What is the epidermis?Schematic representation of the anatomy and structure of the epidermis. Click to enlarge.
The term epidermis is derived from the Greek word epi (about) and dermis (skin), and refers to the outermost layer of skin in vertebrates. The excretory ducts of the sweat and sebaceous glands end in this superficial layer of the skin.
Their secretion is responsible for moisturizing and lubricating the skin. The epidermis contains no nerves and vessels, which is why injuries in this skin layer neither hurt nor bleed. The supply of nutrients takes place through the fine blood vessels of the underlying skin layer, the dermis (dermis).
The epidermis is the skin layer that can be affected by cosmetic products. The effect of individual products can, depending on the property, promote blood flow, Aufpolsternd or cell protecting.
Anatomy & Construction
Anatomically, the epidermis is divided from the inside to the outside into the following five layers:
- Basal layer (stratum basale)
- Spiny cell layer (stratum spinosum)
- Grain layer (stratum granolosum)
- Luster layer (Stratum lucidum)
- Horny layer (stratum corneum)
For the most part (about 90%) the epidermis consists of so-called keratinocyte-horn-forming cells. This cell type produces keratin and differentiates during the cornification process from basal cells in the deepest to shallow, coreless horny cells in the outermost layer of the epidermis. This process takes about 4 weeks to complete - so the epidermis renews every month.
When they reach the uppermost layer, the cells are then gradually destroyed again, and as a fine hide they peel off from the skin through contact or washing. During wound closure, new skin cells are formed starting from the basal layer, which then migrate slowly over the healing wound. The cohesion between the individual keratinocytes form the Desmosen (cellular adhesive structures). They ensure stabilization of the cell network against shear and tensile forces.
Function & Tasks
The epidermis, as the outermost layer of skin, forms the immediate protective cover against the environment. Due to the dense association of the cells in this layer, microorganisms are confronted with a usually insurmountable barrier.
Embedded in the epidermis are also the melanocytes. These cells produce the pigment melanin, which gives our skin color and prevents the penetration of deeper layers of the skin under dangerous UV radiation. This protects the cells from burning and altering the DNA.
In addition, the epidermis has the following function: By a more pronounced cornification, it can adapt to stronger mechanical loads. This results in a very variable thickness of the epidermis. In the area of the sole of the foot, for example, the epidermis is up to 2 mm thick, while in the area of the eyelids it measures only about 0.05 mm.
Also in the plant world leaves have an epidermis. Here too, they form the terminating tissue to the outside and are also responsible for the protection of the underlying plant tissue.
Diseases & complaints
The term epidermolysis bullosa describes a group of inheritable skin diseases characterized mainly by the fragility of the epidermis.
Due to weakness of the connective tissue between the epidermis and the underlying dermis, blisters on the skin are produced in response to minor mechanical stresses. These can be extremely painful and also occur on the mucous membranes inside the body (for example, in the mouth area). Depending on the type, the effects of the disease vary from minor disability to severe disability or even death.
The Impetigo contagiosa (Latin impetere = attack, contagiosus = contagious) is a highly inflammatory, purulent inflammation of the epidermis. Most commonly, this disease occurs in newborns and children. Synonyms for this term are "Eiterflechte", "Grind lichen" or "Schleppeiter".
Basically, a distinction is made between a small and large bubble variant - both forms have their beginning mainly in the face. Here red spots form, which rapidly change into bubbles filled with watery liquid. After drying, characteristic yellow crusts form. The therapy is carried out with a local antibiotic application.