Hi there, I'm Mrs. Kemp, and welcome to today's lesson all about the gas exchange system in healthy humans.

This is part of the disease and drugs unit, but you will recognise a lot of the information from back in year eight when you learned about the breathing and respiration system.

So then let's get started.

Our outline for today then, or sorry, our outcome for today is, I can describe the function and structures of the human gas exchange system in healthy humans.

These are some of the key terms that you're going to be using today.

If you'd like to pause the video and read them through in detail, please do.

If not, please be assured that actually I will go through each one of them as we work through our slides.

We've got three learning cycles today.

We've got structure of the lungs, ventilation, and also gas exchange, and we'll start then with the structure of the lungs.

So almost all living things will need oxygen to survive.

Remember, we use oxygen for respiration.

Very small organisms, like bacteria, that we can see in that picture there, they're actually able to absorb enough of the oxygen that they need just by simple diffusion in through their membranes.

However, larger organisms, such as ourselves, we need a gas exchange system in order to get enough oxygen in for all of the cells all over our body.

And we have got a set of lungs in order for that to happen.

It provides us with an exchange surface so that we can get oxygen in and carbon dioxide out.

We can see in the image here, this is our gas exchange system.

We take in our air through our nose and our mouth, it travels down our trachea, and down into the bronchi, which are the branches that come off the trachea, and then those bronchus then divide again into tiny little tubes known as the bronchioles.

At the end of the bronchioles we find those little air sacks that we call alveoli.

Now we're gonna have a look at a lung dissection here, and you might be able to do one with us as you go, okay, and this one comes from a sheep, and we can look at the parts of the gas exchange system in a bit more detail.

They've actually got a very, very similar gas exchange system to ourselves.

So we can see here that we've got our trachea, okay, which is the windpipe just down here, and also the two lungs on either side.

You might notice on this image that actually there seem to be some funny little cuts being made in each of those lungs.

They wouldn't normally be there, but the abattoir, when they kill the animal, they will often check the lungs, and also the heart and other organs, to make sure that they're healthy in order for that meat to go into our food chain.

So here's a closeup image of the trachea.

If you feel your neck here, you can probably feel that the trachea is a little bit ridgy.

And that's caused by the rings of cartilage, and you can see those quite clearly in the picture.

It's kind of like a soft bone, and being ring shaped allows for the oesophagus, which is the part of the digestive system, to run quite closely behind it, okay, but actually not prevent air from passing through the trachea.

Because it's softer than normal bone, it allows us to move our head like this, and also withstand those pressure changes that we'll talk about in a moment.

The trachea will then branch into smaller tubes known as the bronchi so that it can get into each one of those lungs, and we can see here that it's singular, the right bronchus, okay? Bronchi being plural, bronchus being singular, is able to enter the right lung.

At the end of those bronchi then it splits again into tiny little bronchioles, and at the end of the bronchioles we've got the alveolus, alveolus being a single air sac, and pleural being many.

Now actually our lungs contain many of these alveoli, okay, actually about 240 million alveoli in one of your lungs.

So you've actually got double that on both sides.

You've got about 30,000 bronchioli, so 30,000 of those little tubes.

And actually, because of all of those alveoli then, because of all those tiny little air sacks, your lungs have got a kind of spongy texture, and if you are able to do the dissection, you can actually feel that when you touch them.

If you cut a tiny little bit of the lung off and put it into some water, then it will actually float.

And comparatively to other organs then, it's got a really low density about it, which is why it's then able to float in water.

It's really quite amazing.

So let's go onto our first check of today then.

What is the function of the lungs? Is it A, to breathe in carbon dioxide and breathe out oxygen"? To provide a gas exchange surface for oxygen and carbon dioxide? Or C, for respiration to take place? I'll give you a moment to think about it, but if you need more time, please do pause the video.

Okay, did you say to provide a gas exchange surface for oxygen and carbon dioxide? Excellent, really well done.

Onto our next check, what is the path of air moving from the outside to the lungs? Can you put these into an order? Bronchioles, trachea, bronchi, alveoli.

Again, I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, first of all it goes into our trachea, then to our bronchi, then to our bronchioles, and finally down into that gas exchange surface at the alveoli.

Excellent, well done.

Our first task of the day, then if you wanna get your worksheet out, there's already this outline for you on that worksheet, so it'll make it a little bit easier.

What I would like you to do is on that outline, could you please complete the drawing of the parts of the gas exchange system and label? I'll give you some time to think about it, but if you need more time, please pause the video.

Okay, so what we should have included then was the rest of the trachea running down and then splitting off into our bronchi.

Then that should split again into the bronchioles, finally having the alveoli there as well.

You may have also remembered from back in year eight that actually we should have a diaphragm running underneath the lungs, which is going to be important for our next section.

So our next section is ventilation.

And this is really the process of breathing.

So breathing in and out.

Let's have a go at that, it's really easy, isn't it? Let's put one hand on our chest and the other hand on our stomach, and what we're going to do is just gonna take a really big deep breath in and see what happens.

Okay, what we should have noticed that actually our chest and our abdomen, so where our stomach is, they should both rise and fall as we breathe in and out.

So why is that happening? Well, that's because of one thing, our rib cage, okay? Now our rib cage is made of bone, isn't it, and it's there in order to protect our lungs, but it also helps to ventilate them.

So you can see that our ribcage form that really nice protective structure around our lungs.

But actually in between those ribs, okay, there are muscles, okay? They are known as the intercostal muscles and they're really important to be able to move that rib cage.

And what they do is they can contract, so squeeze together, or they can relax and then separate those ribs again.

So let's think about what happens when we breathe in.

This is called inhalation.

So those muscles between our ribs, they will contract and lift up our rib cage.

Now what that does is it creates a bigger volume inside our rib cage.

At the same time, the diaphragm, which is like a dome shape, contracts also, and when it contracts, it actually flattens.

So it's contracting and flattens.

Again, both of those things then, increase our volume, okay? If the volume, so the size of what's inside our rib cage increases, that has a knock on effect of pressure and pressure will decrease.

Because pressure is decreased, our body wants to try to equalise that with what's outside, and so air is sucked in, okay, in order to fill up that space and increase that pressure again.

What happens when we exhale then, so when we breathe out, is that those muscles that have contracted, they're going to relax, okay? So our contracted rib cage will relax back down, our diaphragm that is contracted downwards will lift back up, and that makes that whole space smaller again.

And so therefore the volume into the space that's inside that ribcage has decreased, and what that's gonna do is that's gonna increase the pressure inside there and force the air back out, okay? Because your body wants to have an equal pressure with the outside.

Alright then, can you please now sort these statements about exhalation into the correct order.

We've got air moves out, the diaphragm relaxes and curves up, the intercostal muscles relax, the rib cage moves downwards and inwards, pressure increases, volume decreases.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did we have, first of all, the intercostal muscles relax, then the rib cage move downwards and inwards, the diaphragm relaxes and curves back up, the volume decreases, therefore the pressure increases, and air moves out? Excellent, really well done.

Okay, so regular exercise can actually improve your lung capacity, so the volume of air that you can take into your lungs.

And it'll also strengthen your muscles all over your body.

Do you remember back when you did the respiration and breathing unit, you may have actually calculated your own lung capacity by using this piece of equipment.

So just a large bottle turned upside down in some water with some markings on it to measure the volume, and then you can actually breathe fully into that bottle, exhaling all of the air in your lungs, and that will tell you what your lung capacity is.

A larger lung capacity will mean that your lungs can exchange oxygen and carbon dioxide more efficiently, which is obviously really important for lots of bodily functions as we need that oxygen for respiration.

So the intercostal muscles in the diaphragm are muscles, just like any other muscle in your body, and so therefore when we exercise and we are using them more actively, then actually they're going to strengthen, okay, just like those ones that we have in our skeletal muscles.

Stronger muscles then will lead to more efficient ventilation of the lungs, again, you're going to be able to get more of oxygen in, more carbon dioxide out more efficiently.

Alright then, onto our next check, true or false.

Exercise can increase a person's lung capacity, is that true or false? Can you justify your answer? Exercise strengthens the intercostal muscles and diaphragm? Or B, only skeletal muscles get stronger when we exercise? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, did you say that that was true? Excellent, well done.

And that is of course because exercise strengthens the intercostal muscles and the diaphragm.

Really well done.

Onto our next task of the day then.

So this is in two parts.

Again, you can record this on your worksheet if you wish.

First of all, would you like to write a flow diagram, so like a step by step of what happens to show the mechanisms involved in inhalation, remember that one is breathing in? Second of all then, Lucas is explaining to his mum why exercise is important to keep their lungs healthy.

Can you help him think of two reasons that he should explain to his mum? I'll give you a moment to think about it, but if you need more time, please pause a video.

Okay, so this is our flow diagram, first of all, to show the mechanisms involved in inhalation.

We've got the intercostal muscles contract, this pulls the ribcage up and outwards, the diaphragm contracts and flattens, the volume of the lungs increases.

This decreases the pressure in the lungs and air is drawn in.

Number two then, let's think of what Lucas could have said.

So exercise can increase your lung capacity, it can strengthen your intercostal muscles and diaphragm.

This will help make your lungs more efficient at gas exchange.

I hope you've got all of those points, but if not, you may want to add some into your answer.

Excellent, well done.

Okay, onto our final learning cycle of today then.

This is gas exchange.

So the alveoli are an exchange surface for oxygen and carbon dioxide.

Okay, so air is taken into the lungs and oxygen is then taken from inside the alveoli into our blood, carbon dioxide is passed back from the blood into the alveoli and breathed out with the rest of the air.

Gas exchange happens by a process known as diffusion.

You've met diffusion in previous units, such as cells.

We can see here that we've got our alveoli, the oxygen is shown as a little red dot there, and oxygen needs to diffuse from the alveoli and then into the blood.

Carbon dioxide is the blue one, and this is going to move from the blood into the alveoli.

In order for that to happen then, we always need to make sure that the concentration gradients are the right way round, because gases will move from an area of high concentration to an area of low concentration.

The rate of diffusion will be affected by a number of different factors.

Now, we can see here that we've got some red particles that are on the left hand side, and they will be moving to where there are not as many of them on the right.

So they're moving from a high to low concentration.

The distance that those molecules need to move will affect how fast a fusion will happen.

Also, what the differences between the concentration on one side to the other, this is known as the concentration gradient, will also affect how fast rate of diffusion is.

If the concentration gradient is higher, the molecules will move faster, okay? If it is lower, the molecules will move slower.

The surface area then, we can see this cell here is a sort of wiggly shape.

By being that shape, it actually increases the amount of surface area for that cell, and therefore more particles can move in at any time.

So by increasing the surface area of an organism, then actually diffusion rate is going to increase.

Now if you increase the temperature, which actually inside us that doesn't happen because we remain at a stable temperature, being warm blooded animals.

But if you did increase the temperature, the particles are moving around faster, they've got more energy, and therefore diffusion rate would happen faster.

So the alveoli are adapted for faster diffusion by taking into account those factors that affect the rate of diffusion.

So for a start, the walls of the alveoli and also the capillaries are actually only one cell thick.

What that does is it reduces the distance that the particles need to move and therefore increases the rate of diffusion, okay? So because they're so thin, it hasn't got to travel as far, and therefore diffusion is faster.

Ventilation, so that breathing in and out all the time, makes sure that the concentration gradient is the right way round, and therefore the gases move the right way.

So when you breathe in, you are always replenishing that oxygen.

So oxygen is in high concentration in the alveoli comparatively to that blood, okay, and so it will always move into the blood.

The blood is also carrying the oxygen away, so the concentration of the oxygen in the blood is going to be lower, so again, it will always move into the blood.

It's the opposite way round for carbon dioxide then.

The carbon dioxide will be in high concentration in the blood as it enters the lungs and low concentration in the alveoli.

So it'll always move from the blood into the alveoli, and then you breathe it out.

We have millions, we talked about it earlier, didn't we, of those tiny alveoli, and so put together, they have a really large surface area, okay, which makes the much more efficient, much faster diffusion of oxygen and carbon dioxide.

They're so tiny, but actually because there are so many of them, if you spread them all out and flatten them all out, it would be about the size of a badminton court, which is absolutely massive when you really think about it.

So let's go onto our next check.

Which of the following are adaptations of the alveoli? A, a constant ventilation? B, large surface area? C, high temperature? D, walls only one cell thick? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, there's quite a few of them.

There's constant ventilation, which was A, B, large surface area, and D, walls only one cell thick.

High temperature does affect the rate of diffusion, but remember that we are warm-blooded animals and so therefore our temperature remains constant.

Okay, so oxygen diffuses from a high concentration in the alveoli to the low concentration in the blood.

You can see that there are many more of those red dots that is representing oxygen inside the alveoli comparatively to in the blood.

Blood then transports oxygen all over the body because all cells require oxygen.

Together with glucose, the cells use that oxygen as fuel for respiration.

Remember that that happens in the part of the cell that is called the mitochondria, and what this does is it provides the energy for the cell to carry out all of its different processes.

For instance, building and making proteins.

Carbon dioxide then is then produced by respiration, okay? And so it will be in a high concentration in that blood as it's returning to the alveoli.

It will have a higher concentration in the blood than the alveoli, and therefore it will diffuse into the alveoli.

It's actually a waste product from respiration.

If it was in really high levels and high concentrations, then it would be poisonous for our body cells.

So we do need to excrete it, we need to get rid of it.

Blood vessels are able to transport the carbon dioxide from all those body cells that have been producing it back to the lungs so that we can breathe it out.

Okay, let's go on to our next check then.

Which way do you think oxygen will move on this picture? Think about the concentration gradient.

I'll give you some time to think about it, but if you need more time, please pause the video.

Of course, it will remove from inside the alveoli into the blood, excellent, well done.

What about this true or false then? Mitochondria use carbon dioxide for respiration, is that true or false? Can you justify your answer? Water and glucose are used as fuel for cellular respiration? Or B, oxygen and glucose are used as fuel for cellular respiration.

I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, of course that is false, and that's because it's actually oxygen and glucose that are used as fuel for cellular respiration.

Carbon dioxide, remember, is that waste product.

This is our final task of the day then.

So can you first of all get your worksheet to record your answers? And then draw and label an alveolus and a capillary? Then label the adaptations of the alveoli for efficient gas exchange.

Can you use some particle diagrams, so little dots, okay, to represent oxygen and glucose to show their movement into an out of the alveoli? I'll give you a moment to think about it, but if you need more time, please pause the video.

Okay, hopefully you drew something that looked like this.

Okay, so we've got our alveoli, and we're showing that inside the alveoli, then we've actually got lots of oxygen, less in that blood vessel, and then we've got carbon dioxide, more in the blood vessel than in the alveoli.

The oxygen is travelling into the blood, the carbon dioxide is travelling into the alveoli.

The alveoli's got a really good blood supply and constant ventilation, this will maintain the concentration gradient.

It's also got a short diffusion pathway because the walls are only one cell thick and there's actually millions of those tiny alveoli, which gives it a really large surface area.

Hopefully you've got all of those, but if you need to add to your diagram, please do pause the video.

So we have come to the end of our lesson, so let's go through those key learning points before we finish.

So large organisms require a gas exchange so they can absorb enough oxygen into their bodies for respiration.

Carbon dioxide is produced during respiration and needs to be excreted from the body.

Ventilation consists of inhalation and exhalation, and involves the intercostal muscles and diaphragm.

We ventilate the lungs by a process known as breathing.

In humans, gas exchange takes place in the alveoli in the lungs.

The alveoli are adapted for gas exchange, large surface area, short diffusion pathway, and good blood supply.

Thanks very much, it's been a great lesson.

Hope to see you again soon, bye.