Chapter 4 of 8

All 8 chapters
  1. 1Organs and systems, readunderstood
  2. 2Digestion, readunderstood
  3. 3Nutrients and diet, readunderstood
  4. 4Breathing, readunderstood
  5. 5Gas exchange in the lungs, readunderstood
  6. 6The heart and blood, readunderstood
  7. 7Pulse, breathing and exercise, readunderstood
  8. 8Drugs, alcohol and health, readunderstood

S3.3.4 Chapter 4

Breathing

How does air get into my chest when I breathe in?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Make a model lung with a plastic bottle and a bag
  • Explain how the ribs and diaphragm move air in and out

You breathe all day and all night, and you hardly think about it. How does the air get in? A model will show you. Build it up one step at a time.

Draw it first

Draw the model lung

  1. A model lung drawn in two steps. First, a bottle with no bottom, with a balloon hanging inside on a straw and a sheet stretched flat across the open bottom. Second, the sheet is pulled down, the room inside is bigger, the balloon is bigger, and an arrow shows air coming in through the straw. Labels: straw, balloon, bottle, sheet, air in, pull.strawballoonbottlesheet

    1 Draw a bottle with no bottom. Hang a balloon inside it on a straw. Stretch a sheet across the open end.

  2. A model lung drawn in two steps. First, a bottle with no bottom, with a balloon hanging inside on a straw and a sheet stretched flat across the open bottom. Second, the sheet is pulled down, the room inside is bigger, the balloon is bigger, and an arrow shows air coming in through the straw. Labels: straw, balloon, bottle, sheet, air in, pull.strawballoonbottlesheetair inpull

    2 Now pull the sheet down. The room inside gets bigger, and the balloon fills with air.

In the model, the bottle stands for your chest. The balloon is a lung, the straw is the windpipe, and the sheet is the diaphragm.

Pull the sheet down and the room inside gets bigger. The air in the bottle, round the balloon, is spread thinner, so it squeezes the balloon less. Air from outside squeezes more, so it pushes in through the straw and blows the balloon up.

Push the sheet up and the room gets smaller. The air is squeezed, and it flows out through the straw.

Your chest works the same way. The lungs are two soft bags full of tiny air spaces. They have no muscles that move them. They are filled and emptied by the movement of the chest around them.

The chest from the front when breathing out. The diaphragm under the lungs is a high dome. The ribs are low. The lungs are smaller. A short arrow shows the diaphragm moving up, two arrows show the ribs moving down and in, and an arrow shows air leaving the windpipe. A flat hatched breastbone runs down the middle between the lungs, below the windpipe. Labels: windpipe, ribs, lungs, diaphragm, breastbone, air out.ribswindpipelungsair outbreastbonediaphragm
Breathing out. The diaphragm domes up. The ribs move down and in. The chest gets smaller.
The chest from the front when breathing in. The diaphragm under the lungs is flat and lower. The ribs are higher and further out. The lungs are bigger. An arrow shows the diaphragm moving down, two arrows show the ribs moving up and out, and an arrow shows air entering the windpipe. A flat hatched breastbone runs down the middle between the lungs, below the windpipe. Labels: windpipe, ribs, lungs, diaphragm, breastbone, air in.ribswindpipelungsair inbreastbonediaphragm
Breathing in. The diaphragm tightens, flattens and moves down. The ribs move up and out. The chest gets bigger.

The diaphragm is a sheet of muscle under the lungs. When you breathe in, it tightens, flattens and moves down. The muscles between your ribs lift them up and out.

The chest gets bigger, so the air inside the lungs is squeezed less. Its pressure falls, and air from outside flows in. When you breathe out, these muscles relax. The diaphragm goes back up into a dome, and the ribs drop. The chest gets smaller and air flows out.

A standing skeleton seen from the front, with two parts named. The ribs make a cage round the lungs and the heart. The spine runs down the middle of the back. Labels: ribs, spine.ribsspine
The ribs make a strong cage round the lungs. They can still move a little, so the chest can grow bigger.

See it three ways

With things

Put your hands on the sides of your ribs. Breathe in slowly. Feel your ribs move out. Breathe out and feel them go back.

As a picture

Three boxes joined by arrows, each arrow marked with the word air. Nose or mouth, then windpipe, then lungs. Labels: nose or mouth, windpipe, lungs, air.nose or mouthwindpipelungsairair

In words

Air goes in through the nose or mouth. It goes down the windpipe and into the lungs. It comes out the same way. This is breathing in and breathing out.

Try it

Make a model lung

You need: a clear plastic bottle, a balloon, a straw or a short tube, a strong plastic bag, string and tape, a grown up to cut the bottle.

Be safe: A grown up must cut the bottle, because the cut edge is sharp. Cover it with tape. Never put the straw or the balloon in your mouth. Keep balloons and bags away from small children.

  1. A grown up cuts the bottom off the bottle. Cover the cut edge with tape.
  2. Push the straw into the neck of the balloon. Tie it tight with string.
  3. Push the straw through the neck of the bottle, so the balloon hangs inside. Seal the neck with tape, so air can only move through the straw.
  4. Tape the plastic bag over the open end of the bottle, a little loose. Tape a small tab to the middle of the bag, to pull it by.
  5. Pull the tab down, gently. Then push the bag up, gently. Watch the balloon each time.

What you will see: When you pull the bag down, the balloon fills. When you push the bag up, the air comes out of the balloon.

If you cannot try it, this is what happens.
The model lung when the sheet is pushed up. The sheet bows up into the bottle, the room inside is smaller, the balloon is smaller, and an arrow shows air leaving through the straw. Labels: straw, balloon, bottle, sheet, air out, push.strawballoonbottlesheetair outpush

A wrong idea many people have

The lungs are muscles that pull air in.

Why it feels right: Your chest moves when you breathe, and the lungs are inside it.

The test that breaks it: In the model, nothing pulls on the balloon. It fills only because the room around it grows. Your lungs work the same way.

What is true: The lungs have no muscles that move them. The diaphragm and the rib muscles change the size of the chest. Then air flows in or out.

Key words

lungs
the two soft bags in the chest that fill with air.
windpipe
the tube that takes air from the nose and mouth to the lungs.
ribs
the curved bones that make a cage round the lungs.
diaphragm
the sheet of muscle under the lungs.
breathing in
taking air into the lungs. The chest gets bigger.
breathing out
pushing air out of the lungs. The chest gets smaller.

Back to your guess

The answer is B: The ribs and a sheet of muscle make the chest bigger, so air flows in.

The lungs have no muscles. A sheet of muscle called the diaphragm and the ribs make the chest bigger. Then air flows in.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. In the bottle model, which part stands for the diaphragm?

    Tap your answer.

    1. Yes, that is right. The sheet is pulled down and pushed up. In the body, the diaphragm moves down and up in the same way.

    2. Not this one. The balloon stands for a lung. It is filled by air, not pulled by muscle. Go to S3.3.4. Try another.

    3. Not this one. The straw stands for the windpipe. Air goes through it. Go to S3.3.4. Try another.

    See the answer

    The sheet over the open end

    The sheet is pulled down and pushed up. In the body, the diaphragm moves down and up in the same way.

    • If you chose B: The balloon stands for a lung. It is filled by air, not pulled by muscle. Go to S3.3.4.
    • If you chose C: The straw stands for the windpipe. Air goes through it. Go to S3.3.4.

  2. In the model, what happens to the balloon when the sheet is pulled down?

    The model lung when the sheet is pulled down. The sheet bows down, the room inside is bigger, the balloon is bigger, and an arrow shows air coming in through the straw. Labels: straw, balloon, bottle, sheet, air in, pull.strawballoonbottlesheetair inpull
    Tap your answer.

    1. Yes, that is right. The room inside gets bigger, so air flows in through the straw and fills the balloon.

    2. Not this one. Pulling the sheet down makes more room, not less. A smaller balloon is what you see when the sheet is pushed up. Go to S3.3.4. Try another.

    3. Not this one. The room grew, so air from outside flows in. The balloon cannot stay the same size. Go to S3.3.4. Try another.

    See the answer

    It fills with air

    The room inside gets bigger, so air flows in through the straw and fills the balloon.

    • If you chose B: Pulling the sheet down makes more room, not less. A smaller balloon is what you see when the sheet is pushed up. Go to S3.3.4.
    • If you chose C: The room grew, so air from outside flows in. The balloon cannot stay the same size. Go to S3.3.4.

  3. When you breathe in, what do the diaphragm and the ribs do?

    Tap your answer.

    1. Yes, that is right. These two movements make the chest bigger, and air flows in.

    2. Not this one. That is what happens when you breathe out. Breathing in makes the chest bigger. Go to S3.3.4. Try another.

    3. Not this one. The lungs have no muscles that pull. The diaphragm and the ribs move. Go to S3.3.4. Try another.

    See the answer

    The diaphragm moves down and the ribs move up and out

    These two movements make the chest bigger, and air flows in.

    • If you chose B: That is what happens when you breathe out. Breathing in makes the chest bigger. Go to S3.3.4.
    • If you chose C: The lungs have no muscles that pull. The diaphragm and the ribs move. Go to S3.3.4.

  4. Why does air flow into the chest when the chest gets bigger?

    Tap your answer.

    1. Not this one. The lungs have no muscles that move them. They are filled by the chest getting bigger. Go to S3.3.4. Try another.

    2. Not this one. The nose and mouth only let the air through. The air flows in because of the bigger room. Go to S3.3.4. Try another.

    3. Yes, that is right. The bigger room squeezes the air in the chest less. Air from outside is squeezed more, so it pushes in.

    See the answer

    The bigger room squeezes the air less, so air flows in from outside

    The bigger room squeezes the air in the chest less. Air from outside is squeezed more, so it pushes in.

    • If you chose A: The lungs have no muscles that move them. They are filled by the chest getting bigger. Go to S3.3.4.
    • If you chose B: The nose and mouth only let the air through. The air flows in because of the bigger room. Go to S3.3.4.

  5. Which path does air take on its way in?

    Tap your answer.

    1. Not this one. The gullet carries food to the stomach. Air goes down the windpipe. Go to S3.3.4. Try another.

    2. Yes, that is right. Air goes in through the nose or mouth, down the windpipe and into the lungs.

    3. Not this one. Air goes to the lungs. The stomach is for food. Go to S3.3.4. Try another.

    See the answer

    Nose or mouth, windpipe, lungs

    Air goes in through the nose or mouth, down the windpipe and into the lungs.

    • If you chose A: The gullet carries food to the stomach. Air goes down the windpipe. Go to S3.3.4.
    • If you chose C: Air goes to the lungs. The stomach is for food. Go to S3.3.4.

  6. From an earlier chapter

    Which tube takes food from the mouth to the stomach?

    Tap your answer.

    1. Not this one. The windpipe carries air to the lungs. Food goes down a different tube. Go to S3.3.2. Try another.

    2. Yes, that is right. The gullet squeezes food down to the stomach. The windpipe is next to it, but it carries air.

    3. Not this one. The large intestine comes at the end of the gut, after the stomach. Go to S3.3.2. Try another.

    See the answer

    The gullet

    The gullet squeezes food down to the stomach. The windpipe is next to it, but it carries air.

    • If you chose A: The windpipe carries air to the lungs. Food goes down a different tube. Go to S3.3.2.
    • If you chose C: The large intestine comes at the end of the gut, after the stomach. Go to S3.3.2.

Keep it

Copy this into your exercise book.

The lungs have no muscles. Breathing in, the diaphragm moves down and the ribs move up and out. The chest gets bigger and air flows in. Breathing out is the reverse.

Draw: Draw the bottle model with the sheet pulled down. Label the straw, the balloon, the bottle and the sheet.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (799 KB). It opens on any phone.