cushion against knocksand pressure.

Works as an insulator to keep inbody warmth.

Middle layer - dermis

Contains sweat glands, hair roots

(follicles), most of the microsensors

for touch, and tiny blood vessels

called capillaries.

Also contains fibers of thesubstances collagen for strengthand elastin for elasticity.

sensory nerve

blood vessels

body fat

A person can lose 10.515 pintsof sweat before the body suffers

from the loss of important saltsand minerals.

DANGEROUS SWEAT

Outermost layer - epidermis

Varies greatly in thickness from0.019 to more than 0.2 in.

If it has l ots of wear, such asusing hands often or walkingbarefoot, it can make itself twiceas thick as normal, for extraprotection. This is called a callus.

Microscopic cells at its base multiplyfast, fill with the tough substancekeratin, move outward, becomeflatter and die, and form the surfacelayer which is continually rubbedaway.

hair root

See pages 2223 forinformation on eye.

See pages 3637 forinformation on blood circulation.

SKIN MICROPARTS

TOUCH

Wearing warm clothes in winterhelps protect our skin from feeling the cold.

EXTRA SENSITIVE

SHED SKIN

0.2

0.1

hair shaft


7/35

HAIR GROWTH

N A I

WHY HAVE

A nail is a strongdead, flat plate mthe same dead sas hairs, keratin.acts as a flat, rigthe back of the f

Touch When you press ge

object, the fingertipbetween it and the

This makes it easierpressure and the haobject. Without a nfingertip would ben

Scratching You also use nails to

get rid of objects on

Hairs are glued-togetherrods of dead, flattened,microscopic cells filled withthe tough, hard bodysubstance, called keratin.

A hair grows at its root, whichis buried in a pocket-like pitin the skin, called the follicle.

Extra cells are added to theroot, which pushes the restof the hair up out of the skin.

The part of the hair above theroot is called the shaft.

Protection

Head hair protects aand bruises.

It also shields the toand the delicate brafrom heat or cold.

Warmth

Body hairs stand onyoure cold, each pumuscle attached to ithe erector pili musc

These goosebumpsbody helps to trap ain body warmth.

Safety Our hair can also st

when we feel frighteour body hairs wereprehistoric times, thalso made us look bmore impressive to

H A I

W H Y H A V

After this final slow down, theyusually fall out and are replacedby new hairs growing up fromthe same follicles in the skin.

This means, on average, about100hairs are lost from the headevery day.

In eyebrow hairs, the life cyclelasts about 20weeks.

In eyelash hairs, the life cyclelasts around 10weeks.

In scalp hairs, this life cycle lastsup to 5years.

HAIR & NAILS

Scalp hairs grow 0.0110.015in.each day, which is almost 0.5in.each month.

Eyebrow hairs grow slowly, only0.0005in. per day, reaching agreatest length of 0.2in.

Eyelash hairs grow at a similar rateto eyebrow hairs, but usually stopgrowing at 0.270.31in. long.

Hairs and nails, like the epidermis, the outer layer of skin, are dead.

Your body has hairs all over, except for a few places, like your

palms, the palm sides of your fingers, and the soles of your feet.

However, some hairs grow thicker and longer, and so we notice them more.

These are the hairs on the head, eyebrows, and eyelashes. As we grow up,

hairs also appear under the arms, called axillary hair, and between the legs.

Nail plateThe main flat part of the nail.

Free edgeThe end of the nail which you trim,not attached to the underlying finger or toe.

Nail bedThe underside of the nail plate, which isattached to the underlying flesh but slidesslowly along as it grows.

LunulaThe pale half-moon where the youngest partof the nail emerges from the flesh of the fingeror toe.

EponychiumThe cuticle fold where the nail base disappearsunder the flesh of the finger or toe.

Nail root

The growing part of the nail, hidden in the fleshof the finger or toe.

ost nails grow about 0.019 in.ach week.

general, fingernails grow fasteran toenails.

ails grow faster in summer thanwinter.

youre right-handed, nails onour right hand grow faster thanose on your left, and the otheray round if youre left-handed.

NAIL GROWTH

WHERE INTHE BODY?

hair folliclehair shaft

brow hairs

p to stop sweat dripping intoeyes.

lash hairs

p to whisk away bits of windblown, dirt, and pests like insects fromeyes.

Most scalp hairs are around0.0019in. thick, so 500in arow would be almost 1in.thick.

Light colored hairs are usuallythinner than dark hairs.

Eyelashes are thicker, up to0.003in.

Hair growth is faster at nightthan during the day.

Hair growth is faster in summerthan in winter.

Hair growth is faster aroundthe ages of 1525years thanany other time.

FASTER HAIRGROWING

Finger nails have manydifferent parts.

See pages 89 for

information on THE SKIN.

inches of hair growth per month

The number of hairs onthe head varies accordingto the color of the hair.In a typical adult, thenumber is:

Fair hair 130,000

Brown 110,000

Black 100,000

Red 90,000

NUMBER OF HAIRS

Hair is found almostall over our bodies.

Nails grow at the end ofeach toe and finger.

Most kinds of hairs grow for a time, gradually slow downin growth rate, then hardly grow at all.

EYEBROWS AND EYELASHES

See pages 2223 forinformation on eyes.

See page 51 forSIGNSOF AGING

HAIR LIFE CYCLES

NAIL PARTS

THE THICKNESSOF A HAIR

HY HAVE EYELASHESAND EYEBROWS?

HAIR STRUCTURE AND THICKNESS

0.5in

0.25in

0in

Scalp Hair

Eyebrow Eyelash

Different kinds of hairsgrow at different rates.

Because most scalp hairs growfor only 3-5years, theirmaximum length is 2031in. before they fall out andare replaced.

However, some people haveunusual hair that falls outmuch less often, and canreach lengths of 26feet.

Hair growth in thin, fairhair is slower than in thick,dark hair.


8/35

MUSCR E C O

There are about 6skeletal muscles.

They form about the body weight men, and slightlyone-third of bodyadult women, giboys.

Plenty of exercisemakes muscles gand stronger. Thup to half of bod

MUSCR E C O

Bulkiest

The gluteus maximus,of the buttock. It workpull your thigh back body forward when yrun, and jump.

Smallest

The stapedius, deep iWhen the e ar detectsnoises it pulls on the smallest bone, the stito prevent it moving tdamaging the delicatof the ear.

Longest

The sartorius, which side of the hip down front of the thigh to tside of the knee.

Most powerful fo

The masseter, which rcheekbone to the lowthe lower jaw and bu

you chew.

Busiest

The orbicularis oculi, as the eyelid musclesup to 50,000 times e

you blink an d wink.

Biggest tendon

The calcaneal tendonthe calf muscles to thIt takes the strain wheon tip-toe and is ofte

Achilles tendon .

INSIDE A MUSCLEMUSCLES AND MOVEMENT

l muscles need energy to work,hich is brought by the blood ine form of blood sugar (glucose).

ou use about 40 facial musclesfrown, but only half as manysmile.

Muscles power all of your bodys movements, from blinking to

jumping high in the air. Muscle actions are controlled by messages

from your brain along nerves called motor nerves. Muscles are the

bodys largest single system and are found throughout the body. Half of a

grown human beings body weight is from their muscles.

The body has three mainkinds of muscles: skeletal,visceral, and cardiac.

Skeletal muscles are mostlyattached to the bones of the

skeleton and pull on them tomake you move.

These are the ones wenormally mean when wetalk about muscles.

Skeletal muscles are alsocalled voluntary muscles,because you can control themat will just by thinking.

Skeletal muscles are also calledstripedor striated musclesbecauseunder the microscope they have apattern of stripes or bands.

Visceral muscles formsheets, layers, or tubes inthe walls of the inner bodyparts (viscera) like thestomach and bladder.

Visceral muscles are alsocalled involuntarymusclesbecause theywork automatically.

Visceral musclesare also calledsmooth musclesbecauseunder the microscope theylack any pattern of stripesor bands.

The third type of muscleis cardiac muscle, whichforms the walls of the heart.

This list shows the power ofthe bodys muscle comparedto various machines, in watts(the scientific units of power).

Laser-pen pointer 0.002

Heart by itself 2

All the bodys musclesworking hard 100

Family car on thehighway 100,000

Space shuttle 10,000 million

MUSCLEPOWER COMPARED

Muscles are foundoughout the body. They helps to move, from walking to

lifting objects.

WHERE INTHE BODY?

Actin

Epimysium

The muscles outercovering.

Muscle Fiber

Long, thin part, about asthick as a hair.

Exercise can increase the size ofmuscles, but they have no effecton the actual number of musclesor the number of muscle cellsthis stays the same.

Some people have very smallversions of certain muscles ornone at all. This is part of thenatural variation betweendifferent people.

For example, a few people lackthe thin, sheet-like muscle in theneck, called the platysma.

INDIVIDUALVARIATIONS

A muscle is a bundle of fibers. These bundlesare called fascicles. Within each fiber is agroup of fibrils. A single fibril containsmyosin and actin filaments. These slidepast each other to shortenthe muscle.

See pages 3637 forinformation on BLOOD.

Myosin

See pages 3233 for information on THEH EART.

Muscles work by contracting andpulling their ends closer together.

In most skeletal muscles, the endstaper to rope-like tendons, whichare joined firmly to bones.

Muscles cannot push or forcefullyget longer, they are stretchedlonger when other muscles workelsewhere.

Muscles contain two bodysubstances, or proteins, called actinand myosin, which are shaped likelong threads.

In each muscle, millions of thesethreads slide past each other tomake the whole muscle shorten.

Most muscles can shorten orcontract to about two-thirds theirresting length.

A muscle bulges in the middlewhen it shortens but its overallsize or volume does not change.

See pages 2021 for information on the brain.

See pages 4041FOODAND NUTRIENTS.

SAVE ENERGY GIVE A SMILE

Skeletal muscles,seen from the back.

TYPES OF MUSCLE

MUSCLES THAT MAKE FACES

We use our muscles to communicate and send informationand not just by speaking,which uses about 40 muscles. We also use muscles for facial expressions.

Muscle name Site What it does ExpressionFrontalis Forehead Raises eyebrows Surprise

Procerus Between eyes Pulls eyebrows in an d down Stern, concentration

Auricularis Above and to side of ear Wiggles ear (only for some people)

Buccinator Cheek Moves cheek Blowing, sucking

Risorius Side of mouth Pulls corner of mouth Grin

Depressor labii Under lip Pulls lower lip down Frown

Face muscles allow us to make a huge range of expressions.

Muscle fibrils

Even thinner parts,forming a bundle withineach muscle fiber.

HOW MUSCLES WORK

frontalis

levator labii superioris

orbicularis oris

depressor labii inferioris

Muscle fascicle

Bundle of musclefibers.


9/35

A human skeletonon average, 206 They are divided groups through t

Skull

Cranium (brain ca

Face 14

Ear 3 tiny bones e

Total: 28 bones

Throat (hyoid bo

Backbone

Neck (cervical ver

Chest (thoracic ve

Lower back (lumbvertebrae) 5

Base of back (saccoccyx) 2

Total: 26 bones

Rib cage

Ribs 24

Breastbone 1

Total: 25 bones

Arms

Shoulder 2

Upper arm 1

Forearm 2

Wrist 8

Palm 5

Fingers and thum

Total: 32 bones in (includes hand)

Legs

Hip 1

Thigh and knee 2

Shin 2

Ankle 7

Sole of foot 5

Toes 14

Total: 31 bones in (includes foot)

N U M B E RB O NTHE SKELETON

The main tasks of theskeleton are to:

Hold up the body, giving supportto softer parts.

Allow the body to move whenpulled by muscles.

Provide openings for the nose andmouth to breathe and eat.

Protect certain body parts, forexample, the upper skull aroundthe brain, the front skull aroundmost of the eyes, and the ribs

around the lungs and chest. Store many body minerals, such

as calcium and magnesium, fortimes when food is scarce andthese minerals are in short supplyfor other body processes, likesending nerve messages.

Make new microscopic cells for theblood, at the rate of 3 million everysecond. These cells are produced inthe soft jelly-like bone marrowfound in the centers of some bones.

ere are three bones in body not joined to anyer bone.

oid

-shaped bone in the front of theer neck, near the throat and thee of the tongue.

eecap or patella

is inside a muscle tendon andes over the front of the kneet, helping to protect it.

ONES NOT JOINED

TO OTHER BONES

Your skeleton consists of all the bones in your bodyover 200 of

them. Its like an inner framework that supports the softer body

parts such as organs, nerves, and blood vessels. Your skeleton is not

fixed and stiff. It is a moving framework that muscles pull into hundreds of

different positions every day.

Imagining our bodies as various everyday objects can helpus to understand how they work.

Most bones of the skeleton beginnot as real bone, but as a slightlysofter, bendier, smooth substancecalled cartilage(gristle).

In a developing baby, the shapesof the eventual bones form first ascartilage.

Then, as the baby grows into achild, the cartilage shapes becomehardened into real bones.

Even in the adult skeleton, somebones are partly cartilage.

For example, the front end ofeach rib, where it joins to the

breastbone, is made not of bonebut of cartilage called costalcartilage.

The nose and ears are mainlycartilage, not bone, which is whythey are slightly flexible.

NOT ALL BONE

The bones of the skeleton arestronger, size for weight, thanalmost every kind of wood orplastic.

If the skeleton was made ofsteel, it would weigh four timesas much.

The thigh bone can stand apressure of 21 tons per sq. in.when we jump and land.

The skeleton can also menditself, which no kind of plasticor metal can.

nes are the found throughoute body. Flexible parts of thedy, such as fingers and toes,

have more bones.

WHERE INTHE BODY?

The skeleton provides some protection for v ital body parts,but it is helpful to provide extra protection, such as a helmet

when riding a bike.

Monkeys and humans are descended from the same distant ancestors.

Our skeleton is made ofliving bones that can mend

themselves if broken.

Most of a babys skeleton is made of cartilage, not bone.

SIZE AND VARIATIONS

Our bones are a strong inner framework that hold up the softinner parts of the body.

SKELETON STRENGTH

he lowest part of the backbonecalled the coccyx.s made of three to five smaller

ones fused together into one,aped like a small prong. It is all

that is left of the long tail that ourvery distant ancestors had,millions of years ago, when theylooked like monkeys and lived intrees.

TAIL END

There is no truth in theold belief that men and

women h ave di ffere ntnumbers of ribs. Both have 24ribs, as 12 pairs.

However, the total number ofbones varies slightly as partof natural differences betweenpeople.

For example, about oneperson in 20 (man or woman)has an extra pair of ribs,

making 21 pairs instead ofthe usual 20.

There are more bones, over

300, in the skeleton of a baby. As the baby grows, some of

these enlarge and fusetogether to make biggersingle bones.

The skeleton forms aboutone-seventh of the bodystotal weight.

See pages 5051 for information on STAGESOF LIFE.

LeversThe long b ones of the ar ms andlegs work like levers, with theirpivot, or fulcrum, at the joint.

A bicycle chainThe many separa te bones orvertebrae of the backbone onlymove slightly compared toeach other. But over the wholebackbone, this movement addsup to allow bending double,like the links of a bicycle chain.

A cageThe ribs wor k like t he moveablebars of a cage. This protects theheart and lungs, yet gets bigger

and smaller as the lungs breathein and out.

An eggshellThe dome shape of the crani umaround the brain is a very strongdesign, like an eggshell. Anysharp ridges or corners would

weaken it.

See pages 1617 for information on BONESAND JOINTS.

WHAT ARE BONES LIKE?

SKELETONS MAIN TASKS


10/35

D E S I G N O

J O I

The different desibodys joints are compared to machmechanical gadge

Hinge jointAllows the bones to mand forth, not side to door hinge).

Examples: knee and smof fingers.

Ball-and-socket joinAllows the bones to mforth, side to side, androtate.

Examples: hips, shouldknuckles.

Saddle joints

Shaped like a saddle fand sliding.

Example: thumb.

Washer jointsLimited tilting with a paof cartilage between th

Examples: joints betwebackbones, where the is called the interverte

Fixed or suture joiNo movement at all, bbones are firmly joine

Examples: between the bcranium (upper skull) aro

PARTS OF A BONE

BONES & JOINTS

The word skeletoncomes from anancient word meaning dried up. Butliving bones are not dry, they areabout one-quarter water. (Overall,the body is two-thirds water.)

The main minerals in bone arecalcium, phosphate, and

carbonate. These form tiny crystalswhich give bone its hardness andstiffness.

Bone also contains tiny fibers ofthe substance collagen, which

makes it slightly flexible underpressure, and less likely to snap.

If a bone is soaked in a specialacid chemical, the crystals ofcalcium phosphate and calciumcarbonate are removed. Only thecollagen fiber are left. This meansthat it is so flexible that a long

bone like the upper-arm bone canbe tied in a knot.

BONE RECORDS

Your skeleton holds you up, but you would not be able to move if it

was not for the joints that link your bones together. More than half of

your bodys bones112 out of 206are in your wrists, hands,

fingers, ankles, feet, and toes. So are more than half of your 200-plus joints.

Your bones, muscles and joints work so closely together that they are

sometimes viewed as a single system, called the musculoskeletal system.

The two topmost backbones(cervical vertebrae), justunder the skull, have specialjoint designs. They allow thehead to make importantmovements.

The axis (uppermost) backbone

has a curved shape like a saddle.It allows the head to tilt to theside and nod.

The atlas (second uppermost)backbone is more like a ring andallows the head to turn or rotateto look to the side.

Where the ends of a bone touchin a joint, they are covered with

smooth, glossy cartilage, toreduce wear and rubbing.

The space between the bones isfilled with a slippery liquid calledsynovial fluid, thatreduceswear evenmore.

The fluid is kept in by a loose bagaround the joint, the joint capsule.

New synovial fluid is alwaysbeing made by

the inner lining of this bag, calledthe synovial membrane.

REDUCING WEAR AND TEAR

Joints allow the skeletono move. They can be found

all over the body.

WHERE INTHE BODY? Longest

The thigh bone (femur), formingabout one-quarter of total bodyheight.

Widest

The hip bone (pelvis), forming thebodys broadest part.

Smallest

The stirrup (stapes) deep inside theear, a U shape just .031 in. long.

Toughest

The lower jaw (mandible), usedhundreds of times daily when

Nodding and shaking yourhead is only possible with

two special joint designs inthe backbone.

Head

The rounded end ofa long bone.

Tubercle

A lumpy projection on abone, usually where a

muscle is attached.

Shaft

The slimmer middlepart of a long bone.

iosteum

outer covering wrapped allund the bone.

amen

all hole in a bone, where a nervelood vessel passes inside.

mpact bone

y strong, hard outer layer ofe, like a shell.

eons (Haversian systems)

cells of bone substance bundledglued together to makepact bone.

ongy or cancellous bone

r layer of a bone, under thepact bone, that has holesa sponge.

rrow

y-like substance in the centermost bones.

d marrownd in all bones of a baby, buty in the long bones of the arms

legs, ribs, backbone,astbone and upper skull in anlt. Makes new microscopic cellshe blood.

ow marrow

dults, found mainly in smalleres of the hands and feet.tains fat for use as an energyrve, but can change to redrow if needed.

Bones are held together at ajoint by stretchy straps calledligaments, which stop themmoving too far or coming apart.If the bones slip and come out oftheir usual position, a dislocationoccurs.

L igament Mus cle

During long space flights, the lackof gravity puts bones under lesspreasure than they are on Earth.The bones start to lose mineralsand become weaker. Astronautsexercise regularly to keep their

bones strong.

Even a large joint like the hipcontains only about a teaspoonof synovial fluid.

PARTS OF A BONE

LIGAMENTS YES AND NO

BONE MAKE UP

Your single biggest joint, the knee,has an unusual design with extracartilages and ligaments.

In addition to the cartilage covering theends of the thigh and shin bones,the cartilage covers the knee withtwo pieces of moon-shapedcartilage.

The cartilage pieces are called

menisciand help the knee tolock straight so you can standup easily.

When atheletes have tornknee cartilage, its usually oneof these menisci which isdamaged.

The knee has two strongsets of ligaments, the lateral

ligaments on the outer side andthe medial ligaments on the

inner side (next to theother knee).

As well as these, it hastwo ligaments inside, keeping

the ends of the bones very closetogether.

These two ligaments form anX-like shape and are called

cruciate ligaments.

Exercising and playing sportscan sometimes damage

your knee. It isimportant to always

warm up. See pages1213 for information

on muscles.

See pages 4041FOODAND NUTRIENTS

There are eight bonecranium. They are futo protect the brain

BIGGEST JOINT


11/35

12 pairs of craniajoin directly to thand link it to theparts:

1. NoseFor smelling

2. EyesFor seeing

3. Eyeball-moving

4. Eyeball-moving

5. Skin and touchOn forehead, face, chjaw muscles, muscles

6. Eyeball-moving

7. TongueFor taste, saliva glandtear glands, facial exp

8. EarFor hearing and bala

9. Rear of tongueFor taste, swallowing

10. Swallowing mAlso lungs and heart i

11. Voicebox muscFor speaking

12. Tongue muscleFor speaking and swa

D I R E C T T

B R ANerves are flexible but tough, so they can move easily at joints butwithstand being squeezed by the muscles around them.

Each nerve fiber is the long, wire-like part of a single microscopicnerve cell, called a neuron.

Usually near one end, the nervecell has a wider part, called thecell body.

Branching from the nervecell body are even thinnerspidery-looking parts, calleddendrites.

Nerve messages from othernerve cells are picked up bythe dendrites, processed and

altered as they pass aroundthe cell body, and then sentby the axon (fiber) toother nerve cells.

Most nerve fibers are 0.0003 in.wide, so 4000 side by sidewould be just over 1 inch.

They have a covering wrappedaround them, called the myelinsheath. It makes nerve messagestravel faster and stops themleaking away.

Joins the brain to the mainbody.

Is about 17 in. long in a typicaladult.

Has 31 pairs of nerves branchingleft and right from it.

Is protected inside a tunnelformed by a row of holes throughthe backbones.

Like the brain, it has a layerof liquid around it, calledcerebrospinal fluid, to cushion itfrom injury.

NERVE LENGTHS All the nerves in the body,

taken out and joined endto end, would stretch about62 miles.

The longest single nerve fibers,found in the legs, are up to 3feet in length.

The spinal cord, in the back, is one of the most important partsof our nervous system.

Each nerve cell receives

signals from thousands ofother cells and passes onsignals to thousands more.

Individual nerve cells do notactually touch each other wherethe ends of their dendrites andaxons come together.

The ends are separated by tinygaps, at junction points, calledsynapses.

The gap inside a synapse is just1 microinch wide, which means1 million in a row would stretch1 inch.

Nerve messages jump across asynapse not as electrical signals,but in the form of chemicals,called neurotransmitters.

This chemical jump takes less

than

1

1,000

th of a second.

A typical nerve looks likewire or string.

Synapses are so small thatscientists have to use special

electron microscopes tostudy them.

Nerves are conneevery body part.

The thickest ones neand spinal cord arenerve trunks.

The thinnest ones spbody parts are callefibers.

NERVT O E V E R Y

THE NERVOUS SYSTEM

The nervous system controls every movement and action we make, as

well as every process that happens inside the body. Your nervous

system is made up of your brain, spinal cord, and nerves. It works by

sending tiny electrical signals, called nerve impulses. Millions of these travel

around the body and brain every second.

A nerve signal is a tiny pulse of electricity made by movingchemical substances into and out of the nerve cell.

Average signal strength is 110 th of a volt. Average signal length is 11000th of a second. Average recovery time before another signal can pass

is 1500 th of a second. Slowest signals travel 19 inches per second.

Fastest signals travel 459 feet per second.

NERVE SIGNALS

Some parts of the nerve systemwork automatically.

Those processes are called theautonomic nerve system.

They control heartbeat, fooddigestion, body temperature,and blood pressure.

AUTOMATIC SYSTEM

ere are two mainvous systems within the

dy. The central nervousstem is the brains maintrol center. It sendsve impulses to the restthe body using theipheral nervous system.

e have conscious controler the central andipheral nervous systems.

ntral nervous system:ain

de the top half of the head.nal cord

main nerve link betw eenbrain and the body.

ripheral nervous system:nial nerves

nect directly to the brainher than the spinal cord.y go mainly to parts in thed like the eyes, ears, ande.nal nerves

nch out from the spinal cordhe arms, legs, back, chest, all other body parts.

MAIN PARTS OF THE

NERVOUS SYSTEM

The sciatic nerve,in the hip and upperthigh, is about thewidth of its ownersthumb. This is thickerthan the spinal cord,which is usually thewidth of its ownerslittle finger.

ves run throughout the body,carrying electrical signals

from the brain.

WHERE INTHE BODY?

We have no conscious controlover some parts of our body,

such as the systems thatcontrol digestion.

NERVES AND NERVE CELLS

axons

A nerves outer covering is called theepineurium. Inside are bundlesof nerve fibers, called axons,each too small to seewithout a microscope.

SLOW TO HURTWhen you hurt a finger, youprobably feel the touch first, andthen the pain starts a moment later.This is because the signals abouttouch travel faster along the nervesthan the signals about pain.

See pages 2021 forinformation on THE BRAIN.

See pages 89 forinformation on THE SKIN.

THICKEST NERVE

epineurium

NERVE JUNCTIONS

SPINAL CORD

NERVES AND NERVE CELLS


12/35

Nerve messages from the bodycross over from left to right at thebase of the brain.

This means the left side of the brainreceives signals from, and sendsthem to, the right side of the body.

In most people, the left side of thebrain is more active in speakingand reading, scientific skills, usingnumbers and maths, and workingout problems in a logical way.

The right side of the brain is more

active in dealing with shapes andcolors, artistic skills like paintingand music, and having creativeideas.

In a right-handed person, the leftside of the brain is generallydominant. In a left-handed person,the right side of the brain isgenerally dominant.

Even when asleep, the brain is justas active sending nerve messagesaround itself as it is when awake.

This is shown by recordings of itselectrical nerve signals.

Older people tend to sleep morehours overall but often in severalshorter sessions, such as cat-naps through the day.

Usual sleep needs for most peopleevery 24 hours:

New born 20 hours

10-year-old 10 hours

Adult 78 hours

SLEEP

The brain has four small chambersinside it called ventricles.

These are filled with a pale liquidcalled cerebrospinal fluid, CSF.

CSF is found around the brain,between two of the protectivelayers, called meninges, thatsurround it. CSF is also found inand around the spinal cord.

The total amount of CSF insideand around the brain and spinalcord is about 4.2 fl.oz.

This fluid flows very slowly and isgradually renewed about threetimes every 24 hours.

CSF is important as it helps tocushion the brain from damage.

The liquid also supports the brainwithin the skull, bringsnourishment, and takes awaywastes.

HOLLOW BRAIN

CerebrumThe big wrinkled, domed partcovering most of the top of thebrain, forms more than four-fifths of the whole brain. It hasa thin outer layer of graymatter, the cerebral cortex,

which is mainly nerve cel ls,covering an inner mass ofwhite matter, which ismainly nerve fibers. Hypothalamus

Just below and infront of the thalamus,is a main center for

powerful feelings,emotions, and urgessuch as anger, fright,love, and joy.

ThalamusThis is two egg-shaped partsalmost at the center of thebrain. It helps to sort andprocess information fromfour of the senses (sight,hearing, taste, and touch)going to the cerebrumabove.

CerebellumA smaller wrinkled part at thelower back, looks like a smaller

version of the whole brain. infact its name means little brain.It carries out detailedcontrol of muscles so

we can move about,

keep our balance, and carryout skilled actions.

The brain stemAt the base of the brain contains the main life support areas forheartbeat, breathing, blood pressure, and control of digestion. Its lower

end merges into the top of the spinal cord.

In a left-handed person, theright side of the brain is

generally dominant.

T H E G R O

B R A

The developmentbrain happens quconception. It congrow in size afteand makes new connections throuchildhood.

Inside the womb

The brain is one o

main body parts to

three weeks after c

as a large arched

head end.

Four weeks after

The brain is almos

the rest of the bod20 weeks after co

Brain weighs abou

At birth

The brain is 1417

one-third of its fina

In comparison, a n

body is about 1/2

of its final adult siz

Growing up

By 3 years, the bra

approaching fully g

2.4 lbs.

The brain does not

new nerve cells aft

The brain does ma

connections betwe

perhaps millions e

we take in knowl ed

skills and learn new

From 20 years ol

The brain shrinks boz. of weight per y

represents the loss

10,000 nerve cells

Certain drugs, incl

can speed this cell

the brain shrink fas

See pages 5for information

STAGES OF

Bigger brains are not necessarilysmarter, and there is no linkbetween the size of a healthybrain and intelligence.

The average female brain isslightly smaller than the averagemale brain.

But the average female body issmaller, in comparison, to theaverage male body.

Compared to body size, womenhave slightly largerbrains than men.

SIZE ISNT EVERYTHING

The brain contains more than 100 billion nerve cells, called neurons

about as many stars as in our galaxy, the Milky Way. The brain also

contains perhaps ten times as many support cells, called neuroglia.

Its not the size of a brain which makes it smart, or the number of cells. It

depends on how often its owner uses it, and in how much detailby looking,

listening, learning, remembering, using imagination, and having ideas.

THE BRAIN

e brain is inside the cranium,forming the upper half of

the head.

WHERE INTHE BODY?

he brain consumes about one-fth of all the energy used byhe body.

ut the brain forms only about50 th of the whole body.

hat means the brain uses tenmes more energy for its size,ompared to most otherody parts.

his energy is mainly in theorm of blood sugar, called

glucose, brought to the brain byts main blood vessels, thearotid and vertebral arteries.

verage blood flow to the brains 1.5 pints per minute, aboutne-eighth of the hearts totalutput.

his flow is the same whether

he body is at rest or very active.

his is unusual because bloodow to other body partshanges greatly between restnd activity. For example,t increases to the muscle byen times and decreases to thetomach by half.

UNGRY FOR ENERGY

The weight of an averageadult brain is 3 pounds.

The largest accuratelymeasured normal humanbrain is 6.3 pounds.

THE WEIGHT OFTHE BRAIN

planningmovement

making movement

hearing

speech

touch on the skin

vision

The outer gray layer of thecerebrum, over the top of thebrain, is called the cerebral cortex.

Spread out flat, it would be thearea of a pillowcase, and almost asthin.

However, deep grooves, called sulci,are wrinkled and folded into thespace inside the upper skull.

The cortex has about half thebrains total number of nerve cells,around 50 billion.

Each of these can have connectionswith more than 200,000 othernerve cells.

The connections are made by thespidery-looking arms, calleddendrites, and a much longer, wire-like part, the nerve fiber.

The cortex is the main place wherewe become aware of what we see,hear, smell, taste, and touch..

It is also the place where weplan movements and actionsand get them started, known asmotor skills.

Each of these sensory and motorprocesses takes place ina different area of the cortex,known as a center.

The cortex is also the major site forthinking and consciousness, whatwe call our mind.

The cortex is also involved inlearning and memory, althoughscientists are not quite sure how.

See pages 3435for information on theCIRCULATORYSYSTEM

See pages 2227 forinformation on the senses.

See pages 1213 for

information on muscles.

CORTEX IN CONTROL

MAIN BRAIN PARTS

LEFT AND RIGHT


13/35

M O V I N G

EYEB

Behind the eyebasix small ribbon-muscles that makand swivel in itsor eye orbit.

Medial rectus

Moves the eye inwardthe nose.

Lateral rectus

Moves the eye outwarfrom the nose.

Superior rectus

Moves the eye upwarat the sky.

Inferior rectus

Moves the eye downw

at the floor.

Superior oblique

Pulls eye inwards and

Inferior oblique

Pulls eye upwards and

In total the eye can tilt

look up by 35 de

look down by 50

look inward towaby 50 degrees.

look outward by 4

Every person in the world hasdifferent fingerprints, which canbe used for identification andsecurity checks.

The same applies to the colouredpart of the eye, the iris.

Each person has a different colorand detailed pattern of marks onthe iris.

Scans of the iris, fed into acomputer, can be used likefingerprints for identification andsecurity checks.

Rarely does a person have twodifferent colored irises, though itcould happen at birth, or throughinjury.

20/20 means a person can see,at a distance of 20 feet, whatnormal eyesight can show.

The larger the second number, theworse the eyesight.

Someone with 20/60 vision cansee at 20 feet what normaleyesight sees clearly at 60 feet.

Nearsightedness, or myopia, isdue to the eyeball being toolong form front to back.

Farsightedness, or hypermetropia,is due to the eyeball being tooshort from front to back.

Astigmatismis when the curve ofthe eyeball is not the same in alldirections.

We spend about up to 30 minutes ofour waking day with our eyes shut

during blinks.

Blinking washes soothing, cleansingtear fluid over the eye. The fluidwashes away dust and helps to

kill germs.

Tear fluid comes from the lacrimalgland, just above and to the outerside of each eye, under a fold of skin.

On average:Number of blinks per minute: 6

Length of blink: 0.3-0.4 seconds

Total amount of tear

fluid made in a day: 50 ml

This can treble if surroundings are dustyor have chemical fumes.

BLINKING AMAZING

20/20 VISION

MAIN PARTS OF THE EYE

M E A S U

THE E

The eyeball is almperfect sphere orshape.

Side-to-side: 0.94 i

Front-to-back: 0.94

Top-to-bottom: 0.91

The eyeballs tota0.81 oz.

The eye is one of parts that grows birth to adulthoo

PupilHole in the iris, through whichlight enters the eye s interior.

IrisColored ring of muscle that can alter thesize of the hole within it, the pupil,making it smaller in bright light toprotect the delicate inside of the eye.

ScleraTough outer layer around the wholeeye apart from the cornea.

CorneaThick clear dome at the frontof the eye.

ConjunctivaSensitive covering at the front of theeyeball, over the cornea.

LensPea-shaped blob about 0.4 in. acrossthat alters in shape to see and focusclearly, from looking at farawayobjects to nearby ones.

RetinaInner layer lining the eyeballs interior.

ChoroidBlood-rich layer between scleraand retina.

Ciliary muscleRing of muscle around the lens thatalters its shape.

Aqueous humorThin, clear fluid filling the spacebetween the cornea and the lens.

Vitreous humor

Thick, clear jelly-like substance fillingthe main eyeball and giving itsrounded shape.

Usually, people with darkerskin and hair have browneririses. People with lighter skinand hair have bluer irises.

See pages1213 for information

on muscles.

The eyes inner lining, the retina,is where light rays are changed to

nerve signals.

The retina has an area about thesame as a larger postage stamp.

It has millions of microscopic cellsthat make nerve signals when hitby light rays.

125 million are rod cells, whichwork well in dim light, butcannot see colors, only shades ofgray.

7 million are cone cells, whichsee fine details and colors, but

work only in bright light.

Most of the cones areconcentrated in a slightly bowl-shaped hollow at the back of the

retina, the fovea, or yellow spot.

This is where light falls to give usthe clearest, most detailed view.

Experts believe that over half of the information we process comes in

through our eyes, as words (through reading), pictures, drawings,

real-life scenes, and images on screens. Yet the eye does not really

see. It turns patterns of light rays into patterns of nerve signals, which go to

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