Your respiratory system is like a sophisticated air conditioning unit... Show more
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14 Dec 2025
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Understanding the Human Respiratory System: AQA A-Level PE Guide
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Respiratory System Structure
Ever wondered how your lungs manage to get oxygen into your bloodstream so efficiently? It all comes down to the brilliant design of alveoli - tiny air sacs that are perfectly built for their job.
Alveoli work through diffusion, where gas molecules naturally move from areas of high pressure to low pressure. Think of it like air rushing out of a balloon - it always flows from where there's more pressure to where there's less.
The structure of alveoli is absolutely genius for gas exchange. Their walls are incredibly thin (just one cell thick), creating the shortest possible pathway for gases to cross. They're surrounded by a massive network of capillaries ensuring excellent blood supply, and there are millions of them in each lung, giving you a massive surface area for oxygen uptake.
Key Point: The thinner the wall, the shorter the distance gases need to travel, making the whole process much more efficient!
Mechanics of Breathing
Here's something that might surprise you - breathing is all about pressure differences. Air always moves from high pressure to low pressure, and the bigger the difference, the faster it flows.
To get air into your lungs, the pressure inside needs to be lower than atmospheric pressure. To push air out, lung pressure needs to be higher than outside pressure. It's like creating a vacuum cleaner effect in reverse.
Your body achieves this through clever volume changes in your thoracic cavity. When you increase the volume, you reduce the pressure inside (drawing air in). When you decrease the volume, you increase the pressure (forcing air out). This is why your ribcage expands and contracts with each breath.
The beauty of this system is that it works automatically - you don't have to think about creating these pressure changes, your body does it for you.
Key Point: Breathing is basically your body playing with air pressure - bigger chest cavity equals lower pressure equals air rushing in!
Breathing During Exercise
When you're just chilling, inspiration only needs your diaphragm and external intercostal muscles. But during exercise, your body recruits extra help - scalenes, sternocleidomastoid, and even your pec major muscles join the party.
Expiration at rest is completely passive - your muscles just relax and let everything spring back naturally. During exercise though, you actively use internal intercostals and abdominal muscles to force air out more quickly.
Your breathing is controlled by three main factors during exercise: neural control (your brain and nervous system), chemical control (monitoring blood acidity), and hormonal control. When blood acidity rises due to increased CO₂ and lactic acid, chemoreceptors in your carotid artery and aortic arch detect this change.
The medulla oblongata acts like a control centre, receiving this information and sending impulses through the phrenic nerve to adjust your breathing rate, depth, and rhythm until everything returns to normal levels.
Key Point: Your body has built-in sensors that automatically speed up breathing when you exercise - it's like having an internal fitness coach!
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This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
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Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
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Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
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This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
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The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
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In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Understanding the Human Respiratory System: AQA A-Level PE Guide
Your respiratory system is like a sophisticated air conditioning unit that keeps your body supplied with oxygen and removes waste carbon dioxide. Understanding how your lungs work and what happens during exercise will help you grasp why you breathe harder... Show more
Respiratory System Structure
Ever wondered how your lungs manage to get oxygen into your bloodstream so efficiently? It all comes down to the brilliant design of alveoli - tiny air sacs that are perfectly built for their job.
Alveoli work through diffusion, where gas molecules naturally move from areas of high pressure to low pressure. Think of it like air rushing out of a balloon - it always flows from where there's more pressure to where there's less.
The structure of alveoli is absolutely genius for gas exchange. Their walls are incredibly thin (just one cell thick), creating the shortest possible pathway for gases to cross. They're surrounded by a massive network of capillaries ensuring excellent blood supply, and there are millions of them in each lung, giving you a massive surface area for oxygen uptake.
Key Point: The thinner the wall, the shorter the distance gases need to travel, making the whole process much more efficient!
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Mechanics of Breathing
Here's something that might surprise you - breathing is all about pressure differences. Air always moves from high pressure to low pressure, and the bigger the difference, the faster it flows.
To get air into your lungs, the pressure inside needs to be lower than atmospheric pressure. To push air out, lung pressure needs to be higher than outside pressure. It's like creating a vacuum cleaner effect in reverse.
Your body achieves this through clever volume changes in your thoracic cavity. When you increase the volume, you reduce the pressure inside (drawing air in). When you decrease the volume, you increase the pressure (forcing air out). This is why your ribcage expands and contracts with each breath.
The beauty of this system is that it works automatically - you don't have to think about creating these pressure changes, your body does it for you.
Key Point: Breathing is basically your body playing with air pressure - bigger chest cavity equals lower pressure equals air rushing in!
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Breathing During Exercise
When you're just chilling, inspiration only needs your diaphragm and external intercostal muscles. But during exercise, your body recruits extra help - scalenes, sternocleidomastoid, and even your pec major muscles join the party.
Expiration at rest is completely passive - your muscles just relax and let everything spring back naturally. During exercise though, you actively use internal intercostals and abdominal muscles to force air out more quickly.
Your breathing is controlled by three main factors during exercise: neural control (your brain and nervous system), chemical control (monitoring blood acidity), and hormonal control. When blood acidity rises due to increased CO₂ and lactic acid, chemoreceptors in your carotid artery and aortic arch detect this change.
The medulla oblongata acts like a control centre, receiving this information and sending impulses through the phrenic nerve to adjust your breathing rate, depth, and rhythm until everything returns to normal levels.
Key Point: Your body has built-in sensors that automatically speed up breathing when you exercise - it's like having an internal fitness coach!
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
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Most popular content: Respiratory System
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Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.9/5
App Store
4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because it’s too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user