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10 Dec 2025
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The Human Circulatory System - A Level Biology Edexcel B Topic 4
Hannah
@hannah_studys1012
The Heart's Structure and Blood Flow
Your heart has four chambers working in perfect harmony to move blood through your body. Deoxygenated blood returns from the body through the vena cava into the right atrium, then passes through the tricuspid valve to the right ventricle. From there, it travels to the lungs via the pulmonary artery.
After picking up oxygen, blood returns through the pulmonary vein to the left atrium, passes through the bicuspid valve into the left ventricle, and finally exits through the aorta to the body. Special tendinous cords prevent valve backflow, while semilunar valves ensure blood flows in one direction.
The left ventricle has a thicker muscle wall than the right because it needs to generate higher pressure to pump blood throughout the entire body. The right ventricle only needs to pump blood to the nearby lungs, requiring less pressure. The septum separates the chambers, preventing oxygenated and deoxygenated blood from mixing.
Did you know? The pressure difference between chambers is crucial for proper blood flow. When ventricle pressure exceeds atrial pressure, the atrioventricular valves close, preventing backflow and creating the first heart sound ("lub").
The Cardiac Cycle and Electrical System
The cardiac cycle consists of coordinated contractions (systole) and relaxations (diastole) of the heart chambers. During atrial systole, the atria contract, pushing additional blood into relaxed ventricles through open AV valves. This is followed by ventricular systole, where ventricles contract, closing the AV valves and opening semilunar valves to eject blood.
Blood pressure fluctuates throughout this cycle. When ventricular pressure exceeds aortic pressure , the semilunar valves open. When ventricles relax, pressure drops, closing the semilunar valves and creating the second heart sound ("dub"). Eventually, atrial pressure exceeds ventricular pressure, opening the AV valves for the cycle to repeat.
The heart's electrical system controls these contractions through myogenic stimulation - the heart's ability to contract without external nerve signals. The sinoatrial node (SAN) initiates impulses that spread through the atria. These impulses reach the atrioventricular node (AVN) where they're briefly delayed, allowing atria to fully contract before ventricles.
Remember: The AVN delay is crucial - it ensures atria finish contracting before ventricles begin, optimizing blood flow. Without this delay, the heart's pumping efficiency would be significantly reduced.
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Stefan S
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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.
Samantha Klich
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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.
Anna
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Best app on earth! no words because it’s too good
Thomas R
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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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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.
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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
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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
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The Human Circulatory System - A Level Biology Edexcel B Topic 4
Hannah
@hannah_studys1012
The heart's intricate cycle of blood pumping is essential for delivering oxygen throughout the body. Understanding how the chambers, valves and electrical system work together reveals how this remarkable organ functions continuously throughout our lives.
The Heart's Structure and Blood Flow
Your heart has four chambers working in perfect harmony to move blood through your body. Deoxygenated blood returns from the body through the vena cava into the right atrium, then passes through the tricuspid valve to the right ventricle. From there, it travels to the lungs via the pulmonary artery.
After picking up oxygen, blood returns through the pulmonary vein to the left atrium, passes through the bicuspid valve into the left ventricle, and finally exits through the aorta to the body. Special tendinous cords prevent valve backflow, while semilunar valves ensure blood flows in one direction.
The left ventricle has a thicker muscle wall than the right because it needs to generate higher pressure to pump blood throughout the entire body. The right ventricle only needs to pump blood to the nearby lungs, requiring less pressure. The septum separates the chambers, preventing oxygenated and deoxygenated blood from mixing.
Did you know? The pressure difference between chambers is crucial for proper blood flow. When ventricle pressure exceeds atrial pressure, the atrioventricular valves close, preventing backflow and creating the first heart sound ("lub").
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The Cardiac Cycle and Electrical System
The cardiac cycle consists of coordinated contractions (systole) and relaxations (diastole) of the heart chambers. During atrial systole, the atria contract, pushing additional blood into relaxed ventricles through open AV valves. This is followed by ventricular systole, where ventricles contract, closing the AV valves and opening semilunar valves to eject blood.
Blood pressure fluctuates throughout this cycle. When ventricular pressure exceeds aortic pressure , the semilunar valves open. When ventricles relax, pressure drops, closing the semilunar valves and creating the second heart sound ("dub"). Eventually, atrial pressure exceeds ventricular pressure, opening the AV valves for the cycle to repeat.
The heart's electrical system controls these contractions through myogenic stimulation - the heart's ability to contract without external nerve signals. The sinoatrial node (SAN) initiates impulses that spread through the atria. These impulses reach the atrioventricular node (AVN) where they're briefly delayed, allowing atria to fully contract before ventricles.
Remember: The AVN delay is crucial - it ensures atria finish contracting before ventricles begin, optimizing blood flow. Without this delay, the heart's pumping efficiency would be significantly reduced.
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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