Habitually, the skin is considered from the point of view of its aesthetic qualities, often forgetting that it is a vital organ with a special structure and a whole range of functions. Its main purpose is to protect internal organs and tissues from the impact of negative environmental factors.

The histological structure of the skin explains it unique properties. Appearance and fortune play quite a few important role in the diagnosis of various disorders. The skin is studied not only by the section of anatomy - histology, but also by such areas in medicine as dermatology and cosmetology.

Soft, elastic fabric is resistant to temperature changes, various liquids, non-concentrated acids and alkalis. It is sensitive, but very durable, has a complex system of receptors that convey information to the brain about the state of the environment. One of its most important functions is aesthetic.

The salons offer a wide range of services through which it becomes possible to prolong youth and beauty. Only knowing the structural features of the skin, you can provide it with proper, high-quality care.

The epidermis and its structure

Human skin consists of three layers, which are subdivided into smaller ones. The surface layer of the skin is the epidermis. This is a kind of barrier between the body and the outside world. It protects the body from external influences, signals a malfunction in the functioning of internal organs, requires careful treatment and proper care.

Most of the cosmetics on the market and cosmetic procedures are aimed at maintaining an attractive appearance of the epidermis. Its structure is very complex.

• The basal layer is located at the very bottom of the epidermis, adjacent to the dermis, consists of cells containing 70% water. New cells are formed here, which then rise to the upper layers. Basal or as it is also called - the growth layer provides normal flow regenerative processes in the tissues of the epidermis.
• The spinous layer is formed from living cells with a nucleus, which look like small spikes under a microscope. Its main purpose is to launch the processes of keratin synthesis.
• The granular layer is the densest, here small cells are closely pressed against each other. They are responsible for hydration skin, retain certain substances, secrete intercellular fat necessary for the connection of corneocytes. The granular, spiny, and basal layers are collectively referred to as the Malpian layer, as they are composed of living cells containing a nucleus.
• The shiny layer protects the skin from friction, wear, it consists of flat cells without a nucleus, is present only on the palms and soles.
• The stratum corneum of the skin consists of a large number of non-nuclear cornetocytes, in which metabolic processes do not occur. There is a connection between the cells that provides the skin with reliable protection from the negative influence of external factors.

The uppermost layer of the skin is a thin film consisting of small horny scales connected by intercellular lipids. The latter have powerful moisture-repellent properties, protect the skin from dehydration and liquid penetration from the outside. In the process of development, the cells of the stratum corneum lost their organelles and nucleus, turning into scales.

Cosmetics consist of substances alien to the body, therefore, upon contact with them, the outer layer of the skin weakens, which is fraught with loss of moisture and other unpleasant manifestations. High-quality care products can give the upper layer of the epidermis elasticity and firmness, and moisturize it.

Corneocytes or horny scales throughout their lives are subjected to mechanical stress, friction and other factors that do not affect them. the best way they wear out and are replaced by new ones.

Features of the dermis

The dermis is the skin itself, protected by the epidermis. These two large layers are connected by a basement membrane. The structure of the dermis is organized in a special way. It contains lymphatic and blood vessels that provide proper nutrition to the cells.

The middle layer of the skin is formed from collagen fibers, which provide it with elasticity and the necessary rigidity, and elastin fibers - elasticity, the ability to stretch and return to its original position.

The interfiber space of the dermis is filled with a specific substance resembling a gel. Mainly hyaluronic acid. It is responsible for retaining moisture in the cells. Human skin, that is, the dermis itself, consists of two layers.

• The papillary layer is a loose connective tissue, which was formed from elastic, reticular and collagen fibers. It contains follicles, from which hairs, sweat glands then grow. The difference of this layer of the dermis is that it has a complex vascular system, resembling a dense network of small capillaries. They diverge and unite, nourish the cells, saturate them with oxygen.
• The basis of the reticular layer is a dense connective tissue consisting of fibroblasts and dermal melanocytes, which do not have the ability to synthesize melanin pigment. This ball of the dermis is intended to ensure the strength of the skin.

The structure of facial skin in cosmetology plays an important role, as it allows specialists to develop effective means and methods for providing high-quality, full-fledged skin care, slowing down age-related and destructive processes in it.

The cells of the dermis and epidermis under the influence of certain factors are damaged and replaced by new ones. Regeneration processes slow down with age, which causes the formation of wrinkles, irregularities, loss of contour definition and other defects.

Changes occurring in the epidermis, dermis and hypodermis are due to age characteristics structure and function of the skin. The older a person becomes, the slower the skin is renewed, damaged cells accumulate inside, which causes loss of firmness and elasticity.

Fat and muscle tissue

A special set of functions is performed by the lipid layer of the skin, consisting of fat cells. It is also called the hypodermis or subcutaneous adipose tissue. This is a supply of nutrients necessary for the normal functioning of the skin, a support for the dermis, a pantry of energy. And also this inner layer of the skin is involved in the synthesis of some sex hormones, softens the mechanical stress on the body, gives the forms elasticity, bulge.

The lipid layer is a tissue that consists of many small lobules, blood vessels pass inside it. Due to malnutrition, drinking alcoholic beverages, smoking, pathological processes in the body, this layer undergoes dystrophic changes (fat in the lobules accumulates in excess, the partitions thicken, inflammation and swelling may occur). This will definitely affect the appearance.

The structure of human skin is considered together with the musculoaponeurotic system. The structure of the facial skin contains muscles that provide facial expressions (change of expression, movement of lips, eyebrows, smile). Their feature is that they are not connected to bone tissue. The muscles are firmly attached to the skin, create heaviness, as a result of which the structure of the epidermis of the skin changes.

Today, the cosmetology market offers various services that involve the introduction of special preparations for muscle paralysis. This helps to keep the skin youthful, structure and function, however, there may be side effects or habituation develops over time if such procedures are abused.

Vascular system of the skin

Not only the structure of the skin itself is complex, but also the system of blood vessels that are responsible for nourishing the dermis and some layers of the epidermis with oxygen and useful substances. The action of various cosmetics is aimed at activating blood circulation. They are used to tone and strengthen the capillaries that form a complex network under the skin. With the help of massage, you can also improve the movement of blood through small vessels.

The speed of blood circulation in the cells that make up the skin affects the regeneration processes. Some scientists argue that the cells of the epidermis and dermis are able to retain toxic substances, preventing their penetration into the bloodstream, with which they are carried throughout the body.

Passive and active functions of the skin

Another important question: what is the significance of the skin? There is a definition that this is the most extensive and largest vital organ that provides reliable protection to the entire body. The thickness of the skin is different - from 0.5 to 5 mm.

The functions of the epidermis, middle layer and fiber differ. They can be divided into basic and additional, active and passive. The skin protects the body from exposure to cold and heat, mechanical damage, chemicals, pathogenic microorganisms. These functions can be classified as passive.

Active functions of the skin:

• fights pathogenic microbes inside the dermis, hypodermis, lower layers of the epidermis;
• supports normal temperature due to the release of sweat and the receipt of certain signals from the brain through the nerve endings;
• receives signals from the environment (touch, pain);
• some cells of the dermis and epidermis are able to recognize allergens and respond accordingly to their action;
• takes part in the production of vitamin D;
• due to melanocytes, it produces melanin - a coloring pigment;
• regulates water and mineral metabolism.

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The value of the skin is difficult to overestimate. People spend a lot of money and effort to slow down the aging process in it, to maintain its attractive appearance until old age. Every year there are more and more plastic and surgical techniques to prolong the youth and beauty of the skin.

Knowing the scheme of the skin, the features of its structure, experts develop ways to influence this organ.

Cosmetic and folk remedies are able to improve the condition of the skin, moisturize, give shine to the surface layers of the epidermis. To influence the deeper layers, it will take time and special preparations. It is not always possible to achieve a positive result using traditional methods, because in some cases the tissue categorically refuses to accept foreign substances.

Before carrying out any procedure that involves a deep effect on living cells, a thorough examination should be carried out, contraindications should be excluded, and individual characteristics of the organism should be taken into account. This will help to get a good result and avoid negative consequences.

Practicing cosmetologist. Higher medical education. The author of this site. The beauty of the skin excites me both as a specialist and as a woman.

Comments 1

The skin is the largest human organ that covers the body. The complex structure and functions of the skin developed in the process of human evolution.

What is skin?

Skin - the outer cover, the thickness of which varies in different parts of the skin from 0.5 to 5 mm (not counting the hypodermis). It is an elastic, porous tissue that protects the human body from physical and chemical effects.
The skin has important properties:

• stretching;
• water resistance;
• sensitivity.

The skin is a natural barrier to pathogens. Thanks to temperature, tactile, pain receptors, the skin reacts to heat and cold, touch, and pain. All over the body (with the exception of the feet and palms) hairs grow that protect the skin from overheating and react to external stimuli.

The thickest skin is found on the palms and soles. The thinnest and softest - on the eyelids and male genital organs.

Internal structure

The skin is made up of three layers:

• upper - epidermis or skin;
• medium - dermis or skin itself;
• internal - hypodermis or subcutaneous fat.

Rice. 1. General structure of the skin.

The description of the layers is presented in the table “Structure and functions of the skin”.

Layer	Structure	Functions
Epidermis	Consists of keratinocytes - cells containing keratin (skin protein). The thinnest layer, consisting of five layers: Horny - keratinized cells; Brilliant - 3-4 rows of elongated cells; Granular - 2-3 rows of cylindrical, cubic, rhomboid cells; Spiny - 3-6 rows of spiny keratinocytes; Basal (germ) - 1 row of young cells. In the basal layer, there is a constant division and growth of cells. Here are melanocytes - cells that secrete a protective pigment (melanin), and immune cells. Gradually rising (due to the growth of the lower layer), the cells die, are completely filled with keratin and become the stratum corneum, which peels off over time	Mechanical protection; Water repellency; UV protection due to melanin; Protection against the penetration of pathogenic microbes
	The most functional layer. Contains living cells, blood vessels, receptors, sweat glands. Here are the hair follicles from which sensitive hairs grow. Consists of two collagen layers: Papillary - under the epithelium; Reticulated - over the hypodermis. From the dermis through diffusion, nutrients enter the epidermis layer	Giving skin elasticity due to the sebaceous glands; Thermoregulation due to the work of sweat glands (up to 5 liters of sweat are released to cool the surface of the body); Perception of an external stimulus
Hypodermis	The thickest layer. On the skull it is 2 mm, on the buttocks - 10 cm or more. Consists of dense adipose tissue	Thermal insulation; Accumulation of nutrients for skin cells

Rice. 2. The structure of the epidermis.

Hair, nails and skin glands (sweat, sebaceous, milk) are modified human skin and are called skin appendages. Their rudiments are in the dermis.

Rice. 3. The structure of the dermis.

Metabolism

In addition to protecting against water, microorganisms, ultraviolet light, as well as thermoregulation and irritation, the skin is involved in metabolic processes.
Some decay products are excreted through the skin, in particular:

• urea;
• ammonia;
• salt;
• toxic substances;
• medications.

The skin covers the entire human body and is the largest organ. human body, which has a variety of functions and is closely related to the whole organism.

The value of human skin is enormous. It is the human skin that directly perceives all environmental influences.

First, there is a reaction of the skin to any negative impact and then the whole organism. The surface of the skin contains numerous folds, wrinkles, grooves and folds, forming a characteristic relief that is purely individual and persists throughout life.

♦ About 70% of human skin is water and 30% is proteins (collagen, elastin, reticulin), carbohydrates (glucose, glycogen, mucopolysaccharides), lipids, mineral salts (sodium, magnesium, calcium) and enzymes.

♦ People have different height, fullness, respectively, and skin area different people will differ, but on average this figure is at the level of 1.5-2.5 m2.

• The weight of the multi-layered skin is over 11-15 percent of a person's weight.

♦ skin function. Its main function is protective.

• protective function against overheating of the body and mechanical damage, from radiation, including the ultraviolet part of the light spectrum, from microbes and harmful substances;
• the function of regulation through the mechanism of sweating equilibrium in terms of the amount of water, the presence of certain substances;

• through the skin, the body and the environment exchange the necessary substances, the skin is to some extent an auxiliary respiratory organ;
• The skin, under certain conditions, can serve as a synthesizer useful substances. For example, when hit sun rays complex processes occur on the skin that contribute to the synthesis of vitamin D. From this point of view, sunburn is useful, but we should not forget about the properties of ultraviolet rays that are detrimental to all living cells.
• tactile function: receptors are built into the skin, due to them a person has a sense of touch;
• appearance shaper function: features of the skin of the face and subcutaneous mimic muscles allow you to visually distinguish one person from another and convey your emotions.

♦ The structure of the skin. The skin consists of three layers, the upper layer is the epidermis, the middle layer is the dermis and the lower layer is the hypodermis (subcutaneous fatty tissue).

Epidermis

The epidermis is approximately 10.03-1 mm thick. Every three to four weeks, this layer of the skin is renewed, this is due to the deepest layer of the epidermis - the basal one, in this layer of creatine - a very important protein for the skin - new cells are formed. Within a few weeks, these cells rise to the surface of the epidermis. By the end of their journey, they become dry, flat and lose their cell nucleus.

The epidermis or outer layer covers the dermis and is the surface of the skin with bulges and depressions, includes approximately 15 layers. This is the epithelium, constantly created by the basement membrane layer. The epidermis is divided into 3 layers. The outer or stratum corneum, strong and impermeable to water, consists of dead cells that are constantly separated from the epidermal layer by small scales under the action of new cells originating from the inner layers. The middle layer of the epidermis contains adult (scaly) cells that renew the outer layer. The middle layer or basement membrane layer creates new cells, which usually develop into squamous cells. The basement membrane layer also contains melanocytes, the cells that produce the melanin pigment. Sun exposure stimulates the production of melanin to protect the skin. That is why after exposure to the sun a tan appears. Some artificial tanning creams stimulate the formation of melanin, others contain an ingredient (dihydroxyacetone) that gives the skin a red-brown color similar to a tan.

Dermis

The dermis is the main layer of the skin. The dermis is rich in connective fibers (75% of the structure) that maintain the elasticity (elastin) and resistance (collagen) of the skin. Both substances are extremely sensitive to solar (ultraviolet) rays, which destroy them. Cosmetics based on elastin and collagen cannot restore them, because their molecules are too large and cannot penetrate the outer skin. In the dermis there are receptors that perceive various external stimuli.

Hypodermis

This layer includes adipose tissue, subcutaneous nerve and vascular channels. The hypodermis also contains hair follicles and sweat glands.

♦ Color of the skin, sexual and racial characteristics are possible due to the distribution of four main components on the surface of the skin:
- melanin, a brown pigment - carotene, the color of which varies from yellow to orange
- oxyhemoglobin: red
- carboxyhemoglobin: purple

Skin color is affected by genetic factors, environment (sun exposure) and nutritional factors. The complete absence of the first two pigments causes albinism.

♦ Freckles most often appear in adolescence and almost disappear by the age of 30. They don't darken randomly.

The presence of freckles means that in the human body it will reduce the level of melanin, a photoprotective pigment. That is, freckled skin is most vulnerable to harmful ultraviolet radiation. Therefore, people with freckles are strictly recommended to smear protective cream and avoid overly revealing clothing.

♦ Skin thickness varies depending on the areas under consideration from 0.5 mm to 2 mm on the palm and sole.

• In a baby, the thickness of the skin is one millimeter. As it grows older, it remains thin only on the eyelids. In an adult, the average value of skin thickness increases several times.
• The skin has a significant resistance to stretching.
• The thinnest skin is on the eyelids and eardrums - from 0.5 mm and thinner, but the thickest is located on the feet, here it can reach a thickness of about 0.4-0.5 cm.

♦ Nails and hair also belong to the skin - they are considered its appendages.

♦ The skin has about 150 nerve endings, about 1 kilometer of blood vessels, more than 3 million cells and about 100-300 sweat glands.

♦ Vascular system skin contains a third of all blood circulating in the body - 1.6 liters. The skin tone also depends on the state of the capillaries (they are expanded or narrowed) and their location.

♦ sweat glands act as a temperature controller.

• Approximately in every square centimeter of human skin there are about a hundred sweat glands, 5 thousand sensory points, six million cells, as well as fifteen sebaceous glands.
• Their total number is from two to five million, most of these glands are located on the palms and feet, approximately 400 per square centimeter, followed by the forehead - about three hundred per square centimeter.
• Asians have fewer sweat glands than Europeans and Africans.
• Human skin releases about 1 liter of sweat per day.

♦ skin cells in the body, there are from 300 to 350 million. During his life, each person loses up to a hundred kilograms of horny scales, which turn into dust.

• In a year, the body must produce more than 2 billion skin cells. The fact is that during the year the change of all skin cells occurs at least 6 times (complete replacement - in 55-80 days). The process of completing the cell cycle occurs at a rate of 0.6 million horny scales / hour (this amount corresponds to a weight of 0.7-0.8 kg).
• For a lifetime man renews the skin about 1000 times.
• The skin that a person sheds over a lifetime weighs up to 18 kilograms.
• Skin cells are renewed more and more slowly with age: in newborns every 72 hours, and in people from 16 to 35 years old, only once every 28-30 days.

♦ In one day sebaceous glands skin produces approximately 20 grams of sebum. After that, the fat is mixed with sweat and forms a special film on the skin, which protects it from fungal and bacterial damage.

• The number of sebaceous glands depends on the area of ​​the body. There are few of them on the back of the hands, and on the T-zone of the face (forehead - wings of the nose - chin), under the hair on the head, in the ears, as well as on the chest and between the shoulder blades, they can be from 400 to 900 per 1 sq. cm. It is there that acne and the so-called black dots appear - comedones, by which you can identify a clogged pore.

♦ On the surface of the skin there are colonies of beneficial microorganisms that help in the fight against pathogenic bacteria.

If you achieve absolute sterility, you can weaken the double protection: excessive sterility is harmful to the skin.

• For one sq.cm. skin accounts for 30,000,000 different bacteria.

♦ On the skin of an adult, on average, there are from 30 to 100 moles., but sometimes their number can exceed 400. British scientists saw this as a connection with the speed with which the body ages.

According to the results of the study, the number of moles is proportional to the length of telomeres - the end fragments of chromosomes that shorten with each cell division. There is a hypothesis that people with many moles are less likely to suffer from age-related diseases.

♦ The skin is aging due to ultraviolet radiation, stress, lack of sleep, reduction of collagen and fibroblasts.

♦ The smoothness of the skin depends on the condition collagen. In a young body, its cells are twisted, which makes the surface of the skin more stretched and smooth. With age, from lack of nutrition and poor water, collagen cells are filled with heavy metals and straighten, and skin tone decreases.

• Collagen makes up 70% of the dry dermis and decreases by 1% every year.

♦ Vascular meshes or asterisks can occur if there is a lack of vitamin D in the body, this disease occurs in 90% of people, therefore good nutrition is necessary for good skin.

♦ Waterproof skin provides its outer layer of the epidermis. Its cells are in very close contact with each other and have a layer of fat on the outer surface.

If the body is in water for a long time, the extracellular layer of fat becomes thinner and water gains access to the skin cells, as a result, it swells. We saw how in the water wrinkled skin your fingers? This transformation serves to improve traction (just like treads in car tires).

♦ Flaccid skin syndrome- a rare connective tissue disease in which the skin easily stretches and forms loose folds.

In flaccid skin syndrome, mainly elastic fibers are affected. The disease is usually hereditary; in rare cases and for unknown reasons, it develops in people who do not have precedents in the family.
Some hereditary forms are quite mild, others are accompanied by some degree of delay. mental development. Sometimes the disease leads to death.

With sluggish, flabby skin, it easily gathers into folds and hardly returns to its previous position.

In hereditary forms of the disease, excessive skin folds already exist at birth or form later. The "excess" and laxity of the skin is especially evident on the face, so that the sick child has a "mournful" look. A hooked nose is typical.
In general, flaccid skin syndrome is a connective tissue pathology.

Since the connective tissue is part of all body systems, the manifestations of the syndrome are very diverse. Both the osteoarticular, and pulmonary, and cardiovascular, and digestive systems are affected.
Treatment has not been developed. In people with a hereditary form of the disease, reconstructive surgery significantly improves the appearance. However, excess skin can form again. Reconstructive surgery is less successful in the case of an acquired form of the disease.
According to videoplastica.ru, popular-medicine.rf

The human skin has a complex structure. In different places of the body, its thickness is different and varies from 0.1 to 4 mm. The thickest is the skin of the neck, back, skull, thighs, palms and feet. The appearance and condition of the skin undergo changes depending on age, general condition of the body, nutrition, external influences, etc. Its color and elasticity depend on living conditions, gender, age, profession, season, climate, race, hereditary characteristics, etc. On the skin surface, a fine network of tiny grooves is visible to the naked eye, due to the special anatomical structure of the skin.

The skin is made up of three main layers: outer (epidermis), middle (dermis, or true skin) and inner (hypoderm, or subcutaneous layer).

Epidermis consists of several layers of microscopically small cells. The cells of the deepest layer, called the germinal layer, constantly multiply and are gradually forced out to the surface of the skin. Over time, they are filled with horny substance and form the most superficial layer of the epidermis. Horny cells are continuously shedding and falling off, but this process is very slow and goes unnoticed in a healthy person.

Dermis (true skin) It consists of fine fibers of connective tissue, collected in bundles, and of special elastic (collagen) fibers that give elasticity to the skin. The skin of young people is smooth, taut and elastic, as it is rich in elastic fibers. Over time, however, these fibers become thinner, their elasticity and number are lost, which is why in old age the skin relaxes, becomes inelastic, wrinkled, which is especially noticeable on the face and neck.

The dermis also contains a dense network of blood vessels and nerves. It also contains many muscle fibers, which are connected to the hair root with their inner end. When they contract, the hair rises and the skin becomes rough (goose bumps).

Hypodermis (subcutaneous layer) consists of intertwined bundles of connective tissue fibers. They connect the dermis to the underlying tissues. When deviated, the bundles form a weak network filled with grains of subcutaneous fat. This fat gives a rounded shape to the body and, being a poor conductor of heat, protects it from cooling. Fat is unevenly distributed throughout the body, and its amount depends on age, gender, nutrition, physical stress, etc. In women, it accumulates most of all in the abdomen, thighs and buttocks.

The dermis and hypodermis also contain a dense network of lymphatic vessels, nerves, and nerve fibers. Free nerve endings perceive pain. Other nervous apparatuses of various devices perceive touch, pressure, heat or cold, itching, burning and tickling.

Skin color is determined by several factors. The most important of these is Brown pigment melanin, which is in the form of grains in the cells of the deepest layer of the epidermis. The amount varies from person to person. Dark-skinned people have more melanin than fair-skinned people.

The skin of children, girls and young people contains comparatively less pigment and is thinner. It has more blood vessels and therefore it is more pink, delicate and fresh. Another factor that determines the color of the skin is transparency, and this, in turn, depends on the thickness of the skin. With age, the epidermis thickens, coarsens and the skin becomes thinner, irreversible aging processes occur in it. Skin color also depends on the pinkish-red color of the blood pigment (hemoglobin) in the capillaries and on the yellowish color of the pigment of the horny substance (keratin) located in the epidermis. Under the influence of ultraviolet rays (solar or quartz lamps), the amount of melanin rapidly increases and the harmful penetration of these rays into the depths of the body decreases.

skin glands. There are two types of glands - sweat and sebaceous.

sweat glands are a thin tube that opens on the surface of the skin into a separate sweat pore. The inner end of the tube is curled in the form of a ball. Human skin contains from 2 to 15 million sweat glands, distributed unevenly in the skin. The skin of the palms, armpits, inguinal folds, feet, forehead and back is richest in sweat glands. Sweat production depends on the condition nervous system, which determines the sharp sweating with a strong fright or excitement.

Sebaceous glands are in the dermis. They adjoin the hair and open into the hair canal. Human skin contains about 900,000 sebaceous glands, which secrete 2-3 g of sebum daily. They are scattered throughout the body (with the exception of the palms and feet), but are most densely located on the head, face, back and chest. With abundant fat secretion, the skin and hair become oily, shiny and elastic. With reduced secretion, the skin is dry, rough, even cracks sometimes form, and the hair is dry and brittle.

Hair and nails. The hair consists of a shaft, a root and a bulb. The shaft is the part that is outside the skin. The hair root is hidden in the skin and starts from the bulb. Hair growth is determined by the reproduction of bulb cells. Each bulb is associated with a nerve branch and blood vessels, on which its condition depends.

The hair cells of young people contain a pigment that determines the color of the hair. In adults, this pigment is gradually replaced by air bubbles, which gives the hair a white color.

There is a relationship between hair color and thickness. Blondes have the most fine hair(0.04mm). Thicker hair in brown-haired women and brunettes. Blondes have about 140,000 hairs on their heads, brown-haired women have about 110,000, and brunettes have about 100,000 hairs. Hair grows constantly, but unevenly. They grow faster in spring and autumn. In one month, the hair grows by 1 - 1.5 cm. Over a certain period - from several months (for eyelashes) to several years (for head hair), hair falls out and a new one grows in its place. Different people lose from 20 to 120 hairs a day. The number of hair loss is individual.

Nails grow by multiplying the cells of the basal part. On the arms in one week they grow by 1 mm, and on the legs in 3-4 weeks by 1 mm. The nails of young people grow faster than adults, and faster in summer than in winter. The growth and thickness of nails, and hence their strength, depend on the state of health of the body, profession, gender, age, etc.

Leather- this is the outer cover of the body, it is an organ with a very complex structure that performs a number of important vital functions. In addition to protecting the body from harmful external influences, the skin performs receptor, secretory, metabolic functions, plays a significant role in thermoregulation, etc.

The area of ​​the skin of an adult reaches an average of 1.6 m 2. The color of the skin depends on the translucence of the blood and the greater or lesser presence of melanin pigment. In the area of ​​\u200b\u200bnatural openings (mouth, nose, anus, urethra,) the skin passes into the mucous membrane. On the surface of the skin, one can find a peculiar pattern of triangular and rhombic fields, limited by grooves; it is especially distinct on the palms, fingers and soles. Almost all over the skin is covered with hair.

Rice. 1. The structure of the skin of a human finger: 1-5 - epidermis (1 - basal layer; 2 - spiny layer; 3 - granular layer; 4 - shiny layer; 5 - stratum corneum); 6 - excretory duct of the sweat gland; 7 and 8 - dermis (7 - papillary layer; 8 - reticular layer); 9 - terminal section of the sweat gland; 10 - adipose tissue.

Skin structure. Two sections are distinguished in the skin: the upper one is epithelial (epidermis) and the lower one is connective tissue (the skin itself is the dermis). The boundary between the epidermis and the dermis appears as an uneven wavy line due to the presence of special outgrowths on the surface of the dermis, the so-called dermal papillae (Fig. 1).

Epidermis consists of five layers of cells. The layer of the epidermis located directly on the border with the dermis is called the main basal layer. It consists of a single row of cells separated by narrow slit-like tubules and interconnected by protoplasmic processes. The cells of the basal layer have two features: 1) they constantly multiply and by differentiation form cells of the overlying layers; 2) melanin pigment is formed in these cells, and also contains.

The second layer is called the subulate. It consists of several rows irregular shape cells with a light nucleus, also separated by slit-like tubules. The third layer is called granular: it consists of one or two rows of elongated, elongated cells, closely adjacent to each other.

In their protoplasm there are grains of keratohyalin, which is the first stage in the formation of horny substance. The fourth layer is called brilliant. It is found only in areas with a thick epidermis (palms, soles), has the appearance of a shiny strip, consisting of flattened non-nuclear cells, and is the next step in the formation of the horny substance. The last, upper, layer is the stratum corneum, consisting of thin nuclear-free cells, closely interconnected and containing a special protein substance - keratin. In the outermost part, the stratum corneum is less compact, individual plates lag behind each other, causing a constant physiological discharge of obsolete epithelial elements. The thickness of the epidermis and, in particular, its stratum corneum varies in different parts of the skin. It is most powerful on the palms and soles, much thinner on the lateral surfaces of the body, especially thin on the eyelids and external genitalia of men.

Dermis- connective tissue part of the skin, consisting of two layers: subepithelial, the so-called papillary, and mesh. The papillary layer is built from soft fibrous, consisting of thin bundles of collagen, elastic and argyrophilic (reticulin) fibers. The latter, on the border with the epithelium, together with the interstitial substance, form the so-called basement membrane, which plays an important role in the metabolic processes between the epithelium and the dermis. The collagen fibers of the papillary layer gradually pass into thicker bundles of the reticular layer and form here a dense plexus with a large number of elastic fibers. The reticular and papillary layers contain various cellular elements (fibroblasts, histiocytes, mast cells, etc.); among the connective tissue fibers are small bundles of smooth muscles associated with hair follicles.

Thick bundles of collagen fibers of the reticular layer pass directly into the subcutaneous adipose tissue, where they form a wide network, the loops of which are filled with fat cells. Adipose tissue determines the movable attachment of the skin to the underlying tissues and protects it from mechanical damage and ruptures.

The skin has a large number of blood and lymph vessels.

Arterial vessels form two networks. The first of them is located on the border between the dermis and subcutaneous tissue, smaller vessels depart from it into the reticular layer of the dermis. At the border with the papillary layer, they branch out and form a second network, from which capillaries extend, penetrating into the papillae (capillary loops). Venous vessels form three networks. One of them is located under the papillae, the second - in the lower half of the dermis and the third - in the subcutaneous adipose tissue. The epidermis is deprived