skin functions. The structure and functions of the skin as a human organ

24.07.2019

MAIN FUNCTIONS OF THE SKIN

The skin is the outer covering of the body and performs a complex set of physiological functions. It is actively involved in the process of metabolism, especially water, mineral, fat, carbohydrate, vitamin and energy. The skin is a huge depot of carbohydrates, toxins, circulating immune complexes, antigens, antibodies and other products of general and tissue metabolism. Participating in all vital processes of the body, the skin performs a number of important special functions. functions: immune, protective, secretory, receptor, etc.

The skin is an immune organ. Healthy skin and intact mucous membranes are a barrier to most microorganisms, with the exception of those with a special penetration apparatus. This protective function of the skin was previously explained only by mechanical factors - the stratum corneum, water-lipid mantle, high elasticity and subcutaneous fatty tissue. However, at present, there is information about the immune activity of the main structures of the skin that implement the immune response: the epidermis, dermis, and subcutaneous fatty tissue.

Due to the fact that T-lymphocytes are the main element of the immune system, the anatomical, molecular and functional similarity of epidermal keratinocytes with epithelial cells of the thymus has been proven. These include epidermal thymocyte-activating factor (ETAF), interleukins-1, 2 (T-cell growth factors), interleukin-3 (mast cell proliferation and degranulation factor), natural killer activating factor (FANK), epidermal granulocyte activity factor . In addition to them, keratinocytes produce a number of nonspecific mediators, biologically active factors involved in the immune and inflammatory reactions of the skin. Among them, the most studied are fatty acid metabolites (prostaglandins, leukotrienes, fatty acid hydroxides), plasminogen activator and inhibitor.

Keratinocytes promote the maturation of T-lymphocytes by the action of deoxynucleotidyltransferase. epidermal cells

able to induce the expression of this enzyme, as well as the secretion of thymopoietin in the process of T-lymphocyte differentiation. The important role of epidermal cells in immune processes in the skin is also confirmed by their ability to express immunoassociative antigens (HLA-DR) on their surface. Some researchers believe that these receptors facilitate the migration of white process epidermocytes into the skin, others believe that with their help, keratinocytes can present antigen and interact directly with lymphocytes.

The similarity of keratinocytes to thymic epithelial cells is confirmed by common heteroantigens found in the basal cells of the epidermis and the hormonal epithelium of the thymus. The common morphological features of these organs were established during the cultivation of the thymus epithelium. It turned out that thymus cells, when cultivated in the medium, turn into typical epidermal keratinocytes. Subsequently, an antigen characteristic of the cells of the basal layer of the epidermis was found in the receptors of the thymus bodies (Hassal bodies). In the deeper structures of the thymus bodies, antigens characteristic of the prickly, granular and stratum corneum of the epidermis were identified, which allows us to consider the epidermis as an organ functionally similar to the thymus gland.

In the dermis, immune activity is mediated by lymphocytes around postcapillary venules of the superficial choroid plexus and skin appendages. Immunomorphological methods have established that T-lymphocytes make up 90% of all skin lymphocytes and are located mainly in the epidermis and upper layers of the dermis. B-lymphocytes are found in the middle and deep layers of the dermis. The lymphocytes of the perivascular areas consist of almost the same number of helpers and suppressors, and the helper-suppressor index is 0.93-0.96. Most of these cells are in an activated form, which is confirmed by the detection of immunoassociative antigens (HLA-DR) and interleukin-2 receptors on their surface.

Endothelial cells of postcapillary venules of the superior vascular plexus and the macrophage system play a significant role in the development and formation of skin immune responses. The macrophage system is represented in the dermis and subcutaneous adipose tissue by fibroblasts, phagocytic macrophages (histiocytes), and dendritic cells. Morphologically differentiated tissue histiocyte is a process cell with a large number of

microvilli. Histiocytes contain RNA and enzymes in the cytoplasm. On the surface of histiocytes, like all macrophages, there are receptors for C3 and the Fc fragment of lgG. The macrophage system of the skin also includes mast cells involved in the migration of T-lymphocytes in antigen-antibody reactions of the type of immediate hypersensitivity. The implementation of immune processes in the skin also involves blood cells migrating into the skin (monocytes, eosinophils, neutrophils, basophils, erythrocytes), which perform various immune functions, the basis of which is the interaction of T-lymphocytes with nonspecific defense factors.

The immune function is also performed by white process epidermocytes, which are an altered variety of the population of tissue macrophages. Like mast cells, fibrocytes and macrophages, these cells do not have immune specificity, but when activated by antigens or cytokines, they exhibit physiological activity with the release of biologically active substances.

protective function. The barrier properties of the skin as an organ of mechanical protection are provided by significant electrical resistance, the strength of collagen and elastic fibers, and elastic subcutaneous fatty tissue. The skin is protected from drying out by a compact stratum corneum and a water-lipid mantle located on the surface of the skin. The stratum corneum is resistant to many chemical and physical damaging effects.

The protective function of the skin against microbial flora is very important. This is facilitated by the rejection of keratinized epithelium and the secretion of sebaceous and sweat glands. In addition, the skin has sterilizing properties due to the acidic reaction of the water-lipid film, which simultaneously inhibits the absorption of foreign substances. At the same time, the water-lipid mantle of the skin prevents the penetration of microorganisms, and the low molecular weight fatty acids contained in it have a depressing effect on the growth of pathogenic flora (“its own sterilizer”).

Chlorides are present in the skin in a significant amount, more than 2 times the content of this anion in muscle tissue. It is believed that this is a means of protection against pathogenic microorganisms. In the presence of myeloperoxidase, localized in the azurophilic granules of neutrophils and monocytes, hypochlorite is formed from chlorine and hydrogen peroxide, which destroys the structure of the microbial membrane, which leads to the death of the organism.

The protective function of the skin is also carried out by proteoglycans, which consist of polysaccharides (95%) and protein (5%) units. These polyanions, which are very large in size, bind water and cations, forming the basic substance of the connective tissue. Proteoglycans act as a molecular sieve for substances diffusing in the extracellular matrix: small molecules penetrate the network, while large ones are retained.

The mucous membrane of the mouth, whose structure is similar to the structure of the skin, also performs protective functions, although to a lesser extent. This is facilitated by the constant wetting of the oral mucosa with saliva, which leads to its supersaturation with water, a decrease in the sweating of the interstitial fluid, and thus makes it difficult for the penetration of microbial flora and foreign substances. The bactericidal properties of lysozyme contained in saliva enhance the protective role of the oral mucosa.

Under the influence of high-energy ultraviolet rays of the sun, free radicals form in the skin. Such molecules easily enter into chemical reactions, including chain ones. Violation of the function of biological membranes, built mainly of proteins and lipids, is one of the most important biological effects of ultraviolet rays. Protection of the body from the damaging effects of the ultraviolet rays of the sun, which lie outside the light visible to the human eye (less than 400 nm), is carried out using several mechanisms. The stratum corneum thickens in the skin, skin pigmentation increases, urocanic acid passes from the trans-isomer to the cis-isomer, enzymatic and non-enzymatic systems of antiradical protection are mobilized. The shielding layer of the pigment either absorbs light of all wavelengths or filters out particularly dangerous rays. Melanin, in particular, absorbs visible light and ultraviolet rays in the entire range.

The more melanin in the skin, the more fully it provides protection from rays harmful to the body. In the skin, a rapid renewal of melanin occurs, which is lost during the desquamation of the epidermis, and then re-synthesized by melanoblasts. The synthesis of melanin is influenced by the hypozysis hormone (melanin-stimulating hormone), an important role is played by tyrosinase, which catalyzes the oxidation of tyrosine, and doxyphenylalanine (DOPA). Biochemical mechanisms of antioxidant defense provide inhibition of free radical reactions at the stages of initiation, branching and termination of oxidation chains.

secretory function. This function is carried out as a result of the secretory activity of keratinocytes, immunoregulatory cells, as well as the functional activity of the sebaceous and sweat glands.

The formation of keratin - the main protein of the epidermis - is a complex secretory process, it is carried out by keratinocytes. The initial stage takes place in the cells of the basal layer, where keratin fibrils appear in the form of tonofilaments. In the cells of the spiny layer, the protein of tonofilaments is converted into α-keratin, similar to prekeratin - actomyosin.

More specific structures are observed in the cells of the granular layer. Keratohyalin granules appear in them, which contain fibrils. Fibrils turn into eleidin, and then into filaments of keratin, which forms the basis of the cells of the stratum corneum. As cells move from the basal layer to the upper layers of the epidermis, the nuclei and other cell organelles keratinize into tonofilaments, which gradually form protoplasm protein into keratin.

The growth and reproduction of epidermal cells under normal physiological conditions are influenced by complex mutually competing extracellular and intracellular factors. Intracellular mediators mediating the action of hormones and other biologically active substances on cell mitosis include cyclic nucleotides, prostaglandins, chalones, leukotrienes, interleukins (especially IL-1 and IL-2) and calcium ions, which affect the activity of phosphodiesterase and cAMP to cGMP ratio. The epidermal growth factor significantly affects the intracellular control of mitosis. This polypeptide has a hyperplastic effect on epithelial tissues. Its activity depends on the function of the pituitary-adrenal system.

Thus, the state of a complex physiological system - corticosteroid hormones and adrenaline in cooperation with intracellular mediators, including phosphodiesterase, adenylate cyclase, cAMP and cGMP - determines the activity of the epidermal growth factor and its effect on the secretion of keratin by epidermocytes. An important role in the implementation of the secretory function of the skin is played by the sebaceous and sweat glands.

The sebaceous glands produce sebum, which is composed of fatty acids, cholesterol esters, aliphatic alcohols, small amounts of carbohydrates, free cholesterol, glycerol, and small amounts of nitrogenous and phosphate compounds. In the sebaceous glands

the secret is in a liquid or semi-liquid state. Standing out on the surface of the skin and mixing with sweat, sebum forms a water-lipid mantle. It protects the skin, has bactericidal and fungistatic activity. It is believed that the sterilizing effect of sebum is due to the content of free fatty acids in it. In addition to secretory, the sebaceous glands also perform an excretory function. With sebum, toxic substances formed in the intestines, medium molecular weight peptides, as well as many medicinal substances - iodine, bromine, antipyrine, salicylic acid, ephedrine, etc.

The amount of sebum produced is different for each person, it is uneven in different parts of the skin. So, the largest amount of sebum is released on the skin of the scalp, forehead, cheeks, nose (up to 1000 sebaceous glands per 1 cm 2), in the central part of the chest, interscapular region, upper back and perineum. The function of the sebaceous glands is regulated by the endocrine and nervous systems. Testosterone and related substances stimulate, while estrogens suppress the secretion of sebum.

The sweat secreted by the eccrine sweat glands is slightly acidic. In addition to water, it contains a small amount of dissolved inorganic (sulfates, phosphates, sodium chloride, potassium chloride) and organic (urea, uric acid, ammonia, amino acids, creatinine, etc.) substances.

The chemical composition of sweat is not constant and can vary depending on the amount of fluid drunk, emotional stress, mobility, general condition of the body, ambient temperature, and also depends on the topography of the sweat glands. Sweat from the forehead contains 6-7 times more iron than sweat from the skin of the hands or feet. The content of chlorides in sweat depends on the rate of sweating, metabolic rate, skin temperature and age of the person. Medicinal substances - iodine, quinine, antibiotics - can also be excreted from the body with sweat. On average, 750-1000 ml of sweat is released per day, but at high temperatures several liters of sweat can be excreted. In the regulation of the activity of the sweat glands, the leading role belongs to the central and autonomic nervous system. The main stimulator of the activity of these glands is an increase in external temperature.

The excretory function of the skin is combined with the secretory. In addition to the secretion of organic and inorganic substances by the sebaceous and sweat glands,

substances, products of mineral metabolism, carbohydrates, vitamins, hormones, enzymes, trace elements and a significant amount of water are removed from the body. Sweat is released constantly and continuously. Distinguish invisible sweating in the form perspiratio insensibilis and profuse, occurring with increased thermoregulation.

The function of the apocrine glands is related to the activity of the gonads. They begin to function with the onset of puberty and cease their function in menopause. Apocrine glands, as well as sebaceous and sweat glands, respond to emotional, endocrine dysfunctions, stressful situations and changes in the thermal regime.

Respiratory and resorption functions. The resorption properties of the skin depend on the functional activity of the sebaceous hair follicles, the state of the water-fat mantle, and the strength of the stratum corneum. The surface of the palms and soles has a weak resorption capacity as a result of physiological hyperkeratosis. In places where the sebaceous and sweat glands are abundant, the stratum corneum is weakly expressed, the resorption properties of the skin are enhanced: fat-soluble drugs are absorbed - iodine, phenol, pyrogallol, resorcinol, salicylic acid, boric acid, etc. In inflammatory changes in the skin, resorption processes are activated, therefore drugs for external use should not exceed therapeutic concentrations. Participation of the skin in respiration, i.e. uptake of oxygen and release of carbon dioxide is negligible. The skin absorbs 1/180 of the oxygen and releases 1/90 of the pulmonary carbon dioxide exchange.

thermoregulatory function. Adaptive mechanisms that maintain a constant body temperature are diverse. In addition to the reduced thermal conductivity of the stratum corneum of the epidermis, the fibrous substances of the dermis and subcutaneous fatty tissue are essential. An even more significant influence on thermoregulation is exerted by the state of blood and lymph circulation and the excretory capacity of the sebaceous and sweat glands.

The sweat glands that produce sweat cool the skin by evaporating it to maintain a constant body temperature. Evaporation of sweat is an energy-intensive process: the evaporation of 1 liter requires 2400 kJ, which corresponds to 1/3 of the total heat generated at rest for the whole day. The activity of the sweat glands is mainly regulated by the temperature factor in the skin of the trunk, the back surface of the hands,

extensor surface of the forearms and shoulders, neck, forehead, nasolabial folds. Heat transfer by heat radiation and evaporation is increased with vegetodistonic and dyscirculatory disorders.

exchange function. The role of the skin in metabolism is especially significant because of its deposition ability. The hydrophilicity of connective tissue cells, elastic, collagen and argyrophilic fibers, subcutaneous adipose tissue causes a delay in intracellular and extracellular fluid and minerals, vitamins, microelements. Carbohydrates, cholesterol, iodine, bromine, amino acids, bile acids and slags formed in the process of lipid peroxidation are deposited in the skin. In this regard, long before general metabolic disorders in the skin, a number of pathological processes occur in the form of persistent itching in case of impaired liver function or persistent pyogenic elements in latent diabetes mellitus.

Many chemicals that have penetrated into the stratum corneum remain in it for a long time. The administration of prednisolone labeled with a radionuclide by percutaneous iontophoresis made it possible to detect the drug even 2 weeks after local iontophoresis, and when taken orally, it is detected only for 24 hours.

vitamins have a great impact on the condition of the skin. In particular, vitamins of group B, which support the normal course of redox processes, vitamin PP (nicotinic acid), which promotes the removal of metabolites and detoxification, vitamins A, E, D, being anti-infective factors, activate protein metabolism, normalize the process of keratoplasty in the epidermis, contribute to regeneration of the epithelium in inflammatory processes.

receptor function. The skin not only protects the body from various influences, but is also a multifactorial analyzer, as it is an extensive receptor field. The receptor functions of the skin are provided by a wide variety of sensitive nerve endings and sensory bodies, dispersed unevenly throughout the skin. There is tactile (sense of touch and pressure), pain and temperature (sense of cold and heat) skin sensitivity. Tactile sensitivity is most characteristic of the skin of the terminal phalanges of the fingers, the skin in large folds and on the mucous membrane of the tongue. Such sensitivity includes sensations of density, softness and other features of the consistency of objects. Nerve formations that perceive cold and heat (it is assumed that these are Ruffini's bodies and Krause's flasks) are located

in the skin is uneven, so the perception of heat and cold is different in certain areas of the skin.

The mucous membrane of the mouth is also rich in a variety of nerve endings that perceive heat, cold, pain and touch. However, unlike the skin, the sensitivity of all types to less intense stimuli is more pronounced.

The receptor field of the skin functionally interacts with the central and autonomic nervous systems, constantly participates in dermoneurotropic, dermovisceral connections. The skin continuously responds to a variety of stimuli coming from the environment, as well as their central nervous system and internal organs. It is logical to imagine that the skin is like a screen on which functional and organic changes in the activity of internal organs, the central nervous system, the endocrine and immune systems are projected. Often, even with a slight disorder in the activity of the body and its individual functions and systems, changes occur in the skin, sometimes allowing one to confidently assume one or another visceral or endocrine pathology.

Peripheral pathways for pain and itching (the proximity of these sensations allows us to combine them with the term "nociception"), most authors associate with the fibers of afferent nerves.

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Leather- this is one of the human organs that perform a protective role and a number of biological functions. The skin covers the entire human body, and depending on height and weight, its area is from 1.5 to 2 m 2, and its weight is from 4 to 6% of the human mass (excluding hypodermis).

The article discusses the structure of human skin, its structure and functions of each layer, how skin cells are formed and renewed and how they die.

Skin functions

The main purpose of the skin- This is of course protection from external environmental influences. But our skin is multifunctional and complex and takes part in a number of biological processes in the body.

The main functions of the skin:

mechanical protection- the skin prevents soft tissues from mechanical impact, radiation, microbes and bacteria, foreign bodies from entering the tissues.
UV protection- under the influence of solar treatment, melanin is formed in the skin as a protective reaction to external adverse (with prolonged exposure to the sun) effects. Melanin causes temporary darkening of the skin. A temporary increase in the amount of melanin in the skin increases its ability to retain ultraviolet (delays more than 90% of radiation) and helps neutralize free radicals formed in the skin when exposed to the sun (acts as an antioxidant).

thermoregulation- participates in the process of maintaining a constant temperature of the whole organism, due to the work of the sweat glands and the thermal insulating properties of the layer hypodermis consisting mainly of adipose tissue.
tactile sensations- due to nerve endings and various receptors located close to the skin surface, a person feels the influence of the external environment in the form of tactile sensations (touch), and also perceives temperature changes.
maintaining water balance- through the skin, the body, if necessary, can excrete up to 3 liters of fluid per day through the sweat glands.
metabolic processes- through the skin, the body partially removes by-products of its vital activity (urea, acetone, bile pigments, salts, toxic substances, ammonia, etc.). Also, the body is able to absorb some biological elements from the environment (trace elements, vitamins, etc.), including oxygen (2% of the total gas exchange of the body).
vitamin synthesisD- under the influence of ultraviolet radiation (sun), vitamin D is synthesized in the inner layers of the skin, which is subsequently absorbed by the body for its needs.

Skin structure

The skin is made up of three main layers:

epidermis(epidermis)
dermis(corium)
hypodermis(subcutis) or subcutaneous adipose tissue

In turn, each layer of the skin consists of its own individual structures and cells. Consider the structure of each layer in more detail.

Epidermis

Epidermis- this is the top layer of the skin, formed mainly on the basis of keratin protein and consisting of five layers:

horny- the uppermost layer, consists of several layers of keratinized epithelial cells, called corneocytes (horny plates), which contain insoluble protein keratin
brilliant- consists of 3-4 rows of cells, elongated in shape, with an irregular geometric contour, containing eleidin, from which keratin
grainy- consists of 2-3 rows of cells of a cylindrical or cubic shape, and closer to the surface of the skin - diamond-shaped
prickly- consists of 3-6 rows spiny keratinocytes, polygonal shape
basal- the lowest layer of the epidermis, consists of 1 row of cells called basal keratinocytes and having a cylindrical shape.

The epidermis does not contain blood vessels, so the intake nutrients from the inner layers of the skin to the epidermis going on at the expense diffusion(penetration of one substance into another) tissue(intercellular) liquids from the dermis into the layers of the epidermis.

interstitial fluid It is a mixture of lymph and blood plasma. It fills the space between cells. Tissue fluid enters the intercellular space from the terminal loops of blood capillaries. There is a constant exchange of substances between the tissue fluid and the circulatory system. Blood delivers nutrients to the intercellular space and removes waste products of cells through the lymphatic system.

The thickness of the epidermis is approximately equal to 0.07 - 0.12 mm, which is equal to the thickness of a simple paper sheet.

In some parts of the body, the thickness of the epidermis is slightly thicker and can be up to 2 mm. The most developed stratum corneum is on the palms and soles, much thinner on the abdomen, flexion surfaces of the arms and legs, sides, skin of the eyelids and genitals.

Skin acidity pH is 3.8-5.6.

How does human skin cells grow?

In the basal layer of the epidermis cell division occurs, their growth and subsequent movement to the outer stratum corneum. As the cell matures and approaches the stratum corneum, keratin protein accumulates in it. Cells lose their nucleus and major organelles, turning into a "pouch" filled with keratin. As a result, the cells die, and form the uppermost layer of the skin from keratinized scales. These scales are shed over time from the surface of the skin and replaced by new cells.

The whole process from the origin of the cell to its exfoliation from the surface of the skin takes an average of 2-4 weeks.

Skin permeability

The scales that make up the uppermost layer of the epidermis are called - corneocytes. The scales of the stratum corneum (corneocytes) are interconnected by lipids consisting of ceramides and phospholipids. Due to the lipid layer, the stratum corneum is practically impermeable to aqueous solutions, but solutions based on fat-soluble substances are able to penetrate through it.

Color of the skin

Cells within the basal layer melanocytes, which highlight melanin- a substance that determines the color of the skin. Melanin is formed from tyrosine in the presence of copper ions and vitamin C under the control of hormones secreted by the pituitary gland. The more melanin contained in one cell, the darker the color of human skin. The higher the melanin content in the cell, the better the skin protects against ultraviolet radiation.

With intense exposure to the skin of ultraviolet radiation, the production of melanin sharply increases in the skin, which provides the skin with a tan.

The effect of cosmetics on the skin

All cosmetics and procedures, designed for skin care, affect mainly only the top layer of the skin - epidermis.

Dermis

Dermis- this is the inner layer of the skin, from 0.5 to 5 mm thick, depending on the part of the body. The dermis is made up of living cells., supplied with blood and lymphatic vessels, contains hair follicles, sweat glands, various receptors and nerve endings. The basis of the cells in the dermis is fibroplast, which synthesizes the extracellular matrix, including collagen, hyaluronic acid and elastin.

The dermis is made up of two layers:

reticulate(pars reticularis) - extends from the base of the papillary layer to the subcutaneous fatty tissue. Its structure is formed mainly from bundles of thick collagen fibers located parallel to the surface of the skin. The mesh layer contains lymphatic and blood vessels, hair follicles, nerve endings, glands, elastic, collagen and other fibers. This layer provides the skin with firmness and elasticity.
papillary (pars papillaris), consisting of an amorphous structureless substance and thin connective tissue (collagen, elastic and reticular) fibers that form papillae that lie between the epithelial ridges of spiny cells.

Hypodermis (subcutaneous adipose tissue)

Hypodermis- This is a layer consisting mainly of adipose tissue, which acts as a heat insulator, protecting the body from temperature changes.

The hypodermis accumulates nutrients necessary for skin cells, including fat-soluble vitamins (A, E, F, K).

The thickness of the hypodermis varies from 2 mm (on the skull) to 10 cm or more (on the buttocks).

With inflammatory processes in the hypodermis that occur during certain diseases, cellulite occurs.

Video: Skin structure

The area of the entire skin of an adult is 1.5 - 2 m 2
One square centimeter of skin contains:

over 6 million cells
up to 250 glands, of which 200 sweat and 50 sebaceous
500 different receptors
2 meters of blood capillaries
up to 20 hair follicles

With an active load or high external temperature, the skin can release more than 3 liters of sweat per day through the sweat glands.
Due to the constant renewal of cells, we lose about 10 billion cells a day, this is a continuous process. Over the course of a lifetime, we shed about 18 kilograms of skin with keratinized cells.

Skin cells and their function

The skin is made up of a large number of different cells. To understand the processes occurring in the skin, it is good to have a general idea of the cells themselves. Consider what the various structures are responsible for (organelles) in a cage:

cell nucleus- contains hereditary information in the form of DNA molecules. In the nucleus, replication occurs - doubling (multiplication) of DNA molecules and the synthesis of RNA molecules on a DNA molecule.
kernel shell- provides exchange of substances between the cytoplasm and the nucleus of the cell
cell nucleolus- it synthesizes ribosomal RNA and ribosomes

cytoplasm- a semi-liquid substance that fills the interior of the cell. Cellular metabolism takes place in the cytoplasm
ribosomes- necessary for the synthesis of proteins from amino acids according to a given matrix based on genetic information embedded in RNA (ribonucleic acid)
vesicle- small formations (containers) inside the cell in which nutrients are stored or transported
apparatus (complex) Golgi is a complex structure that is involved in the synthesis, modification, accumulation, sorting of various substances inside the cell. It also performs the functions of transporting substances synthesized in the cell through the cell membrane, beyond its limits.
mitochondrion- the energy station of the cell, in which the oxidation of organic compounds occurs and the release of energy during their decay. Generates electrical energy in the human body. An important component of the cell, the change in activity of which over time leads to aging of the body.
lysosomes- necessary for the digestion of nutrients inside the cell
interstitial fluid fills the space between cells and contains nutrients

1. Protective function.

The skin protects the body from various external influences: physical, chemical and biological. Among the physical effects on the body, the most frequent are mechanical, thermal and light. A variety of mechanical influences - touch, pressure, stretching, blows, injections, cauterization, cooling, and others - depending on the frequency and strength, act favorably on the skin surface in some cases and unfavorably in others. The skin provides protection from mechanical influences due to the presence of a water-fat mantle in it; a special complex in the epidermis; basement membrane; dermis, abundantly saturated with a network of collagen and elastic fibers, as well as subcutaneous adipose tissue (hypoderm). In medical cosmetics, mechanical factors affecting the skin (massage, acupuncture, baths, gymnastics) are widely used.

The protective function of the skin in relation to various chemical factors should be well known to ARGO consultants, especially when using active agents such as vitamins, proteins, amino acids, and other chemicals used in skin care. Chemicals are difficult to penetrate through healthy skin, mainly through the hair follicles. The most effective barrier for them is the stratum corneum and the water-fatty mantle. Amino acids on the surface of the stratum corneum protect the skin from acids and bases. But if the protective barrier of the skin is broken, chemical solutions destroy the stratum corneum and water-fatty layer.

The skin well protects the body from the action of biological factors, most often represented by microorganisms. Various microbes, getting on the surface of healthy skin, cannot develop due to the enzymatic activity of the water-fat membrane rich in fatty acids. Constant renewal of epidermal cells and desquamation of the superficial stratum corneum of the skin leads to the mechanical removal of microbes that have fallen on the skin. There is also a normal bacterial flora on the skin, which limits the development of pathogenic bacteria.

Human skin is adapted to prolonged exposure to ultraviolet rays, especially in the inhabitants of sunny regions of the globe. Such exposure, if intense and prolonged, is harmful to health. The skin is the only barrier against such exposure. The horny layer of the epidermis reflects or absorbs the most carcinogenic part of the ultraviolet radiation spectrum (long-wave).

2. Thermoregulatory function.

The thermal effect on the skin is characterized by continuous dynamics, and this function is associated with it, thanks to which the body maintains a constant temperature.

In the cold, the narrowing of blood vessels occurs, due to this, heat transfer decreases, and when the ambient temperature rises, the skin vessels expand, as a result of which heat transfer increases. Sweat glands are actively connected to this process, the evaporation of the secretion of which leads to a "cooling" of the skin.

3. Excretory function of the skin carried out through the sweat and sebaceous glands.

Sweat secretion. Sweat released to the surface is a solution of common salt (sodium chloride). Sweat contains 98-99% water and 1-2% inorganic and organic substances. Among the inorganic substances, in addition to sodium chloride, sweat contains potassium chloride, sulfates, phosphates, traces of iron, zinc, cobalt, tin, magnesium, copper, etc. Organic substances are mainly represented by urea, ammonia, uric acid, amino acids, keratin.

The chemical composition of sweat is similar to that of urine. It varies depending on the intensity of the kidneys and other factors. Sweat itself is odorless. A typical specific smell appears due to the bacterial decomposition of sweat.

Sebaceous secretion. The secret of the sebaceous glands is secreted continuously in an amount proportional to the size of the glands, performing an important function - protecting the skin from wind, cold, sunlight, and pathogens.

The sebaceous glands, together with fat, secrete some toxic substances that are formed in the body as a result of metabolism. In the presence of toxic substances in the intestines, the secretion of the sebaceous glands increases. Therefore, in the treatment of seborrhea, substances are prescribed inside that adsorb intestinal toxins.

Age and gender factors affect the secretion of the sebaceous glands: in childhood it is insignificant; increases in adulthood, especially in men; weakens with age, especially in women. After 40 years of life, the production of sebum is noticeably reduced, but if you thoroughly wash your skin with soap or wipe it with alcohol, the activity of the sebaceous glands will increase and the fatty film of the skin will be restored in 3-4 hours.

4. The skin performs respiratory and gas exchange functions in the body along with the lungs. The skin is certainly permeable to gases (oxygen, carbon dioxide, hydrogen sulfide) and volatile liquids (chloroform, ether, alcohol). Through it, oxygen is absorbed from the air, carbon dioxide is released.

5. Huge role of the skin as a sense organ.

There are tactile, pain, heat and cold skin sensitivity.

Different types of skin sensitivity are unevenly distributed over the surface. The tips of the fingers, the red border of the lips, the tip of the tongue have the greatest tactile sensitivity; temperature sensitivity is more pronounced on the skin of the face.

6. Exchange function of the skin

Being the second largest after the muscles, the depot of water introduced into the body, the skin participates in the body's water metabolism, in addition, deposits (deposits) sodium chloride (salt metabolism), and is also one of the links in vitamin, nitrogen and carbohydrate metabolism.

The skin is very sensitive to all changes occurring in the body. A number of diseases of the internal organs and endocrine glands dramatically affect the condition of the skin, causing various changes in it.

A beautiful clear complexion, an even blush almost always indicate good health; on the contrary, pallor, yellowness of the skin often indicate anemia, cardiovascular insufficiency, diseases of the liver, lungs, dysfunction of the endocrine glands and other pathologies.

7. Protective (immune) function.

In addition to the above, the skin plays an important role in the development of the body's defenses.

So, the skin reflects the state of our body. This is not a shell, but an organ with a multifaceted, complex activity associated with the work of all human organs and systems.

Keratinocytes promote the maturation of T-lymphocytes by the action of deoxynucleotidyltransferase. epidermal cells

protective function. The barrier properties of the skin as an organ of mechanical protection are provided by significant electrical resistance, the strength of collagen and elastic fibers, and elastic subcutaneous fatty tissue. The skin is protected from drying out by a compact stratum corneum and a water-lipid mantle located on the surface of the skin. The stratum corneum is resistant to many chemical and physical damaging effects.

secretory function. This function is carried out as a result of the secretory activity of keratinocytes, immunoregulatory cells, as well as the functional activity of the sebaceous and sweat glands.

The excretory function of the skin is combined with the secretory. In addition to the secretion of organic and inorganic substances by the sebaceous and sweat glands,

Respiratory and resorption functions. The resorption properties of the skin depend on the functional activity of the sebaceous hair follicles, the state of the water-fat mantle, and the strength of the stratum corneum. The surface of the palms and soles has a weak resorption capacity as a result of physiological hyperkeratosis. In places where the sebaceous and sweat glands are abundant, the stratum corneum is weakly expressed, the resorption properties of the skin are enhanced: fat-soluble drugs are absorbed - iodine, phenol, pyrogallol, resorcinol, salicylic acid, boric acid, etc. In inflammatory changes in the skin, resorption processes are activated, therefore drugs for external use should not exceed therapeutic concentrations. Participation of the skin in respiration, i.e. uptake of oxygen and release of carbon dioxide is negligible. The skin absorbs 1/180 of the oxygen and releases 1/90 of the pulmonary carbon dioxide exchange.

thermoregulatory function. Adaptive mechanisms that maintain a constant body temperature are diverse. In addition to the reduced thermal conductivity of the stratum corneum of the epidermis, the fibrous substances of the dermis and subcutaneous fatty tissue are essential. An even more significant influence on thermoregulation is exerted by the state of blood and lymph circulation and the excretory capacity of the sebaceous and sweat glands.

extensor surface of the forearms and shoulders, neck, forehead, nasolabial folds. Heat transfer by heat radiation and evaporation is increased with vegetodistonic and dyscirculatory disorders.

exchange function. The role of the skin in metabolism is especially significant because of its deposition ability. The hydrophilicity of connective tissue cells, elastic, collagen and argyrophilic fibers, subcutaneous adipose tissue causes a delay in intracellular and extracellular fluid and minerals, vitamins, microelements. Carbohydrates, cholesterol, iodine, bromine, amino acids, bile acids and slags formed in the process of lipid peroxidation are deposited in the skin. In this regard, long before general metabolic disorders in the skin, a number of pathological processes occur in the form of persistent itching in case of impaired liver function or persistent pyogenic elements in latent diabetes mellitus.

vitamins have a great impact on the condition of the skin. In particular, vitamins of group B, which support the normal course of redox processes, vitamin PP (nicotinic acid), which promotes the removal of metabolites and detoxification, vitamins A, E, D, being anti-infective factors, activate protein metabolism, normalize the process of keratoplasty in the epidermis, contribute to regeneration of the epithelium in inflammatory processes.

receptor function. The skin not only protects the body from various influences, but is also a multifactorial analyzer, as it is an extensive receptor field. The receptor functions of the skin are provided by a wide variety of sensitive nerve endings and sensory bodies, dispersed unevenly throughout the skin. There is tactile (sense of touch and pressure), pain and temperature (sense of cold and heat) skin sensitivity. Tactile sensitivity is most characteristic of the skin of the terminal phalanges of the fingers, the skin in large folds and on the mucous membrane of the tongue. Such sensitivity includes sensations of density, softness and other features of the consistency of objects. Nerve formations that perceive cold and heat (it is assumed that these are Ruffini's bodies and Krause's flasks) are located

in the skin is uneven, so the perception of heat and cold is different in certain areas of the skin.

List and describe the functions of the skin. By what signs can you determine the condition of the child's skin.

Leather- the largest organ of our body, which plays an important role in the life of the body and performs a complex set of physiological functions.

It is actively involved in the process of metabolism, primarily water, mineral, energy, fat, carbohydrate.

The skin is a powerful depot for carbohydrates, for circulating immune complexes, antibodies and antigens, for various other metabolic products, including waste products and toxins.

It performs a number of important special functions : protective, receptor, thermoregulatory, secretory, respiratory, resorption (suction), immune.

Being the outer shell of the body, uniting all organs and systems holistically, the skin performs mechanical protection function due to the strength of collagen and elastic fibers, significant electrical resistance of structures, the presence of elastic subcutaneous fat. The compact stratum corneum and the water-lipid mantle that covers the skin, protect the skin from drying out. The water-lipid mantle also prevents the penetration of microorganisms from the outside, and the low molecular weight fatty acids contained in it inhibit the possible growth of pathogenic flora, so the mantle performs the function of the "sterilizer" of the skin. Elastic subcutaneous tissue helps in protecting against external injury.

Thermoregulatory function skin is carried out by a variety of mechanisms that maintain a constant body temperature. These are changes in the thermal conductivity of the stratum corneum of the epidermis, and the properties of the fibrous substance of the dermis and subcutaneous fat, and the state of blood and lymph circulation, and the excretory capacity of the sweat glands.

Receptor function skin is colossal. On the one hand, the skin protects the body from many environmental influences, on the other hand, it is a powerful multifactorial analyzer, it is an extensive receptor field. The receptor field of the skin closely interacts with the central and autonomic nervous systems. The skin continuously reacts to many stimuli coming from the environment, as well as from the internal organs and the central nervous system. The skin can be imagined as a screen onto which changes in the activity of various organs and systems of the human body are projected.

secretory function skin is carried out by the activity of sweat and sebaceous glands, as well as through the formation of keratin, the main protein of the epidermis.

In addition to the secretory glands, the sebaceous glands also carry out excretory (excretory) function. With sebum, toxic substances formed in the intestines, some medicinal substances are released. The function of the sebaceous glands is greatly influenced by the endocrine and nervous systems.

Testosterone (male sex hormone) stimulates and estrogens (female sex hormones) inhibit sebum secretion. Sweat glands largely determine the control of body temperature. By producing sweat, they cool the skin and help maintain a constant temperature in the body.

Healthy skin and mucous membranes are an immune barrier to microorganisms. Due to the immunological activity of the main structural parts of the skin, they implement the immune response of the epidermis, dermis and subcutaneous fatty tissue.

Respiratory and resorption functions skin depends on the activity of sebaceous hair follicles, the strength of the stratum corneum, the state of the water-fat mantle.

In this regard, the surface, for example, the rear of the palms and soles is characterized by a weak suction capacity as a result of physiological hyperkeratosis and the absence of sweat and sebaceous glands. In places of their abundant location and a weakly expressed, thin stratum corneum, the resorption properties of the skin are well manifested.

Respiratory function skin is to absorb oxygen and release carbon dioxide, but it is generally much less significant compared to pulmonary metabolism. The role of the skin in metabolism, which was mentioned earlier, is especially important because of its great deposition capacity.

In addition to the mentioned functions inherent in the skin, one should name also the perception of ultraviolet radiation and participation in the metabolism of vitamin D, protection from the damaging effects of sunlight, and, of course, very important for the psycho-emotional comfort of a person - cosmetic function.

When assessing the condition of the skin use questioning and objective methods:

Inspection; - palpation; - determination of tissue turgor; - determination of skin elasticity; - determination of the state of skin vessels; - dermographism.

If necessary, skin biochemistry, morphological and immunohistochemical studies are performed.

On examination, changes in skin color, rashes, scars, swelling of the skin and subcutaneous fat, subcutaneous emphysema, and impaired hair growth are detected. Usually the skin of the child has a soft pink color. In some cases, it may be pale with an earthy, gray tint, acquire a marbled pattern. The most common are skin pallor, cyanosis, jaundice, and flushing of the skin. Skin pallor is one of the most commonly observed skin changes in childhood. Among the many causes of pallor of the skin, the main ones are a change in the tone of the skin vessels, edema, a decrease in the concentration of hemoglobin and the content of erythrocytes in the peripheral blood. However, pale skin is not always a sign of a pathological process. Pallor of the skin is accompanied by anemia, acute rheumatism, diseases of the lungs, digestive organs, chronic intoxication, severe cardiovascular diseases, bleeding, etc. Paleness is a clinical sign of shock. In children who do not stay enough in the fresh air, pallor of the face is periodically observed.

Particular attention is paid to the skin folds behind the auricles, on the neck, in the armpits, inguinal region, on the thighs, under and between the buttocks, in the interdigital spaces. The skin of the scalp, palms, soles, and anus is carefully examined. Attention is drawn to the presence of edema and their prevalence (on the face, eyelids, limbs, general edema - anasarca - or local).

Normally, the skin of a child has moderate moisture. In diseases, dry skin, increased humidity and increased sweating (hyperhidrosis) can be observed. Determination of moisture on the palms and soles of prepubertal children is especially important. An important diagnostic value is the determination of skin moisture at the back of the head in infants, which is often a sign of rickets in them. Hyperhidrosis can be observed in systemic diseases