Biology
Chemistry
AP Chemistry
English
AP English Literature
Biology
Dec 2, 2025
241
5 pages
kenzie e @kenzieeffrig
The skin is more than just a cover for your body—it's your largest organ and performs essential functions... Show more
Ever wondered what your skin actually does? The integumentary system (your skin and accessory organs) performs multiple critical functions remembered by the acronym SHAPES Sensation through sensory receptors, Heat regulation to maintain body temperature, Absorption of certain chemicals, Protection from the environment, Excretion of wastes, and Synthesis of vitamin D (essential for calcium absorption).
Your skin consists of three main layers. The outermost epidermis is made primarily of epithelial tissue. Beneath it lies the dermis, which contains a mix of connective tissue, blood vessels, and nerves. The deepest layer, the subcutaneous layer (hypodermis), contains loose connective tissue and fat.
About 90% of your epidermis consists of keratinocytes—tough squamous cells that form your skin's protective barrier. The epidermis has two main sections an upper layer of dead cells that you see and touch, and a lower layer of rapidly dividing cells that constantly produce new skin cells.
💡 Your body is constantly renewing itself! Every hour, you shed approximately 30,000-40,000 skin cells, and the entire epidermis regenerates every 2-4 weeks.
Your skin is in a constant state of renewal. The lower layer of your epidermis produces new cells that gradually push older ones toward the surface. As these cells move upward, they flatten, produce a waterproof protein called keratin, and eventually die, forming your skin's protective outer layer.
The thickness of your epidermis varies throughout your body—it's thinnest on your eyelids and thickest on your palms and feet. When skin is regularly rubbed or pressed, cell division increases to form protective calluses, preventing damage to deeper tissues.
Specialized cells called melanocytes in the deep epidermis produce the pigment melanin, which gives skin its color and absorbs harmful UV radiation. Interestingly, all humans have roughly the same number of melanocytes—skin color differences come from the amount of melanin produced and the size of pigment granules.
🌍 Nature's adaptation People whose ancestors lived near the equator typically produce more melanin as protection against intense UV radiation, resulting in darker skin tones.
When your skin is exposed to UV light, melanocytes increase melanin production as a natural defense mechanism. This melanin moves outside the melanocytes to protect deeper skin layers, resulting in tanning or freckling. Sunburns occur when melanocytes can't produce enough melanin fast enough to prevent UV damage to blood vessels.
Melanoma, the most deadly (though not most common) type of skin cancer, results from uncontrolled production of melanocytes. It typically starts on or near a mole and appears most commonly on women's legs and men's backs.
The dermis lies beneath the epidermis with an uneven, wavy boundary. Dermal papillae extend upward into the epidermis, strengthening the connection between layers (and forming your unique fingerprints!). This layer contains dense connective tissue with fibers that give skin its toughness and elasticity. The dermis houses blood vessels, nerve endings, hair follicles, and glands.
🎨 Tattoo fact Tattoo ink is injected into the dermis rather than the epidermis. If placed in the epidermis, tattoos would quickly fade as skin cells shed every few weeks!
Unlike the epidermis, the dermis doesn't regularly shed, but it can regenerate when injured. When damaged, it produces new tissue with a different texture than surrounding skin, forming a scar. Stretch marks result from rapid growth that tears elastic tissue in the dermis, causing similar scarring.
The subcutaneous layer (hypodermis) attaches your skin to underlying organs and contains adipose tissue that insulates your body. There's no sharp boundary between the dermis and hypodermis, and blood vessels here provide nutrients to all skin layers.
Your skin's accessory organs include nails and hair. Nails protect the ends of your fingers and toes. The whitish half-moon shape (lunula) covers the most actively growing region where cells divide and become keratinized, pushing the nail plate forward. Fun fact your thumbnail grows the slowest while your middle fingernail grows fastest!
Hair covers almost all body surfaces except palms, soles, lips, nipples, and parts of reproductive organs. Each hair develops from a group of epidermal cells called hair follicles. As these cells divide and grow, older cells are pushed upward, become keratinized, and die—making hair essentially dead epidermal cells.
🔍 Did you know? Your rate of nail growth can indicate your overall health status, with faster growth generally reflecting better health!
Each hair follicle has a bundle of smooth muscle cells attached to it called the arrector pili muscle. These muscles are positioned so that when they contract, they pull the hair into a more upright position.
This reaction is what causes "goosebumps" when you're cold or frightened—your body's attempt to trap a layer of warm air near the skin for insulation (much more effective for furry animals than humans with our relatively sparse body hair). This ancient reflex also made our ancestors appear larger to predators when threatened.
👻 Next time you get goosebumps from fear or cold, remember you're experiencing an evolutionary response that dates back millions of years—one that was much more useful to your hairier ancestors!
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.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
46
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Notes on different homeostatic disorders of the stomach (like GERD, appendicitis, etc.) for anatomy and physiology classes. My tummy hurts too, man.
BiologyUncover the secrets of life with this comprehensive Biology flashcard set. Perfect for grade 10 students studying Living Environment.
BiologyShort Intro of GMO
Biologyflashcards for cell membrane
BiologyExplore the fundamentals of genetics, including the roles of DNA, mRNA, and tRNA in protein synthesis. Understand key concepts such as alleles, genotypes, phenotypes, and the processes of transcription and translation. This summary provides essential insights into genetic inheritance and the expression of traits.
BiologyNotes on the reproductive system along with diagrams. WARNING: Talks about genitals.
BiologyApp Store
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
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
kenzie e
@kenzieeffrig
The skin is more than just a cover for your body—it's your largest organ and performs essential functions to keep you alive. This fascinating system protects you from the environment, regulates body temperature, and even helps produce vital vitamins. Let's... Show more
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Ever wondered what your skin actually does? The integumentary system (your skin and accessory organs) performs multiple critical functions remembered by the acronym SHAPES: Sensation through sensory receptors, Heat regulation to maintain body temperature, Absorption of certain chemicals, Protection from the environment, Excretion of wastes, and Synthesis of vitamin D (essential for calcium absorption).
Your skin consists of three main layers. The outermost epidermis is made primarily of epithelial tissue. Beneath it lies the dermis, which contains a mix of connective tissue, blood vessels, and nerves. The deepest layer, the subcutaneous layer (hypodermis), contains loose connective tissue and fat.
About 90% of your epidermis consists of keratinocytes—tough squamous cells that form your skin's protective barrier. The epidermis has two main sections: an upper layer of dead cells that you see and touch, and a lower layer of rapidly dividing cells that constantly produce new skin cells.
💡 Your body is constantly renewing itself! Every hour, you shed approximately 30,000-40,000 skin cells, and the entire epidermis regenerates every 2-4 weeks.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Your skin is in a constant state of renewal. The lower layer of your epidermis produces new cells that gradually push older ones toward the surface. As these cells move upward, they flatten, produce a waterproof protein called keratin, and eventually die, forming your skin's protective outer layer.
The thickness of your epidermis varies throughout your body—it's thinnest on your eyelids and thickest on your palms and feet. When skin is regularly rubbed or pressed, cell division increases to form protective calluses, preventing damage to deeper tissues.
Specialized cells called melanocytes in the deep epidermis produce the pigment melanin, which gives skin its color and absorbs harmful UV radiation. Interestingly, all humans have roughly the same number of melanocytes—skin color differences come from the amount of melanin produced and the size of pigment granules.
🌍 Nature's adaptation: People whose ancestors lived near the equator typically produce more melanin as protection against intense UV radiation, resulting in darker skin tones.
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
When your skin is exposed to UV light, melanocytes increase melanin production as a natural defense mechanism. This melanin moves outside the melanocytes to protect deeper skin layers, resulting in tanning or freckling. Sunburns occur when melanocytes can't produce enough melanin fast enough to prevent UV damage to blood vessels.
Melanoma, the most deadly (though not most common) type of skin cancer, results from uncontrolled production of melanocytes. It typically starts on or near a mole and appears most commonly on women's legs and men's backs.
The dermis lies beneath the epidermis with an uneven, wavy boundary. Dermal papillae extend upward into the epidermis, strengthening the connection between layers (and forming your unique fingerprints!). This layer contains dense connective tissue with fibers that give skin its toughness and elasticity. The dermis houses blood vessels, nerve endings, hair follicles, and glands.
🎨 Tattoo fact: Tattoo ink is injected into the dermis rather than the epidermis. If placed in the epidermis, tattoos would quickly fade as skin cells shed every few weeks!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Unlike the epidermis, the dermis doesn't regularly shed, but it can regenerate when injured. When damaged, it produces new tissue with a different texture than surrounding skin, forming a scar. Stretch marks result from rapid growth that tears elastic tissue in the dermis, causing similar scarring.
The subcutaneous layer (hypodermis) attaches your skin to underlying organs and contains adipose tissue that insulates your body. There's no sharp boundary between the dermis and hypodermis, and blood vessels here provide nutrients to all skin layers.
Your skin's accessory organs include nails and hair. Nails protect the ends of your fingers and toes. The whitish half-moon shape (lunula) covers the most actively growing region where cells divide and become keratinized, pushing the nail plate forward. Fun fact: your thumbnail grows the slowest while your middle fingernail grows fastest!
Hair covers almost all body surfaces except palms, soles, lips, nipples, and parts of reproductive organs. Each hair develops from a group of epidermal cells called hair follicles. As these cells divide and grow, older cells are pushed upward, become keratinized, and die—making hair essentially dead epidermal cells.
🔍 Did you know? Your rate of nail growth can indicate your overall health status, with faster growth generally reflecting better health!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Each hair follicle has a bundle of smooth muscle cells attached to it called the arrector pili muscle. These muscles are positioned so that when they contract, they pull the hair into a more upright position.
This reaction is what causes "goosebumps" when you're cold or frightened—your body's attempt to trap a layer of warm air near the skin for insulation (much more effective for furry animals than humans with our relatively sparse body hair). This ancient reflex also made our ancestors appear larger to predators when threatened.
👻 Next time you get goosebumps from fear or cold, remember you're experiencing an evolutionary response that dates back millions of years—one that was much more useful to your hairier ancestors!
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.
You can download the app in the Google Play Store and in the Apple App Store.
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
46
Smart Tools NEW
Transform this note into: ✓ 50+ Practice Questions ✓ Interactive Flashcards ✓ Full Mock Exam ✓ Essay Outlines
Notes on different homeostatic disorders of the stomach (like GERD, appendicitis, etc.) for anatomy and physiology classes. My tummy hurts too, man.
BiologyUncover the secrets of life with this comprehensive Biology flashcard set. Perfect for grade 10 students studying Living Environment.
BiologyShort Intro of GMO
Biologyflashcards for cell membrane
BiologyExplore the fundamentals of genetics, including the roles of DNA, mRNA, and tRNA in protein synthesis. Understand key concepts such as alleles, genotypes, phenotypes, and the processes of transcription and translation. This summary provides essential insights into genetic inheritance and the expression of traits.
BiologyNotes on the reproductive system along with diagrams. WARNING: Talks about genitals.
BiologyApp Store
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
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
Health
Algebra
Calculus 1
Algebra 1
Overige