Skin: Structure

2023 Author: Wallace Forman | [email protected]. Last modified: 2023-08-25 11:04

Skin: structure and function

With an area of one and a half to two square meters, our skin is both a delimitation from the outside and a protective shield. It is only a few millimeters thick. It performs a wide range of tasks, including being responsible for the heat balance, involved in metabolism, important for the immune system and the metabolism of hormones. The skin is elastic, protects against tension, pressure, injuries, wind and weather and against drying out. The body shell also gives us information about environmental influences. If the temperature increases, we react by sweating, and in the cold we get goose bumps. In addition, the skin and appendages - such as hair and nails - make up the unique appearance of each individual.

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Structure of the skin

The body shell consists of several layers from the outside in:

• Upper skin (epidermis),
• Dermis and
• Subcutis.

The so-called skin appendages include hair, nails and skin glands (sweat, scent and sebum glands).

Epidermis

It forms the topmost protective layer, the direct boundary to the environment. It is relatively thin, in some places it is only 30 micrometers “wafer-thin”, in other places it is somewhat thicker - for example on the soles of the feet or the inside of the hands. The outermost layer of the body shell is constantly renewed.

If the skin tans in the sun, this is due to the melanocytes, the pigment-forming cells of the epidermis. The sun not only tans the skin, it also thickens - both of which serve to protect against UV light to a certain extent.

In addition, the so-called Merkel cells are located in this skin layer, through which mechanical stimuli such as touch, pressure and vibrations can be perceived. Our skin is also connected to the immune system through the Langerhans cells. These can absorb antigens and “boost” the immune system.

Dermis (cutis, dermis)

The dermis lies under the epidermis. It consists of connective tissue and a gel-like basic substance with various cells (e.g. cells of the body's defenses such as lymphocytes). Collagen fibers give it stability, elastic fibers ensure its elasticity. Blood vessels supply the dermis and are involved in regulating temperature and blood pressure.

In the dermis there are also special receptors that report touch, the Meissner bodies. The Ruffini bodies are also important for the sensation of pressure and the perception of stretching, tension and cooling. After all, many nerve fibers end in this layer, so that in addition to pressure and touch or pain, itching and temperature (fluctuations) can also be perceived. Hair roots and skin glands (sweat, scent and sebum glands) are also components of the dermis.

Subcutis

The subcutis consists of loose connective and fatty tissue in which nerves and blood vessels run. One of the tasks of the subcutaneous tissue is to connect the skin with underlying structures (such as muscles, bones, etc.) and to ensure a certain mobility. As a so-called subcutaneous fatty tissue, it serves to store energy and provide thermal insulation. This fatty tissue is distributed differently on the body. Special mechanoreceptors in the subcutis, the Vater-Pacini lamellar bodies, are responsible for the perception of vibrations.

Glands, hair & nails

The skin appendages fulfill different tasks and are distributed to different extents in the different regions of the body.

• Sweat glands are found almost all over the body, but are particularly numerous on the palms of the hands and soles of the feet. They give off the sweat that is needed to regulate the body's heat. In addition, the sweat secretion is important for the acid mantle of the skin, which in healthy skin is in the slightly acidic range (pH 5.7) and is intended, among other things, to prevent the penetration of germs. Some special sweat glands (apocrine glands) are also called scent glands. You can find them in the armpits, for example. The production of their secretions is controlled by hormones and only begins with puberty.
• Sebum jets release the sebum, which is rich in fatty acids. It gives the hair shine and suppleness to the skin. If sebum production is reduced, skin and hair become dry. The glands are usually particularly active in the face. When the sebum glands are overactive, seborrhea occurs, which is involved in the development of acne. The sebum glands are also subject to hormonal control.

Toenails and fingernails are made of horny scales. They offer toe and fingertip protection. The nails also help the fingers to feel. Our body hair is also made up of horny layers. Today they have more of an aesthetic function and are only involved in maintaining body temperature to a small extent.

Functions of the skin

Our body shell consists of different layers and cells that fulfill very different functions.

Protective function

The outermost layer of the skin has a "renewal mechanism" and shields from the sun's rays to a certain extent:

The epidermis is constantly renewed - roughly every four weeks. The so-called basal cells are formed anew, lose fluid, are shifted outwards and become keratinized. The body then finally separates from them in the form of flakes of skin, while new cells follow suit.

Melanocytes, pigment-forming cells in the epidermis, are stimulated by UV rays to produce more of the pigment melanin. The skin turns brown and thickens (called light calluses). These processes protect the skin. The period in which the skin protects us from damage from UV radiation is the so-called self-protection time of the skin. The more melanin there is, the longer this "natural buffer time" is. However, staying too long in the sun or in the solarium or too much UV radiation can lead to damage - the risk of skin cancer increases.

Exchange function & temperature regulation

The skin is also involved in maintaining body temperature. It gives off heat - for example through evaporation of sweat. The shell of the body also protects against the loss of fluid and is therefore important for the body's water balance.

The subcutaneous fatty tissue insulates against the cooling down of the body. When it is cold, blood circulation in the skin is also reduced. We still develop goose bumps, for example when we are shivering, and this causes our hair to stand up. However, this mechanism is not quite as effective as in the animal world. Although the skin is a good insulator, it can absorb substances such as medication in the form of ointments, creams, plasters, or sprays.

Sensory function & communication

Pressure, pain, temperature - the skin provides us with all of these perceptions, among other things through various receptors that are linked to corresponding nerve fibers. They tell us whether an object is rough or smooth, feels cold or warm, and tell us through pain when we are injured. We are particularly sensitive in some areas of the skin, such as the fingertips or the face. Even very light touches are perceived as tickling, for example when a mosquito sits on the skin. Cold and heat receptors in the skin provide information about the respective temperature. As a reflection of what is inside, it also “reveals” emotions or the state of health - for example when we blush or are pale as a sheet.