Lesson video

Hello, and welcome to today's lesson.

My name is Mr. Swaithes, and I'm really looking forward to teaching you today.

We're going to be looking at the mechanics of breathing.

We'll be exploring what happens when we breathe in, (inhales) what happens when we breathe out, (exhales) and also learning a little bit about the different lung volumes.

I'm sure you've heard the terms inspiration and expiration or inhalation and exhalation before, but what do they really mean? And what about things like tidal volume and minute ventilation? Today's lesson is called The Mechanics of Breathing, and it comes from the Anatomy and Physiology: the Cardio-Respiratory Unit.

By the end of this lesson, you'll be able to explain the mechanics of breathing and how air volumes are measured.

So I'm wondering if you already know anything about what muscles are involved in breathing and how their contractions cause air to rush in or out of the lungs? Have a little think.

So the key words for today's lesson are inhalation, exhalation, tidal volume, and vital capacity.

You might want to pause the video now to make a note of them, but I'll explain them fully as we come across them in the lesson.

And also to note, we'll be also talking around residual volume, inspiratory reserve volume, and expiratory reserve volume, so lots of terms to get your head around in today's lesson.

So today's lesson, we're gonna split it up into three parts.

The first part gives us a chance to describe the process of inhalation, or inspiration, breathing in.

The second part gives us a chance to explore in depth about exhalation, or expiration.

And then the third part will give us a chance to explain how lung volumes respond to exercise.

You might have done some of this already in science, so don't forget to draw on some of that knowledge as you're thinking.

I hope you're ready.

Let's get started.

So here, we've got an illustration of the lungs during inhalation, or inspiration.

As you can see there, with the purple arrows, the lungs are moving up and out at the same time as the diaphragm moving down, and that means there's a bigger volume within the thoracic cavity for the lungs to expand into.

So inhalation, or inspiration, is that process of breathing in by expanding the lungs.

And during inhalation, the diaphragm contracts from a dome shape down, and the intercostal muscles, which are in between each of your rib cage, sorry, in between each of your ribs, they also contract, and that's what helps pull your rib cage up and out.

This increases the volume of the chest cavity, and as a consequence of that, air rushes into the lungs.

So we create a volume change which causes the pressure to decrease, which enables air to rush in.

So let's have a quick check.

True or false? Inhalation and inspiration mean the same thing.

That's right, it's true.

So these terms are often used interchangeably to refer to breathing in.

(inhales) But remember, inspiration can also refer to creativity or motivation to act in a different context, so, you know, maybe you've got a teacher that inspires you or a sports person.

Okay, let's have a little look at these air pathways then.

So air rushes in through the nose and mouth, illustrated by those two arrows there.

(inhales) It travels down the trachea, or the windpipe, which branches off into two which are called the bronchi, one into the left lung, one into the right lung, and then those bronchi branch off again into bronchioles.

They almost look a bit like the roots of trees.

And then right at the very end of that, we've got alveoli, which are the little air sacs, and it's at those alveoli that the oxygen in the air comes into contact with the bloodstream because the alveoli are wrapped in a capillary network.

And remember, capillaries are only one cell thick, so they enable gaseous exchange to take place, so that diffusion of oxygen into the bloodstream and carbon dioxide out of the bloodstream, ready to be breathed out again.

So perhaps interesting to note that the air we breathe in is made up of about 78% nitrogen, about 21% oxygen at sea level.

There's less oxygen if you're at altitude.

And then about 0.

04% carbon dioxide and then varying amounts of water vapour, or H2O, depending on the humidity of where you are.

So let's remember, we've gotta be careful we don't ever say, "Oh, I breathe in oxygen." Well, actually you don't.

You breathe in air, and then your body strips the oxygen out of that air.

And the more oxygen there is in the air, the easier it is for your body to grab a hold of it and transfer it into the bloodstream.

So I've perhaps given away the clue here, but Sam's asking, "Which of these is it that the body needs? And what changes when we breathe out?" Well, it's the oxygen that we need, isn't it? And as a consequence of using up that oxygen, we end up breathing out less oxygen than we breathed in, and we breathe out more carbon dioxide than we breathed in, and that's why that human relationship with trees, which do the opposite, is so important.

Okay, so which of the following is correct? This is a nice, quick check.

The mechanics of breathing enable us to, A, inspire air to get fresh oxygen into the lungs, or B, expire air to get rid of excess carbon dioxide, or C, decrease the volume of the chest cavity when inhaling, or D, increase the quantity of oxygen brought into the body during exercise.

Remember, the question is asking which of the following is incorrect.

That's right, it's C, because we actually increase the volume, (inhales) my rib cage moving up and out, my diaphragm moving down, which is expanding that thoracic cavity, the area that my lungs take up inside my rib cage, and that increase in volume causes a decrease in pressure, which means air can rush in through my nose and mouth.

Okay, time for a practise task.

So what I'd like you to do for this first task is fill the gaps to explain what happens to get oxygen from the atmosphere into the bloodstream.

So we've got a word bank on the right-hand side there with lots of words and lots of gaps.

Pause the video now whilst you have a go at it.

Come back to me when you're ready.

Okay, so let's run through what I hope you came up with.

So the intercostal muscles are the ones that contract and pull your ribcage up and out whilst at the same time it's your diaphragm, that big sheet of muscle underneath your lungs, which contracts and flattens down from a dome shape to a flat shape.

This increases the volume of the chest cavity, and consequently, it initiates inhalation, also known as inspiration.

Maybe you got those two the other way round.

So air rushes in via the nose and mouth.

It travels down the trachea, or windpipe, enters the left and right lungs through the bronchi, and then they further subdivide into bronchioles before air reaches the alveoli.

And then it's at that alveoli that gaseous exchange happens where oxygen diffuses into the blood and carbon dioxide diffuses out, ready to be breathed out again.

I hope that's what you came up with.

Okay, moving on to the second part of the lesson then.

So let's have a little look at exhalation.

So we've covered breathing in, but what does breathing out look like? So exhalation, or expiration, is the process of breathing out.

And we breathe out air by reducing the lung volume.

And if we're going to let the rib cage move back down and in and we're gonna let the diaphragm contract back up, sorry, relax back up into that dome shape, then as a consequence, the volume inside there decreases, and that's what forces air out of the lungs.

And interestingly, gravity helps the ribcage move down and in, and as we know, when a muscle relaxes, it returns to its resting state.

But actually, during exercise, we sometimes want that air to come out even faster, so we have another set of intercostal muscles that can pull the ribcage down and in.

And sometimes we actually mobilise our abdominals muscle as well to help pull the rib cage down and in to blow out quickly.

So if you have a go at that now, take a big breath in, (inhales) (exhales forcefully) and if you wanna force air out, you can feel your abdominals contracting to help do that at speed.

So let's have another little look here.

So air containing a decreased percentage of oxygen and a bigger percentage of carbon dioxide travels from the alveoli, up to the bronchioles, on up to the bronchi, then from the bronchi into the trachea, or windpipe, on up and out through the nose and mouth, and then out into the atmosphere.

So let's have a quick check.

Which of the following happens when we breathe out? Is it A, the diaphragm returns to a flat shape? Is it B, the ribs move up and out? Is it C, the chest cavity increases in size? Or is it D, the diaphragm returns up to a dome shape? That's right, it's D.

The diaphragm, when it's relaxed, is a dome shape.

Moving on then.

So the air that we breathe out is made up of still 78% nitrogen, so we don't use the nitrogen at all in the human body, about 16% oxygen, and that varies a bit between rest and during exercise.

But the big change is there's been a massive increase in carbon dioxide that we're breathing out and even more so if we're exercising.

And then there's probably an increase in water vapour, or H2O, as well because of the moisture that we've got in our respiratory tract.

So that's quite often why if we go out on a cold day, we can see almost the steam, that water vapour as we breathe out.

So Laura's got a question for us.

"Why have these percentages changed from breathing in?" And of course it's because we've used oxygen to keep our living tissues alive, but also, particularly for us as sports performers, we're using that oxygen for our muscles to contract.

So every time our muscles contract, they're utilising oxygen that we've breathed in, and one of the waste products of that is carbon dioxide.

So that's why we use oxygen as a human body, and we give off carbon dioxide as a waste product from that.

So another check.

True or false? We breathe out more carbon dioxide than we breathe in.

That's right, that's true.

So carbon dioxide is that waste product of respiration.

So we extract oxygen from the air that we breathe in and replace it with carbon dioxide, which we'll then breathe out.

When we exercise, this gaseous exchange or gaseous exchange happens more.

Okay, on to the second task of this lesson then.

So for this one, I'd like you to explain what happens to carbon dioxide from the bloodstream out of the body.

Ensure that you use all the words in this word bank within your answer.

So a bit similar to Task A where we looked at what happens during inhalation, I now want you to think about what happens during expiration.

And I've got a collection of words there, and I want you to use all of them as part of your paragraph.

Pause the video now whilst you do that, and come back to me when you're ready.

Well done.

That was a tough one, wasn't it? So let's have a little look.

I'm hoping you said something along the lines of, the intercostal muscles relax, causing the ribs to move down and in.

You might have actually said that the internal intercostal muscles contract, and that's what pulls the ribs down and in.

And importantly, at the same time, the diaphragm is relaxing back up into that natural dome shape, and this decreases the volume of the chest cavity, which initiates exhalation, or expiration.

As a consequence of that, gaseous exchange and diffusion can happen at the alveoli where oxygen diffuses into the blood and carbon dioxide diffuses out, ready for us to breathe it back out again.

Carbon dioxide rushes from the alveoli up through the bronchi, sorry, through the bronchioles to the bronchi, then from the bronchi to the trachea.

And then from the trachea, it exits the body through the nose and mouth.

And this is why it's really important that we take quite deep breaths 'cause if you do very shallow, quick breaths, for example, if you are having an asthma attack, you don't actually give enough chance for that carbon dioxide to get out of the body.

It gets halfway up the respiratory tract, and then you're sucking it back down again.

So that's why it's really important, perhaps in an asthma attack or a panic attack, to try and slow your breathing down.

(inhales) Big breaths to get fresh oxygen in (exhales) and carbon dioxide out of the body.

Okay, moving on to the third and final part of this lesson then.

So let's explore some of those lung volumes and how they respond to exercise.

So at rest, we breathe about 12 to 20 times per minute.

It's actually quite hard to count your resting breathing 'cause you start consciously taking over and interrupting that natural flow of breathing in and breathing out, breathing in and breathing out.

This is known as breathing rate, BR for short, or breathing frequency.

Meanwhile, during each breath, there's amount of air, a volume of air that transfers in and out of the lungs, so a little bit like the waves, so a tidal wave of air coming in and out.

And at rest, each breath brings in about 500 millilitres of air into the lungs to enable gaseous exchange to happen, so actually quite a big volume of air that's sucked in and then pushed back out again.

And that volume of air that's inhaled is known as tidal volume.

So that 500 millilitres of inhalation during normal quiet breathing is known as tidal volume.

And that tidal volume repeats with every single breath, so you're in 500 millilitres, out 500 millilitres, in 500 millilitres, out 500 millilitres, assuming you're at rest and you're a fully grown adult.

Obviously those numbers would be smaller if you're smaller or a child.

Okay, moving on then.

So it's important to be able to calculate the total volume of air that enters the lungs per minute.

And the way we do that is to do some calculations that combine that tidal volume with your breathing frequency.

And actually, we strap people up to what we call a Douglas bag or a minute ventilation machine.

So minute ventilation, or VE, is the total volume of gas inhaled or exhaled by the lungs per minute.

It's very similar to how cardiac output is the volume of blood ejected from the heart per minute.

Minute ventilation is the volume of air that is inhaled or exhaled by the lungs per minute.

So another little formula there.

So similar to cardiac output equals heart rate times stroke volume, we've got minute ventilation equals breathing rate times tidal volume.

So Lucas is wondering, "Given that you know typical values for breathing rate and tidal volume, what do you think someone's minute ventilation is at rest?" So we know the formula, minute ventilation is breathing rate times tidal volume, and we've said already that perhaps at rest, 12 to 20 breaths per minute.

Well, I'm gonna take 15, so 15 breaths per minute timesed by 500 millilitres per breath equates to 7,500 millilitres per minute or 7.

5 litres per minute.

So we would typically exchange about 7.

5 litres of air in and out of the lungs per minute.

So what about during exercise then? How does the body respond, and what do the lungs do differently? Well, our breathing rate increases for sure.

We can definitely feel that panting, that faster breathing.

Our tidal volume increases, too, so we're breathing more in with each breath and breathing more out with each breath.

Minute ventilation, as a consequence, will also increase, won't it? Because that's the product of breathing rate timesed by tidal volume.

So as a consequence of that, we can massively increase the amount of air reaching our alveoli for gaseous exchange to occur.

Consequently, we can pull out way more oxygen and push way more carbon dioxide out to the body.

Human body's an amazing thing.

So the most important lung volumes that you need to understand, there's three of them.

Tidal volume, so that volume of air that's breathed in per breath.

Minute ventilation, so that's tidal volume timesed by breathing frequency, so that's the total volume of air that's breathed in per minute.

And vital capacity is the new one.

So we've got a picture there of my friend Lee who's using a peak flow metre, and what he's done there is he's taken a maximal breath in followed by a maximal breath out to see what volume of air he's able to forcibly expire after maximum inspiration.

I'm wondering, can you have a go at recalling each of those definitions on your own? Let's do a quick check.

So which of the following is a measure of the maximum amount of air that can be expired after a maximum inhalation? Is it A, tidal volume, B, vital capacity, or C, minute ventilation? That's right.

It's B, vital capacity.

So just watch me for a moment.

So I'm (inhales) breathing in as much as I can, (exhales forcefully) I blow out as much as I can, and that is my vital capacity.

And in fact, that's what they do as a breathalyser test when the police pull you over for potential drink driving, not that I know from experience, of course.

Okay, so we can draw a spirometer trace, which is basically a graphical representation of the volume of air that a person breathes in and out over time, and it might look a little bit like this.

So we've got that in, out, in, out, in, out.

And then what I've drawn there is a big maximum inhalation.

And to do that, you take a normal breath in, and then what extra air can you suck in to fully inflate your lungs, that's known as your inspiratory reserve volume.

And then I blow out all the air that I can.

So I'm pushing that vital capacity out, and I've got down to that expiratory reserve volume, which I can suck back in to take me back to kind of a normal resting level.

And interestingly, we have this residual volume, this amount of air that's always left in our lungs to stop them collapsing in on themselves, so we've gotta keep the sides a little bit open to enable them to inflate and deflate easily.

So, again, if you've come across anyone that's perhaps, in a contact sport, that's had a punctured lung, the real danger there is that that residual volume can come out of the lungs.

So just to recap on this diagram, we can see tidal volume, so that amount of air being breathed in or out in a normal breath.

We can see inspiratory reserve volume, that extra volume of air that can be breathed in after a normal breath in.

We can see expiratory reserve volume, so you take a normal breath out and then see how much extra air you can force out of the body.

Then we've got residual volume, so that's the volume of air that's always left in the lungs.

And then we've got vital capacity, which is that maximum breath in followed by a maximum breath out, and we can use a peak flow monitor to test that.

Often, if you've got anyone in your class that's an asthmatic or maybe you are, you'll have probably had a go at that peak flow test which measures your vital capacity.

And then your total lung volume is all of that added together, so the residual volume added on to the vital capacity.

So let's have a little look at that in action to help you understand those different lung volumes.

So can you take a normal breath in, i.

e.

, your tidal volume, and then see how much extra air you can breathe in by fully expanding your lungs? So we're breathing in normally, (inhales) and then how much extra (inhales forcefully) after that.

We can remember that as the inspiratory reserve volume.

And when we exercise, we breathe in more deeply, so we use up some of that inspiratory reserve capacity.

I wonder if you can now demonstrate that expiratory reserve volume.

How would you do that? That's right, you take a normal breath out, and then (exhales forcefully) force out as much extra air as you can from your lungs.

What about vital capacity? Well, as I've modelled a couple of times, that's that maximum breath in followed by a maximum breath out.

Show me.

Brilliant.

Okay, so just a quick reminder then.

Vital capacity is the maximum breath in followed by a maximum breath out, and you certainly start to work towards that vital capacity if you're riding a bike up a hill.

Endurance trained athletes have a much bigger vital capacity as they're used to having to breathe more frequently and deeper to cope with the demands of exercise.

That's why quite often we see them with broader shoulders and that bigger lung capacity.

Swimmers are another example of people that often have huge vital capacities.

So here, we've got a nice little illustration.

You might have seen one of these in science.

And the balloons represent the lungs.

The glass jar represents, I guess, the ribcage.

And then at the bottom there, the hand is pulling on what the diaphragm is like, so that sheet of metal, sorry, sheet of muscle, not metal at all, sheet of muscle.

And as that pulls down, you can see the effect is a volume change, a pressure change, and therefore air rushing into the lungs, or balloons in this case, okay? The residual volume is the amount of air that will always remain in the lungs, and that helps keep them inflated, stops them sticking to each other, which is a problem.

The harder you exercise, the faster that breathing rate, but also the bigger the tidal volume of air flowing in and out of the lungs.

Okay, so the last task of this lesson, I want you to label the lung volumes A to E on this diagram and provide a definition of each.

Pause the video now whilst you do this, and come back to me when you're ready.

Okay, let's have a little look at what you came up with.

Hopefully you've marked A as the inspiratory reserve volume, B as the vital capacity, C as the total lung volume, D as that residual volume that's always left in your lungs, and then E, the expiratory reserve volume.

And then on to the second part of that task, I was asking you to give a bit of a definition for each.

So that inspiratory reserve volume is the additional volume of air that can be forcibly inhaled after a normal inhalation.

B is the vital capacity, and that is the maximum amount of air a person can exhale after a maximum inhalation.

C, that total lung volume is the total amount of air the lungs can hold.

D, that residual volume is the volume of air that remains in the lungs after a maximal exhalation that keeps them inflated.

And E is the expiratory reserve volume, so that's the additional volume of air that could be forcibly exhaled after a normal exhalation.

So that leaves us just a couple of moments to summarise today's lesson all about the mechanics of breathing.

So during inhalation, the intercostal muscles, which are in between each of your ribs, they contract and pull your ribcage up and out at the same time as the diaphragm contracting down, and that expands that chest cavity volume so that air rushes in.

The reverse happens during exhalation, so that intercostal muscles relax, or maybe even those internal intercostal muscles contract to actively pull your rib cage down and in.

And the diaphragm returns up to its resting position, which reduces the volume, which increases the pressure.

And a bit like if you get a puncture in a tyre, that's what makes the air rush out until that pressure equalises with atmospheric pressure.

Tidal volume is the amount of air breathed in or out during normal breathing, and we calculate it and we use sort of 500 millilitres for a normal person at rest.

Vital capacity is the maximum amount of air that a person can exhale after a maximum inhalation.

You can almost think of yourself trying to blow up a balloon.

That is a good way of getting your vital capacity out.

And then a spirometer trace is that graphical representation of lung volume changes over time during breathing.

Thanks for joining me for today's lesson, and I look forward to seeing you next time.