DIE HAUT - AUFBAU & FUNKTION
The skin, also called the epidermis, is our largest organ and covers the entire outer surface of the body. It consists of three layers, the epidermis, the dermis and the subcutis, all three of which differ significantly in their anatomy and function.
The structure of the skin consists of a complicated network that serves as the body's first barrier against pathogens, UV light, chemicals and mechanical injuries. It also regulates temperature and the amount of water that is released into the environment. Here you will get an overview of the relevant anatomical structures of the skin, its components and its function.
An important component of the skin is the skin's protective barrier. On our page on the skin protection barrier you will find a detailed and easy-to-understand description of the most important building blocks and how our lipid barrier works.
STRUCTURE OF THE SKIN
The epidermis consists of stratified squamous epithelium. It consists of layers of flattened cells. Skin, hair and nails are keratinized (keratinized), meaning they have a dead and hardened impermeable surface made of a protein called keratin. Mucous membranes, by comparison, are non-keratinized and moist.
The epidermis consists of three main types of cells:
- Keratinocytes (skin cells)
- Melanocytes (pigment-forming cells)
- Langerhans cells (immune cells).
Special stains are often required to distinguish between melanocytes and Langerhans cells. A fourth, less visible cell of the epidermis is the Merkel cell.
The epidermis has an undulating appearance, with the epidermis protruding at regular intervals into the upper layers of the underlying dermis (rete ridges or pegs). In some areas of the body, such as the palms and soles, the rete ridges are less pronounced. The columns of the dermis adjacent to the rete cones form the rete ridges. The small area of epidermis between the rete cones is called the suprapapillary plate.
The thickness of the individual skin layers varies depending on the body region and is classified according to the thickness of the epidermal and dermal layers. The hairless skin on the palms and soles is thickest because the epidermis contains an additional layer, the stratum lucidum. The upper back is considered thickest because of the thickness of the dermis, but is considered "thin skin" histologically because the epidermis is thinner than the hairless skin without the stratum lucidum layer.
The keratinocytes become more mature or differentiated and accumulate keratin as they move outward. Eventually, they drop or rub off. They form five different layers, which are are listed from the top to the innermost layer in the following table:
|Stratum corneum (horny layer)||
|The stratum lucidum (2-3 cell layers)||
|Stratum granulosum (granular layer)||
|Stratum spinulosum (thorny, spiny or prickly cell layer)||
|Stratum basale (basal layer)||
Immediately beneath the epidermis is the basement membrane, a special structure that lies between the epidermis and the dermis. It comprises various protein structures that connect the basal layer of keratinocytes to the basement membrane (hemidesmosomes) and the basement membrane to the underlying dermis (anchoring fibrils). The basement membrane plays an important role in ensuring that the epidermis is firmly attached to the underlying dermis.
Melanocytes are located in the basal layer of the epidermis. These cells produce a pigment called melanin, which is responsible for the different skin color. Melanin is packaged into small packets (or melanosomes), which are then passed on to keratinocytes.
Langerhans cells are immune cells found in the epidermis that help the body identify and later recognize new "allergens" (substances foreign to the body).
Langerhans cells break down the allergen into smaller parts and then migrate from the epidermis to the dermis. They find their way to the lymphatics and blood vessels and finally reach the lymph nodes. Here they present the allergen to immune cells called lymphocytes. Once the allergen has been successfully "presented", the lymphocytes set in motion a series of events to initiate an immune response.
Merkel cells are cells found in the basal layer of the epidermis. Their exact role and function are not yet fully understood. Special immunohistochemical staining is required to visualize Merkel cells.
The dermis is the fibrous connective tissue or supportive layer of the skin.
The dermis is connected to the epidermis at the level of the basement membrane and consists of two connective tissue layers, the papillary and the reticular layer, which merge into each other without clear demarcation. The papillary layer is the upper, thinner layer composed of loose connective tissue that contacts the epidermis. The reticular layer is the deeper layer, thicker, less cellular, and consists of dense connective tissue or bundles of collagen fibers.
The dermis contains the sweat glands, hair, hair follicles, muscles, sensory neurons and blood vessels.
The main fibers of the dermis are:
- Collagen fibers: This type of fiber predominates in the dermis. Collagen fibers have tremendous tensile strength and provide strength and toughness to the skin. The collagen bundles are small in the upper or papillary dermis and form thicker bundles in the deeper or reticular dermis.
- Elastin: This type of fiber gives the skin the properties of elasticity and suppleness.
The collagen and elastin fibers are interconnected by a ground substance, a mucopolysaccharide gel, in which nutrients and waste products can diffuse to and from other tissue components.
The dermis also contains nerves, blood vessels, epidermal adnexal structures and cells.
Normal cells in the dermis include:
- Mast cells. They contain granules filled with histamine and other chemicals that are released when the cell is disturbed.
- Vascular smooth muscle cells. They enable blood vessels to contract and dilate, which is necessary for body temperature control.
- Specialized muscle cells. Myoepithelial cells are located around sweat glands, for example, and contract to secrete sweat.
- Fibroblasts. These cells produce and store collagen and other elements of the dermis needed for the growth or repair of wounds. A dormant fibroblast has very little cytoplasm compared to an active cell and appears to have a "naked" nucleus.
- Immune cells. There are many types of immune cells. The function of tissue macrophages (histiocytes) is to remove and digest foreign or degraded material (this is called phagocytosis). There are also a small number of lymphocytes in the normal dermis.
Transient inflammatory cells or leukocytes are white cells that leave blood vessels to heal wounds, fight infections, or cause disease. They include:
- Neutrophils (polymorphic). They have segmented cell nuclei. They are the first white blood cells to enter the tissue during acute inflammation.
- T and B lymphocytes. These are small inflammatory cells with many subtypes. They arrive later but persist longer in inflammatory skin diseases. They are important in regulating the immune response. Plasma cells are specialized lymphocytes that produce antibodies.
- Eosinophils. They have binucleated nuclei and pink cytoplasm in H&E staining.
- Monocytes. They form macrophages.
Skin cells communicate by releasing a large number of biologically active cytokines and chemotactic factors that regulate their function and movement. They are too small to be seen with the light microscope.
The subcutis lies deep beneath the dermis and is also known as the subcutaneous fascia. It is the deepest layer of the skin and contains fat lobules and some skin appendages such as hair follicles, sensory neurons and blood vessels. It is also called subcutaneous tissue, hypodermis or panniculus.
Adipocytes are organized into lobules separated by structures called septa. The septa contain nerves, larger blood vessels, fibrous tissue and fibroblasts. The fibrous septa can form dimples in the skin (called cellulite).
FUNCTION OF THE SKIN
Our skin is subject to continuous processes, to maintain their natural and primarily protective functioning.
These are summarized below:
- It serves as a barrier against water, the penetration of microorganisms, mechanical and chemical trauma and damage caused by UV light.
- The epidermal water barrier is formed by the cell envelope, a layer of insoluble proteins on the inner surface of the plasma membrane, and prevents transepidermal water loss.
- The skin is the first site of immunological defense through the action of Langerhans cells in the epidermis, which are dendritic epidermal T lymphocytes and belong to the adaptive immune system.
- The skin maintains the body's homeostasis by regulating temperature and water loss, performing both endocrine and exocrine functions.
- Endocrine functions include the production of vitamin D in keratinocytes, which are responsible for converting 7-dehydrocholesterol in the epidermis into vitamin D, with the help of UV light from the sun.
- The exocrine functions of the skin are carried out by the sweat and sebaceous glands.
- Another important function of the skin is the sensation of touch, heat, cold and pain through the action of nociceptors.
The epidermal layer of the skin contains much of our normal flora, and the epidermal microbiome varies by body region. The microorganisms that inhabit our skin surface are not pathogenic and can be comensalistic (a species that feeds on the organic residues of a host organism without harming it) or mutualistic (not related and mutually useful).
The predominant bacteria include
- Staphylococcus epidermidis
- Aureus, Cutibacterium acnes
- Clostridium perfringens
When the protective skin barrier is disturbed, infection can occur. With the understanding of the complex and sensitive functioning of our skin, it is obvious to deal with it as gently and preventively as possible.
HOLISTIC SKIN CARE
Our skin barrier is exposed to many external and internal factors. In order to best protect and care for or heal our skin, it is advisable to look at all the daily habits that have an impact on our health.
We believe in a holistic skin care concept for the well-being in your skin with all facets that belong to it. Our goal is to accompany you in this process with products that have been carefully developed with a focus on mild and effective care.
Choose gentle products that hydrate your skin, provide nourishing lipids and balance your skin's protective barrier. Every skin benefits from a fragrance-free routine, skin-friendly pH levels and a balanced supply of moisture and the right lipids.
The path to your skin's well-being is unique, and skin problems require patience and understanding. By treating your skin gently, products that focus on the essentials can make a big improvement.
You can additionally support your skin health by focusing on other pillars that significantly influence your well-being:
1. inner attitude & relaxation
The first step to healing your skin on the outside is taking care of it on the inside. By practicing gratitude and patience with your skin, by learning about the natural function of your skin, you can find new ways to care for your skin from the inside out.
Meditation is an important component to support your skin. Regular relaxation can help regulate the body's inflammatory processes and initiate regenerative processes. In our article about Meditation as part of a holistic skin care routineyou can read more about the background and benefits of relaxation for your skin.
2. intuitive & whole food diet
For skin health, it's also important to be conscious about your diet and lifestyle. A lack of minerals or high inflammation levels can have a huge impact on the skin's appearance.
There are many foods that can lower inflammation levels in the body with their ingredients. A varied, wholesome diet and an occasional addition of one or the other superfood are perfectly sufficient to get all the important nutrients. And if you ever have an appetite for chocolate or something "unhealthy," you shouldn't feel guilty after eating it. It is just important to keep the balance. Our article about "a wholesome diet for healthy skin" can provide you with interesting impulses.
3. exercise for a healthy skin appearance
Physical exercise is another important pillar for holistic skin health. Exercise, whether in the fresh air or indoors, gets the metabolism going and increases blood circulation. Only through sufficient exercise are nutrients and oxygen transported through the bloodstream to all cells, all the way to the skin. Your complexion also benefits from the increased blood circulation and appears rosy, plump and fresher.
The elimination of waste products, toxins and other metabolic products via the entire organism, e.g. the lymphatic system, is also stimulated and can function sufficiently. Strengthening and nourishment of connective tissues is supported, muscle building is stimulated and consequently our skin is kept healthy and gains radiance and resistance.
We hope you enjoyed this little excursion into the deep layers of our skin. If you have any questions, feel free to send us an email!