Hi everyone, and welcome to this lesson from the Oak National Academy.

Today's lesson is all about the human gas exchange system and breathing.

I'm sure you've heard of breathing before, but what about the human gas exchange system? Well, the human gas exchange system, also known as the respiratory system, is the organ system in our bodies that enables breathing to take place.

Please don't worry if you've never heard of it before.

That's what today's lesson is all about.

I'm Mrs. Wii, and by the end of today's lesson, you'll be able to describe how humans breathe, including the roles of different parts of the gas exchange system.

Let's look at our keywords.

So our first keyword is gas exchange system, also known as the respiratory system.

They're the same thing.

Then we've got pressure, volume, inhalation, and exhalation.

I'm gonna show you the definitions for our keywords.

I'll explain what each of them mean as we go through the lesson.

But if you like, you can pause the video and read through them or even copy them down so you can refer back to them later.

Here they are.

First off, we'll talk about the gas exchange system.

So all the different parts and what they do, how they help us breathe.

Then we're gonna talk about the pressure and volume changes that occur in the body to enable us to breathe.

But first of all, the gas exchange system.

Have a look at the organisms I have here on my slide.

They're all very different.

We have mammals, fungi, different types of invertebrate, fish, and plants.

They're all different, but there are some things that they all have in common.

For example, there are few things that they all need to stay alive.

One of them is water.

Can you think of another one? Pause the video here and have a think about something else all these very different organisms need to stay alive.

It's oxygen.

Humans, other animals, plants and fungi need oxygen from the air to stay alive.

They need oxygen for cellular respiration in mitochondria in their cells.

Hopefully you remember that cellular respiration provides energy for life processes.

Organisms need this energy to live.

So almost all organisms need oxygen to live, and they all need energy, but not all organisms breathe.

Breathing is a process that you need lungs in order to do.

So if an organism doesn't have lungs, they can get their oxygen they need for respiration in a different way.

Pause the video and have a think about which of these organisms on the slides use their lungs to breathe.

Okay, so the ones that breathe are the humans, the fox, and the owl.

All of the other organisms gain that oxygen through other really interesting methods.

For example, insects have holes on the outside of their body that air diffuses into.

Worms taken air through their skin.

Plants taken oxygen through these tiny holes on the underside of their leaves, which we'll learn all about in a future unit when we learn about photosynthesis.

And you may already know that fish have gills that take and dissolved oxygen from that water around them.

So it's important to remember that whilst the vast majority of organisms need oxygen, they don't all breathe in order to get it.

Humans and some other animals like birds and reptiles breathe to take in oxygen from the air, and this is what we'll be focusing on today.

Breathing involves the lungs.

When we breathe, air is moved in and out of the lungs.

However, it's not just the lungs that are involved in breathing.

We're gonna look at the rest of the organ system that helps us to breathe.

Many parts of our gas exchange system work together to enable us to breathe.

Now the gas exchange system is an organ system, so it's made up of different organs.

Let's look at those different organs now.

To start with, we've got the nose and the mouth.

And next, we have a tube in the throat called the trachea.

The trachea is also known as the windpipe, but I'm gonna refer to it by its proper scientific name, trachea.

Take a deep breath in.

You can actually feel the air entering your nose and your mouth and starting to move down the top of your windpipe, your trachea.

So they all form a passageway for the air to move in and out of the lungs.

Next, we have the lungs, which are a pair of organs in humans and some other animals such as mammals, reptiles, and birds.

Next, we have the diaphragm, which some people find difficult to spell and to say because of that silent G.

So although you might wanna say diaphragm when you see it written, I can assure you it's pronounced diaphragm.

The diaphragm is a sheet of muscle underneath the lungs, which contracts and relaxes to help move air in and out of the lungs.

Right, let's see if we've understood that.

Which structure is not a part of the human gas exchange system? Is it A, the diaphragm, B, the heart, C, the lungs, or D, the trachea? Pause the video whilst you think about that answer.

I'm gonna give you about five-second break.

It is the heart.

The heart is not a part of the human gas exchange system.

Great job if you got that right.

Remember, the diaphragm is a sheet of muscle underneath the lungs.

The lungs are a pair of organs in the chest, and the trachea is a tube that enables air to enter the body.

So the heart is part of the circulatory system, which has to do with providing all of our body with oxidative blood.

It's not a part of the gas exchange system.

Let's look at all the structures that air flows through when we breathe in.

So to start off, the air enters our bodies through the nose and the mouth.

That then flows down the trachea, also known as the windpipe.

The trachea branches off into two smaller tubes called bronchi.

So bronchi is plural.

We say bronchi when we're talking about both of them.

We say bronchus.

That's singular when we're just talking about one of the tubes.

Then the bronchi branch off into bronchioles, which are even smaller.

And then finally, at the end of each bronchiole, we have a tiny air sac called alveoli.

We say alveoli when there's tonnes of them, when we're talking about more than one, and we say alveolus when we're just talking about one of them.

So the tissue of the lungs, the alveoli, there are millions and millions and millions of them, and they massively increase the surface area of the lungs.

Let's see if we can remember that.

Label this diagram of the human gas exchange system.

Pause the video whilst you have a think about your answer.

You've got about five-second break.

Let's go through those answers.

So A was the trachea, B, bronchioles, C, alveoli, D, bronchi, and E, the diaphragm.

Great job if you got all of those.

Starting with the mouth, sort these structures into the order the air passes through when we breathe in.

Pause the video whilst you sort those.

Let's look at the correct order.

It should be mouth, trachea, bronchi, bronchioles, and then alveoli.

Great work.

Here's our first practise task.

Describe the journey of an oxygen molecule from the mouth to an alveolus in the lungs.

Pause the video whilst you write your answer down.

Let's look at the answer.

The oxygen molecule moves from the mouth into a tube called the trachea.

Then it moves into one of two narrower tubes called bronchi.

After this, it moves into an even narrower tube called a bronchiole.

Then the oxygen molecule moves into an alveolus, which is a tiny air sac in the lungs.

Great job if you've got all of those keywords in the right order.

So to understand how breathing occurs, we need to think about pressure and volume.

Imagine a box filled with oxygen gas.

Have a look at this box down there.

I put red oxygen molecules in there to help you visualise it.

So the oxygen molecules in the box move around randomly.

They collide with the walls of the box, and this creates pressure.

Look at these two different boxes now.

What's different about them, and how might that affect their pressure? Pause the video whilst you think about that.

I'm giving you a five-second break.

Box B has a larger volume than box A, but it contains the same amount of gas.

So in box B, the molecules have more space to move around, so they collide with the walls less often, and so the pressure inside the box is lower.

Let's see if we understood that.

Which box has got the largest volume? Is it A, B, or C? Pause the video whilst you have a think about that.

It is C.

Well done if you got that right.

Okay, now look at the same boxes.

Which one has got the highest pressure? Pause the video whilst you think about that.

The answer is A.

Well done so far.

You're doing really well.

Air can move into or out of a container, it will.

It will move in when the pressure inside is lower.

It will move out when the pressure inside is higher.

Let's have a look at example with a syringe.

So if I pull back the plunger, so I've created more space inside the syringe, what's that gonna do to the volume? And so what's gonna happen to the pressure inside the syringe? Pause the video whilst you think about that.

So there's more space in the syringe now, so the volume has increased.

The molecules have got more space to move around.

And so they're less likely to hit the walls of the container, collide with the walls of the container, and that decreases the pressure.

What's gonna happen to the air then? Is it gonna move out of the syringe, or is it gonna move into the syringe? Pause the video whilst you have a think.

Air is gonna move into the syringe.

Well done if you got that.

Let's look at the opposite way around.

So syringe again, except this time, I've pushed down the plunger.

So what's happening to the volume in the syringe? What's that gonna do to the pressure? And then where is the air gonna move? Pause the video whilst you think about all that and see if you can explain why that's happening.

So there's less space in the syringe now, so the volume has decreased.

That's increasing the pressure.

The molecules are more likely to hit the walls of the syringe.

And so that is gonna cause the air to move out.

Okay, great.

What's that got to do with breathing? When we breathe, muscles and bones move to change the volume and pressure inside the chest.

Let's have a look at those muscles and bones.

We've got the ribs.

So the rib bones form a structure called the ribcage around the lungs.

And we've got intercostal muscles.

Those are muscles in between the ribs, which can contract and relax.

Now we're going to look at the way the intercostal muscles, ribcage and diaphragm change to allow us to breathe.

We'll look at inhalation, which is breathing in, first.

But before we start, I want you to put your hands on your ribs and take a really deep breath in.

Did you notice any changes in your body just then? Think about your ribcage in particular.

Take another inhale.

What did you notice when you breathe in just then? Pause the video and have a think.

What changes did you notice when you were just breathing in? Okay, let's see if what you notice matches up with what's happened inside our bodies during an inhalation.

So when we breathe in, the intercostal muscles, remember those in the muscles that are in between the ribs, they contract, which pulls the ribcage upwards and outwards.

Did you notice that when you were breathing in? Some of you might have been able to feel the diaphragm contracting and flattening, particularly if you're a singer.

You might be tuned into this already, but you can actually feel that happening in your body when you're breathing in.

This increases the volume of the lungs, and it decreases the pressure.

And that causes air to move into the lungs.

So those are all the changes that happen during an inhalation.

Let's look at exhaling.

So again, put your hands on your ribs.

Take a deep breath in and now force it out.

(breath whooshing) What did you notice changing in your body? Did you feel your ribcages moving? How was it moving? Pause the video and have a think about that.

Okay, let's see if that matches up.

The intercostal muscles this time are relaxing, and this causes a ribcage to move downwards and inwards.

Did you feel that when you were breathing out? The diaphragm relaxes now, and it curves upwards.

So the volume decreases of the lungs, and the pressure increases.

And this time, we've got air moving out of the lungs.

Let's check our understanding of that by sorting these statements about inhalation into the correct order.

So the first ones we're done for you.

The first one we're thinking about is the intercostal muscles contract.

Sort the rest of them in the right order.

We've got the diaphragm also contracts and flattens.

This decreases the pressure in the lungs.

This pulls the ribcage up and out.

Air is drawn into the lungs.

The volume of the lungs increases.

Pause the video whilst you sort those into the correct order.

Let's go through the answers now.

We knew which one was the first.

Then we should have number two.

This pulls the ribcage up and out.

Then the diaphragm also contracts and flattens.

The volume of the lungs increases.

This decreases the pressure in the lungs.

Air is drawn into the lungs.

Well done if you've got all of that in the correct order.

We can't see inside the chest with a naked eye.

So someone at some point created a model of the changes that occur in the chest during inhalation and exhalation.

It's not a perfect model as there are differences between it and how our bodies actually work, but models can be incredibly useful to help us visualise things that are hard to imagine.

So how this one works is we have a glass bell jar, and this represents the ribcage.

These balloons here, they represent the lungs.

The rubber sheet at the bottom, that represents the diaphragm.

I've got a little video here of the bell jar model being used.

And hopefully, that will not only give you a good idea of how this apparatus works, but it will demonstrate what happens inside our chest when we breathe.

Here we go.

So remember, the glass jar, the bell jar represents the ribcage in our bodies.

The rubber sheet at the bottom that's being pulled and pushed in, that represents the diaphragm.

And the balloons inside the bell jar, those represent the lungs.

Let's start by talking through inhalation.

In order to simulate inhaling, you need to pull down on the rubber sheet.

That represents the diaphragm contracting.

This increases the volume of the jar and decreases the pressure.

And that causes the balloons to inflate, which is representing air moving into the lungs.

So that's how you use the jar to represent inhalation.

Let's look at exhalation.

So the rubber sheet is pushed in.

This represents the diaphragm relaxing.

This decreases the volume of the jar and increases the pressure.

And the balloons deflate.

So that represents air moving out of the lungs.

This is the last practise task of today's lesson.

Well done from making it here so far.

Describe the similarities and differences between breathing in humans and the bell jar muzzle of breathing.

So have in your head, what changes occur in a human's body when we're breathing in? How does a bell jar show that, the similarities and the differences? Pause the video whilst you write your answer.

Let's go through the answers.

So the similarities.

The rubber sheet is pushed up, which is similar to how the diaphragm curves up during exhalation.

The balloons inflate and deflate, which is similar to how air moves into and out of the lungs as the volume and pressure in the chest change.

We've got some differences though.

Did you spot them? There is nothing to represent the intercostal muscles.

Oh, intercostal muscles in the bell jar model.

And the bell jar doesn't move, but that ribcage is pulled upwards and outwards during inhalation and moves downwards and inwards during exhalation.

So the glass jar, the bell jar part, that stays the same in the whole model, and that's not what happens when we're breathing.

You can put your hands on your ribs now and breathe in.

You can feel your ribs move up and out.

The bell jar doesn't move at all.

So that's another difference.

We've covered so much this lesson, and we've done excellent work, learning the parts of the human gas exchange system and discovering how volume and pressure changes in our lungs help us to breathe.

Let's go through it one more time to help it really stick in our memories.

Many parts of the human gas exchange system work together to enable us to breathe.

Muscles in the gas exchange system contract and relax, which changes the volume and pressure inside the chest.

This causes air to move into the lungs, this is known as inhalation, and out of the lungs.

This is known as exhalation.

Great work.

We've learned so many new keywords and new ideas today.

Have a bit of a break now, and I'll see you soon for our next lesson.