How Our Body Works: A First Guide

Your Amazing Body

Right now, without even thinking about it, your body is doing hundreds of jobs. Your heart is beating. Your lungs are breathing. Your tummy is busy turning your last meal into energy. Your brain is reading these very words. And all of this happens at the same time, every second of every day.

Your body is the most amazing machine you will ever own. It is made of many different parts, and each one has its own special job. But the real magic is that all these parts work together as a team.

In this book you will take a tour of your own body. You will meet your bones and muscles, your busy heart and lungs, your clever brain, your hungry tummy, and your five senses. You will also learn how to keep this wonderful machine running well. Let's start with the frame that holds you up.

Your Bones and Skeleton

Reach out and feel your arm. Press gently and you will feel something hard underneath your skin. Those are your bones. All your bones together make up your skeleton.

Your skeleton has three big jobs. First, it supports your body and gives it shape, like the frame inside a building. Without your skeleton you would flop to the floor like a jellyfish! Second, your skeleton protects the soft parts inside you. Your skull is a hard, bony helmet that guards your brain, and your curved ribs make a cage around your heart and lungs. Third, your bones work with your muscles to help you move.

A grown-up has 206 bones. The smallest bones are deep inside your ears and are tinier than a grain of rice. The longest bone is in your thigh. Bones are strong and hard, but they are not solid all the way through — the inside is a bit spongy, which helps make new blood. Bones can even mend themselves if they break, slowly growing back together.

Your Muscles

Your skeleton holds you up, but it is your muscles that move you. Muscles are soft parts that pull on your bones to make them move.

A muscle works by squeezing and getting shorter. When a muscle squeezes, it pulls the bone it is attached to. Try this: bend your arm up and feel the muscle on the front, called your bicep, become hard and round. That muscle is squeezing to lift your arm. Muscles can only pull, never push, so they usually work in pairs. One muscle pulls your arm up, and a different muscle pulls it back down.

You have muscles all over your body — more than 600 of them! Some you can control, like the ones that move your legs when you run. Others work all by themselves without you even thinking, like the muscle that makes your heart beat. The more you use your muscles, by running, playing and climbing, the stronger they grow.

Your Heart and Blood

Place your hand on the left side of your chest. Can you feel a steady thump, thump, thump? That is your heart beating.

Your heart is a muscle about the size of your own fist, and it has one very important job: it pumps blood all around your body. It never stops, not even when you are asleep. Every beat squeezes blood out through tubes called blood vessels, which carry it to every part of you, and then back again.

Why is blood so important? Your blood is like a delivery service. It carries oxygen and food to all the tiny parts of your body to keep them alive and working. It also carries away the waste your body does not need. Blood is red because of a special part inside it that grabs hold of oxygen.

When you run around, your body needs more oxygen, so your heart beats faster to deliver it more quickly. That is why your heart pounds after you sprint or climb the stairs. A beating heart is a sign that your body is hard at work.

Your Lungs and Breathing

How does the oxygen get into your blood in the first place? That is the job of your lungs.

You have two lungs, one on each side of your chest, protected by your ribs. When you breathe in, air rushes down your throat and fills your lungs like two soft balloons. The air you breathe contains a gas called oxygen, which your body needs to stay alive. Inside your lungs, the oxygen passes into your blood, ready to be pumped around by your heart.

When you breathe out, your lungs push out air that your body has finished with, including a gas called carbon dioxide. So breathing in brings the fresh air your body needs, and breathing out gets rid of the stale air. You breathe all day and all night without even thinking about it — try counting your breaths and you will see how automatic it is.

When you exercise, you breathe faster and deeper, because your working muscles need more oxygen.

Your Brain and Nerves

Inside your skull sits the boss of your whole body: your brain. The brain is the control centre. It helps you think, learn, remember, feel happy or sad, and control everything your body does.

Your brain is always busy. Right now it is helping you read and understand these words. It tells your muscles when to move, keeps your heart beating, and stores your memories of yesterday and last year. It works so fast that you do not even notice.

The brain sends and receives messages through a network of thin threads called nerves, which reach into every part of your body. If you touch something hot, your nerves zip a message to your brain in a flash, and your brain quickly tells your hand to pull away. These messages travel faster than you can blink. Your brain and nerves work together as your body's lightning-fast messaging system.

Your Tummy and Food

When you eat a meal, where does the food go? It begins a journey through a long system called your digestive system, which turns food into the energy and goodness your body needs.

It starts in your mouth. Your teeth chew the food into small pieces, and spit, called saliva, makes it soft and mushy. Then you swallow, and the food slides down a tube into your stomach. Your stomach is like a stretchy bag that churns the food up and mixes it with special juices to break it down even more.

Next, the food moves into your intestines, which are long, coiled tubes. Here, the goodness from your food — the energy and the tiny bits your body needs to grow — passes into your blood to be carried everywhere. The parts your body cannot use carry on through and leave your body when you go to the toilet. This whole journey is how a sandwich becomes the energy that lets you run and play.

Your Five Senses

How do you know what is going on in the world around you? Through your five senses. Each sense uses a special part of your body to gather information and send it to your brain.

• Sight comes from your eyes. They let in light and let you see colours, shapes and movement.
• Hearing comes from your ears. They catch sounds travelling through the air, from a whisper to a roar.
• Smell comes from your nose. It picks up tiny scents in the air, like fresh bread or flowers.
• Taste comes from your tongue. It tells you whether food is sweet, salty, sour or bitter.
• Touch comes from your skin. It feels whether things are hot or cold, soft or hard, smooth or rough.

Your five senses work together to help you understand and enjoy the world. They also keep you safe, by warning you of things like a hot stove or a loud, sudden noise.

Keeping Your Body Healthy

Your amazing body works hard for you, so it is your job to take good care of it. The good news is that staying healthy is simple if you follow a few habits.

Eat well. Your body needs a mix of healthy foods to grow strong, especially fruits and vegetables. Food gives you energy, like fuel for a car. Drink water too, because your body is mostly made of water.

Stay active. Running, jumping, playing and dancing keep your heart, lungs and muscles strong. Sleep well, because while you sleep your body rests, grows and repairs itself. Keep clean by washing your hands, especially before eating, to keep away germs that can make you ill. And brush your teeth to keep them healthy.

Look after your body, and it will look after you.

What We Learned

What a journey through your own body! You really are an amazing machine.

We learned that the body is made of many parts that work together as a team. Your skeleton supports and protects you, while your muscles move you. Your heart pumps blood to deliver oxygen and food, and your lungs take in the oxygen from the air. Your brain is the control centre, sending messages along your nerves. Your tummy turns food into energy, and your five senses help you understand the world. Finally, we learned that eating well, staying active, sleeping and keeping clean all keep your body healthy.

The next time you run, eat or simply take a breath, remember the amazing teamwork happening inside you.

Want to learn even more about yourself? Step inside your head with How Your Brain Works, or read the full guide in The Human Body: An Owner's Guide.