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What is Epidermis? - Definition, Function & Layers

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  • 0:01 What is the Epidermis?
  • 0:35 Function
  • 1:30 Layers
  • 3:38 Cells
  • 4:51 Lesson Summary
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Lesson Transcript
Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

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.

Cross-Section of Skin
Cross section of skin

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.

Layers of the Epidermis
Epidermis

If we were to take a closer look, we find that the stratum corneum is composed almost exclusively of dead cells. It may come as no surprise that we lose skin cells on a regular basis. In fact, the dead cells of the stratum corneum slough off so often that we end up with a completely new outer layer about every 35 days.

And how, you may be wondering, do we have any skin left if we are always losing cells? This is where the stratum basale comes in. Just as its name suggests, it is the base or deepest layer of the epidermis. A cell-producing factory, the basale layer contains stem cells which are constantly dividing to make new ones. These fresh new cells make their way up to the stratum corneum to replace those that have sloughed off. This cycle runs on a continual basis, keeping our epidermis healthy and strong.

Cross-Section of Epidermis under Microscope
Cross-Section of Epidermis

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.

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