The skin (cutis lat.) is surface area (but not on the real surface; intestine up to 450 m²), the largest (depending on body size and body size 1.5 – 2 m2), the heaviest (up to 10 kg) and functionally the most versatile organ of the human or animal organism. It serves the definition of interior and exterior (Hüllorgan), protection against environmental influences, representation, communication and maintenance of homeostasis (equilibrium). In addition the skin acquires important functions in the field of immunology and metabolism and has a variety of coping mechanisms. The skin can tolerate the pH of 5.5 is best.

Structure of the skin

The outer skin (cutis) basically divided into 3 main layers:

* Upper skin (epidermis)
* Leather skin (dermis or Corium)
* Subcutis (Subcutis)

Epidermis (skin)

The epidermis, or “skin” is one of the epithelial tissues, it is a multi-layered squamous keratinisation, usually between 0.03 to 0.05 millimeters, the palms and soles but up to several millimeters thick.

From outside to inside, the following layers are distinguished:

* Horny layer (stratum corneum)
* Gloss layers (stratum lucidum)
* Grains layer (stratum granulosus)
* Stachelberg cell layer (stratum spinosum)
* Basalschicht (stratum basale).

Dermis (Corium, dermis)

The dermis consists mainly of Bindegewebsfasern and serves the food and anchoring of the epidermis. This provides the fine kapillarisierte blood vascular system of the border zone to the epidermis. The origin of the sebaceous and sweat glands found in the lower dermis. It contains the major temperature for smooth muscles and blood vessels.

The dermis is placed in a stratum papillare (Papillenschicht, cone layer, Papillarkörper) and a stratum reticulare (network layer) divided.

Subcutis

The Subcutis forms the base for the overlying skin layers and contains the larger blood vessels and nerves for the upper layers of skin and the subcutaneous fat and loose connective tissue. In the subcutis are sensory cells for strong pressure stimuli.

Skin appendages

Among the so-called skin appendages of the skin include hair with their sebaceous glands and the Haarbalgmuskel (Musculus Arrector pili), nails, horns and sweat glands, the latter in ekkrine and sweat glands apokrine subdivided. Not least is the mammary gland with a modified skin gland.

Bar skin and skin fields

Looking at the skin, or more precisely with a magnifying glass, it is a fine relief visible. After this the skin is divided into two types.

The bar skin occurs on the fingers, the hand inside (palmar) and sole of the foot (plantar) on. The epidermis shows fine Papillarlinien (skin strips), which arise because the Lederhautpapillen arranged in longitudinal rows. It is any skin bar Papillarkörperreihen two subordinate. The skin strips represent individual samples from different geometrical figures (Eddy, arc, loop, double loop). These patterns are used in the Daktyloskopie (fingerprint recognition) forensic technology as a form of biometrics data. The bar skin contains many sweat glands, except, no skin appendages.

The remaining skin areas are the fields covered skins. This show the surface by fine grooves defined rhombic fields (Chutney areola). The furrows appear on the papillenfreien Epidermisbereichen and pass on increased skin tension. They serve as a reserve wrinkles because the skin is less dehnungsfähig than the dermis. The size of the skin fields of the body varies according to region. The skin contains all the fields of skin appendages and is less than 1 / 10 mm thick. On it is thinnest in the area of the eye and the genital organs.

Parts of the skin and their functions

Skin protection from heat and sun rays, absorption of touch stimuli horny layer: protection against injuries and dehydration

Keimschicht: reproduction of skin cells

Pigment layer: protection against burns from the sun’s rays

Switzerlan Spore: protection against overheating by evaporation of sweat

Free nerve endings: transformations of touch stimuli, pain sensation

Lamellar body Chien: Recording of pressure stimuli

Sweat glands: Production of welding

Cold body Chien: Recording of temperature stimuli “cold”

Chien Body Heat: Temperature Recording Reizen “warm”

Hair muscle: for example, allows the erection of hair

Sebaceous gland: production of sebum (grease)

Tastkörperchien: inclusions of touch stimuli

Fat storage: protection against pressure and hypothermia

Blood vessel: the skin with nutrients and oxygen

The skin as a border institution

The skin protects the body against invasion by pathogens or gaseous, liquid or solid foreign substances in the broadest Sense, mechanical injury, radiation damage, but also fluid-electrolyte and protein losses, which in severe burns of the skin reaching dangerous levels. Bacteria and fungi, the so-called skin flora populates it.

Heat budget

About the skin, the body can regulate its heat balance. One effect of overheating the skin with sweat glands opposite. Through the sweat production and the resulting heat of evaporation is close to the running of the skin capillaries, which are wide open, removed (see sweating). With the help of the subcutaneous fat and lower in mass by the heat of the hair is held back. When cold, the skin and subcutaneous fat only low-flow and both acts as an insulator layer. The hair may be a result of the low hair dress of the people only low isolation function. Still, it can be the active principal Fellkleides still a good watch. When occurring in the cold shiver directed Arrector pili muscle of the hair on. A closed polity enables a much better protection against hypothermia.

UV Protection

The strength of the incident UV radiation on the Earth’s surface depends on the time of day, geographic location, season, altitude, the thickness of the ozone layer, clouds and many other local parameters. Against the harmful effects of UV radiation on the skin and underlying tissues exist following safeguards:

* The coat (fur) of mammals or the plumage of birds is a very effective protection against UV radiation, because the largest percentage of UV absorbed and reflected.
* The horny layer (stratum corneum) usually absorbs and reflects approximately 10% of UVB and 50% of UVA radiation, these figures apply to human skin. On increasing the UV exposure, the skin reacts with a thickening of the horny layer; particularly after strong sun fires trained (“Lichtschwiele”).
* The protection of the skin pigmentation is based on the physical absorption of UV by dyes (pigments). Many animals have a pigmentation of the skin. The variable pigmentation of human skin is in the animal kingdom, but (so far) a unique adaptation and protection against UV radiation dar. There are few animals whose skin is in a position to the pigmentation in such a measure to change, as in humans is possible.
* As a so-called “instant tan” (engl. immediate pigment darkening) is a short-term, only lasting a few hours of skin tanning after UV exposure. Instant tan is based on a modification of the chemical conformation of melanin molecules, as well as a redistribution of pigment cells in the epidermis, and has almost no protective effect against UV radiation.
* The (delayed) UV tanning continues until approximately 72 hours after UV exposure one. The melanocytes of the skin respond to ultraviolet radiation with increased production and delivery of Eumelanin (or Phäomelanin among people of skin type 1), the skin of a brown (Phäomelanin: reddish) hue, and UV highly absorbed, with much Phäomelanin less UV is absorbed. The ethnically different skin colors of people resulting from their skin.

The skin as a stem cell storage

The skin contains valuable stem cells based on the latest findings from science and research that in all other organ tissues (all three germ layers of the human organism) to continue to develop. These are therefore truly pluripotent stem cells. Moreover, one finds in the skin a new kind of stem cells, ABCB5 P-glycoproteins positive cells, which is obviously a much higher regenerative potential than any previously found adult stem cells. The skin is thus a crucial key position as a reservoir for stem cells. This gives the skin an ideal source of pluripotent stem cells for innovative therapies in regenerative medicine. In future, adult stem cells from the skin in various areas of stem cell transplantation and the manufacture of tissues from adult stem cells by tissue engineering in existence. The stem cells from the skin tissue can be up to the advanced adulthood and won for medical applications may be necessary for life are to be kept. Stem cells from the skin’s own tissues have been compared to the most commonly transplanted stem cells from the bone marrow, umbilical cord blood or peripheral blood several advantages:

* The skin contains a large number of valuable stem cells
* There is a molecular marker for the isolation of stem cells for clinical application allows
* The skin as an organ is easy to reach
* The removal of a small amount of skin tissue is simple and risk -
* The removal can be up to the advanced adulthood easily be made.

Immuno logical system of the skin

Cells act as antigen in the skin, the Langerhans cells.

The skin contact and sensory organ

The skin is the visible part of the human body such as dar. Meets the skin a range of communicative functions. Attraction is to host the skin with different types of receptors composed of:

* Pain receptors: they lie in the dermis, their density varies depending on the region (up to 200/cm2 skin).
* Pressure receptors (father-Pacini corpuscles): It is the perception of pressure sensations, and in the subcutis. Its density is up to 100/cm2.
* Thermo receptors (Krause-corpuscles and free nerve endings): You are very close to the chin, nose, ear, earlobe (9 to 12/cm2) and lips (> 15/cm2). Overall, there are approximately 250,000 human skin cold receptors. The number of heat receptors is only about 1 / 10, they are also working much more slowly than cold receptors.
* Stretch receptors (Ruffini-cells): You register the strain state of the skin and are in the dermis (stratum reticulare). Its density is up to 2/cm2 skin.
* Tastrezeptoren (Meissner corpuscles and Merkel cells): Tastrezeptoren come in the hairless skin. Particularly dense (distance: 1-5 mm), they are in the fingertips, lips, tongue, the nipples, the external sexual organs and the after region.
* Haarfollikelrezeptoren: You register the hair position (see also sinus hair).

The psychogalvanische skin reaction is to draw conclusions about emotional processes (see also polygraph).

The skin as a representational body

Since the skin the appearance of the human influence, it is the main object of beauty. Natural phenomena are freckles, liver spots and age spots. Artificially altered the appearance of the skin through tattoos, African Skarifizierung, fire scars, or the Indian Mehndi body painting. Furthermore, the skin-makers of all types of body jewelry.