The structure of our skin is rather complex. Some skin structures are very easy to recognise; one just has to look at the skin carefully. Other skin structures, however, are only visible under the microscope.
If you look at your skin thoroughly, you will discover that the different layers of the skin are visible even to the naked eye. This external, so-called “macroscopic” skin structure is visible e. g. on our hands and feet. The palms of one’s hands and the soles of the feet are covered by hairless ridged skin. The rest of the body is covered by so-called meshed skin, where hair is growing. These differences are determined genetically.
Under the microscope you would be able to see further skin layers. This finer “inner” structure is called “microscopic structure”. The fine structure of the skin consists of three layers and can only be distinguished under the microscope. Every layer shows typical cell structures with specific tasks.
| Epidermis |
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The outer layer of the skin is called epidermis. The epidermis is the outer border to the surrounding world. Its thickness varies in different body regions: it is thinnest on the eyelids (0.05 mm) and thickest on the palms and soles (1.5 mm). Age, sex and lifestyle can have an influence on the thickness of the epidermis. If you walk around on bare feet a lot, the horny layer under your feet will be strikingly thicker than if you don’t.
The epidermis is built up by keratinocytes. Keratinocytes are horn cells that produce the horny substance, the so-called keratine. Keratine is water-repellent and makes the skin elastic. The epidermis does not possess blood vessels, nerves or glands. In the lowest layer of the epidermis the melanocytes are located. Melanocytes are cells that produce the skin colouring substance melanine. Melanine colours the skin; when the skin is exposed to the sun, melanine darkens the skin and thus protects it from sunlight. In this way, the UV rays cannot enter the deeper skin layers. Too much exposure to sunlight can damage the epidermis cells and cause a malignant development. |
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| Dermis |
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The dermis consists of loosely woven connective tissue and is therefore elastic. The thickness of the dermis also varies according to location. It is about 0.3 mm on the eyelid and up to 2.4 mm on the palms of the hands and on the soles of the feet.
Very fine blood vessels run in the dermis, the capillary vessels, which supply the epidermis and the dermis with nutriments. The capillary vessels are also responsible for the temperature regulation (heat and cold) of the body. In heat, they are dilated and thus can discharge heat; in cold they constrict and make sure that the warmth produced by the organism stays inside the body.
Furthermore, the dermis also harbours hair follicles, sweat, apocrine and sebaceous glands. Usually, every sebaceous or oil gland is connected to one hair follicle. Only around the eyes, on eyelids, lips etc. we have sebaceous glands that work without a hair follicle. Foot soles and palms of the hands don’t possess any oil glands. The oil glands produce sebum (oil), a substance that prevents the skin from drying out and makes it elastic. In addition, the dermis contains pain receptors and receptors for touch and pressure. |
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| Subcutis |
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The subcutis consists of loose connective tissue in which, like little cushions, fat pads are integrated. It is their function to keep the body warm and to isolate it from external temperature changes. This layer is crossed by extensions of the epidermis’ solid fibres. These fibres connect the skin with the underlying tissues like retaining straps. The skin can be moved more or less above this underlayer, depending on the strength of these fibres (more on the back of the hand, less under the sole of the foot). Depending on the location, the subcutaneous tissue is followed by musculature, bones, cartilage and fat. The subcutaneous tissue also harbours the end pieces of hair follicles and receptors for pressure and vibration, the so-called Pacinian Corpuscles.
Subcutaneous tissue varies in thickness depending on the location. How many fat cells are incorporated depends on the nutritional state of a person. There is no subcutaneous tissue without fat cells. The tissue serves as protection against the cold, as energy store and as buffer against blows. |
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Finger and toe nails and the scalp hair also belong to the skin – they are called “skin appendages”.
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Besides the skin as described above there is also the mucosa. Mucous membranes line the insides of the hollow organs, e. g. the intestines or the mouth. Mucosa can also be found on the sexual organs. The upper coating of the male glans is a mucous membrane, for example, and the female vagina is lined by a mucous membrane without glands. Mucosa, in contrast to normal skin, does have neither a horny layer nor hair. |
