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12 Dec 2025
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B5 Homeostasis and Response - AQA GCSE Revision Notes
F
Freya Playford
@freyaplayford_mnhy
1 / 6
Homeostasis and Body Systems
Ever wondered how your body keeps everything running smoothly even when conditions change? Homeostasis is your body's amazing ability to maintain a stable internal environment, no matter what's happening inside or outside.
Your body uses a simple three-step process: receptors detect changes (like temperature drops), coordination centres (your brain and spinal cord) figure out what needs doing, and effectors (muscles and glands) actually make the changes happen.
You've got two main control systems working for you. The nervous system sends electrical impulses through nerves - it's lightning fast and super precise, perfect for quick responses. The endocrine system uses hormones in your bloodstream - it's slower but affects your whole body and lasts much longer.
💡 Quick tip: Think of the nervous system as a phone call (instant) and the endocrine system as a letter (takes time but has lasting impact).
The Nervous System and Reflexes
Your nervous system is basically your body's electrical wiring, carrying impulses at incredible speeds through branched connections. The real magic happens at synapses - tiny gaps where signals jump between nerve cells.
Negative feedback is crucial here - it does the opposite of whatever change occurred, bringing things back to normal. Your central nervous system processes information and coordinates responses through different types of nerve cells.
Reflex arcs are your body's emergency shortcuts - they bypass your brain for super-fast automatic responses. When you touch something hot, sensory neurones detect it, relay neurones in your CNS process it, and motor neurones tell your muscles to pull away before you even think about it.
💡 Remember: Reflexes happen automatically because they go straight through your spinal cord, not your brain!
The Endocrine System and Key Glands
Hormones are your body's chemical messengers - small molecules that travel through your bloodstream to target specific organs. The endocrine system consists of glands scattered throughout your body, each with special jobs.
Your pituitary gland is the 'master gland' at the base of your brain. It controls other glands and tells them when to release their hormones. The thyroid gland in your neck produces thyroxine, which controls your metabolism and growth.
Here's where negative feedback gets interesting: when your pituitary detects low thyroxine levels, it releases thyroid stimulating hormone (TSH) to tell your thyroid to get busy. Once thyroxine levels rise, the pituitary backs off - it's like a thermostat for your body chemistry.
💡 Key insight: The pituitary gland is like your body's control tower, monitoring and directing other glands.
More Essential Glands
Your adrenal glands sit on top of your kidneys and pump out adrenaline when you're stressed or excited. This 'fight or flight' hormone increases your heart rate and blood pressure, giving you that energy boost when you need it most.
The pancreas is your blood sugar controller, releasing insulin to regulate glucose concentrations. Meanwhile, testes produce testosterone (and sperm in males), whilst ovaries produce oestrogen and store egg cells in females.
Here's the key difference: the endocrine system relies on hormones transported by blood - they're slower, last longer, and act generally throughout your body. The nervous system uses electrical impulses along nerve cells - they're fast, don't last long, and target specific areas precisely.
💡 Think of it this way: Nervous system = text message (instant, specific). Endocrine system = email newsletter (slower, affects everyone).
Blood Glucose Control
After a big meal, glucose floods into your bloodstream from your intestines. Your pancreas detects this spike and releases insulin, which tells your cells to absorb the excess glucose. Some gets stored as glycogen for later use.
When glucose levels drop too low, your pancreas switches tactics and releases glucagon instead. This hormone breaks down stored glycogen back into glucose, raising your blood sugar levels again.
This is a perfect example of a negative feedback loop in action. High glucose triggers insulin release (bringing levels down), whilst low glucose triggers glucagon release (bringing levels up). Your body constantly monitors and adjusts to keep everything balanced.
💡 Memory trick: Insulin = in (glucose goes into cells). Glucagon = go (glucose goes up in blood).
The Menstrual Cycle and Hormone Recap
The menstrual cycle shows hormones working together beautifully. Days 1-7 involve menstruation (uterus lining breaking down), followed by the lining rebuilding thanks to oestrogen. LH (luteinising hormone) triggers egg release, whilst progesterone maintains the uterus lining.
FSH (follicle stimulating hormone) helps eggs mature, whilst adrenaline from your adrenal glands prepares your body for action by increasing heart rate, blood pressure, and converting glycogen to glucose for instant energy.
Thyroxine works through negative feedback too - it's produced by your thyroid gland to increase your metabolic rate. When levels get too high, your body naturally reduces production to maintain balance.
💡 Exam tip: Remember that most hormones work through negative feedback - the body always tries to return to its 'sweet spot'.
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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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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
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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
B5 Homeostasis and Response - AQA GCSE Revision Notes
F
Freya Playford
@freyaplayford_mnhy
Your body is constantly working to keep everything balanced, like maintaining the right temperature and blood sugar levels. This process, called homeostasis, involves two main communication systems - your nervous system (fast electrical signals) and your endocrine system (slower chemical... Show more
Homeostasis and Body Systems
Ever wondered how your body keeps everything running smoothly even when conditions change? Homeostasis is your body's amazing ability to maintain a stable internal environment, no matter what's happening inside or outside.
Your body uses a simple three-step process: receptors detect changes (like temperature drops), coordination centres (your brain and spinal cord) figure out what needs doing, and effectors (muscles and glands) actually make the changes happen.
You've got two main control systems working for you. The nervous system sends electrical impulses through nerves - it's lightning fast and super precise, perfect for quick responses. The endocrine system uses hormones in your bloodstream - it's slower but affects your whole body and lasts much longer.
💡 Quick tip: Think of the nervous system as a phone call (instant) and the endocrine system as a letter (takes time but has lasting impact).
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The Nervous System and Reflexes
Your nervous system is basically your body's electrical wiring, carrying impulses at incredible speeds through branched connections. The real magic happens at synapses - tiny gaps where signals jump between nerve cells.
Negative feedback is crucial here - it does the opposite of whatever change occurred, bringing things back to normal. Your central nervous system processes information and coordinates responses through different types of nerve cells.
Reflex arcs are your body's emergency shortcuts - they bypass your brain for super-fast automatic responses. When you touch something hot, sensory neurones detect it, relay neurones in your CNS process it, and motor neurones tell your muscles to pull away before you even think about it.
💡 Remember: Reflexes happen automatically because they go straight through your spinal cord, not your brain!
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The Endocrine System and Key Glands
Hormones are your body's chemical messengers - small molecules that travel through your bloodstream to target specific organs. The endocrine system consists of glands scattered throughout your body, each with special jobs.
Your pituitary gland is the 'master gland' at the base of your brain. It controls other glands and tells them when to release their hormones. The thyroid gland in your neck produces thyroxine, which controls your metabolism and growth.
Here's where negative feedback gets interesting: when your pituitary detects low thyroxine levels, it releases thyroid stimulating hormone (TSH) to tell your thyroid to get busy. Once thyroxine levels rise, the pituitary backs off - it's like a thermostat for your body chemistry.
💡 Key insight: The pituitary gland is like your body's control tower, monitoring and directing other glands.
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More Essential Glands
Your adrenal glands sit on top of your kidneys and pump out adrenaline when you're stressed or excited. This 'fight or flight' hormone increases your heart rate and blood pressure, giving you that energy boost when you need it most.
The pancreas is your blood sugar controller, releasing insulin to regulate glucose concentrations. Meanwhile, testes produce testosterone (and sperm in males), whilst ovaries produce oestrogen and store egg cells in females.
Here's the key difference: the endocrine system relies on hormones transported by blood - they're slower, last longer, and act generally throughout your body. The nervous system uses electrical impulses along nerve cells - they're fast, don't last long, and target specific areas precisely.
💡 Think of it this way: Nervous system = text message (instant, specific). Endocrine system = email newsletter (slower, affects everyone).
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Blood Glucose Control
After a big meal, glucose floods into your bloodstream from your intestines. Your pancreas detects this spike and releases insulin, which tells your cells to absorb the excess glucose. Some gets stored as glycogen for later use.
When glucose levels drop too low, your pancreas switches tactics and releases glucagon instead. This hormone breaks down stored glycogen back into glucose, raising your blood sugar levels again.
This is a perfect example of a negative feedback loop in action. High glucose triggers insulin release (bringing levels down), whilst low glucose triggers glucagon release (bringing levels up). Your body constantly monitors and adjusts to keep everything balanced.
💡 Memory trick: Insulin = in (glucose goes into cells). Glucagon = go (glucose goes up in blood).
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The Menstrual Cycle and Hormone Recap
The menstrual cycle shows hormones working together beautifully. Days 1-7 involve menstruation (uterus lining breaking down), followed by the lining rebuilding thanks to oestrogen. LH (luteinising hormone) triggers egg release, whilst progesterone maintains the uterus lining.
FSH (follicle stimulating hormone) helps eggs mature, whilst adrenaline from your adrenal glands prepares your body for action by increasing heart rate, blood pressure, and converting glycogen to glucose for instant energy.
Thyroxine works through negative feedback too - it's produced by your thyroid gland to increase your metabolic rate. When levels get too high, your body naturally reduces production to maintain balance.
💡 Exam tip: Remember that most hormones work through negative feedback - the body always tries to return to its 'sweet spot'.
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?
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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