Skin – structure, layers, receptors. Features of the skin

Proven content

The skin is called the largest organ of the human body. The surface of the skin sometimes exceeds 2 m2, and its task is to maintain the stability of all internal parameters that enable the functioning of the human body. A significant function that the skin must fulfill is also the protection of internal organs against harmful external factors, as well as injuries. What is the structure of the skin and what functions does this important organ of the human body perform?

It may seem shocking to many, but the skin of an adult human being can weigh as much as 20 kg, so it accounts for about 25% of the body’s weight. Depending on the location, it has a thickness of 0,5 to 4 mm. Compared to other mammals living on earth, human skin is slightly hairy, but highly vascularized, which allows it to actively participate in the process of thermoregulation of the whole organism.

The structure of the skin – layers

There are three basic layers in the skin. The outer skin is made up of the epidermis, followed by the dermis and the subcutaneous tissue. In addition, the skin contains sebaceous and sweat glands, blood vessels, nerve endings and lymph vessels. There are also hair follicles in the skin.

The skin is divided into two basic types. The first is the scalp, limbs and torso. It is a leather with a three-layer structure, characterized by high sliding. The second type of skin is the one on the palms and soles of the feet. A distinctive feature of this type of skin is that there are no sebaceous glands in it, no hair follicles.

Skin problems and changes should be consulted with a dermatologist. You can now make an appointment via the halodoctor.pl portal. The consultation then takes place online in a form convenient for the patient.

See also: Skin diseases – symptoms, treatment. What do skin changes mean?

The epidermis – structure and functions

The epidermis is formed by a multilayer epithelium. Its base layer is the lowest layer of the epidermis and there are many processes in it that ultimately lead to the production of keratin. Moreover the epidermis has a spinous and granular layer and an intermediate zone, which appears mainly on the feet and hands, as well as a light layer made of tightly adhering keratinocytes. The light layer is resistant to UV rays and its place is on the soles of the feet and on the palms. It is of great importance in keratosis disorders.

The outer, visible layer is the stratum corneum, which is made up of horny cells, and it is precisely its task to protect the entire body against water loss. The cells that make up the stratum corneum die, and the keratin contained in them prevents undesirable chemical compounds, radiation and even microelements from penetrating deep into the skin.

As for the granular layer, it consists of rows of spindle-shaped cells. Ceramides are formed inside the keratinizing cells of the granular and spinous layers, which in the granular layer escape into the intercellular space, forming lamellas (lipid plaques). Lamelles are contained in a natural moisturizing factor, creating cellular cement, which is responsible for the correct level of water in all layers, which ultimately translates into softness and elasticity of the skin. It is worth adding that above the granular layer there is a very thin membrane insoluble for water and substances soluble in it, called the Rein barrier, whose task is to limit water loss from the body.

The spinous layer is the thickest layer of the epidermis and is made up of many rows of cellsthat do not fit tightly together and flatten as they move upward. In the intercellular space of this layer there are mucopolysaccharides, which are the medium for spiny cells.

In addition, the epidermis consists of one more layer called the basal layer, which is the lowest of all. It consists of a series of closely adjacent cylindrical cells that constantly divide to form young ones. This layer is composed of: Langerhans cells, also known as the phlegm cells (responsible for immunological processes), keratinocytes (the process of producing keratin), melanocytes (pigment cells, producing melanin), Merkel cells belonging to the nervous system.

The condition of the skin will be assessed by a package of laboratory tests, which can be found in the offer of the Comprehensive Rehabilitation Center. Healthy skin is a showcase of every human being, so it should be remembered that it is often it that reflects the state of our health. Check at medonetmarket.pl. Also remember about proper skin care depending on its needs. Try, for example, Dr Duda’s set of moisturizing cosmetics for beautiful skin.

Check it out: Autoimmune skin diseases

Skin – the structure of the dermis

The thickest layer of the skin is the dermis, which is even about 2 mm thick. It is made up of connective tissue with blood vessels, nerve endings and skin appendages. It is an elastic layer that is highly resistant to any damage. It is thanks to the nerve endings in it that a person feels pain, touch and external temperature.

In addition to it, we can also distinguish the papillary, sub-papillary and reticular layers. The former is strongly wavy (skin warts), which causes the surface of contact with the epidermis to be significantly increased, which increases elasticity while preventing abrasion of the epidermis.

The papillary layer contains connective tissue fibers (reticulin fibers), forming a mesh around the capillaries, sebaceous and sweat glands, as well as hair follicles and nerve fibers.

The sub-papillary layer is a thin and uniform layer made of collagen and elastic fibers, on which the warts are placed. Nerves, superficial veins and arteries run in this layer, forming the superficial (sub-papillary) plexus and the deeper superficial arterial network. The sub-papillary venous plexus plays an important role in regulating body temperature.

As for the third layer, i.e. the mesh layer, it is made of collagen and elastin fibers, and the spaces between them are diamond-shaped. The mesh layer also contains a basic substance that binds the fibers of tissues together, and a few free cells. There are also smooth muscle cells, which, for example, in the vicinity of the hair form the so-called periparous muscles. Capillary blood vessels are rather small in the reticular layer, but they are numerous in the papillary layer, and only the branches of the arteries and veins of the subcutaneous tissue run deeper, usually directed perpendicular to the skin surface.

The dermis contains cells such as fibroblasts, histiocytes, and fibrocytes. This layer also includes three types of fibers: mesh, elastic and collagen, which are responsible for the proper elasticity and tension of the skin. The weakening of these fibers is the direct cause of the skin’s loss of youthful appearance. With age, both the quantity and quality of these fibers decline, the skin becomes thin and flaccid, and wrinkles form on its surface.

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Worth knowing: Skin diseases. The seven worst skin diseases

Skin – subcutaneous tissue

Although this layer is closely related to skinis not considered part of it. It consists mainly of adipose tissue, and only a small percentage is connective tissue. In the structures of the subcutaneous tissue there are nerve fibers and blood vessels. The main task of the subcutaneous tissue is its participation in the thermoregulation process, which is of great importance for the entire body.

Also read: Viral skin diseases – types

Skin – functions of the skin

The skin plays primarily a protective role for the entire human body. It protects it from both cold and excessive heat. It is thanks to it that a too large dose of harmful radiation does not reach the inside. The skin is an effective barrier against the penetration of microorganisms and chemicals harmful to the body. Melanin and vitamin D are also produced in the skin layers.

In addition, our skin has many more functions, such as: perceptual, diagnostic, barrier and immune, thermoregulatory and finally resorptive. The former is responsible for receiving stimuli from the outside world thanks to the use of nerve endings.

The diagnostic function, in turn, is important because it allows us to see with our own eyes what the condition of our body is, because the skin reflects the condition of the body. Various diseases can cause the structure and appearance of the skin to change dramatically. Thanks to this function, we can see with the naked eye what is the level of skin hydration and when it is insufficiently hydrated, it becomes dry, thin and inelastic and wrinkles appear on it.

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Another function is barrier and immune, thanks to which a layer called “acid-lipid coat” is formed on our skin. The mantle is made possible by the action of sweat and sebaceous glands located on the surface of the skin. This “coat” provides us with protection against alkaline substances and microorganisms, and in addition, such a protective layer prevents the skin from cracking.

In turn, thermoregulatory function manifests itself through the involvement of the skin in regulating the temperature of the entire body. At low temperatures, blood circulation in the vessels under the skin increases, and at high temperatures, our body secretes sweat, thanks to which it cools down.

The last function of our skin is resorptive, it is due to the fact that our skin is involved in the water and fat balance. Our epidermis is able to absorb some of the substances soluble in water and fats (it has resorptive properties). Such substances include collagen, herbal extracts and vitamins. They are the ingredients of cosmetics used for skin care.

Check it out: What do you need to know about skin diseases?

Formations of the epidermis

It is worth mentioning that in the epidermis, or rather in its reproductive layer, certain products are formed, namely:

1. Nails – which have a protective function on the fingertips.
2. Hair – in the form of flexible and elastic horn fibers. Their structure is distinguished by the essence: medullary, forming axial cell strands, cortical made of keratinized spindle cells, in which there is also a dye that determines the hair skin, and an integumentary essence, which consists of flat and keratinizing epithelial cells. At the very beginning, hair played a key role in terms of survival. Namely, they protected humans against heat loss, but now they appear on the head, in the armpit and reproductive organs, and in the remaining parts of the body there is only residual hair.
3. Sweat glands – which are scattered between the dermis and the subcutaneous tissue. In terms of function, they can be divided into two categories: merocrine glands, spread over the entire body surface, in which the cell undergoes no changes or damage during the secretion process, and apocrine glands – in this case, the secretion is stored in the apical part of the cell, and the glands themselves are present in armpits, anus and vulva. Interestingly, adults can have up to 2 million sweat glands, and their greatest accumulation can be observed in the soles, hands and armpits.
4. Sebaceous glands – whose place is near the hair. These glands belong to the group of holocrine glands, i.e. the entire content of the cell is transformed into a secretion in the form of sebum, which is used to lubricate the skin and hair. As a result, the skin becomes more elastic and more resistant to drying out. In addition, the secretion protects the epidermis against dangerous water losses.

The skin is the largest organ of the human body and performs many important functions, therefore it requires proper care. For home care of the body, e.g. while bathing, it is worth using stones, sponges, massage gloves, natural soaps. This type of products is offered by the Tadé Pays du Levant brand. Its founder was inspired by the oriental and Mediterranean culture, in which the body was and is very important to every human being.

Skin receptors

It is also worth adding that our skin has sensory receptors of different structures and functions. Their main tasks can be divided into three categories:

1. Feeling of touch and pressure – the receptor responsible for the feeling of touch is called Meissner bodies, and those responsible for the feeling of pressure are called Vater-Pacini bodies. The touch is registered by our body with the help of mechanoreceptors, which include basket receptors, which are located in the vicinity of the hair bulb, and tactile cells, located under the spiky layer of the epidermis.
2. Feeling pain – we owe our pain sensation to free nerve endings, which are a dense network spread over the entire skin surface. The nerve endings have a density of approximately 50 to 200 per cm2. They have their place in the connective tissue membranes of internal organs and in blood vessels. The pain impulse received by them is transmitted to the central nervous system, where the body converts it to a known stimulus.
3. Feeling cold and warm (Krause body and Ruffini body) – the feeling of cold and warmth is perceived by our body thanks to thermoreceptors. Krause’s bodies are responsible for the feeling of cold, which are located closer to the surface of the skin (up to 0,18 mm) and there are definitely more of them than heat cells, i.e. Ruffini’s bodies. The latter are located in the deeper parts of the skin (up to 0,3 mm).

See also: The type of receptor determines the progression or inhibition of inflammation

Properties of the skin

Our skin is probably more amazing than we think because it has many properties.

One of them is the ability to regenerate, perhaps not as advanced as in the case of lizards or snakes, which shed it when it becomes “too tight” but it is still impressive. In the case of humans, old epidermal cells exfoliate and give way to new ones. Over the years, this process begins to slow down, i.e. instead of taking 28 days, it takes 35 or even 50 days.

Interestingly, our skin “works” intensively during the night, getting rid of impurities, which in turn travel to the lymphatic system. Night as the regeneration time is the period in which elastin fibers renew, the lipid layer on the surface of the epidermis is rebuilt and the water level in the skin’s tissues equalizes. At night, when we are asleep, the cosmetics that we put on our skin in the evening are absorbed best.

Regenerative properties are also manifested when the continuity of the skin (epidermis and dermis) is broken, because then the healing process begins. Then, the blood enters the resulting wound, in which there are platelets sticking into a plug, which is to prevent further blood flow. Over time, the factors responsible for blood clotting become active, leading to the formation of a clot, which in turn ‘sticks’ the edges of the wound.

In the final phase of wound healing, thanks to the action of macrophages and fibroblasts, the wound is cleared of bacteria and collagen synthesis begins. A scab is formed that is actually a natural dressing. Over time, it will fall off, leaving in its place at most a mark in the form of a scar.

The skin also has the properties of sensing stimuli. This is due to the fact that there are nerve endings in it. What’s more, our skin has a very rich nervous network, the ends of which are irregularly located all over the body. They entangle the hair follicles, sweat and sebaceous glands. Their task is to register the sensations of touch and pain. They have the ability to feel stimuli in a radius of 1 to 12 mm. Touch receptors are responsible for the feeling of touch (such as, for example, Merkel tactile menisci, which are responsible for locating the stimulus, or Meissner tactile bodies). The more densely these receptors are placed, the greater our sensitivity to pressure.

However, when it comes to touch, the most important are hairless places on our body, such as lips, fingertips or the tip of the nose. They are the most sensitive and cause a reaction, for example, on the tip of the nose, it is enough to pinch yourself gently there (with a force of only 2 g / mm2). Interestingly, to produce the same effect, but on the skin of, for example, arms, you need to use up to 20 times more force.

The action of the receptors is to transmit information directly to the brain, more specifically to the thalamus and the sensory cortex, thanks to which we can feel the temperature, pain or touch through our skin. All this is possible by analyzing the incoming signals. For example, in the case of a feeling of humidity, the touch and cold receptors are stimulated so that we can actually feel this moisture on our skin. By analyzing the signals received, the brain can decide on the degree of vascular contractility or the release of histamine (taking part in the development of inflammation, for example). Thanks to the receptors, we are also able to feel temperature changes, pain or the sensation of itching.

If we are talking about pain, it appears when the tissues are damaged. Then, due to the strength of the stimulus, which begins to increase, the feeling of e.g. pressure or cold may turn into pain and it is closely related to a chemical reaction. Damaged tissues begin to secrete mediators, i.e. chemical compounds that affect nerve endings and trigger reactions in them leading to the creation of an electrical impulse.

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Leather – color

The color of our skin depends on the melanin content. For example, in the case of orangutans, melanin is found both in the epidermis and in the dermis, and in the case of gibbons, chimpanzees, and humans, melanin is mainly found in the epidermis. Interestingly, only in the case of humans does the skin color vary. This is probably due to the different intensity of ultraviolet radiation.

See also: Sleep and skin color