In this lesson, learn what the epidermis is as well as how it functions. Discover more about it as well as explore the actual cells it is comprised of.
What is the Epidermis?
When we think of protecting our bodies from the elements, we may think of putting on a jacket, or shoes and socks. Perhaps you use sunscreen, and wear a hat and sunglasses. Fortunately, in addition to what we wear, we also have a built-in protective covering that keeps our insides safe from our external environment. Our skin, the largest organ in our body, serves this crucial purpose with a layer known as the epidermis as our first line of defense.
In this lesson, we will take a closer look at this skin layer and gain an understanding of why it is so important to our body.
Function of the Epidermis
The epidermis is the outermost layer of our skin. Tough and resilient, protection is its number one job. Think of a parka you may wear in the winter. The inside is lined with soft fleece, providing a layer of warmth. But the outside is made of a strong waterproof material that lets nothing through.
It is a similar situation with our own epidermis.
The protective qualities of our outer layer are vast. Our epidermis is waterproof, which is why we don’t swell with liquid each time we bathe.
The cellular structure of the epidermis also forms a highly effective barrier against germs. When skin is healthy and intact, it is difficult for bacteria and viruses to make an entrance. In addition, cells of the epidermis have the miraculous ability to regenerate, or grow back, unlike many other cells in the body. When we suffer from a wound, healthy skin heals and replaces damaged cells with ease.
Layers of the Epidermis
The epidermis is composed of four main strata, or layers. The outermost layer is called the stratum corneum, which is Latin for ”horny layer.” While we aren’t literally covered in horny scales, this layer is tough nonetheless.
It also varies in thickness depending on the body part it covers. If you often go barefoot, the stratum corneum on the sole of your foot is probably quite thick. Compare that to the skin on your eyelids and you can see the drastic difference.
Two additional layers are sandwiched between the stratum corneum and stratum basale.
The stratum spinosum borders the stratum basale. Here we find spiny keratinocytes that help bond other cells together. Finally, the stratum granulosum lies beneath the stratum corneum. Cells in this layer produce a waxy material that aids in waterproofing the skin.While most of our body’s epidermis is made up of four layers, on the palms of our hands and the soles of our feet, there is one extra layer of skin.
The stratum lucidum is a translucent layer that provides extra thickness to these areas of the skin.
Cells of the Epidermis
Now let’s zoom in on the actual cells that make up the epidermis. In general, the skin is made of epithelial cells, or cells that are tightly packed together in layers. Cells known as keratinocytes are the primary members of the epidermis. These are the cells that are made by the stratum basale and move outwards towards the stratum corneum. You may recognize the word ‘keratin’ within that term. Keratin is a type of protein that is very fibrous and gives the stratum corneum its tough but flexible properties.
In addition to keratinocytes, there are three other types of cells found in the epidermis. Melanocytes are small cells located in the basal layer. These produce pigment known as melanin that helps to protect the skin from UV damage from the sun. Two other cell types found in the epidermis are Langerhans cells and Merkel cells. Langerhans cells are part of our immune system, and they patrol for invaders such as bacteria trying to enter the body through the skin.
Merkel cells are a part of the nervous system, connecting to deeper nerve endings in the body.
The epidermis is the outermost layer of our skin. Its main purpose is protection. The epidermis is made of four main layers, or strata:
- The stratum corneum is the thick, tough outer layer.
It is made mostly of dead cells that slough off constantly.
- The stratum basale is comprised of new cells that are constantly dividing to replace the stratum corneum.
- The stratum spinosum, which helps bond skin cells together, and stratum granulosum, which produces a waxy material that aids in waterproofing the skin layers, are located between the stratum corneum and the stratum basale.
- The stratum lucidum is a translucent layer that provides extra thickness to the skin on the palms of our hands and the soles of our feet.
The epidermis is made mostly of cells called keratinocytes, which contain the fibrous protein keratin. These cells develop in the deepest stratum basale and move outwards towards the most exterior stratum corneum. Other cells found in the epidermis are melanocytes, which produce UV-protecting melanin; Langerhans cells, which work to protect us as part of our immune system; and Merkel cells, which are part of the nervous system and help the skin to connect to nerve endings deeper in the body.
Epidermis Vocabulary & Definitions
- Epidermis: protective outer layer of human skin; comprised of four layers: stratum corneum, stratum basale, stratum spinosum and stratum granulosum, stratum lucidum
- Keratinocytes: cells that contain the fibrous protein called keratin
- Melanocytes: cells provide UV ray protection through the production of melanin
- Langerhans cells: cells working as part of our immune system; they patrol for invaders trying to enter through skin
- Merkel cells: nervous system cells that connect the skin to nerve endings within the body
When this lesson ends, students should be able to:
- Define epidermis
- Describe the layers of epidermis in humans
- Recall how each layer of the epidermis aids the human body
- Discuss the function of the types of cells that are part of the epidermis