Connection zone between dermis and epidermis | Anatomy and function of human skin

Connection zone between dermis and epidermis

The two layers of the skin (cutis) are closely connected. This connection is ensured by so-called reteleiste, among other things. A basal membrane (thin separating layer) between the layers controls the exchange of cells and molecules.

It consists of 2 layers. One of these layers is connected to the next skin layer by means of anchoring filaments. The inner layer is connected to the dermis and the outer layer to the outer epidermis.

2. the dermis

The second part of the cutis (skin), the dermis, is the connective tissue under the epidermis and extends deep into the subcutaneous fat (subcutaneous = under the cutis skin). Its main components are cells and connective tissue fibers embedded in a gelatinous basic substance. These are collagen fibers, elastic fibers and reticulin fibers.

This ensures the tear resistance and reversible (restorable) deformability of the skin. The dermis is divided into two layers: The dermis also contains networks of vessels (vascular plexus). They serve to supply the skin with nutrients and regulate the temperature.

• The papillary layer (stratum papillare), which lies against the epidermis and
• The reticular stratum, which is directly adjacent to the subcutis. Hair follicles and sweat glands originate in the braided layer.

Subcutis – Subcutaneous tissue

This so-called subcutaneous tissue connects to the stratum reticulare of the dermis. It consists of loose connective and subcutaneous fatty tissue.

Tasks of the skin

The skin has very diverse functions, which can be explained by the individual components in the different layers. With its natural skin flora and its somewhat acidic pH value, it represents a protective barrier against bacteria, for example. The skin contains cells of the immune system and thus represents a part of our immune system.The horny layer protects us from dehydration and injuries.

Sweat glands are important to prevent overheating and sebaceous glands grease our skin. Not only the sweat glands are important for regulating the temperature, but also the subcutaneous fatty tissue and blood vessels, which run close to the surface and can regulate the release of heat through the blood circulation. Through the hair and many sensory cells in different layers, contact with the outside world is established, which allows us to absorb a wide range of stimuli such as pain, touch, pressure and temperature sensation.

Furthermore, our skin protects us from UV rays. When exposed to the sun, it reacts with a tan, as UV rays would otherwise very quickly cause severe damage to our skin. In addition, the skin basically envelops our entire body from the outside, so that it is a barrier to the environment.

Although the skin can withstand some mechanical stress, it does not withstand blunt or pointed violence. This results in wounds, such as bruises, stab wounds or a laceration. There are so called skin appendages in the layer of the epidermis.

These include, for example, glands that secrete fatty substances and hair follicles. The epidermis with its horny layer, the secreted fat and its acidic pH value serves as protection against external influences. The exact pH value is now somewhat controversial.

For a long time, it was assumed to be between 5 and 6, but there are now studies that suggest a pH value below 5. In any case, it is in the acidic range and thus has a protective function against certain pathogens on the one hand, and on the other hand it allows “desired” bacteria that belong to the normal skin flora to survive. Another function of the epidermis that is essential for survival is protection against dehydration.

Without the top layer of skin, up to 20 liters of water would be lost through the body surface every day. This explains why people with burns are at high risk of dehydration (drying out) and therefore need to be supplied with a lot of water. Below the epidermis lies the dermis (leather skin).

It mainly contains fibroblasts, i.e. cells that produce connective tissue, especially collagen. But also cells of the immune system, so-called histiocysts and mast cells, develop here. The dermis also contains nerves and blood vessels.

The skin has – as already mentioned – important functions in the area of homeostasis. It plays a major role in the regulation of body temperature. In particular through the evaporation of water, it has a regulating effect here.

Furthermore, the skin has an immense importance for the absorption of stimuli. Whether touch, pain or temperature. This is done by receptor cells.

The skin is densely populated with microorganisms. This sounds dangerous at first, but it is not. This is called normal skin flora.

The bacteria that belong to this normal flora are not harmful. They are called commensals. This means that they benefit from the fact that they colonize the human skin, but do not do much good or harm to humans.

In part, they have a protective influence by protecting against the penetration of pathogenic germs. The skin therefore has a multitude of functions (see: Functions of the skin), which can only be guaranteed if the skin is in balance. For example, the pH value must be correct, the skin surface must be intact and the resident normal flora of the skin also plays a role in a balanced skin appearance.

There are different types of skin cancer, which are classified according to the cells from which they originate. One must distinguish between benign and malignant (malignant) cancers. The most common skin cancer is the basal cell carcinoma, which is caused by uncontrolled cell division in the basal cell layer.

The basal cell carcinoma is only partially malignant, as it can infiltrate surrounding tissue, but only rarely forms metastases. In most cases, the basal cell carcinoma develops in places that are strongly exposed to the sun and thus UV rays, such as the facial region. On the other hand, there is the malignant melanoma, which is a very malignant tumor of the melanocytes (pigment cells).

It grows infiltratively and metastasizes early. As with all types of cancer, the early detection of possible degenerations is important. Therefore, it is recommended to pay attention to skin changes and to consult a dermatologist in case of abnormalities.Harmless pigment spots can be distinguished from suspicious pigment marks by: regular, symmetrical shape and sharp, clear edges, as well as uniform coloring and no change in size, color, shape or thickness.

Itching (pruritus) is an unpleasant sensory perception that wants to be answered with mechanical resistance in the sense of scratching. It originally serves to remove foreign bodies or parasites. However, there is also a chronic itching that lasts for at least six months and is no longer triggered by an adequate stimulus.

The nerve fibers used to detect itching belong to the pain receptors (nociceptors) and are mainly located within the top two skin layers, the epidermis and dermis. The stimuli are absorbed via non-markless C-fibers and transmitted to the central nervous system where there are itch-specific areas. There are numerous hormonal triggers that can cause itching.

The best known is probably histamine. For this reason, antihistamines are often prescribed to treat itching, i.e. drugs that act against histamine. However, since numerous other substances, such as serotonin, adrenaline, prostaglandins and dopamine, can also initiate itching, these drugs are often ineffective.

A large number of diseases can cause itching. Those that are localized in the skin area, i.e. dermatological diseases, but also internal and psychiatric diseases. As an example, here are some diseases that can be accompanied by itching: Dermatological diseases that often show itching as a symptom include drug exanthema (rashes caused by taking medication), neurodermatitis (atopic eczema), hives (urticaria), psoriasis and scabies.

Internal diseases that can be accompanied by itching include kidney failure, liver diseases such as primary biliary cirrhosis, malignant diseases such as leukemia and Hodgkin’s disease, metabolic diseases such as diabetes mellitus and iron deficiency. Psychiatric conditions that can be associated with itching include schizophrenia, depression and anorexia. Numerous medications can also trigger itching.

For example, ACE inhibitors, antibiotics, calcium antagonists, beta-blockers, antifungals, immune modulators, lipid reducers, psychotropic drugs and many others. In dermatological diseases the itching is often rather localized, i.e. it is particularly pronounced in certain areas, whereas in internal diseases it usually affects the whole body. The therapy of itching depends mainly on the cause.

Thus the respective disease leading to itching must be treated specifically. This is called causal therapy. A purely symptomatic therapy aims to relieve the itching, but does not eliminate its cause.

There are various creams available for symptomatic therapy: There are creams which have a light anaesthetic effect (contain lidocaine), creams which contain anti-inflammatory glucocorticoids like cortisone or creams which contain immunomodulators like tacrolimus as active agents. Furthermore, as mentioned above, antihistamines such as cetirizine can provide relief, these are usually administered in tablet form. Psychotropic drugs such as neuroleptics or tricyclic antidepressants can also help.

All in all, however, when itching is a symptom, it is always necessary to look for the causal disease and treat it causally – if possible – in order to treat the itching in the long term. The skin is constantly in exchange with the environment and is therefore exposed to many stimuli. Burning skin is a sign that the skin has come into contact with a substance that it cannot tolerate.

These can be intolerance reactions or allergic reactions, for example to food or substances in care products or cosmetics. Burning skin can also occur in the secondary disease or late consequence of chickenpox, the so-called “shingles“. People who contracted chickenpox in their childhood are immune to a renewed outbreak of chickenpox, but the virus remains in the body for life.

If the immune system is weakened, for example by stress or a cold, the virus can be responsible for the occurrence of shingles. It manifests itself in a belt-shaped rash with reddish blisters, usually in the abdominal region, which is very burning and itchy. Another possibility of skin burning may be due to the hypersensitivity of nerves.Often in this case the burning is accompanied by a tingling and/or numbness.

In case of abnormalities such as severe burning or rashes, a doctor should be consulted and the causes clarified. Human-pathogenic fungi, i.e. those that are relevant for the damage to human health, are divided into three classes: Most fungi are facultative pathogenic, i.e. they do not infect a healthy person, but can make a person with a weakened immune system or a disturbed skin defence system very well ill. Dermatophytes only attack skin, hair and nails while yeast fungi such as Candida albicans and moulds such as Aspergillus flavus can also attack internal organs.

Skin fungus is thus mainly caused by dermatophytes, it is then called tinea. The most frequent pathogen of the tinea in Central Europe is the fungus Trichopyhton rubrum. The fungal infestation of the skin can be classified according to the penetration depth of the pathogen.

A distinction is made here between superficial tinea (Tinea superficialis) and deep tinea (Tinea profunda). The Tinea superficialias often impresses by almost round reddish-brown foci on the skin, which have a pronounced edge seam. However, there are numerous other manifestations of the superficial skin fungus.

The more invasive form of tinea is called tinea profunda (deep lying), the pathogens penetrate deeper into the skin. It is mainly found on more hairy parts of the body such as the beard or scalp. In addition, the skin fungus can be subdivided according to its location.

Thus, the most common place for fungal infections are the interdigital spaces between the toes. A fungus occurring in this area is called tinea pedis (athlete’s foot). The athlete’s foot can be dangerous in so far as entry ports for bacterial pathogens can develop here.

Thereby it can come to bacterial superinfections which spread in the body. A typical example of a disease whose pathogens often enter the body through such an entry port is erysipelas. Furthermore, after localization, a tinea palmoplantaris that is accompanied by scaling on the soles of hands and feet, a tinea capitis that is noticeable by almost round hairless foci on the scalp, a tinea corporis that is conspicuous by often round reddish foci on the trunk, arms and legs and a tinea ungium of the toenails (nail mycosis) can be distinguished.

Whether it is a fungal infection of the skin can be determined by a smear from the edge of the affected skin area with subsequent microscopic examination. In uncomplicated cases, skin fungus is treated locally (topically), i.e. not with tablets but with solutions or creams. It depends on the pathogen in question, as yeast fungi (Candida) can also cause skin infections and sometimes respond to a different therapy than the dermatophytes just discussed.

In the meantime, however, broad-spectrum antimycotics are frequently used which are effective against both types of fungi. These include ciclopiroxamine, clotrimazole as well as terbinafine and amorolfine. Fluconazole is particularly suitable for the therapy of yeast infections.

They are available – depending on the preparation – as cream, solution or nail varnish. However, some types of skin fungus can only be treated systemically, i.e. by means of tablets, whereby the therapy usually lasts for several weeks. It is usually combined with a local therapy.

• Dermatophytes
• Yeast fungi
• Molds.

Skin bleaching is also called skin whitening. It is mainly used for cosmetic purposes, but is also partly used in cases of pathological overproduction of the colorant melanin (hyperpigmentation). The history of cluster bleaching is probably based on the fact that in earlier epochs a very light complexion was considered the ideal of beauty.

The well-off people were often of a very pale complexion and the “workers” were mostly dark tanned by the sun. Thus, a light skin color was also a sign of social status. Skin whiteners generate significantly more sales worldwide than tanning and sun protection products.

The only active ingredient approved in Germany for lightening the skin is Pigmanorm. It contains the active ingredients hydroquinone, hydrocortisone and tretionin and is used to treat melanin-related hyperpigmentation.It is used in the normal coat only on small areas of the skin and should be applied carefully and for a limited period of time. Many other products are not approved in many countries and are associated with sometimes massive side effects.

They contain toxic substances such as mercury, benzenes and hydrogen peroxide, among others. A side effect that is common to almost all of these agents is the significant inhibition of the skin’s defense function against UV radiation. This is due to the fact that the whitening agents destroy the body’s own melanin, which provides UV protection.

The consequences can be skin burns and – with a latency of years – the development of skin cancer. Perhaps the best-known celebrity example of the excessive use of skin bleaching agents was Michael Jackson.