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Rebekah
12/7/2025
Biology
The kidney
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Dec 7, 2025
•
Understanding How the Kidney Works
Rebekah
@rebekah_liz
1 / 5
The Kidney's Essential Functions
Think of your kidneys as your body's ultimate filtration system - they're constantly cleaning your blood and managing your fluid balance. The kidneys perform two crucial jobs: excretion (removing toxic waste like urea and creatinine) and osmoregulation (controlling water levels in your body fluids).
Blood flows into each kidney through the renal artery, gets filtered, then leaves via the renal vein. The waste products and excess water form urine, which travels down the ureter to your bladder for storage.
Each kidney has an outer cortex where filtration happens and an inner medulla that's divided into pyramid-shaped sections. The real star of the show is the nephron - the kidney's functional unit that acts as a microscopic filter.
Quick Tip: Remember that blood enters the nephron through an afferent arteriole, forms a ball of capillaries called the glomerulus inside Bowman's capsule, then exits via an efferent arteriole.
How Blood Gets Filtered
The Bowman's capsule is where the magic of filtration begins, and it's got three key layers working together. You've got the capillary endothelium with tiny pores, the crucial basement membrane that does the actual filtering, and specialised podocytes with foot-like processes creating filtration slits.
High hydrostatic pressure forces fluid out of the blood to create filtrate. The key equation you need to remember is: net filtration force = ψ_plasma - ψ_filtrate. This pressure difference drives the filtration process.
Once filtrate forms, the proximal convoluted tubule (PCT) gets to work on selective reabsorption. About 70-80% of water gets reabsorbed back into the blood, along with useful stuff like glucose, amino acids, and some salts.
Exam Focus: The PCT is perfectly adapted for reabsorption with microvilli, mitochondria for ATP, and protein carriers for active transport.
Fine-Tuning Your Blood Chemistry
The distal convoluted tubule (DCT) might seem less exciting than other parts, but it's your body's chemistry lab. It actively pumps sodium ions and hydrogen carbonate ions to control your blood's acid-base balance and ionic composition.
This is also where your kidneys get rid of nasty toxic substances like creatinine by secreting them from blood into the filtrate. Think of it as your kidney's final quality control check.
The DCT's cuboidal epithelium comes equipped with microvilli and plenty of mitochondria, just like the PCT. This gives it the power to fine-tune your blood chemistry and maintain that perfect internal environment your cells need.
Remember: The DCT raises blood pH when necessary and controls the ionic composition of surrounding blood.
Water Balance Control
Osmoregulation is your body's way of maintaining perfect water balance, and it's controlled by a hormone called antidiuretic hormone (ADH). The hypothalamus produces ADH, which gets released from the posterior pituitary when your body detects changes in blood concentration.
When you're dehydrated, sweating loads, or eating salty food, osmoreceptors detect the change and trigger ADH release. This hormone increases the permeability of the collecting duct walls, allowing more water to be reabsorbed back into your blood.
The result? You produce a smaller volume of concentrated (hypertonic) urine, conserving precious water. This is a classic negative feedback system - when water levels return to normal, ADH secretion drops.
Real-Life Connection: This explains why you produce less urine when you're dehydrated and why it's much more concentrated and darker in colour.
The Loop of Henle's Clever Trick
The Loop of Henle is basically your kidney's secret weapon for producing concentrated urine. This U-shaped structure dips deep into the medulla and uses a brilliant mechanism called the countercurrent multiplier.
The descending limb is permeable to water, so water leaves by osmosis as the filtrate becomes more concentrated. Meanwhile, the ascending limb has thick walls packed with mitochondria and actively pumps out sodium and chloride ions, but water can't follow.
This creates a salt gradient in the surrounding tissue - the deeper you go into the medulla, the saltier it gets. When the collecting duct passes through this salty region, water gets drawn out by osmosis, concentrating your urine even more.
Key Concept: The countercurrent multiplier allows mammals to produce hypertonic urine, which is essential for surviving in environments where water is scarce.
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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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user
Understanding How the Kidney Works
Rebekah
@rebekah_liz
Your kidneys are working 24/7 to keep you alive by filtering out toxic waste and controlling your body's water balance. Understanding how these remarkable organs work will help you grasp one of the most important homeostatic processes in your body.
The Kidney's Essential Functions
Think of your kidneys as your body's ultimate filtration system - they're constantly cleaning your blood and managing your fluid balance. The kidneys perform two crucial jobs: excretion (removing toxic waste like urea and creatinine) and osmoregulation (controlling water levels in your body fluids).
Blood flows into each kidney through the renal artery, gets filtered, then leaves via the renal vein. The waste products and excess water form urine, which travels down the ureter to your bladder for storage.
Each kidney has an outer cortex where filtration happens and an inner medulla that's divided into pyramid-shaped sections. The real star of the show is the nephron - the kidney's functional unit that acts as a microscopic filter.
Quick Tip: Remember that blood enters the nephron through an afferent arteriole, forms a ball of capillaries called the glomerulus inside Bowman's capsule, then exits via an efferent arteriole.
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How Blood Gets Filtered
The Bowman's capsule is where the magic of filtration begins, and it's got three key layers working together. You've got the capillary endothelium with tiny pores, the crucial basement membrane that does the actual filtering, and specialised podocytes with foot-like processes creating filtration slits.
High hydrostatic pressure forces fluid out of the blood to create filtrate. The key equation you need to remember is: net filtration force = ψ_plasma - ψ_filtrate. This pressure difference drives the filtration process.
Once filtrate forms, the proximal convoluted tubule (PCT) gets to work on selective reabsorption. About 70-80% of water gets reabsorbed back into the blood, along with useful stuff like glucose, amino acids, and some salts.
Exam Focus: The PCT is perfectly adapted for reabsorption with microvilli, mitochondria for ATP, and protein carriers for active transport.
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Improve your grades
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Fine-Tuning Your Blood Chemistry
The distal convoluted tubule (DCT) might seem less exciting than other parts, but it's your body's chemistry lab. It actively pumps sodium ions and hydrogen carbonate ions to control your blood's acid-base balance and ionic composition.
This is also where your kidneys get rid of nasty toxic substances like creatinine by secreting them from blood into the filtrate. Think of it as your kidney's final quality control check.
The DCT's cuboidal epithelium comes equipped with microvilli and plenty of mitochondria, just like the PCT. This gives it the power to fine-tune your blood chemistry and maintain that perfect internal environment your cells need.
Remember: The DCT raises blood pH when necessary and controls the ionic composition of surrounding blood.
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Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Water Balance Control
Osmoregulation is your body's way of maintaining perfect water balance, and it's controlled by a hormone called antidiuretic hormone (ADH). The hypothalamus produces ADH, which gets released from the posterior pituitary when your body detects changes in blood concentration.
When you're dehydrated, sweating loads, or eating salty food, osmoreceptors detect the change and trigger ADH release. This hormone increases the permeability of the collecting duct walls, allowing more water to be reabsorbed back into your blood.
The result? You produce a smaller volume of concentrated (hypertonic) urine, conserving precious water. This is a classic negative feedback system - when water levels return to normal, ADH secretion drops.
Real-Life Connection: This explains why you produce less urine when you're dehydrated and why it's much more concentrated and darker in colour.
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
The Loop of Henle's Clever Trick
The Loop of Henle is basically your kidney's secret weapon for producing concentrated urine. This U-shaped structure dips deep into the medulla and uses a brilliant mechanism called the countercurrent multiplier.
The descending limb is permeable to water, so water leaves by osmosis as the filtrate becomes more concentrated. Meanwhile, the ascending limb has thick walls packed with mitochondria and actively pumps out sodium and chloride ions, but water can't follow.
This creates a salt gradient in the surrounding tissue - the deeper you go into the medulla, the saltier it gets. When the collecting duct passes through this salty region, water gets drawn out by osmosis, concentrating your urine even more.
Key Concept: The countercurrent multiplier allows mammals to produce hypertonic urine, which is essential for surviving in environments where water is scarce.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the 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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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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
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
I think it’s very much worth it and you’ll end up using it a lot once you get the hang of it and even after looking at others notes you can still ask your Artificial intelligence buddy the question and ask to simplify it if you still don’t get it!!! In the end I think it’s worth it 😊👍 ⚠️Also DID I MENTION ITS FREEE YOU DON’T HAVE TO PAY FOR ANYTHING AND STILL GET YOUR GRADES IN PERFECTLY❗️❗️⚠️
Thomas R
iOS user
Knowunity is the BEST app I’ve used in a minute. This is not an ai review or anything this is genuinely coming from a 7th grade student (I know 2011 im young) but dude this app is a 10/10 i have maintained a 3.8 gpa and have plenty of time for gaming. I love it and my mom is just happy I got good grades
Brad T
Android user
Not only did it help me find the answer but it also showed me alternative ways to solve it. I was horrible in math and science but now I have an a in both subjects. Thanks for the help🤍🤍
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
I found this app a couple years ago and it has only gotten better since then. I really love it because it can help with written questions and photo questions. Also, it can find study guides that other people have made as well as flashcard sets and practice tests. The free version is also amazing for students who might not be able to afford it. Would 100% recommend
Aubrey
iOS user
Best app if you're in Highschool or Junior high. I have been using this app for 2 school years and it's the best, it's good if you don't have anyone to help you with school work.😋🩷🎀
Marco B
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 app is phenomenal down to the correct info and the various topics you can study! I greatly recommend it for people who struggle with procrastination and those who need homework help. It has been perfectly accurate for world 1 history as far as I’ve seen! Geometry too!
Paul T
iOS user