Human Body Encyclopedia

Human Body Encyclopedia

Language: English

HumanBody Encyclopedia 

A DORLING KINDERSLEY BOOK

Contents Human body 4-5 Your amazing body 6-7 What makes you you? 8-9 Building blocks 10-11 Organizing the body Skeleton and bones 12-13 Skeleton 14-15 Head case 16-17 Bendy backbone 18-19 Living bone 20-21 Bone and cartilage 22-23 Moving joints Moving muscles 24-25 The body’s muscles 26-27 How muscles work 28-29 Muscle power Brain and senses 30-31 Headquarters 32-33 Network of nerves 34-35 Touchy feely 36-37 Taste and smell 38-39 Look out! 40-41 How we see 42-43 Eye to brain 44-45 Listen here 46-47 Balancing act Senior editor Penny Smith Senior art editor Cheryl Telfer Editors Ben Morgan, Zahavit Shalev Additional design Jacqueline Gooden, Tory Gordon-Harris, Claire Patane, Laura Roberts Illustrator Peter Bull Digital illustrator Pilar Morales Consultants Dr Penny Preston, DrFrances Williams Publishing manager Sue Leonard Managing art editor Clare Shedden Jacket design Victoria Harvey Picture researchers Marie Ortu, Rob Nunn Production controller Shivani Pandey DTP designer Almudena Díaz First published in Great Britain in 2005 by Dorling Kindersley Limited 80 Strand, London WC2R 0RL A Penguin Company 2 4 6 8 10 9 7 5 3 1 Copyright © 2005 Dorling Kindersley Limited, London All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the copyright owner. A catalogue record for this book is available from the British Library. ISBN 1-4053-0848-6 Colour reproduction by Colourscan, Singapore Printed and bound in China by Toppan Discover more at www.dk.com LONDON, NEW YORK, MUNICH, MELBOURNE, and DELHI 2 Test yourself with the questions at the bottom of each page...
3.        3. Heart and blood 48-49 Blood flow 50-51 Boom boom 52-53 All about blood 54-55 Blood cells 56-57 Bumps and cuts 58-59 Hormones Lungs and breathing 60-61 Air bags 62-63 Air and oxygen 64-65 Making sounds 66-67 Ah-choo! Skin, nails, and hair 68-69 All wrapped up 70-71 At your fingertips 72-73 Fairly hairy Fighting disease 74-75 Germs 76-77 Body defences 78-79 Fighting germs 80-81 Allergies Digestive system 82-83 Digestive system 84-85 Chew it over 86-87 From mouth to stomach 88-89 Inside the intestines Urinary system 90-91 Waterworks 92-93 The stretchy bladder About this book This book has special features that will show you how to get your hands on as much information as possible! Use the “become an expert” buttons to find out more about a subject on other pages. 3Youwillalwaysfindtheanswershere! Try putting sugar on different places on your tongue. It tastes sweeter in some places than others. Now try salt, lemon juice, and coffee. get into it Runny nose When you have a cold, tiny hairs in your nose get clogged with mucus. This stops them wafting smell particles deep into your nose and makes it difficult to smell – and taste – things. We need to eat and drink to survive, but taste and smell are what make these everyday activities so enjoyable. Taste and smell Taste detector Your tongue is a big muscle covered in clusters of taste buds. Each cluster recognizes a particular kind of taste. Sweet Salt Salt Bitter Sour Taste buds Saliva in your mouth dissolves your food. The food washes over tiny taste buds between the bumps on your tongue. Taste buds recognize different flavours. Sour S ome noses can recogniz e10,000differentsme lls. Bitter foods, such as coffee can be bad for you. Most poisons are bitter. Sour foods include lemon and vinegar. Food that has “gone off” tastes sour. Salt detecting taste buds can be found on the lips as well as on the tongue. Sweet foods naturally attract us. Our first food – milk – is sweet. 36 37 How much saliva does an average person produce in a day? 1000-1500millilitres. Brain and senses Taste and smell Different tastes There are five types of tastes – bitter, sour, salty, sweet, and umami. Umami is the savoury taste of foods like soy sauce and mushrooms. Smell receptors Special cells deep inside your nose recognize scent particles floating in the air. These cells link directly to your brain. Sensitive nose Much of what we think of as taste is actually smell. The back of your nose is linked to your mouth so you can smell your food as you chew it. 10,000taste buds are crammed onto your to ngue. Your nose and mouth are linked at the throat. Coloured discs contain facts about special topics, such as taste. Circles show close-up images you might not otherwise be able to see. Reproduction and growth 94-95 Making a baby 96-97 Growing in the womb 98-99 Double trouble Life cycle 100-101 The early years 102-103 Growing up 104-105 Growing older Keeping healthy 106-107 What’s in food? 108-109 Sleep 110-111 Doctors and dentists Communication 112-113 Body language 114-115 Use your hands 116-117 Express yourself Reference section 118-119 Amazing facts about YOU! 120-121 Through the ages 122-123 Glossary 124-127 Index 128 Acknowledgements Reproduction and growth 94-95 Making a baby 96-97 Growing in the womb 98-99 Double trouble Life cycle 100-101 The early years 102-103 Growing up 104-105 Growing older Keeping healthy 106-107 What’s in food? 108-109 Sleep 110-111 Doctors and dentists Communication 112-113 Body language 114-115 Use your hands 116-117 Express yourself Reference section 118-119 Amazing facts about YOU! 120-121 Through the ages 122-123 Glossary 124-127 Index 128 Acknowledgements “Get into it” activity buttons show you how you can try things out for yourself.
4.        4. 4 The greatest machine you’ll ever own is your body. It’s more complicated than any computer, it lasts for a lifetime, and it’s yours for free. Body parts Your body is made up of hundreds of different parts. You probably know the names of the bits you can see, but there are many more hidden deep inside you. What do we call the study of the human body? Inside your body Doctors can see inside your body with special cameras. X-ray cameras take pictures of hard body parts like bones. Other cameras, called scanners, can see soft body parts. Two of everything Body parts often come in pairs. You have two feet, two eyes, two ears, two lungs, and so on. This means you have a handy spare in case one of them gets damaged. Human body Your amazing body Cheeks Lips Nose Teeth Eyebrows Eyes Forehead W rists Fingers Hair A chest X-ray shows the bones in your chest. The white shape in the middle is the heart. Ears H ands Become an expert... on the skeleton, pages 12-13 on digestion, pages 82-83
5.        5. 5 Being human Although we look different to animals, our bodies are similar on the inside. Our closest animal relatives are chimpanzees. Water, water Water is the most important chemical in your body. About two-thirds of your weight is water. No substitute The human body is too complicated for robots to copy. Robots can copy the way we walk, but they can’t think or feel like we do. Carbon is the chemical in diamonds and coal. A fifth of you is carbon. Your amazing body Iron makes your blood red. You have enough to make one small iron nail. Phosphorus is in the tips of matches, as well as your bones and teeth. Sodium and chlorine make salt. Blood is one- third as salty as sea water. Potassium is used in some types of soap. It’s also in your body fluids. Robot Curiosity quiz Take a look at the first few pages in this book and see if you can find these pictures. The ingredients Your body is made of just a few simple chemicals, plus water. Chimps have hands like ours. Chimpanzee Compared to chimps, our bodies look almost hairless. Anatomy. Nitrogen is important in muscles. It’s also the main ingredient in air.
6.        6. 6 All human bodies work the same way, but everyone is different. Nobody looks, sounds, or thinks exactly like you. You’re different because of the way your genes and experience shape you as you grow up. How many genes are there in the human body? Curly hair Green eyes Freckles Human body What makes you you? Unique The shape of your face, the colour of your hair, and many other things make you unique – different from everyone else. Black hair Fair skin
7.        7. 7 DNA Your genes are stored in a chemical called DNA, which looks like a twisted ladder with four different types of rung. The rungs make up a four-letter alphabet that spells out your genes, like letters in a book. In the genes Genes are instructions that build your body and tell it how to work. Your genes control many of the things that make you unique, like the colour of your eyes or how tall you’ll be. Changing body Genes don’t control everything – experience also shapes you. If you exercise a lot, for instance, your body gets stronger. About30,000. What makes you you? This girl has a gene that allows her to roll up her tongue. The boy doesn’t have the gene, so he can’t roll his tongue. DNA can split and copy itself. Learning to ride a bike changes your brain and your body. Look in a mirror and see if you can roll your tongue. Don’t cheat by squeezing it with your lips. Test your family to see who has the gene. get into it In the family Your genes came from your parents. Half come from your mother and half come from your father. If you look like your parents, it’s because you share the same genes. There’s e nough DNA inside you to stretc h to the Suna nd back 400 tim es.
8.        8. 8 Every part of your body is made of tiny building blocks called cells, which fit together like bricks in a wall. Cells are so small that hundreds could fit on the point of a pin. How many cells are there in the human body? Making new cells A cell makes new cells by dividing. The two new cells are half the size, but they soon grow back. Millions of your cells die every second, but millions of others divide to replace them. The skin on your fingertips is made of lots of small ridges. Human body Building blocks The nucleus controls the rest of the cell. Tiny generators provide cells with power. The outer skin, or membrane, stops things leaking out. Inside a cell In the middle of a cell is its control centre – the nucleus. The nucleus sends instructions to the rest of the cell, telling the cell what chemicals to make. The new cells pull apart and separate, but they usually stay close neighbours. Before a cell divides, the nucleus splits to make two nuclei. DNA is stored in the cell nucleus. D NA The inside of a cell is packed with a kind of living jelly called cytoplasm.
9.        9. Cells make tissue Your body contains hundreds of different types of cells that do different jobs. Cells of the same type usually group together to form tissue. Fat, muscle, bone, and nerves are types of tissue. Blood is a liquid tissue. Building blocks 9About100trillion. How big are cells? Cells are too small to see with the naked eye, but scientists can photograph them through powerful microscopes. The cells on your skin are about a hundredth of a millimetre wide. Fat cells are bubble shaped. They store fat under your skin. Many blood cells are red. They carry oxygen around the body. Nerve cells are thin and wiry. They carry electrical signals. Bone cells make your bones hard. They live in tiny holes in bones. The cells on the surface of your skin are tough and flat. They overlap to form layer of armour that protects the softer cells below. A microscope can zoom in to see the tiny, flaky cells on the ridges of a person’s fingerprint. More than 2000 dead skin cells f elloffyouwhileyoureadthissentence.
10.     10. Your cells and tissues are organized into larger body parts called organs. In turn, your organs work together to form body systems. Organ transplant If a vital organ stops working, doctors may replace it with an organ from another person. This is called a transplant. Organs An organ is a body part that does a specific job. Your heart’s job, for instance is to pump blood. Kidneys clean blood. The tubes that carry blood away from the heart are called arteries (shown in red). Heart Kidney Brain Human body Organizing the body Systems Organs and tissues work in teams to carry out major tasks, like transporting blood or processing food. These teams are called systems. The heart is the largest organ in the blood system. It pumps blood around the body. 10 Heart and blood Your heart, blood, and blood vessels make up the blood system. It transports vital supplies around your body. The tubes that carry blood back to the heart are called veins (shown in blue). Which body system makes your stomach rumble?
11.     11. Thedigestivesystem. 11 Nerves Your nervous system carries electrical signals around your body. You need this system to see, hear, think, and react. A long, twisting tube makes up your intestines, where digested food is absorbed. Senses, such as touch, rely on nerve cells that send signals to your brain. Muscles change the position of your skeleton by pulling different bones. Signals shoot along nerves to muscles, telling them when to pull. Organizing the body Breathing system: the main organs are your lungs, which take in air. Hormone system: this uses powerful chemicals to control your body and mood. Skin, hair, and nails: these form your body’s protective covering. Immune system: this seeks and destroys germs that get into your body. Urinary system: this cleans blood and gets rid of waste chemicals. Reproductive system: these are the organs that make babies. Other systems Some of your other important systems are shown in this list. Digestive system Your digestive organs break down food to provide your body with energy and raw materials. Muscles Your muscle system is made of tissues that move parts of your body by pulling on them or squeezing them. Your biggest muscles all pull on bones. Skeleton Bones and joints make up the skeletal system, an inner frame that supports the body. Your fingers are moved by muscles in your arm. The most powerful muscles are in your legs. A quarter of your bones are in your feet. Your brain is the nervous system’s control centre. Your mouth is the first part of the digestive system.
12.     12. 12 Your bones all join up to make a frame for your body called the skeleton. This protects your insides, and helps you move about. Skeleton Skeleton Howmanyribshaveyougot?24,unlessyouareoneoftherarepeoplebornwith26.13 Neck bones Did you know that you have seven bones in your neck, the same number as a giraffe? The top one allows you to move your head up and down, the second lets you rotate it from side to side. Smallest bone Around the same length as a grain of rice, this is one of the smallest bones in your body. It lies deep inside your ear. Long lasting Bone is a very hard material and one of the last parts to rot away when a body is buried. This woman lived in the Stone Age, 5000 years ago, but her bones have survived until today. 206 bones There are 206 bones in an adult skeleton. Over half of these are found in the hands and feet – the parts of your body that perform the most complicated movements. Each finger has three bones, except for your thumb, which has two. There are 54 bones in your hands, and 52 in your feet. Your tail bone is at the very bottom of your spine. Thigh bone Shin bone Rib There are 24 bones in your spine. You have eight small bones in each wrist. Pelvis Frogs have very short spines to withstand the strain of the huge leaps they take. Snakes are incredibly bendy thanks to many identical vertebrae forming their long spines. Thethighboneisthebiggestandstrongestinthebody. Your ankle has three larger bones and four smaller ones. Skull Other skeletons Most animals have a backbone and are called “vertebrates”. Animals with no spine, like spiders and bugs, are called “invertebrates”. A fish’s spine allows it to bend its body from side to side so it can swim smoothly. Shoulder blade Jaw bone A giraffe’s long neck helps it to eat leaves off tall trees. Skeletonandbones Become an expert... on bone and cartilage, pages 20-21 on teeth, pages 84-85
13.     13. Label Skeleton and bones The most complex part of the skeleton is the skull. It is made of many bones that fit together tightly, to protect the brain and support the face. Head case Facial features This image shows the relationship between your skull and face. There are no bones shaping the front part of your nose, your lips, or your ears. Your nose and ears are shaped by cartilage. Why does a baby have spaces between its cranial bones? The cranium is the domed part of your sk ull. The frontal bone forms your forehead. Teeth are set into the upper and lower jaws. Helmet The upper part of the skull is like a helmet that protects the brain. The lower part forms a structure for your facial features to attach to. 14 The front of the nose has no bones. Eye sockets are made up of seven different bones. The brain fills most of the cranium.
14.     14. Soitsheadcouldwithstandbeingsquashedwhileitwasbeingborn. Head case Jigsaw The skull bones fit together like the pieces of a jigsaw. All but one of the bones are locked in place. This makes the skull very strong. Face from the past Scientists can work out what a dead person’s face looked like from their skull alone. They examine the facial bones and build up artificial cartilage, muscle, and skin over them. Meet the relatives Chimpanzees and humans share a common ancestor. However, chimps have smaller brains than humans so their craniums are smaller. Chimps also have a large ridge above their eyes, and a jutting jaw. Hole in the head From underneath you can clearly see the big hole at the bottom of this skull. The spinal cord – which runs down your back – meets your brain here. There are two parts to the upper jaw. Upper jaw Bac k of the head The lower jaw is not shown here. Blood vessels pass through small holes in the skull. The spinal cord goes through a large hole in the skull. The lower jaw is hinged. It is the only skull bone that can move. 15
15.     15. 16 Your spine is a length of bones running down the back of your body. Without it you couldn’t hold up your head and body, or make any sort of movement. What is a slipped disc? Stack of bones Your spine contains 24 separate bones called vertebrae. At the bottom are nine more vertebrae. They are much smaller and are fused together. Skeleton and bones Bendy backbone Segments of the spine Each vertebra has a strong, stubby section that supports the weight of your body, and a hole for the spinal cord to pass through. Fr ontofspin e Backofspine Yourspinecurvesgently,abitliketheletter“s”. The spinal cord goes through this hole. The first seven bones are in your neck. They are known as the cervical vertebrae. The next 12 are called the thoracic vertebrae. The five lumbar vertebrae bear most of your weight. The fused bones of the sacrum and coccyx don’t allow much movement. The coccyx consists of four fused vertebrae. A straight back is actually quite curvy. The thoracic vertebrae form joints with the ribs. The five sacral vertebrae are fused together.
16.     16. Bend over. Gently feel the bones of your spine with your fingertips. Can you follow them from neck to waist? 17It’swhenoneofthepadsbetweenthevertebraegetsdamaged. Bendy backbone Shock absorbers You twist and bend your spine almost every time you move. Sandwiched between the vertebrae are pads of cartilage to stop them banging and rubbing against each other and getting worn out. Ribcage Your thoracic vertebrae connect to your ribs. Together they form a cage around your heart and lungs. Rib bones are curved. They are also thinner and more bendy than the bones in your spine. Bendy backbone The amount of movement between each vertebra and its neighbours is actually very small, but added together they allow for a large range of movement. A woman’s pelvis is shaped differently to a man’s. A baby can pass through it when she gives birth. The way the back curves means we can’t bend as far back as we can forwards. Pelvis Reproductive organs and some digestive organs rest in the bowl-shaped hollow of your pelvis. The sacral vertebrae and coccyx form the bottom of the bowl. Yo u could be this bendy...... ...withalotofpractice! Vertebra Pad of cartilage Space for spinal cord get into i t The pads give you a little bit of movement in all directions.
17.     17. 18 What are the most commonly broken bones? Skeleton and bones Their outer surface may be hard and dry but that doesn’t mean your bones aren’t alive. Bones are always growing and repairing themselves. Compact bone The hardest and most dense part of the bones is the outer layer. It is made of calcium, a substance we get from our food. Teeth are made of calcium too. What’s inside our bones? Bone accounts for one sixth of your body’s weight. Its clever structure means it’s often lighter than it looks. Living bone Bone marrow A jellyish substance called marrow fills the centre of many of your larger bones. It supplies your body with red blood cells at a rate of 3 million cells per second. Marrow can be found in the spine, skull, and the main leg and arm bones. Spongy bone Parts of some bones have a honeycomb structure with lots of spaces. This makes them weigh less than if they were solid right through.
18.     18. Living bone Curiosity quiz Take a look through the skeleton and bones pages and see if you can identify where these bony bits come from. If the broken bone ends have slipped apart they must be repositioned by a doctor before healing begins. Broken bone Bones are strong and flexible enough to cope with a lot of pressure, but, as this X-ray shows, they sometimes break. Luckily they can heal themselves. 19 Your b onesarestill growing unt ilyourlateteens. On the mend New cells form at each end of the broken bone, closing the gap between them. It takes about 6 weeks for this to happen. Looking after your bones Calcium from milk and cheese is needed to build strong bones. Weight-bearing exercise like walking, climbing, or skating helps to strengthen bones. Become an expert... on the skeleton, pages 12-13 on skin and nails, pages 70-71 Fingers,wrists,andarms. Padded clothes help protect bones from sudden impact.
19.     19. Bone and cartilage Stick out your ears! Your ears are made of cartilage, not bone. They are strong, but much more bendy than your bony bits. Cross-section of an ear – the cartilage sits between two layers of skin. When you were a baby, you were tiny. Slowly, as you get older and bigger, your bones do a clever trick. Not only do they grow, but they also change. More, less You’ve got more bones than your mum or dad! You were born with over 300 “soft” bones, but as you get older, many fuse together. By the time you’re 25 you’ll have 206 fully formed bones. Making bones Babies’ bones are made out of a soft and bendy material called cartilage. Slowly this hardens and turns into bone. 20 Which foods are rich in calcium, the mineral you need to grow healthy bones? Skeleton and bones Baby bones are entirely made of soft, growing cartilage. Adolescent bones are mostly bone, with a small amount of cartilage. Adult bones have stopped growing. Most no longer contain cartilage. Baby’s hand
20.     20. Bone shows up as purple in these X-rays. The difference between the amount of bone can clearly be seen. The pads of cartilage get squashed from standing up and stretch back out while you’re lying down. 21Milk,cheese,yogurtandice-cream. Smooth coated joints The ends of neighbouring bones are covered in smooth cartilage. That way, they can glide against each other when you move. Bone and cartilage Taller, shorter Between each bone in your spine are small disks of cartilage. During the day these get squashed, and when you rest at night they spread out again. This means you’re a little bit taller in the morning than in the evening. Cartilage coats the ends of these bones. Child’s hand Adult’s hand
21.     21. Fixed joints The bones that make up your skull start to join up soon after you are born. Once they have fused, none of them allow movement except the hinged jaw joint. What is tennis elbow? Skeleton and bones Have you ever used a joystick? That’s a ball and socket joint! Hinge joint Your knee can bend in the middle but it can’t swing from side to side. This joint has a hinge like the one that allows you to open and close a door. 22 Joints are the places where bones meet. Different kinds of joints allow you to move in different ways. Ball and socket Your hips are ball and socket joints. They allow you to move your legs in all directions and even to turn them. Knee joint Moving joints There are 19 moveable joints in your hand – not counting the ones in your wrist!
22.     22. Fabulously flexible People whose joints are particularly flexible are called “double- jointed”. The condition can run in families, but people who are double- jointed must practise if they want to keep their ligaments stretchy. Thenameforsoreelbowtendonscausedbyoveruse. Your elbows have a hinge joint for bending and a pivot joint so they can turn. Moving joints Hip hooray Joints, particularly knee and hip joints, sometimes wear out in old age. When this happens, doctors can remove the worn-out joint and replace it with an artificial one. 23 Bendy bits Different sorts of joints all over your body keep you moving. This woman has stretchy muscles and ligaments that allow her spine to bend further than most people can manage. Wrists have a joint that allows them to turn but not to go right round. Neck bones feature a pivot joint that allows your head to turn. Ligaments Bands of tissue called ligaments act like elastic. They hold your bones together yet still allow you to move. Thank your thumbs Your thumb is the most flexible of your fingers. You rely on your thumbs whenever you handle delicate objects. Tape your thumb to your first finger. See how difficult it is to open a notebook, pick up a pen, and write your name. get into it Your hand is a terrif icfeatofengineering! Ligament Bone Ankles contain different joints for up and down and side to side movement.
23.     23. Every time you move, you use muscles. Muscles make you walk, blink, and smile. Some muscles work without you thinking about them, but others need to be told to move. They all work by shrinking, which makes them pull or squeeze. Pulling strings About 650 of your muscles are wrapped around the bones of your skeleton. They move your body by pulling on the bones. Together they form the muscle system. Heart muscle When you put your hand on your chest, you can feel your heart beating. Your heart is a strong muscle that squeezes blood around your body. Smooth muscle This type of muscle makes things move inside your body. It mixes food in your stomach and pushes food through your intestines. The body’s muscles Moving muscles What weighs more: all your bones or all your muscles? The tibialis muscle bends your foot. Your longest muscle is the sartorius. It helps cross your legs. The biceps muscle bends your arm. Skeletal muscle cells are long and threadlike. Skeletal muscle Skeletal muscles pull on bones to change the shape of your skeleton and move your body. These muscles are voluntary, which means you can use thought to control them. Heart muscle cells are stripy with oval blobs. Smooth muscle cells are short with pointed ends. 24 The pectoralis muscle swings your arm.
24.     24. Tongue twister Your tongue is a bundle of lots of muscles that make it super flexible. It can reach anywhere in your mouth to pull and push bits of food. Its acrobatic movements are also vital to speech. Who’s in charge? You use hundreds of muscles when you run and jump. Your brain controls them all, a bit like a conductor controlling an orchestra. It sends signals along nerves to every muscle, saying exactly when to work and when to rest. Muscle magic Muscles have hundreds of uses. They make up about a third of your body weight. Fastest muscle: this one makes you blink. It works up to 5 times a second. Ear wiggling: a few people can control the muscles around their ears. Smile: a fake smile uses different muscles from a real, involuntary smile. 25Yourmuscles. The body’s muscles Become an expert ... on making sounds, pages 64-65 on how intestines push food, pages 88-89 Hundreds of muscles work in a carefully controlled sequence when you jump in the air. Your tongue contains at least 14 different muscles th at make it amazingly flexib le. Largest muscle: you use the muscle in your buttock for sitting and walking.
25.     25. Muscles work by contracting, which means they shorten. As a muscle contracts, it pulls. The larger the muscle, the more powerfully it pulls. Fibres in fibres Skeletal muscles are made of cells called muscle fibres. Inside these are even finer fibres called myofibrils, which contract to make a muscle shorten. When the triceps muscle contracts, it straightens your arm. Where is the body’s smallest muscle? Your forearm contains pairs of muscles that move your hand and fingers back and forth. When the bicep muscle contracts, it pulls your forearm and bends your arm. Bundle of muscle cells One muscle cell Moving muscles 26 How muscles work Myofibrils inside a muscle cell A typical muscle Working in pairs Muscles can pull but not push. They work in pairs that pull in opposite directions. When one muscle pulls, its partner relaxes.
26.     26. Tendons Muscles are fastened to bones by tough bands called tendons. When you wiggle your fingers, you can see the tendons move on the back of your hand. No rest Muscles work all the time. They hold you upright - without them you would flop on the floor. Muscles also work when you are asleep, keeping your body firm and toned. Making faces Muscles in your face are attached to skin as well as bone. They pull the skin when you change your expression. You use about 17 muscles when you smile. A floppy start A newborn baby has little control over his head or neck muscles. It takes about a month before it can hold up its head, and six months for strong, steady head control. Getting a stitch If you run a lot, you may get a pain in your side. This is a stitch. Scientists aren’t sure exactly why it happens but it might be because the muscles and ligaments in your abdomen are working too hard. 27Intheear. How muscles work Try raising your ring finger with your hand in this position. It’s stuck because it’s joined to the same tendon as the middle finger. Ring finger Middle finger
27.     27. The more you use your muscles,the better they get. Active games and exercise make your muscles larger, stronger, and more flexible. They also help you keep going without tiring. Flexibility When you’re flexible, your joints and muscles can move freely and your body can bend and straighten easily. Exercise that stretches your body, such as gymnastics or dancing, improves your flexibility. Muscle power Strength Pushing, pulling, and lifting make your muscles bigger and stronger. Bodybuilders lift heavy weights over and over again until their muscles are enormous. Stamina If you have stamina, you can keep going for a long time without getting tired. Exercise that makes you feel out of breath, like running, improves your stamina. 28 Moving muscles Become an expert ... on how your heart works, pages 50-51 on healthy food, pages 106-107 You need strong muscles to win a tug-of-war. What happens to muscles if you don’t exercise? This contortionist has made her body more flexible by doing exercises that stretch her back.
28.     28. Body heat This picture shows the heat of a man’s body. Muscles make heat when they work hard, which is why exercise makes you hot. On cold days, your muscles try to warm you up by shivering. Ways to keep fit Exercise is very good for your health. As well as making your muscles bigger, it strengthens your heart and lungs. Walking to school, or going out for walks, builds strength and stamina. Football is great for improving your flexibility and strength. Swimming strengthens your heart muscle and builds stamina. Cycling strengthens your leg muscles and builds up stamina. Muscle food To build strong muscles, you need a type of food called protein. Meat, fish, beans, milk, and eggs are rich in protein. 29Theygetsmallandweak. Muscle power Dancing keeps your body supple and helps build strength. Milk Egg Beans Chicken Fish Most vegetables don’t contain much protein. Fish is a very good source of protein.
29.     29. 30 Brain and senses The brain is the body’s control centre. It is a complicated organ that works very quickly, a bit like a brilliant, living computer. Muscle control Your cerebellum helps you to balance and move your muscles. You use this bit of your brain when you dance. Clever calculator The cerebrum is also responsible for thinking, speaking, and complicated tasks such as sums. Sense signals The cerebrum is the main part of your brain. It gets and stores sense information and also controls your movements. Your brain stem works at the same rate whether you’re awake or asleep. Does your brain hurt when you have a headache? Cerebrum Headquarters 24 hours a day Whatever else you do, the brain stem makes sure your heart and breathing never stop. Br ainstem Cerebellum
30.     30. 31No,yourbraincan’tfeelpainbutthemusclesaroundyourheadcan. Headquarters Curiosity quiz Take a look through the brain and senses pages and see if you can spot where these come from. 31 Short-term memory Your short-term memory only holds information for about a minute. You use it to compare prices when you go shopping, or to remember a name when you meet someone new. Learning When you learn to do something you create connections between cells in your brain. Next time you do it the connections are already there so it is easier. Brain box Your skull is a bony shell that fits together like a jigsaw around your brain. Shock- absorbing liquid fills the space between the brain and skull. Long-term memory Your name, phone numbers you know by heart, and skills such as riding a bike can be kept for many years in your long-term memory. In relation to the size of our bodies, humans have the biggest brains of any animal. Skull Brain
31.     31. No need to think You do some things without needing to think about them. These are called reflex actions and include blinking, coughing, and the knee-jerk reflex. Brain cells viewed through a microscope. Needing to urinate is a response to the message that your bladder is full. Itching is an irritating feeling. Your body reacts by making you scratch. Network of nerves Quick as a flash Nerve cells lie next to one another forming long chains. They pass messages to their neighbours – rather like a speedy relay race – to and from the brain. You’ve got 150,000 km (93,200 miles) of nerves in your body. Brain A good night’s sleep Your body and brain slow down when you sleep, but they don’t stop working. Your brain needs sleep to sort out the events of the previous day. Messages Your brain controls your body. It receives messages from all parts of your body and decides what to do. Pain gets a very quick response. You move away from what’s hurting you. Walking is the result of your brain telling your leg muscles to move. Hunger is your stomach telling your brain that it’s empty and you must eat. Blinking happens without you needing to think about it. Breathing is automatic too. It carries on even when you are asleep. Messagestravelfasterthanahigh-speedtrain. Pins and needles Sitting cross-legged for a long time squashes the nerves in your legs. When you stand up, the nerves start to work again, producing a tingling feeling. Cross your legs and tap just below the knee. BrainandsensesNetworkofnerves Whichisthelongestnerveinyourbody?Theonerunningfromyourbigtoetothebaseofyourspine.3332 All of the body contains nerve cells. These link up to form the network of nerves we call the nervous system. It transports messages between the body and the brain. Pain-killers When you get a filling, the dentist gives you an anaesthetic. This drug stops nerves passing on pain messages for a short time. Spinal cord – the centre of the network Your knee jumps forwards even though your brain hasn’t told it to move.
32.     32. Your skin is in immediate contact with the world. Using your sense of touch allows you to tell if something is hot or cold, dull or sharp, rough or smooth, or wet or dry. How many touch receptors are in a fingertip? Brain and senses Touchy feely Things we can feel Skin is packed with many sense receptors. Each sort responds to different sensations. 34 Ouch! The body has its own system of alarm bells. Pain receptors warn us when a part of the body has been hurt or is about to be harmed. This girl quickly moves her finger away from the thorn to stop the pain. It feels slimy!.... Merkel’s disk responds to light touch and is sensitive to the texture of things. Meissner’s corpuscle senses light touch. Warmth is detected by nerve endings quite close to the surface of the skin. Light touch sensors lie at the root of hairs on your arms and legs. Vibrations from an electric drill trigger vibration sensors. Tickly feelings result from a light and unexpected touch. Cold is felt by different sensors to heat. Extreme cold registers as pain. Deep touch sensors enable you to grip things tightly. Not worth noticing Although your brain receives messages all the time, it filters out the less important ones. That’s why you’re not constantly aware of the clothes against your skin. Sensitive fingertips full of receptors are able to tell coins apart.
33.     33. 35 Reading by touch Braille is a system that uses raised dots to represent letters and numbers. It was invented so that people with bad eyesight would be able to read by feeling the page with their fingertips instead of looking at words. About3,000.That’sroughlythesameasonthewholeofthetrunkofyourbody. Sensitive bits Skin contains more touch receptors than any other part of the body. But some areas are more sensitive than others. Fingertips are packed with sensors, especially light pressure receptors. Touchy feely Lips have very thin skin which is good at detecting heat and cold. Toes are very sensitive, but thick skin makes the heel less sensitive. get into it Put one finger in cold water, one in hot, then put both in warm water. The water feels cold to the hot-water finger and hot to the cold-water finger. Under the skin Dead cells form the surface of your skin. Below that lie sweat glands, hair follicles, and different types of sensory receptors. B I R D Braille was invented over 150 years ago. Surface of skin Free nerve endings respond to heat, cold, and pain. The Ruffini ending responds to firm or continuous touch. .... the message shoots off to the brain....Fat Dermis The Pacinian corpuscle responds to firm pressure and vibration.
34.     34. Try putting sugar on different places on your tongue. It tastes sweeter in some places than others. Now try salt, lemon juice, and coffee. get into it We need to eat and drink to survive, but taste and smell are what make these everyday activities so enjoyable. Taste and smell Taste detector Your tongue is a big muscle covered in clusters of taste buds. Each cluster recognizes a particular kind of taste. Sweet Salt Salt Bitter Sour Taste buds Saliva in your mouth dissolves your food. The food washes over tiny taste buds between the bumps on your tongue. Taste buds recognize different flavours. Sour Bitter foods, such as coffee can be bad for you. Most poisons are bitter. Sour foods include lemon and vinegar. Food that has “gone off” tastes sour. Salt detecting taste buds can be found on the lips as well as on the tongue. Sweet foods naturally attract us. Our first food – milk – is sweet. 36 How much saliva does an average person produce in a day? Brain and senses Different tastes There are five types of tastes – bitter, sour, salty, sweet, and umami. Umami is the savoury taste of foods like soy sauce and mushrooms. 10,000taste buds are crammed onto your to ngue.
35.     35. Runny nose When you have a cold, tiny hairs in your nose get clogged with mucus. This stops them wafting smell particles deep into your nose and makes it difficult to smell – and taste – things. S ome noses can recogniz e10,000differentsme lls. 371000-1500millilitres(35-53floz). Taste and smell Smell receptors Special cells deep inside your nose recognize scent particles floating in the air. These cells link directly to your brain. Sensitive nose Much of what we think of as taste is actually smell. The back of your nose is linked to your mouth so you can smell your food as you chew it. Your nose and mouth are linked at the throat.
36.     36. Sight is the body’s main sense and the main way we learn about our surroundings. Two-thirds of the information we take in comes from our eyes. Wandering eyes Six muscles control each eye. You use both eyes when you look at something, so your eyes move together. Look out! Iris 38 What is the sleep that collects in our eyes? Brain and senses Hidden away Most of your eye nestles safely in its socket and is protected by pads of fat. On the outside, you can see the iris, pupil, and some of the sclera. EyelidPupil Iris Pupil The middle of the eyeball is filled with fluid.The muscles surrounding your eyeball make precise movements so you can smoothly track moving objects. Sclera (or white of the eye) Atn ight,oureyescouldd etect a lighted candle 1.6km(1mile)away. Anirisisasun ique asafingerp rint Sclera
37.     37. Crying Tear glands behind your eyes produce drops of salty fluid. When you blink, your eyelids sweep this fluid over your eyes to keep them clean. If something gets into your eye, or you feel strong emotions, the drops turn into floods of tears. Eye colour The iris is the coloured part of the eye. All eye colours are produced by one substance, melanin. Lots of melanin results in brown eyes, less means a lighter shade. 39Dustandmucuswashedfromoureyesaswesleep. Look out! Either it’s dark or this person has seen something they like. Pupil size The pupil is the opening that controls how much light enters your eye. It’s smaller in bright light to protect the nerve cells in your eye, and bigger in dim light to let more light in. It also gets bigger when you see something or someone you like. Bone in your skull surrounds your brain and the backs of the eyes. Eyebrows sit above your eyes and prevent sweat dripping into them. Eyelids and lashes stop dust entering the eyes and then sweep it well away. Safekeeping Your eyes are fragile, squidgy balls made of watery jelly so they need to be well protected. Your pupils change size automatically. Tears drain into tear ducts. These link to your nose, which is why your nose runs when you cry. Tears are made behind each eyelid.
38.     38. Inside your eye is a lens like the lens of a camera. Its job is to focus light on the back of your eye so you can see things clearly. What is an eye specialist who tests eyesight called? Brain and senses How we see How your eye works Light from an object enters your eye through the pupil. It passes through the lens, and makes an upside down image on the retina at the back of your eye. Cells in your eye send messages down the optic nerve to your brain. Your brain flips the image back the right way round. Lightre flects off an object and enters your eye. Seeing in colour Your eyes contain millions of cells. Cone cells give you colour vision but don’t work well in dim light. Rod cells work well in dim light but see everything in shades of grey. The pupil is a hole that lets light into the eye. Optic nerve The lens is clear and flexible. It focuses on things by changing shape. The retina contains cells that sense light. An object The eye is filled with a semi-solid jelly. 40
39.     39. 41 Contact lenses These work like mini glasses and sit directly in front of the eye. They’re a bit fiddly, but once they’re in you can’t feel them at all. Anoptician. How we see Glasses bend the light entering your eye so it focuses on the retina. Colour blindness Some people cannot tell certain colours apart, especially red and green. This is called colour blindness. It is more common in men than women. Short eyeball If you have a short eyeball you will have difficulty seeing things close up. This is called long sightedness. Blurry vision Sometimes an eyeball is the wrong shape. The lens cannot focus light on the retina and everything is blurry. Glasses make the light focus in the right place to make things clear. Long eyeball It is difficult to see objects that are far away when your eyeball is too long. This is known as short sightedness. Contact lenses are made of very thin plastic. get into it Canyouseeanu mber? If not, you m aybecolourblind . Close one eye and hold a finger in front of your nose. Open that eye and close the other one. The finger appears to move! Each eye sees things differently.
40.     40. Your brain works out what you’re seeing by comparing the images it gets from your eyes to things you have seen in the past. Sometimes it can be fooled! Yourbr ain combines images from bo th eyes. Your blind spot is the part of the eye that can’t see anything. It is where the optic nerve leaves the back of your eye. Brain and senses Eye to brain What can you see? The dark blue in these pictures shows how much animals can see clearly. Light blue shows what they can see less well. Humans have to move their heads to see clearly to the sides or look back. Tigers see well to the front to help them find and catch their prey. Zebras keep a look out for movements to the sides so they can avoid attack. To the brain Our eyes swivel around constantly, taking in sights and adjusting to focus on different things. The information they collect travels to the brain through the optic nerve at the back of the eyes. The yellow areas are the parts of your brain that deal with information from your eyes. Ducks can see all the way behind them, even while facing forwards. Chameleons see small areas clearly. They swivel their eyes to see all around. Eyeball Optic nerve 42 What is it called when you look at something and think it’s something else?
41.     41. Eye to brain Finding your blind spot Close your right eye and look directly at the star. Slowly bring the book to your left eye. You reach your blind spot when the circle disappears. Tallest tower Does the green tower look taller than the others? That’s because it’s further along the track and we expect objects further away from us to look smaller. The colours of the towers also affect the size they seem to be. In fact, all the towers are exactly the same size. Recognizing objects Your brain is very clever – it can recognize this car from different points of view. A computer would have to be taught that both these pictures are of the same object. Do you believe your eyes? Your brain helps your eyes to understand what they see. Sometimes you see things that aren’t actually there... Certain patterns trick your eyes into seeing movement where there is none. 43Anopticalillusion. You see a heart even though the edge of the shape isn’t there because your brain uses the information it has to fill in the gaps.
42.     42. Adults have quite a small range compared to other animals. Children hear higher notes than adults. Your range shrinks with age. Cats, dogs, and rabbits can hear much higher notes than people. When you shout you send out invisible sound waves through the air. Your ears pick up the waves and transmit the sound to your brain. Listen here Why two ears? Sounds normally reach one ear first and then the other. This helps our brains work out where sounds are coming from and how far away they are. The speed of sound We don’t notice the slight delay between someone’s lips moving and the sound actually reaching our ears. It’s too fast! Why do we have ear wax? Brain and senses Bats have excellent hearing. Their range is five times as large as ours. How well can you hear? Your hearing range is from the highest to the lowest notes that you can hear. Headphones feed different sounds into each ear so you feel as if you’re surrounded by instruments. Sound travels through the 44
43.     43. A little help Partially deaf people may use hearing aids. These make the sounds entering the ear louder and easier to hear. Outer ear What we call the ear is really just the part that we can see. Sounds are collected here, and funnelled inwards. Middle ear Sounds arriving here from the outer ear cause the eardrum to vibrate and set off movements in three tiny little bones. Toprotecttheskinliningtheearcanal,trapdust,andrepelinsects. Listen here Inner ear The bones moving cause vibrations in the liquid deep inside the ear. Tiny hairs in your inner ear pick up these vibrations in the liquid around them. The hairs are attached to nerves, which connect to your brain. Ear canal Ear drum Bones Cochlea Inne rear M i ddle ear air to your ear. Outer ear Tiny hairs are moved by sounds. Signals travel along these nerves to the brain. 45
44.     44. As well as hearing, ears help you balance. Sensors in your ears work with those in your eyes, muscles, joints, and feet to let your brain know your body’s position. Keeping track Deep inside your ear are three tiny tubes filled with fluid. They detect the movements your body is making and let your brain know about them. 46 Can astronauts learn to balance in space? Brain and senses One tube is for forward and backward movements, another for up and down, and the third for side to side movements. The movements travel along the hairs, through a nerve, to the brain. Balancing act A jelly-like knob floats in each tube. Inside it are sensitive hairs that detect movement. Ear hole The three semi-circular canals deal with balance. Watch your step! Keeping your balance while walking along a narrow wall takes a lot of concentration. You are responding to information coming from your eyes, muscles, and ears at the same time.
45.     45. Muscle messages When you move, sensors in your muscles send messages to your brain. If a movement isn’t going right, your brain will make you do things differently. Motion sickness Travelling in a car, boat, or plane can make you feel ill. Your eyes tell your brain that you’re staying still in the vehicle, but your body says it can feel movement. This confusion is what causes motion sickness. Why do you feel dizzy? The liquid in the tubes of your ear is like water in a cup. When you spin, it continues to slosh around for a while even after you’ve stopped. Your brain gets confused about which way round you are, and you feel dizzy as a result. 47Yes,butitcantakeacoupleofdaystolearnhow. Balancing actThemoreyoupractisethebetteryouwillbeatbalancing. The brain Basically,your brain is the boss. First make sure there is nothing unsafe nearby for you to crash into. Then spin round and round and make yourself feel dizzy. get into it
46.     46. Blood is the body’s transport system. Pumped by the heart, it travels around the body in tubes called blood vessels, delivering vital supplies to keep your cells alive. Tube transport Blood leaves the heart in large blood vessels called arteries, and it returns in vessels called veins. Between the arteries and veins are tiny vessels called capillaries. Around the body Blood travels round your body, passing through organs on the way. It picks up oxygen in the lungs and food in the liver, then gets rid of waste in the kidneys. Capillaries Arteries split into smaller and smaller branches. Eventually they turn into capillaries, which are finer than hairs. Capillaries lead into veins, which join together and get bigger on the way back to the heart. The vena cava is your biggest vein. The aorta is the biggest blood vessel in your body. It is as thick as your thumb. A blue whale’s aorta is wide enough to swim through! Blood picks up oxygen from the lungs and carries it around the rest of the body. From red to blue The colour of blood depends on how much oxygen it contains. Oxygen-rich blood in arteries is brilliant red. Oxygen-poor blood in veins is dark, purplish red (shown blue on the diagram). Vein Capillary Artery 48 Heartandblood Whenyoucutyourself,whatkindofbloodvesseldoesthebloodusuallycomefrom?Acapillary.49 Blood flow Each major organ has an artery bringing fresh blood and a vein carrying away used blood. Become an expert... on breathing in and out, pages 60-61 on air and oxygen, pages 62-63 Kidney Lung Stomach Lung Liver Kidney Veins Arteries Vein Artery Capillaries (60,000miles)ofbloodvesselsinyourbody.Thereareabout100,000km Bloodflow
47.     47. Double pump Your heart is really two pumps in one. One half pumps blood through your lungs, and the other half pumps blood around the rest of your body. Your heart is a pump that pushes blood around your whole body. Each time your heart beats, it squirts out a small cupful of blood and refills for the next beat. Blood goes out to the body. Blood goes out to the body through the aorta. Blood goes out to the lungs. Blood comes in from the lungs Blood comes from the body. Vena cava Aorta Where is it? Your heart is in the middle of your chest, squeezed between the two lungs. You can feel its beat just left of the bone in the middle of your chest. Onesidepumpsbloodtothelungs... 50 How many times does your heart beat in a year? Heart and blood Boom boom Blood from most of the body enters through the vena cava.
48.     48. One-way system To keep blood flowing one way only, your heart and most veins contain valves. Your heartbeat is the sound of valves shutting when your heart squeezes. Valves stop blood flowing backwards. Blood goes out to the lungs. Curiosity quiz Take a look through the heart and blood pages and see if you can spot any of the cells and tissues below. Beating faster Muscles need extra blood when you’re active, so your heart speeds up. It beats about 70 times a minute if you’re resting but up to 200 times a minute if you’re running. About40milliontimes. Boom boom ...and t heotherpumpsbloodeverywhereelse. 51 get into it Find your pulse by pressing two fingers on your wrist. You should be able to feel a gentle throb as your heart pumps blood around your body. Blood comes in from the lungs.
49.     49. Blood is a warm, soupy mixture of liquid and cells. The cells carry oxygen and fight germs, and the liquid carries nutrients to body cells and takes away waste. Heart and blood Main ingredients Blood contains three types of cells – red blood cells, white blood cells, and platelets. They float in a yellowish liquid called plasma. Redbloodcells make blood red. 52 One drop of blood contains 5 million red blood cells, half a million platelet cells, 7,000 white blood cells, water, sugar, salt, hormones, vitamins, fat, and protein. Lots of plasma Yellow plasma makes up more than half of your blood. Become an expert... on fighting germs, pages 78-79 on air and oxygen, pages 62-63 Red blood cells transport oxygen from your lungs to the rest of your body. White blood cells seek out and kill germs. They also eat up the dead cells that they meet. How long does a red blood cell live for? White blood cells and platelets. All about blood
50.     50. People with blood group O can donate blood to almost anyone. People with blood group B can give blood only to people with B or AB. How much blood? The average adult has about 10 pints (5.7 litres) of blood, but a newborn baby has only a cupful. Blood bank One in ten people who go to hospital need extra blood, so hospitals keep a store of blood in a “blood bank”. The blood is divided into separate supplies of cells and plasma. Your blood type There are four main types of blood, called blood groups. Your blood group affects who you can donate blood to. People with blood group A can give blood only to people with A or AB. People with blood group AB can only give blood to others with AB blood. A O B All about blood The amount of blood in your body grows with you. By age 10 you have up to 4 pints (2 litres). Platelets are cells that become sticky to make blood clot and form scabs. White blood cells andplateletsfightd isease. By a year old a baby has more than 1 pint (half a litre) of blood. Aboutfourmonths. AB
51.     51. Blood cells White blood cell Nearly half the cells in your body are blood cells. They wear out quickly, so you make three million new ones every second. Most are made in bone marrow, a jelly-like tissue in hollow bones. Tiny tunnels Red blood cells are soft and rubbery so as to squeeze through tiny gaps. In the smallest blood vessels they travel in single file. All the bumping and squeezing eventually wears them out. Red blood cells The most common cells in your body are red blood cells. They are circular with dimples in each side. Inside they are packed with a red protein which carries oxygen and is called haemoglobin. 54 Which cells in the human body contain iron? Heart and blood
52.     52. Questiontext? Seeing red You can often see people’s blood in photographs. If you take a picture with a flash, the light reflects off red blood cells in the back of their eyes, turning the pupils red. Soldier cells There are lots of different white blood cells and they all help guard your body against invasion by germs. Some white blood cells creep along the walls of blood vessels and eat any germs they find. Others make chemicals that destroy germs. This white blood cell eats pus and germs. Pupils are normally black but they look red in photographs taken with a flash. Platelets stick together in a blood clot. This white blood cell crawls between other cells looking for germs. 55 Blood cells Stick together Platelets are tiny fragments of cells that help blood to clot. They cluster around breaks in blood vessels and grow spiky stalks that help them stick together. Redbloodcells. Thicker blood When people climb high mountains, their bodies make extra red blood cells to help them breathe in the thin mountain air. As a result, their blood gets thicker.
53.     53. Caught in a net The chemicals released by platelets cause tangled fibres to form in the liquid part of blood. The fibres trap blood cells like fish in a net, forming a solid plug that gets bigger and bigger. Clotting The moment you cut yourself, your blood starts turning solid, or clotting. The clot quickly plugs the broken blood vessels and stops them from leaking. 56 How long does a small cut take to stop bleeding? Blood has the amazing ability to turn from liquid to solid in minutes and so help mend cuts in your skin. Bumps and cuts Tangled fibres trap blood cells. Heart and blood Platelets in the blood start to work as soon as you get a cut in your skin. Platelets in action Platelets start the clotting process. They change shape to become stickier and cluster around the cut. At the same time, they release chemicals into the blood.
54.     54. Bloodsucker A leech is a kind of worm that bites your skin and sucks out your blood. Leech saliva contains chemicals that stops blood from clotting. As a result, the cut keeps bleeding until the leech is full. First aid A plaster can help a cut to heal by closing the skin and keeping out dirt. Plasters also stop you scratching, which can make a cut worse. Scabs keep out germs while new skin grows. Leeches live in wet, swampy places. They often slip down people’s shoes and bite their feet without being noticed. 57Betweenthreeandeightminutes. Bumps and cuts Bumps and cuts Painful bumps and cuts are a part of your body’s natural healing process. Platelets stick to each other and to other blood cells, causing a clot to start forming. After a few minutes, the clot is thick enough to stop blood escaping from the wound. Blisters are bubbles of liquid that form when skin is rubbed a lot. Don’t pop them! Bruises are patches of blood under the skin. They change colour as they heal. Black eyes are bruises that form when blood pools under the skin around the eye. A graze is a group of tiny cuts. It forms when something rough scrapes the skin quickly. Scabs When a blood clot dries, it forms a scab. New skin slowly grows underneath the scab, repairing the wound. When the skin is ready, the scab becomes loose and drops off. can stop blood fr om clotting.Vampire bats an d leeches
55.     55. A hormone is a chemical that changes the way part of your body works. Even tiny amounts of hormones are powerful. Some work slowly over years, but others have instant effects. What carries hormones around the body? Main gland Hormones are made in parts of the body called glands. The most important is the pituitary gland in your brain. Its hormones control many of the other glands. Growth hormone Every day, your pituitary gland releases about eight microscopic doses of growth hormone, mostly when you’re asleep. This hormone makes your bones and muscles grow. The pea-sized pituitary gland is just under your brain. The amount of growth hormone you make in one year is less than this tiny pinch of sugar. Heart and blood Hormones 58 Growing up Toddlers and teenagers have very high levels of growth hormone, which is why they grow so quickly. Adults also make growth hormone, but the level falls with age.
56.     56. Become an expert ... on growing up, pages 102-103 on sleep, pages 108-109 The fright hormone The hormone adrenaline makes you feel scared or excited. It works in an instant, preparing your whole body for sudden action in case you need to escape from danger. Control chemicals Hormones are important – they control many body processes. Oestrogen is the female sex hormone. It turns little girls into adult women. People with diabetes prick their skin to get a drop of blood, so they can check how much sugar it contains. Hormones Testosterone is the male sex hormone. It turns little boys into adult men. Melatonin helps control the daily cycle of sleeping and waking. Glucagon raises the level of sugar in your blood, giving you energy. Parathyroid hormone tells your bones to release calcium into the blood. Sugar control The hormone insulin helps control the level of sugar in your blood. Some people don’t make enough insulin and have to check their blood sugar level regularly. They have a disease called diabetes. Adrenaline travels to your arms and legs and prepares the muscles for action. Adrenaline makes your heart and lungs work harder. Your heart starts to pound and you gasp as your lungs take in extra air. Your brain becomes alert so you can think quickly. Glands above your kidneys release adrenaline. 59Theblood. Your hairs stand on end, making your skin tingle.
57.     57. We have to breathe all the time in order to supply our bodies with oxygen and to get rid of carbon dioxide. We use our lungs to do this. Air bags The muscle under your lungs is called the diaphragm.It moves up and down as you breathe. How many breaths do you take in a day? Lungs and breathing In and out Your ribs and diaphragm help you to breathe. Your lungs fill with air when you raise your ribcage, then empty out when you lower it. A muscle called the diaphragm helps you do this. The diaphragm is Prepare the air Before the air reaches your lungs it travels through your mouth and nose and then goes down your windpipe. It gets warm and damp on its journey. When you breathe in, your lungs stretch out and take in lots of air. When you breathe out your lungs squash down forcing all the air out. The air travels down your windpipe. This flap shuts when you eat so food can’t go down your windpipe. like a trampoline. You breathe in through your nose or mouth. Each lung is a spongy maze of tunnels. 60
58.     58. Windpipe Air from your mouth and nose enters your windpipe, which goes down your throat into your chest. Then it splits into two passages – one for each lung. Curiosity quiz Take a look through these images related to breathing. You should be able to find them all in the next few pages. 61About23,000. Air bags Air sacs Your lungs are full of tunnels ending in tiny air sacs called alveoli. Here, oxygen from the air passes into your blood. Your blood carries oxygen around every part of your body. A helping hand Some newborn babies have trouble breathing. They are put into an enclosed cradle called an incubator. Extra oxygen is pumped into the incubator for them. The view from the bottom of your windpipe. The alveoli are surrounded by tiny blood capillaries to take the oxygen round the body.
59.     59. The air you breathe contains a life- giving gas called oxygen. Oxygen helps your cells get their energy from food. They would die within minutes if you stopped breathing. Air and oxygen 62 Become an expert... on cells, the body’s building blocks, page 8-9 Puffed out Breathing heavily gives your body extra oxygen so it can work harder. You feel puffed out and pant when your lungs can’t supply your body with oxygen quickly enough. What is in air? Air is all around you, but you can’t see, smell, or taste it. You can feel it when the wind blows. Oxygen from trees Trees help to clean the air by filtering out pollution. They also make oxygen, which they release through their leaves. Lungs and breathing During the day, trees take in carbon dioxide from the air and give out oxygen. You normally take about 20 breaths per minute – more if you’re exercising. Carbon dioxide Oxygen What is the kiss of life?
60.     60. Airless places Not every place has air to breathe, so sometimes people carry their own. 63 Fires burn up oxygen and produce thick, poisonous smoke. Mountain tops have thin air with little oxygen. Space and planets near Earth have no air to breathe. Water contains oxygen, but humans cannot breathe it. How much air? You take in about half a litre (0.8 pints) of air with each breath. If you breathe in deeply you can take in about 3 litres (5 pints) in one gulp. You need to be able to control your breathing to blow up a balloon. Hold that breath! People can spend a few moments under water without breathing. Most people can manage about a minute, but the world record is around six minutes. Wet air Have you noticed that when you breathe onto a window or a mirror it becomes wet? That’s because the air you breathe out is slightly damp. On a cold day you can see the water in your breath turn to steam as it meets the air. When you breathe out under water you make bubbles. Air and oxygen Howmu ch puff ha veyougot ? Awayofhelpingsomeonewhohasstoppedbreathingbyblowingintotheirmouth.
61.     61. Humans can make many more sounds than other creatures. Because the shape of your face affects your voice, your voice is unique. Making sounds Adam’s apple Voice box Your voice box has two jobs. You use it to make sounds, and to seal off your windpipe when you eat so you don’t choke. Air supply You use the air coming out of your lungs to produce sounds. So it’s difficult to speak when you’re breathless. Vocal cords Inside your voice box are two flaps called vocal cords. You make sounds by pushing air between them, causing them to vibrate. Fast vibrations produce high sounds, slower ones, low sounds. Adam’s apple During puberty, a boy’s voice box grows bigger, giving him a deeper voice. You can sometimes see it bulging at the front of the throat. It is known as the Adam’s apple. Closed vocal cords Open vocal cords You can speak, whisper, hum, and shout! Why do babies and children have higher voices than adults? Lungs and breathing 64
62.     62. Snoring Sometimes, when people sleep, the fleshy parts at the back of the nose and throat vibrate as they breathe. This rattling is called snoring. It can also happen when you have a cold. Oo is made by pursing your lips and pushing them out. Ah sounds are made with a low tongue and a wide open mouth. Ee is made by stretching your lips and keeping your tongue up high. Shaping words The air coming from the lungs is shaped by the tongue, cheeks, and lips to form specific sounds. Making music You control your breath when you speak, but you need really excellent breath control to sing or play a wind instrument. Loud sounds The harder air is forced out of the lungs, the louder the sound. So when a baby takes a big gulp of air you can expect a really big cry! z zZZ Z Didgeridoo 65Theyhaveshortervocalcords,whichvibratefaster,producinghighersounds. Making sounds ZZ ZZZZ Do y ou know as norer? Become an expert... on puberty, pages 102-103 on body language, pages 112-113
63.     63. 66 You need to keep your airways clear to breathe at all times. If something gets into your airways you have to get it out pretty quickly! Ah-choo! Why do you close your eyes when you sneeze? Lungs and breathing Sneezing Sneezes are a quick way to get rid of unwanted particles that you have accidentally breathed into your nose. A sneeze can travel asfastas a car!!!!
64.     64. 67Tostopyoureyeballsshootingoutofyourfacewiththeforceofthesneeze. Gulp! The sticky mucus (snot) in your nose and airways traps dust and dirt in the air that you breathe. Every day you swallow about a glass of the stuff. Coughing Irritating particles that have entered your throat are thrown out when you cough. Coughing uses your vocal cords, which is why a noise comes out with the cough. Hiccups Sometimes your diaphragm suddenly tightens, causing air to rush into your lungs. This makes your vocal cords snap closed with a “hic”. Hiccups seem to happen for no reason. Yawning Nobody knows why we yawn but we do know one effect of yawning: more oxygen in the lungs. It seems we yawn to perk ourselves up when we’re feeling tired or bored. Nose hairs The tiny hairs in your nose work like brooms to sweep out any particles that you’ve breathed in. They get trapped in mucus and are swept along to be swallowed down your throat. Safety catch Unlike other animals, human beings use the throat both for eating and breathing. The epiglottis is a small flap of cartilage that shuts off your windpipe when you swallow so food can’t accidentally go down it and choke you. Ah-choo! Yawning is catching! Is there anyone nearby? Give a yawn and see if you can start a yawning epidemic! get into it The flap closes when you swallow. Usually the flap is up, holding your windpipe open.
65.     65. All wrapped up Two layers Your skin has two main layers. The top one – the one you can see – is called the epidermis. Underneath is the dermis, where there are nerves and blood vessels. Skin covers your whole body. It protects you from germs, water, and sunshine, and helps keep your body at the right temperature. House dust Dust is mostly made of dead skin. Dust mites feed on this skin. They live in beds, pillows, and carpets. The skin on your eyelids is the thinnest on your body. There are flat cells on the surface of your skin. These are made from a tough material called keratin. When the cells die, they dry out and flake off. Skin is a sort of s tretchyovercoat. 68 Skin, nails, and hair Dust mites aren’t really this big! They’re so small you can’t see them. Thethickestskinon Magnified skin flakes Skin cells lower down replace the dead ones that flake off. Heavy load Skin is the heaviest single part of your body. It can weigh as much as a bag of shopping. How many dead skin flakes fall off every day? Waterproof seal Skin stops water getting into your body when you have a shower or go for a swim. It also stops fluids escaping from inside you.
66.     66. Cooling down When sweat dries on your skin, it helps to cool you down. Sweat comes from coiled tubes under the surface. It gets out through tiny holes called pores. 69 All wrapped up your body is on the soles of y ourfeet. Sweat Sweat pore Sweat gland Soggy skin When you soak in water for a long time, the top layer of your skin gets waterlogged and wrinkly. If you uncurled a sweat gland, it could be over a metre (3ft) long. Skin colour The colour of your skin is affected by a substance called melanin. The more melanin you have, the darker you will be. When you are outside in the sun, your body produces extra melanin to protect your skin. This melanin makes your skin darker and you get a suntan. Abouttenmillion.
67.     67. get into it 70 Nails work with skin to protect your body. They stop you hurting the ends of your fingers and help you to pick things up. At your fingertips Under a microscope, you can see all the folds and flakes of dry, dead skin. Your fingertips have the most sensitive skin on your body. Sweat leaves almost invisible marks on all the surfaces you touch. Police use fingerprints to help catch criminals. 70 Why do you get white spots on your nails? Skin, nails, and hair Arch Loop Whorl On the surface To the naked eye, your hand looks smooth and solid. The skin around your joints is loose and saggy so you can bend them easily. Roll the soft part of your fingertip on an ink pad. Now roll your inky fingertip on a piece of paper. The mark you make is your very own fingerprint. Fingertip patterns Fingertips are covered with swirly ridges that help you grip things. These are called fingerprints. Everyone has different fingerprints with different patterns such as arches, loops, or whorls.
68.     68. Holding on It would be difficult to hold heavy things if you didn’t have fingernails. They help to make your fingertips straight and strong. The other reason you have fingernails is so you can scratch when you’re itchy! Claws look like nails, but they are stronger and sharper. Beaks are very hard so birds can tear food and crack seeds. Horns contain different kinds of keratin. Rhino horns are made of hair keratin. The inside story Although nails are much harder than skin or hair, they’re made from the same basic material. It is called keratin. When you look at nail keratin close up, it has lots of flaky layers. Nail growth Nails start to grow before you’re born, and they carry on your whole life. They grow quicker on your hands than on your feet. 71Thesespotsmeanthenewnailhasbeenbangedorknocked. At your fingertips Ournail s are like animals’ claws. Bone Nails grow from a root under your cuticle. Cuticle Fat Family connections Like humans, birds and animals have body parts that are made of keratin.
69.     69. Skin, nails, and hair Hair is mostly made of keratin, just like skin and nails. You have about 100 thousand hairs on your head and millions more on your body. Hair close up Each hair is covered with scales that overlap like roof tiles. This makes the hair strong and protects it. Hair is dead tissue, which is why it doesn’t hurt to cut it. Fairly hairy Head hair Lots of body heat escapes from your head, so the hair there is long and thick to keep your brain warm. Fine hairs cover every other part of you except the palms of your hands, soles of your feet, and your lips. Slightly curvy follicles produce wavy strands of hair. Like moulds, follicles shape each strand of hair. Straight hair grows out of straight follicles. Hairgrowsforuptosevenyearsbeforeitfallsout. What’s your hair like? Hair grows out of tiny pockets or follicles. The shape of these pockets controls whether hair is straight, wavy, or curly. How many hairs do you lose from your head every day? 72
70.     70. Smooth surface Some men lose their hair as they grow older. In fact, the hair still grows, but it is shorter and falls out more easily. A few people are born without any hair at all – not even eyelashes. Follicles that are very swirly in shape produce tightly curled hair. Fairly hairy About100. 73 Good food If your head is itchy, you may have head lice. These creatures cling to your hair and suck blood from your scalp. When you play with friends, the lice crawl from one head to another. These fussy bugs like clean heads best. Brrrr... When you’re cold, tiny muscles pull your body hair upright so it forms a fuzzy layer to keep warmth in. When the muscles pull, they make little ridges called goose pimples. Colour chart Hair, like skin, gets its colour from a chemical called melanin. If you have no melanin in your hair, it will be white – if you have lots, it will be jet black. Goose pimple
71.     71. Your body is a walking zoo. It’s covered with bugs that feed and breed on you but are mostly too small to see. Many do no harm, but some, called germs, make you ill when they get inside you. Verucca A verruca (wart) is a patch of thickened skin caused by a virus. The virus often spreads from person to person in places where people walk barefoot, such as swimming pools. Germs Vile viruses Viruses are the smallest living things on Earth. They break into cells and force them to make new viruses. Viruses can cause colds, flu, measles, mumps, and warts. 74 What animal has killed more people than any other? Fighting disease Become an expert... on clearing airways, pages 66-67 visiting the doctor, pages 110-111 These viruses give people colds or the flu. Virus es spread through the ai rincoughsandsneezes.
72.     72. Fungi Some germs are fungi (related to mushrooms). Tinea (ringworm) is a type of fungus that grows through skin like a plant, sending out long thin shoots. 75Themosquito. Germs Big bugs Creatures much bigger than bacteria or viruses also feed on your body and can make you sick. Threadworms live in the large intestine and spread on dirty fingers. Giardia live in intestines and spread in dirty water. They cause diarrhoea. Follicle mites live in the roots of most people’s eye- lashes and do little harm. Mosquitos suck people’s blood and spread germs that cause deadly diseases. Billions of Bacteria There are more bacteria on your skin than there are people in the world. Most do little harm, and some actually protect you from other germs. If you touch rotten food or faeces, your hands will pick up more dangerous bacteria. The tinea fungus grows through your skin like a plant, sending out long thin shoots. Beastly bacteria Bacteria are very common germs that often spread by touch. When bacteria get into cuts, they cause swellings and sores. Certain types cause deadly diseases if they get into your stomach or lungs. Yourha nd lea ves bact eriaona nythin gyoutouch
73.     73. Become an expert... on eyes, pages 38-39 on digesting food, pages 88-89 Although you can’t see them, germs are always landing on your body and trying to get inside it. Your body has lots of clever ways of keeping them out. Saved by spit The liquid in your mouth is called saliva. As well as helping you digest food, saliva protects your mouth, tongue, and teeth from attack by bacteria. Acid attack Glands inside of your stomach make acid, which kills germs you’ve swallowed. Your digestive system then breaks down the germs along with your food. Yuk! The feeling of disgust protects you from germs. Anything that smells revolting or looks horrible is probably full of germs. Disgust stops you from touching it. Poison tears Germs that land on your eyes are washed away by tears, which come from glands above your eyes. Tears contain the chemical lysozyme, which kills bacteria by making them burst open. Sticky business Germs get into your lungs when you breathe in. They get trapped in a sticky liquid called mucus, which lines your airways. Tiny beating hairs continually push the mucus up to your throat to be swallowed. Slimy guts The inside of your intestines are covered with slimy mucus, which stops germs from getting into your blood. Your large intestine also contains millions of “friendly” bacteria, which prevent other germs from growing. Earwax flows slowly out of your ears all the time, flushing out dirt and germs. Body defences FightingdiseaseBodydefences Whichisyourlargestdefensiveorgan?Yourskin.7776 Youma ke about 1 litre (2 p ints)ofsalivaada y.
74.     74. If germs break through your outer defences and invade your tissues, your body fights back. The cells of your immune system hunt and destroy germs. This system also remembers germs and protects you from them in the future. Fighting germs Antibodies attacking germs. Killer cells White blood cells called macrophages kill germs by swallowing them. When a macrophage finds a germ, it stretches out, wraps around the germ, and pulls it inside. Digestive juices then destroy it. 78 Fighting disease This white blood cell is called a macrophage. This germ is being swallowed. How many tonsils are in your throat? Heating up Your body gets hotter when it fights germs, which gives you a high temperature. Antibody Antibodies Some white blood cells make chemicals called antibodies. These stick to the surface of germs, telling other body cells to attack.
75.     75. Killer milk Breast milk contains germ-killing antibodies that protect babies from disease. During the first few days of a baby’s life, the mother makes a special milk called colostrum, which is packed with antibodies. Extra protection Doctors protect you from germs with vaccines. Vaccines contain weak or dead germs that your immune system learns to attack. If the real germ ever gets inside you, your immune system remembers it and attacks very quickly. Tonsils At the back of your mouth are several patches of tissue called tonsils. They are full of white blood cells that fight germs in your throat. However, the tonsils sometimes fill with germs themselves and have to be removed. Lymph system Fluid continually leaks out of your blood vessels and tissues. It returns to the blood through tubes called lymph vessels. Dotted along these are swellings called nodes, which filter out germs. 79Twomainonesandfoursmallerones. Fighting germs The swellings in lymph vessels are called lymph nodes.
76.     76. An allergy happens when your body mistakes a harmless substance for a germ and overreacts to it. Food, plants, dust, pets, and many other substances can cause allergies. Allergies Who gets allergies? If you grow up in a large family or on a farm, your immune system will get lots of practice against germs. Some experts think this makes you less likely to get allergies. What’s the most common type of allergy? Mouth Fighting disease Allergens A substance that triggers an allergy is called an allergen. Dust mites Millions of these tiny beasts, which are smaller than full stops, live in your home. They feed on dead skin. Their microscopic faeces are a major cause of asthma. Dust mites are related to spiders and have eight legs. 80 Antibiotic medicines can give allergic people a rash on the skin. Wasp stings can kill people who are allergic to them. Hair and skin from pets can cause an allergy very similar to hayfever. Moulds grow in damp places. Their powdery spores can cause asthma. Biological washing powder can cause a skin reaction.
77.     77. Hayfever. Inhalers squirt out medicine in a spray, helping people with asthma to breathe. Allergies Hayfever People who are allergic to pollen have hayfever. When they breathe in lots of pollen, their noses run and their eyes get sore. Hayfever is worst in spring and summer, when grass flowers release lots of pollen into the air. Food allergies Foods that cause allergies include strawberries, nuts, seafood, and eggs. These can give an allergic person a skin rash, a runny nose, a sore mouth, nausea, and diarrhoea. Hayfever can make your eyes swollen, watery, and red. Peanuts can be deadly to people with a nut allergy Poison ivy Skin allergies If you touch a thing you’re allergic to, itchy red spots may appear on your skin. Poison ivy plants, make-up, jewellery, and clothes can cause skin allergies. Asthma People with asthma can find it hard to breathe. Their chests feel tight and their breathing becomes wheezy. Asthma can be caused by an allergy to dust mites, cat hairs, or other substances in air. Skin allergies cause itchy red spots that can look just like a nettle rash. Pollen A very common cause of allergy is a powdery dust called pollen which is made by flowers. Pollen floats through the air and enters our bodies as we breathe. 81 Poison ivy
78.     78. 82 Food is made up of large, complicated chemicals that your body has to break into small chemicals that your blood can absorb. This process is called digestion. Which is longer: your small intestine or your large intestine? Tube journey Your digestive system is really just a long, tangled tube. Food travels about 9 metres (30 feet) as it passes from start to finish. Chemical digestion Many digestive organs make juices that break down the chemicals in food. The juices contain enzymes, which turn large food molecules into small molecules. Physical digestion Some parts of your digestive system mash up food physically, just like a food processor does. Your mouth breaks food into chunks. Your stomach then churns these around until they form a slushy liquid. Dragonfly Venus flytrap Digestive system Become an expert... on taste and smell, pages 36-37 on what’s in food, pages 106-107 Rectum Small intestine The Venus flytrap catches insects and digests them with enzymes. Digestive system When you swallow, food passes down a tube called the oesophagus. Liver Large intestine
79.     79. 83Yoursmallintestine. Digesting a meal A large meal takes a day or more to pass through your digestive system. Different digestive organs make enzymes that work on different parts of the meal. Digestive system 6pm Food gets swallowed 10 seconds after it enters your mouth. 10pm A meal spends about 4 hours in the stomach, but very rich food can spend twice as long there. 3am The meal is slowly squeezed through your small intestine, sometimes causing loud gurgling noises. The next day Undigested leftovers reach the end of their journey about a day after you swallowed the food. Fat starts to break down in the small intestine. Bread starts to break down in your mouth. Meat starts to break down in your stomach. The fibre in vegetables isn’t digested. Curiosity quiz Take a look through the digestive-system pages and see if you can spot any of the cells and tissues below. 12 1 2 4 57 8 10 11 6 39 12 1 2 4 57 8 10 11 6 39 12 1 2 4 57 8 10 11 6 39 12 1 2 4 57 8 10 11 6 39 Stomach
80.     80. First teeth Your first teeth start to grow when you’re about 6 months old. The front teeth usually appear first. Adult teeth When you are six your first teeth start to fall out. Adult teeth with deeper roots grow to replace them. Wisdom teeth Your back teeth are called wisdom teeth. They appear when you are 17 or older, and sometimes not at all. Molars at the back of your mouth have a flat edge so you can mash your food thoroughly. Premolars roughly crush and grind your food. They are smaller than molars. Canines grip and tear food using a single rounded point. Incisors at the front of your mouth slice up chunks of food. Types of teeth Your mouth contains a selection of different types of teeth. Each type is designed to do a different job. False teeth If you don’t take care of your teeth they will decay and fall out. Then you will need false teeth. A child has 20 teeth, an adult has 32. 84 We use our teeth to bite off and chew our food. During the course of your life you will have two separate sets of teeth. Digestive system Chew it over What is another name for your first teeth? Roots Without long roots your teeth might break or fly out of your mouth if you bit down hard on your food. The root is held in place by a kind of cement.
81.     81. The sugar in sweets sticks to your teeth, forming plaque. Plaque contains bacteria that causes teeth to decay. Brush your teeth! A sticky mixture of food and bacteria builds up on the surface of your teeth if you don’t clean them properly. It is called plaque. Inside a tooth Deep inside your teeth are lots of blood vessels and nerves. The nerves mean you can feel heat, cold, and pain. Decay Bacteria in plaque can eat through tooth enamel and attack the blood vessels and nerves deep inside the tooth. This is called decay. It hurts, and the dentist may need to give you a filling. Enamel The hardest and toughest substance in your body is tooth enamel. It contains no living cells so it can’t repair itself if it is damaged. Enamel 85Milkteethorbabyteeth. Chew it over Blood vessels and nervesGum Brush twice a day to keep decay away. Enamel
82.     82. Seen close up, your tongue is covered by tiny bumps and stalks that make its surface rough to improve its grip. You start digesting food the moment you bite into it. As your teeth tear the food apart, enzymes in your spit begin to attack it chemically. By the time it reaches your stomach, your meal is unrecognizable. Get a grip Your tongue is a super strong, flexible bundle of muscle that pushes food against your teeth as you chew. It has a rough surface for good grip. What is the scientific name for burping? Digestive system From mouth to stomach Mouth watering The slimy liquid in your mouth is saliva. It moistens food to make it easier to chew and swallow. Saliva also contains an enzyme that breaks down starch, one of the main ingredients in bread, rice, and pasta. UvulaTongue 86
83.     83. Swallowing Swallowing is a reflex action, which means it happens automatically without you having to think about it. When your tongue pushes food to the back of the mouth, the swallowing reflex begins. 87 From mouth to stomach When your stomach is empty, its stretchy wall is full of folds. This flap shuts off your nose when you swallow. Stomach action Your stomach’s wall is made of muscles that squeeze in ripples to churn food about. When the food is ready to leave, the muscles squirt it out. Stretchy stomach Your stomach has a very stretchy wall so that it can expand to hold big meals. Glands in the wall make acid and enzymes that start digesting protein in meat. Tongue Eructation. Food leaves your stomach through a small ring of muscle. Down the tube Swallowed food gets pushed down a muscular tube called the oesophagus. The muscles work so well that you would still be able to swallow if you were standing on your head. This flap closes your windpipe as you swallow.
84.     84. When food leaves your stomach, it enters a long, tangled tube. This has two parts. The first is your small intestine, which is long and narrow. The second is your large intestine, which is shorter but fatter. Digestive system Inside the intestines Small intestine The small intestine finishes off the job of digestion. Digested food soaks through its wall and enters the blood to be carried away. Pushed along Your intestines use a special kind of muscle action called peristalsis to move food along. Rings of muscle in the intestines squeeze behind the food, pushing it. Finger blobs Tiny, finger-shaped blobs called villi line the small intestine. They speed up the absorption of food. A squeezing action travels along the intestine in waves. Muscles push food through your intestines just like this hand pushes a ball along a stocking. 88 How tall would you be if your intestines weren’t coiled up?
85.     85. Poo is stored in a pouch called the rectum before it leaves your body. Inside the intestines Large intestine Undigested leftovers end up in the large intestine. Here, water and some vitamins are absorbed. The rest passes out of your body as poo. Slippery slime The walls of the intestines are covered with a slippery liquid called mucus. Mucus helps food slide along and protects the intestines from their own digestive juices. 89About10metres(33ft)tall. Become an expert... on how muscles work, pages 26-27 on nose mucus, pages 66-67
86.   How long do your kidneys take to clean all the blood in your body? Waterworks Your kidneys act like sieves, filtering unwanted substances from your blood and turning them into urine. If you put your hands on your hips and your thumbs on your back, your kidneys are next to your thumb tips. Urinary system Your body gets rid of waste chemicals and excess water by making urine. Urine comes from two organs called kidneys. They filter and clean blood as it flows through, removing chemicals that your body doesn’t need. Kidney The kidneys clean your blood. Urinary system Your kidneys, bladder, and the tubes connected to them make up your urinary system. The last part of the urinary system is the urethra. Urine comes out of this tube when you go to the toilet. Blood flows in and out of the kidneys through large blood vessels. Urine dribbles away through a tube called the ureter. 90 The ureters carry away urine. The bladder stores urine. The urethra gets rid of urine.
87.     87. About25minutes. Waterworks The fluid leaves through this tube. Blood flows through a knot of tiny vessels. Water disposal Here’s how your body gets rid of water. Urine makes up more than half of the water that leaves your body. Breath contains over a quarter of the water your body gets rid of. Sweat is only about one twelfth of the water leaving your body. Poo is fairly dry and contains only a little bit of your liquid waste. Inside a kidney The blood vessels entering your kidneys divide into smaller and smaller branches. These lead to a million tiny filtering units called nephrons. Water control Your kidneys work together with your brain to control your water level. When this level is low, your brain releases a hormone that makes your kidneys save water. Inside a nephron As blood flows through a nephron, fluids leave the blood vessel and pass to a long, looped tube. Useful chemicals are then reabsorbed into blood. ADH travels to your kidneys in your blood. This part of the brain monitors the water level in blood. Balancing act Your kidneys keep the water level in your body perfectly balanced. If you drink too much, your kidneys make watery urine to get rid of any excess. When your body is short of water, your kidneys pass less into your urine. When the water level is low, the pituitary gland releases the hormone ADH. Fluid passes out into a chamber. 91 A low water level also triggers a feeling of thirst, making you drink. Your kidneys save water, making your urine stronger.
88.     88. All day long, a small stream of urine trickles out of each kidney. It collects in an organ called the bladder, which stores the urine until you go to the toilet. How much urine do you make each day? Urinary system X-ray of full bladder X-ray of empty bladder The stretchy bladder Full stretch An adult’s bladder stretches from the size of a plum to the size of a grapefruit and can hold about 500 ml (1 pint) of urine. Your bladder is about the size of an orange when it’s full. Filling up Your bladder stretches as it fills up. This sends a signal to your brain, making you want to go to the toilet. 92 Grapefruit Orange Plum Inside the bladder The bladder has a waterproof lining to stop it leaking. Urine leaves through a tube called the urethra, which is normally kept shut by two muscles. The bladder’s muscly wall squeezes to push urine out. Nappy rash Babies sometimes get a rash under nappies. This happens when urine mixes with poo and makes the skin sore.
89.     89. The stretchy bladder Bladder control In young children, the muscles that open the bladder work automatically. As children get older, they learn to control one of the muscles. Potty training Children gradually gain control of their bladder around the age of two, but they still wet the bed at night. By the age of four, most children can stay dry at night as well. Tubes called ureters bring urine from the kidneys. Camel urine Camels can last for months without water so they can survive in the driest deserts. They save water by making thick, syrupy urine that is twice as salty as seawater. Camels store fat in their humps, which they use for energy. Toddlershavetolearnbladdercontrol. What is urine? Urine is made of water and waste chemicals. The main waste is urea, which your body makes when it breaks down protein. The colour of urine depends on how much you drink. If you drink lots of water, your urine will turn pale. This muscle opens automatically when the bladder is full. We have to learn to control this muscle. 4-8cupfuls,dependingonhowmuchyoudrinkandsweat. 93 Urethra The yellow colour comes from a chemical that is made when old blood cells are broken down.
90.     90. The first cells After 36 hours, the cell has divided and made an exact copy of itself. These are the first two cells of a baby. 94 Making a baby What is another name for the uterus? Eggs are the biggest cells in the human body. But they are still very small – ten would fit across a pinhead. Reproduction and growth Sperm race Millions of sperm swim towards the egg cell. Only one sperm can join with the egg to make a new cell. By the time the baby is born, the fertilized cell will have become 100 trillion cells. Sperm are amazing viewed under a microscope. They look like tiny tadpoles. You can see their tails wriggling as they swim. You need a mother and a father to make a baby. The mother’s body does most of the work, but the father also has an important job – his sperm joins with the mother’s egg and a new life begins...
91.     91. Divide again You don’t grow much in the first few days. The two cells divide to make four, then eight, and so on. At three days The cells have carried on dividing. There are now 16 cells and they are almost ready to plant themselves in the uterus. The future you Each cell is unique to you. Cells are full of instructions about what you will look like. 95 Arriving in the uterus The ball of cells plants itself in the wall of the uterus. In this warm, dark place the baby will spend the next 40 weeks growing and developing. Thewomb. Where it all happens The sperm fertilizes the egg in a tunnel, called a Fallopian tube. The fertilized egg moves down the tunnel towards the mother’s uterus. The journey takes about five days. This is the uterus. It is about the size of a pear and has muscular walls. The cells start dividing as they move down the Fallopian tube towards the uterus. This is the mother’s ovary. It releases one egg every month. Making a baby Millions of sperm from the father travel up here towards the egg..
92.     92. The size of a strawberry The foetus has eyes, a nose, lips, and a tongue. It lives in a protective bag of liquid and uses its tiny muscles to swim around gracefully. The size of a lemon At 16 weeks the foetus can make different faces, clench its fist, and suck its thumb. It can hear its first sounds but its eyes are not open yet. The size of a grapefruit At 20 weeks the foetus is getting more active. It is still quite small so there’s plenty of room to kick around and turn somersaults. Food and oxygen from the mother travel through this special cord. Eight weeks old . Sixteen weeks o ld. Twe nty weeks old. 96 By eight weeks old, the baby is no longer a bundle of cells. It looks like a tiny person and is called a “foetus”. The foetus does not eat, drink, or breathe by itself. All its needs are taken care of by its mother. When do we first start to dream? Boy or girl? Parents can find out about a baby’s health and sex before it is born. A scanning machine shows the baby on a screen. This is many parents’ first sight of their child. Parents often choose not to find out their child’s sex so they can have a surprise on its birthday. Reproduction and growth Growing in the womb
93.     93. 97 Happy birthday! At last, after around 40 weeks, the moment comes for the baby to be born. Newborn babies can breathe, suck, and swallow. They communicate by crying if they are hungry or feel uncomfortable. Beforeweareborn,atabout20weeks. Fuzzy foetus By 22 weeks, the baby is quite well developed but fairly thin. It will spend the next few weeks growing a layer of fat under its skin. It is covered in soft, fine hair. Growing in the womb What’s it like in there? It is quite noisy in the womb with the sounds of the mother’s heartbeat and stomach rumbles. The baby can also hear noises outside the womb and loud bangs may make it jump. It learns to recognize its mother’s voice long before it is born. Twenty-two week sold. You might feel the baby move if you put your hand on a pregnant woman’s tummy.