1. the epidermis

Structure and cells The epidermis, also called epidermis, is a multi-layered structure that has the ability to keratinize. It consists of five different histologically (under the microscope) visible cell layers. The epidermis is of varying thickness in different parts of the body.

It is thicker in places that are exposed to a lot of stress (hand, foot) and thinner in places that are less stressed (arms, face). The thickness varies from 30 to 300 micrometers. As so-called proliferation tissue (proliferation means multiplication), it is subject to constant renewal.

In the epidermis there are many nerves, but no blood vessels. They are supplied by diffusion (passive transport) from the layer below, the dermis. The different layers of the epidermis also contain different types of cells.

The main component, however, are the keratinocytes (horny cells). These cells migrate through the epidermis to the surface of the skin while changing their structure. Once they reach the surface, they are shelled off as horny scales.

The designation of the cells (keratinocytes) during their migration correlates with the layer in which they are located: The duration of such migration is usually about 5 to 7 weeks. Towards the dermis, the keratinocytes are anchored to the basement membrane by hemidesmosomes. In this way, their hold is secured.

Melanocytes are another component of the skin. These large bright cells contain melanosomes in which melanin is synthesized and stored. Melanin is the skin pigment that gives the skin its actual brown color.

The melanin is then released to the neighboring keratinocytes. Melanin is a pigment that causes the skin to tan, for example. Langerhans cells are also found in the epidermis.

They play an essential role in allergies. For those particularly interested: The Langerhans cells are responsible for type IV allergies (e.g. allergic contact eczema). T-lymphocytes have an immunological function and are found sporadically in the epidermis, but especially in the dermis.

They cooperate with the Langerhans cells. Merkel cells are found in the innermost layer of the epidermis. They mediate the tactile sensation.

Basal cell (regeneration layer)
Spiny cell (spiny layer)
Grain cell (grain layer)
Horn cell (horny layer)