Keratin Protein & the Epidermis

What is the Epidermis?

Ever wonder what's underneath your skin? What would happen if your skin couldn't hold itself together? That's what we're going to cover here (pun intended)! You'll learn all about the protein, keratin, and how it holds our skin together. Our skin is actually made of three layers; the epidermis, dermis, and hypodermis. They form a skin sandwich with the epidermis and hypodermis being the bread, and the dermis being the middle.

The epidermis is the layer we're interested in for this lesson. The epidermis is the outer layer of cells in the skin. It is made of flat, scale-like, cells called epithelial cells and specialized cells known as keratinocytes. These cells protect our body and prevent pathogens from penetrating the skin. An important protein called keratin, anchors the cells together and to the layer beneath it, the dermis.

What is Keratin?

Keratin is a protein inside cells. It exists in many types of cells but it is very important for epithelial cells, which make up the skin. Keratin is a type of filament protein, called an intermediate filament. These proteins form long strands inside the cell, hence the name filament. The filaments anchor the cells to each other, which prevents the cells from pulling apart.

Keratin in Skin

Keratin has two main functions in the skin:

1. To hold skin cells together to form a barrier

2. To form the outermost layer of our skin, that protects us from the environment.

To form a barrier, epithelial cells anchor together through proteins called desmosomes. Two epithelial cells line up next to each other and attach using desmosomes. The desmosomes are like glue holding the two cells together. Inside the cell are the keratin fibers, holding the desmosomes to the cell. Without the keratin fibers, the desmosomes would just pull the membrane of the cell away from the center. The keratin anchors the desmosomes to the cell and the desmosomes anchor the cells to each other. See the desmosome junction? The cells attach to each other, and the long filaments within the junction are keratin proteins.

Desmosome junctions in epithelial cells

The second function of keratin is to form the outer layer of the skin. This happens through keratinocytes in a process called cornification. The keratinocytes in the middle of the epithelium start to make more and more keratin. As they do, they move upwards in the epithelium towards the top. The keratinocytes slowly die, leaving a thick shell of filaments inside the keratin protein. These keratin shells form the outer layer of our skin. This skin is dead and constantly flakes off throughout the day. Because the outer layer of skin is dead, it protects us against assaults from the environment like heat, pressure, or physical damage. The dead layer of keratinocytes is shown at the top. Note how the cells are not pink and enlarged, unlike the living keratinocytes below in the epidermis.

Cross section of the epidermis showing the top layer of dead keratinocytes

Keratin Diseases

Since keratin is such an important protein, you can imagine how serious it would be to have a keratin problem. People with defects in their keratin proteins no longer have proper adhesion between the epidermis and the dermis. The result is large blisters on the skin in response to slight rubbing or scratching. These people have trouble keeping their skin intact and are more vulnerable to infection.

Lesson Summary

Keratin is an important protein in the epidermis. Keratin has two main functions: to adhere cells to each other and to form a protective layer on the outside of the skin. In epithelial cells, keratin proteins inside the cell attach to proteins called desmosomes on the surface. The desmosomes act as anchors, holding the cells together. This prevents bacteria from slipping in between the cells and keeps a sturdy barrier between the body and the environment. Specialized cells, called keratinocytes make lots of keratin. Over time, they migrate towards the surface of the skin and slowly die off, forming skeletons of cells made of keratin. This layer of dead cells protects our body from the outside world. People who have problems with keratin proteins may have skin diseases such as severe blistering and a high risk of infection.