What are the layers of connective tissue
Structure and function of the skin
On average, the skin weighs around 14 kg, which is around 20% of the total body weight. It grows by 0.002 mm every day.
It contains a quarter of the water stored in the body, and that's a lot of moisture, because 70% of the human body is made up of water. In 1 cm2 The skin contains around 600,000 cells, 5,000 sensory cells, 4 m nerve tracts, 100 sweat glands, 1 m blood vessels, 15 sebum glands, 5 hairs and 150,000 pigment cells.
The skin consists of the upper and dermis. The two skin layers are elastically "interlocked" with each other through the capillary-guiding dermis papillae. Both clumped sweat glands and hair roots with sebum glands are anchored in the dermis and lead to the surface of the body.
Gerda Raichle, Ulm
The skin (Kutis) consists of three superimposed layers that are firmly connected to each other: epidermis, dermis and subcutaneous tissue.
The Epidermis (Epidermis) is the outermost of the three skin layers and does not have its own blood supply. For its part, it consists of several interlocking layers that are constantly renewed. In the lowest cell layer, the Germ layer (Basal layer), new basal cells are constantly being created through division, which reach the visible surface of the skin within a few weeks. As they migrate, they encamp more and more Horny substance (Keratin) and become scaly horny cells (corneocytes), which are visible to us in the end stage Horny layer (Stratum corneum). This renewal process takes an average of 28 days, a little longer in older people than in younger people, and leads to the rejection of up to 14 g of used horny cells every day.
The condition and moisture content of the horny layer determines whether the skin feels smooth and supple or rough and cracked. The thickness of the horny layer, on the other hand, determines the extent to which the blood vessels shine through and make the complexion appear rosy or pale. A particularly thick one often develops on particularly stressed parts of the body such as the heel and the palms of the hands Cornea.
In the Germ layer Specialized pigment-forming cells (melanocytes) produce the dye Melanin, a black-blue pigment that is stored in the horny cells of the skin and hair and thus determines the degree of skin tanning and the hair color. The color of the skin and hair depend both on the genetic make-up and on the UV radiation absorbed. If the UV radiation is increased, more melanin is produced and stored, the skin becomes tan. In this way, melanin protects the deeper layers of the skin from the effects of UV radiation, which damages the genetic information in the cells (DNA).
In addition to the melanocytes and the future horn cells, the germ layer contains special skin nerve cells as well as cells of the immune system, which penetrate the skin through foreign bodies such. B. Detect pathogens immediately and initiate defense reactions.
The connective tissue located under the epidermis, which determines the tensile strength and elasticity of the skin, is called Dermis (Korium, dermis). It is made up of a fibrous network that mainly contains collagen. The thickness of the dermis is based on the mechanical load: it is the thickest on the soles of the feet at 2.4 mm, while on the eyelids it is particularly thin at just 0.3 mm. In the dermis are the Touch receptors of the skin (Meissner tactile bodies) as well as numerous blood vessels, fatty tissue, hair follicles, nerves as well as sebum and sweat glands. The dermis protects the body from temperature fluctuations and mechanical injuries. It also supplies the vascular epidermis with oxygen and nutrients.
Under the dermis there is the highly stretchable, predominantly loose connective tissue Subcutaneous tissue (Subcutaneous fatty tissue, subcutis). It is traversed by extensions of the firm dermis fibers, which in turn are connected to the underlying tissue. Depending on eating habits, gender and body region, a different number of fat cells are embedded in the connective tissue, arranged in a pillow-like manner, which serve as shock absorbers, cold protection and energy storage.
The subcutaneous tissue also houses the lower areas of the hair follicles as well as special vibration and Push rods (Father Pacini lamellar bodies). In addition, it ensures that the skin can move on underlying tissues such as muscle layers or periosteum.
The skin offers mechanical protection against harmful substances and pathogens as well as against dehydration. V. a. the horny layer is important for the function of this Skin barrier. It consists of about ten to 20 layers of horny cells that lie on top of each other like bricks in a house wall. Moisturizing factors such as urea, hyaluronic acid and amino acids are located between the horny cells as “mortars”.
Smooth, supple skin has a water content of 10–20%. If it sinks, for example with heavy use or in old age, the surface becomes rough and cracked. These cracks in the skin lead to an additional loss of moisture and form the entry point for pathogens, allergens and other pollutants.
AuthorsDr. med. Arne Schäffler in: Gesundheit heute, edited by Dr. med. Arne Schäffler. Trias, Stuttgart, 3rd edition (2014). Revision and update: Dr. med. Sonja Kempinski | last changed on at 13:52
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