THE INTEGUMENTARY SYSTEM
It's alive! Overview of the skin
You may have heard before that the skin is the largest organ of the human body. If you haven’t heard that, congratulations on learning a new fun fact today! Skin is in fact the largest organ of the human body, and like all other organs, it has some extremely important functions that help to keep you alive.
Oftentimes, we think of skin as just a covering for our body, which is one of its many important functions, but we forget that skin is very much a living organ that plays many vital roles in our bodies (though it does include a dead layer). Hopefully this lesson will impress on you just how important your skin is and how much it does for you.
There are several key functions of skin that you should understand, which we will go through in just a second. These functions are very closely tied to the structure of skin, because:
We will go over the structure of skin in a little more detail as we talk about the functions, but we’re more interested in you understanding functions and how this ties in with the general structure than we are in you memorizing names of layers and skin features. Here’s a quick overview, so that you have a general idea of what we’re talking about and something to refer back to as you learn more about the functions of skin:
protection
Barrier
The skin is a barrier that protects your insides from getting all gunked up by dirt, germs, and other junk that is found in the environment. Just think how much dirt and bacteria can get on your skin in one day of playing outside. That’s a lot of grossness, but, since your skin is such a good barrier, that grossness doesn’t seep down into your organs and get you really sick. In fact, it is almost impossible for dirt or bacteria to get through intact skin!
This is really, really important, and without this function, you’d die very quickly. This role is mainly played by a layer of dead skin cells on the outside surface of your body, which are mixed in with lots of oils and waxes to keep that barrier intact. This outer layer of skin is called the epidermis (“epi” means on top of, and “dermis” refers to skin). Keratin is a special type of protein that is very abundant in epidermis, and provides strength and sturdiness to the epidermis.
Waterproofing
Skin is a barrier. This keeps gunk out. It also keeps out junk that we do want, but only in controlled settings, like water. In the environment, water is found at the wrong osmolarity for your cells. Remember back to when we learned about osmosis: If the salts in water are less concentrated than they are in your cells, that water will move into your cells, causing them to burst. If the salts in water are more concentrated than they are in your cells, that water will move out of your cells, causing them to shrink. We want the water around our cells to be at just the right concentration, so we control our body’s environment—especially the amount of water—very closely, through a lot of mechanisms involving your blood, kidneys, lungs, and digestive system.
The main idea is that we don’t want just any water surrounding our cells. We want to keep “environment” water outside our bodies unless we drink it.
Because the skin is such a good waterproofing barrier, it also keeps good stuff in. This includes water. Without skin, a lot of the water in your body would evaporate. You would get dehydrated and die. But, since skin is a barrier and has a lot of water-repelling oils and waxes in it, this doesn’t happen.
The skin is a barrier that protects your insides from getting all gunked up by dirt, germs, and other junk that is found in the environment. Just think how much dirt and bacteria can get on your skin in one day of playing outside. That’s a lot of grossness, but, since your skin is such a good barrier, that grossness doesn’t seep down into your organs and get you really sick. In fact, it is almost impossible for dirt or bacteria to get through intact skin!
This is really, really important, and without this function, you’d die very quickly. This role is mainly played by a layer of dead skin cells on the outside surface of your body, which are mixed in with lots of oils and waxes to keep that barrier intact. This outer layer of skin is called the epidermis (“epi” means on top of, and “dermis” refers to skin). Keratin is a special type of protein that is very abundant in epidermis, and provides strength and sturdiness to the epidermis.
Waterproofing
Skin is a barrier. This keeps gunk out. It also keeps out junk that we do want, but only in controlled settings, like water. In the environment, water is found at the wrong osmolarity for your cells. Remember back to when we learned about osmosis: If the salts in water are less concentrated than they are in your cells, that water will move into your cells, causing them to burst. If the salts in water are more concentrated than they are in your cells, that water will move out of your cells, causing them to shrink. We want the water around our cells to be at just the right concentration, so we control our body’s environment—especially the amount of water—very closely, through a lot of mechanisms involving your blood, kidneys, lungs, and digestive system.
The main idea is that we don’t want just any water surrounding our cells. We want to keep “environment” water outside our bodies unless we drink it.
Because the skin is such a good waterproofing barrier, it also keeps good stuff in. This includes water. Without skin, a lot of the water in your body would evaporate. You would get dehydrated and die. But, since skin is a barrier and has a lot of water-repelling oils and waxes in it, this doesn’t happen.
Padding
The squishiness of the dermis and subcutaneous fat provides some much-needed padding to all the tissues underneath. If you get hit or fall down, for example, these will absorb some of the shock.
Regeneration and Wound Healing
Skin also has other important protective roles that go beyond this function of the nonliving outer barrier, though. This is where it starts to become important that skin is a living organ. The bottom part of the epidermis (closest to the middle layer, which is called the dermis) contains a lot of stem cells that produce new cells for the epidermis. These stem cells are what allows your skin to heal when you get scraped, scratched, or cut, as well as just make new cells when the old ones get sloughed off from the normal wear and tear of life. They make sure that you will always have a healthy, intact protective layer of skin on your outside. Again, super important!
If you’d like to learn more about wound healing, this video gives a great overview:
The squishiness of the dermis and subcutaneous fat provides some much-needed padding to all the tissues underneath. If you get hit or fall down, for example, these will absorb some of the shock.
Regeneration and Wound Healing
Skin also has other important protective roles that go beyond this function of the nonliving outer barrier, though. This is where it starts to become important that skin is a living organ. The bottom part of the epidermis (closest to the middle layer, which is called the dermis) contains a lot of stem cells that produce new cells for the epidermis. These stem cells are what allows your skin to heal when you get scraped, scratched, or cut, as well as just make new cells when the old ones get sloughed off from the normal wear and tear of life. They make sure that you will always have a healthy, intact protective layer of skin on your outside. Again, super important!
If you’d like to learn more about wound healing, this video gives a great overview:
Sunblock
A final protective function of skin is to produce a special kind of sunblock called melanin. Melanin is a pigment (color-giving protein) produced by a special cell type called melanocytes (“cytes” means cells), which are found in the bottom-most layer of your epidermis, right above your dermis. Melanin protects your cells from the harmful UV rays of the sun. These UV rays are powerful enough to cause structural damage to your DNA, which causes cancer. Melanin absorbs the energy of UV rays so that they don’t give you cancer.
Lighter-skinned people have less melanin, and they are therefore more prone to getting skin cancer if they spend a lot of time in the sun. Darker-skinned people have more melanin and are therefore less likely to get skin cancer. It’s especially important for lighter-skinned people to wear sunscreen when they go outside, because they have less natural sunscreen (melanin). It’s still a good idea for everyone to wear sunscreen when they are outside for long periods of time, though.
If you’re interested, this video talks more about the science of skin color:
A final protective function of skin is to produce a special kind of sunblock called melanin. Melanin is a pigment (color-giving protein) produced by a special cell type called melanocytes (“cytes” means cells), which are found in the bottom-most layer of your epidermis, right above your dermis. Melanin protects your cells from the harmful UV rays of the sun. These UV rays are powerful enough to cause structural damage to your DNA, which causes cancer. Melanin absorbs the energy of UV rays so that they don’t give you cancer.
Lighter-skinned people have less melanin, and they are therefore more prone to getting skin cancer if they spend a lot of time in the sun. Darker-skinned people have more melanin and are therefore less likely to get skin cancer. It’s especially important for lighter-skinned people to wear sunscreen when they go outside, because they have less natural sunscreen (melanin). It’s still a good idea for everyone to wear sunscreen when they are outside for long periods of time, though.
If you’re interested, this video talks more about the science of skin color:
sensing the environment
Another very important role of skin, which relies very much on the living middle layer of skin, called the dermis, is sensing the environment. The dermis has many, many nerve endings and specialized nerve cells that help you to feel—either consciously or unconsciously—what is going on in the environment, which helps you to respond to environmental cues properly. In your skin, there are several types of nerves and nerve endings, which sense:
If you’re interested in learning more, this video gives a good overview:
- Touch: Pressure or stretch receptors in your skin help you to know when someone or something is touching you. You can also feel how strongly that thing is touching you, like whether something is gently brushing up against you or is grabbing you very tightly. As you can imagine, that’s a pretty important distinction that helps to determine how you react to your environment.
- Temperature: There are many temperature sensors (both for hot and cold) in your skin. This helps you to be both consciously aware of your environment, so that you can, for example, put on a coat if it’s really cold out, and unconsciously aware of your environment, so that you can, for example, start sweating if it’s really hot out.
- Pain: Pain may be unpleasant, but it is also extremely important. It helps you to know when there is a problem that needs to be fixed. For example, imagine that you put your hand on a hot stove. You need to be able to know to lift your hand off of that stove, so that you don’t get hurt. Pain receptors in your skin help you to do this. Pain is unpleasant to give you a lot of motivation to fix the problem.
If you’re interested in learning more, this video gives a good overview:
temperature regulationSkin doesn’t just sense temperature. It also helps to keep your body temperature at a constant 98 °F (37 °C), or so. Hair in your skin and fat under your skin help to keep you warm. Sweat glands release hot water from your body to cool you down.
Hair follicles and sweat glands are found in the dermis. Subcutaneous fat, which is the type of fat under your skin, is found in a layer of skin below the dermis, called the hypodermis (“hypo” means under). The hypodermis is sometimes called the subcutaneous layer. |
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vitamin d production
The final important function of your skin is Vitamin D production. Vitamin D is an important vitamin in your body that does a bunch of good stuff, including bone growth, brain function, and immune system function (which keeps you from getting sick). It isn’t really found in most food. Instead, your skin makes it by a chemical reaction that requires UV light from the sun. This happens in the epidermis.
If you’d like more information on vitamin D, this video gives a good overview:
If you’d like more information on vitamin D, this video gives a good overview:
skin structure
We’ve just gone through the functions of the skin, as well as the structures that relate to those functions. You should understand these functions and how the structure relates to them, but, again, our emphasis here is on understanding the main purpose of skin and how it accomplishes that, rather than memorizing the names and locations of each feature of the integumentary system.
That said, notice how the structure of skin helps with its function. It has a waterproof, dead, totally replaceable, thin, flat outer layer makes it perfect for acting as a barrier. The stuff that really needs protecting—like subcutaneous fat and all the good stuff in the dermis—is on the inside, protected by the epidermis. Plus, the structures in the skin allow it to have even more functions, like maintaining body temperature and sensing the environment. Structure leads to function!
And that pretty much covers it for skin! (Get it? Because the skin, like, covers you? *Hold for roaring laughter*).
That said, notice how the structure of skin helps with its function. It has a waterproof, dead, totally replaceable, thin, flat outer layer makes it perfect for acting as a barrier. The stuff that really needs protecting—like subcutaneous fat and all the good stuff in the dermis—is on the inside, protected by the epidermis. Plus, the structures in the skin allow it to have even more functions, like maintaining body temperature and sensing the environment. Structure leads to function!
And that pretty much covers it for skin! (Get it? Because the skin, like, covers you? *Hold for roaring laughter*).
Summary
This video gives a good idea of some of the most important ideas we’ve discussed as well as a deeper dive into a few of the structures and functions of skin:
You should understand:
- That the skin is a complex, living organ with many important functions in your body.
- The role of the skin in protecting the body from the outside world, especially acting as a barrier, waterproofing the body (keeping bad water out and good water in), providing padding, wound healing, and protecting us from the sun.
- The role of the skin in sensing the environment, including that it has touch, temperature, and pain receptors.
- The role of the skin in temperature regulation, including the importance of hair and subcutaneous fat in keeping you warm, and sweat in keeping you cool.
- The role of the skin in vitamin D production.
- That the skin’s structure enables it to do its functions.
Learning Activity
Content contributors: Emma Moulton
Some images made with biorender.com
Some images made with biorender.com