epidermis

Eva Rudolf-Müller is a freelance writer in the medical team. She studied human medicine and newspaper sciences and has repeatedly worked in both areas - as a doctor in the clinic, as a reviewer, and as a medical journalist for various specialist journals. She is currently working in online journalism, where a wide range of medicine is offered to everyone.

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The epidermis is the top layer of our three-layer skin. 90 percent of the epidermis consists of a horny layer, made up of special cells that keratinize on the surface of the skin and are then shed. The epidermis is constantly renewing itself. Read everything you need to know about the epidermis!

What is the epidermis?

The epidermis is the top layer of skin, the border between our body and the outside world. Their dense cell network forms a protective barrier against penetrating germs and other foreign substances. The epidermis is vascular and has no nerves. Their thickness varies greatly and depends on the degree of mechanical stress: In unloaded areas (for example on the eyelids) the epidermis is only 0.03 to 0.05 millimeters thick. On the other hand, it is up to two millimeters thick in areas that are exposed to heavy loads (palms of the hands and soles of the feet).

The epidermis is constantly renewed in its lower-lying parts and keratinized in the higher-lying layers.

The layers of the epidermis

The epidermis consists of several layers:

• Superficial horny layer (stratum corneum) with stratum disjunctum, the outermost layer in which the horny cells are shed
• unkorn deep germ layer (stratum germinativum)

The deep-lying germinal layer is also divided into several layers. From the bottom up these are:

• Basal cell layer (stratum basale)
• Prickly cell layer (stratum spinosum)
• Granular layer (stratum granulosum)
• Glossy cell layer (stratum lucidum)

The horny layer (stratum corneum)

The horny layer, the top layer of the epidermis, consists of fused, flattened cells that contain keratin (a fiber protein) and have no nucleus. These so-called keratinocytes are held together by a close connection by means of desmosomes (cell membrane compression). The keratin prevents water from evaporating from the surface of the skin. The sebum, which is produced by the sebum glands, keeps the horny layer supple and water-repellent.

The keratinocytes migrate to the surface of the skin (stratum disjunctum) within four weeks. In this way they become keratinized more and more, are then destroyed and ultimately detach themselves from the skin. So the skin is constantly renewing itself.

The germ layer (stratum germinativum)

The germ layer lies under the horny layer, is firmly interlocked with the dermis underneath and, through division, constantly produces new epithelial cells. It is divided into four layers:

In the bottom layer, the basal cell layer (stratum basale), and the next layer, the prickly cell layer (stratum spinosum), the cells of the epidermis multiply: this is where basal cells and melanocytes are located. The latter produce the brown-black pigment melanin. Depending on the amount of pigment, the skin and hair are more or less heavily pigmented. Melanin protects against excessive exposure and tans the skin.

The top prickly cells are already showing signs of cornification.

Keratohyalin grains are located in the granular cell layer (stratum granulosum), which adjoins the prickly cell layer at the top. They give off fatty substances that give the horny layer its white appearance.

The top layer of the germinal layer, the glossy cell layer (stratum lucidum), is light and shimmering through. It consists of keratinocytes, contains glycogen (storage form of carbohydrates) and eleidin, an intermediate product of keratin.

Epidermis function

The function of the epidermis is to protect the organism from damaging external influences. As the top layer of skin, the epidermis prevents the penetration of harmful microorganisms and protects against UV radiation and mechanical stress.

What problems can the epidermis cause?

The epidermis can cause numerous problems. If the cell contacts in the uppermost layer of the epidermis, the stratum disjunctum, do not loosen properly and the horny cells stick to the epidermis, a scaly skin surface develops, as is the case with psoriasis, for example.

Disturbances in the horny layer give the appearance of dyskeratosis. This means the pathologically premature keratinization of cells.

In acanthosis, the prickly cell layer is thickened beyond the norm. If the granular cell layer is heavily thickened, it is called granulose. Thickening of the horny layer is called hyperkeratosis.

In the case of an incompletely cornified horny layer (parakeratosis), the granular cell layer is completely absent.

If someone has too little or no melanin at all, the skin is very light and the hair is white-blonde. Doctors then speak of albinism.

White spot disease (vitiligo) forms white, pigmentless spots on the skin that can gradually expand.

Birthmarks are rounded pigment spots. If they degenerate, malignant melanoma (black skin cancer) can develop. There are also other forms of skin cancer, such as prickly cell and basal cell carcinoma. They arise from the prickly cell layer or basal cell layer of the epidermis.

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