subcutaneous layer. The structure and properties of human skin: Dermis

The skin is a very complex human organ and plays an important role in the life of the organism. It participates in metabolic processes, regulates body temperature, performs a secretory function and helps internal organs. The skin is a barrier against adverse effects: bacteria, harmful chemical compounds, etc. The structure and functions of the skin everyone is the same, but the appearance depends on many factors. Such as age, race, gender. May vary depending on the conditions of life and profession, climate.

Skin structure

Skin structure includes sweat glands, hair follicles, sebaceous glands, nails, and the skin itself.

sweat glands perform the function of controlling body temperature. Most of the sweat glands are located under the armpits, in the groin and around the nipples. Sweat is controlled by the nervous system. The sweat that comes out is odorless. It is formed as a result of the action of bacteria that appear on a favorable environment for them - wet clothes.
hair follicle- This is the root of the hair, which is located in the skin and grows. It is supplied with nerve fibers and blood vessels. Therefore, it hurts us when you pull your hair.
Sebum- a fatty substance consisting of more than 40 types of organic acids and alcohols. It is secreted from the gland into the hair follicle, where it lubricates the hair. Then, coming to the surface of the skin, it forms a greasy, slightly acidic film (the so-called acid mantle of the skin). The acid mantle of the skin is of great importance for maintaining a healthy, holistic skin, as it has natural antibacterial properties. Sebum prevents the penetration of harmful substances from the outside and does not allow moisture to leave the body.
Sebaceous glands. They secrete sebum. The sebaceous glands are present in the hair follicle. The level of sebum secretion is controlled by androgens - male sex hormones. With their excess at the excretory duct of the sebaceous gland, the cells grow and clog the exit. When in contact with air, they are chemically attacked (oxidized) and turn black. Therefore, an eel formed in this way has nothing to do with clean skin, or with too high-calorie food. The accumulation of sebum behind the formed barrier causes a violation of the integrity of the sebaceous gland, and sebum penetrates into the deeper layers of the skin. In this case, it acts as an irritant and the result is a pimple. When an infection enters it, the pimple turns into an abscess. If the abscess is squeezed out, an even larger focus of inflammation is formed.
Nail- This is a smooth, slightly convex, translucent horny plate with a solid structure. The main component of the nail is the protein keratin. The nail plate grows throughout life. New tissue is formed in the germinal zone (at the base). The nail is always restored.

Skin structure

Skin structure consists of several layers: epidermis, dermis (skin) and hypodermis (subcutaneous fatty tissue).

Epidermis divided into five layers: basal (deepest), granular, shiny and horny. The basal layer is a set of living cells that divide, grow, develop, age and die, moving up the layer. The life cycle of the epidermis is 26-28 days. The top layer of the epidermis, the stratum corneum, is exfoliated and replaced by new cells. The thickest stratum corneum is on the feet and palms. The epidermis performs important functions: antibacterial protection (armor) and maintaining the skin's moisture level. The basal membrane does not allow the penetration of harmful substances, but from above it allows moisture to pass through.

- this is the top layer of the skin, its structure is made up of a network of blood vessels and nerve endings. Contains collagen protein, which evens out skin cells and makes it supple, smooth and elastic. As a result of age-related changes in the skin, collagen fibers and bonds are destroyed, and the skin loses its elasticity, becomes thin and wrinkles appear.

Hypodermis- subcutaneous adipose tissue. The main function of the hypodermis is to provide thermoregulation of the body, that is, to control temperature. Women have a thicker body fat than men. A large concentration of hypodermis in the chest, buttocks and thighs. Therefore, women better tolerate the hot rays of the sun, icy cold and can stay in the water longer.

Approximately twice a day, the skin cells of the basal layer bud off. The most intensive growth occurs in the morning and in the afternoon (the time when the level of the hormone cortisol is low). Therefore, this is the best time for skin care. In the morning it is useful to wash, massage and use creams.

What determines skin color

The structure and structure of the skin in all people is the same, but color of the skin different. What determines skin color? The skin contains the pigment melanin, which is responsible for coloring. The more it is, the darker it is. Melanin is a granular dark pigment in the epidermis, hair, and iris. Gives them a specific color and protects them from the harmful effects of ultraviolet rays. They contain its special cells - melanocytes in the form of granules located in the basal layer. Regardless of skin color, a person is born with the same number of malanocytes. But the ability of these cells to secrete melanin is different. Warm rays, penetrating the skin, provoke the release of melanin for protection. Sunburn and freckles are the result of melanin.

Functions of the human skin

The body conditioner we wear all the time is our skin. 36.6 ° - constant body temperature - both in winter and in summer. This controls our brain, it regulates the release of heat from the skin and perspiration. The skin secretes sweat, freeing the body from harmful metabolic products and poisons that enter along with drink, food, air. It also helps us breathe, removing 800 g of water vapor per day - twice as much as the lungs. The skin has tactile sensitivity, that is, it perceives the slightest touch to it. Our skin contains a thousand nerve endings in the smallest area. 75 sebaceous glands, 650 sweat glands, 25 meters of nerve fibers, 65 more hair fibers - and all this in 1 square centimeter of skin.

Important functions of the skin

1. Protective (barrier) function. The skin protects the body from harmful microorganisms and chemicals.
2. Exchange function. In the skin, transformations specific to it are carried out: the formation of keratin, collagen, melanin, sebum and sweat. The skin assimilates useful substances, participates in the synthesis of vitamin D. Through the circulatory and lymphatic network of blood vessels, skin metabolism is combined with the metabolism of the whole organism.
3. Reserve function. The skin retains toxic substances, protein metabolites (for example, residual nitrogen in a protein diet and some diseases), so it helps to weaken their effect on other organs and the brain.
4. Excretory function. The skin helps to get rid of toxic and excess body products (salts, water, medicinal substances, metabolites, etc.).
5. Temperature control. Helps maintain a constant body temperature.
6. Sensitive (tactile). Perceives external influences (pain, heat, cold, etc.), which ensures an adequate response of the body to stimuli. Recall, for example, how quickly we withdraw our hand after accidentally touching a hot iron.
7. Respiratory. The skin is involved in the process of gas exchange in the body. Carbon dioxide is released and oxygen is absorbed, this process is only 2% of the total gas exchange of the body.

The skin forms a common (outer) cover of the body, the area of ​​​​which in an adult is 1.5-2 m 2, and its thickness varies in different parts of the body from 0.5 to 4 mm, the weight of the entire skin is about 3 kg.

Skin functions

The skin protects the underlying tissues from mechanical damage, protects all internal organs from the effects of the external environment (pressure, friction, rupture, impact), and prevents the penetration of microbes and toxic substances into the body. The skin is constantly in contact with the external environment and has many functional inputs and outputs. Representing a huge receptor surface, the skin perceives the impact of various factors (pressure, humidity, temperature, etc.), provides pain and tactile sensitivity, and performs the function of thermoregulation.

Constantly in contact with the external environment, the skin releases metabolic products harmful to the body. Through the exits of the skin, water, salts and other residual products are removed. So, the skin is involved in metabolism, especially in water-salt metabolism. During the day, about 500 ml of water is excreted through the skin, which is 1% of its amount in the body. Various salts and products of protein metabolism are excreted through the sweat glands. The skin breathes by taking in oxygen and releasing carbon dioxide. In terms of the intensity of water, mineral and gas exchange, the skin is only slightly inferior to the liver and muscles.

The skin also performs many specific functions, the main of which are protective and signaling. The signal function of the skin is provided by numerous sensitive nerve endings - receptors located in all layers of the skin. With their help, we perceive pressure, cold, heat, pain, touch. In some areas of the skin, per 1 cm 2 of its surface, there are up to 200 painful, 12 cold, 2 thermal and 25 endings that respond to pressure. Skin sensitivity plays an important role in the interaction of the body with the external environment, it helps to avoid injuries, burns, frostbite.

Skin structure

The skin is made up of two layers:

• epidermis
• skin proper (dermis) with subcutaneous base

Between the epidermis and the skin itself lies the main membrane.

Epidermis forms the outermost layer of the skin. Its thickness varies from 0.07 to 0.4 mm; The epidermis reaches its greatest thickness in the area of ​​the sole (up to 1.5 mm). The epidermis consists of a stratified epithelium, the outer cells of which are keratinized and desquamated.

1. The germinal layer is the deepest, consisting of 5-15 rows of cells. Cells are born in this layer, which gradually replace the cells of the most superficial, keratinized layer of the epidermis.

   In the germ layer there is a pigment, its amount causes a different skin color. The pigment protects the human body from the penetration of ultraviolet rays. It is formed under the influence of sunlight, which is why the skin darkens when tanned. However, it should be remembered that under the influence of sunlight, the skin becomes rough, loses a lot of moisture, peels off, becomes covered with age spots and wrinkles. To avoid this, it is recommended to use sunscreens and lotions. It is necessary to follow the rules of exposure to the sun: it is necessary to sunbathe gradually, mainly in the morning. The maximum time spent in the sun should not exceed 1 hour. You can not sunbathe immediately after eating or on an empty stomach, it is extremely harmful to sleep in the sun. When exposed to the sun, in addition, the work of the immune system is weakened, the activity of lymphocytes decreases by 25-30%, the number of cells that are not involved in protecting the body from foreign substances increases.

2. Spiny layer - lies above the sprout layer
3. A granular layer consisting of several rows of cells containing keratohyalin in the protoplasm
4. The vitreous layer lies above the granular layer, formed by 3-4 rows of cells, filled with a special shiny substance eleidin.
5. The stratum corneum is the most superficial layer of the epidermis. Consists of flat keratinized (dead) cells. The latter turn into scales, which are gradually exfoliated on the surface of the epidermis, being replaced by new cells originating from the deeper layers of the epidermis, which leads to natural cleansing and skin renewal. For a more complete cleansing, periodic deep cleaning of the skin is recommended, using special cleansing scrubs or peels for this.

   Under the influence of some external and internal factors, the properties of the epidermis can change significantly. So, for example, with strong mechanical influences, with a lack of vitamin A, skin disease - psoriasis, the processes of keratinization and desquamation increase dramatically. When treated with hormones of the adrenal cortex (glucocorticoids), they slow down.

The skin itself (dermis), lying under the epidermis, is formed by fibrous connective tissue with many elastic fibers. Its fibers are intertwined with each other in different directions and form a dense network in which blood and lymphatic vessels, nerve receptors, sebaceous and sweat glands, hair bags lie.

The skin itself consists of two layers:

1. papillary layer - consists of loose connective tissue; it got its name because it carries papillae on its surface that protrude into the epidermis. Between the papillae are the interpapillary grooves. Nerve endings, blood capillaries and blind outgrowths of the lymphatic capillaries of the superficial (subepidermal) network of the skin lie in the papillae.
2. mesh layer - elastic and collagen fibers that are sent from the fascia to the subcutaneous tissue and the skin itself. Elastic fibers form a plexus under the papillae, which sends thin networks and individual fibers to the latter, causing skin elasticity.

Subcutaneous adipose tissue is the deepest layer of the skin. It is formed by loose connective tissue, the voids of which are filled with fatty lobules. This layer serves as a place for the deposition of fat, absorbs the action of various mechanical factors, softens bruises and serves as a "cushion" for internal organs, and provides skin mobility. In the subcutaneous tissue are numerous blood vessels and nerves that can hold up to 1 liter of blood. They serve as custodians of the blood, provide an even supply of nutrients to the skin and its muscles, and maintain a constant body temperature, protecting the body from cooling.

The structure and functions of the skin

Skin derivatives

Hair and nails are derivatives of the skin.

Hair cover the entire human body, except for the palms, lips, soles. There are three types of hair: long (mainly located on the head), bristly (eyebrows, eyelashes) and vellus (cover the rest of the skin). Hair is a horny formation, very durable and able to withstand a load of up to 100 g. Each hair has its own development cycle and life expectancy - from several months to 2-4 years. Every day, about 100 hairs fall out in a person, and at the same time the same number of hairs grows again, so their total number remains relatively constant. Hair roots - hair follicles, from where they continuously grow - lie in hair bags located in the skin itself. Hair grows at different rates: there are periods of active growth and periods of rest. On average, head hair grows 0.5 mm per day, and 15 cm per year.

Attached to the hair follicles are the muscles that raise the hair. Hair eyelashes, eyebrows, nasal openings do not have muscles. There are smooth muscle cells in the skin of the scrotum and in the skin around the nipple of the breast; they are not associated with hair bags, but form a muscular layer that lies in the papillary layer and partly in the subcutaneous tissue. The contraction of the smooth muscles of the skin leads to the appearance of small tubercles on it when it is cooled ("goosebumps"). This increases heat generation.

Hair color is determined by the presence of pigment, and shine and elasticity depend on the amount of fat secreted by the sebaceous glands, the ducts of which open into the hair follicles.

Nails- dense horny plates located on the nail bed and protecting the terminal phalanges of the fingers. The average nail growth rate is 0.1 mm per day; in women, nails grow somewhat more slowly than in men. Complete restoration of the nail occurs on average in 170 days. The growth rate, color, pattern of nails are also largely determined by the state of the body.

The glandular apparatus of the skin

The glandular apparatus of the skin is represented by sebaceous and sweat glands.

The sebaceous glands are located on the scalp, face and upper back. During the day, they secrete up to 20 g of a secret called sebum. Sebum is composed of fatty acid esters, cholesterol, protein products, hormones and other substances, and serves as a lubricant for hair and skin. It softens the skin and gives it elasticity.

Sweat glands are found in almost all parts of the skin, but the pads of the fingers and toes, palms and soles, axillary and inguinal folds are especially rich in them. The total number of sweat glands reaches approximately 2.5 million. With the help of sweat glands, the skin performs the function of thermoregulation and excretory function. These glands produce sweat, it is released in the form of tiny droplets and quickly evaporates. On average, an adult loses from 700 to 1300 ml of sweat per day, and with it up to 500 kilocalories of heat. In addition, urea, salts and other substances come out with sweat.

The total surface of the glandular epithelium of the sweat and sebaceous glands is approximately 600 times greater than the surface of the epidermis.

Skin sensitivity

Skin receptors do not form special sense organs, but are scattered in the thickness of the skin over the entire surface of the body. They have a complex and varied structure. In most cases, these are multicellular bodies of various shapes, inside which a sensitive nerve fiber enters and branches. Between skin cells there are also bare nerve endings that perceive pain stimuli.

Excitation from the skin receptors along the centripetal nerves through the spinal cord enters the zone of skin sensitivity of the cerebral cortex.

The sensitivity of the skin to touch, pain, cold and heat helps the body to perceive the environment and better respond to changes in its conditions.

Skin thermoregulation

Due to thermoregulation, the temperature of the human body is relatively constant, despite fluctuations in the temperature of the external environment. Fat lubrication of the skin surface, subcutaneous fatty tissue and blood vessels of the skin prevent excessive heat or cold from the outside and excessive heat loss.

The significance of these formations in thermoregulation can be illustrated by the following case. In 1646, a festive procession took place in Milan, led by the "golden boy". The child's body was covered in gold paint. After the procession, the boy was forgotten and spent the whole night in a cold castle. Soon the boy fell ill and died. Gold paint caused the expansion of blood vessels in the skin, as a result, he lost a lot of heat, the body temperature dropped sharply. The cause of the death of the child was established only in the XIX century. In an experiment on two men whose bodies were covered with varnish, they showed that the cause was a violation of the body's thermoregulation.

The skin, participating in the processes of thermoregulation, protects the inner sphere from overheating or hypothermia. Through it, 80% of the heat generated in the body is released, mainly due to the evaporation of sweat. Both in winter and summer, the temperature on the surface of the skin of a healthy person is 36.6 ° C, and natural fluctuations do not exceed 2 ° C. When the ambient temperature drops, numerous blood vessels located in the skin narrow (we turn pale), blood flow to its surface decreases and, accordingly, heat transfer decreases, because. more blood enters the vessels of the internal organs, which contributes to the preservation of heat in them. The opposite processes occur when the temperature rises or during increased physical activity, when more heat is produced in the body. Then the blood vessels of the skin expand reflexively, more blood flows through them and heat transfer increases.

In extreme heat, when the body temperature is below the ambient temperature, the expansion of blood vessels can no longer enhance heat transfer. In this case, the danger of overheating is eliminated by sweating. Evaporating, sweat absorbs a large amount of heat from the surface of the skin (evaporation of 1 g of sweat takes 0.58 calories of heat). That is why the human body temperature does not rise even in the hottest weather. A person could withstand a temperature of 70-80 ° C, but at the same time he should have 9-16 liters of sweat in a few hours. An increase in body temperature is observed during many diseases. This is an indicator of a favorable course of the disease, a reflection of the body's active fight against infection and a natural reaction. Elevated body temperature accelerates chemical processes, increases metabolism, increases the activity of leukocytes, that is, mobilizes the body's defenses.

Heatstroke- this is a violation of the functions of the body when it is overheated, as a result of the cessation of heat transfer due to high humidity and high temperature. With heat stroke, headache, dizziness, tinnitus, flickering in the eyes, increased heart rate and respiration, dilated pupils, impaired movement, nausea and vomiting, loss of consciousness, convulsions, fever are observed.

Sunstroke occurs as a result of prolonged exposure to the direct rays of the sun with an uncovered head. At the same time, the vessels of the brain expand, cerebral edema develops, intracranial pressure rises, and the temperature of the human body rises sharply.

In case of heat or sunstroke, it is necessary to call an ambulance, and before it arrives, the patient must be transferred to a cool place, raise his head and unbutton his clothes, put cold on his head and heart area and give him cool water to drink.

frostbite manifested in loss of sensitivity in the affected area of ​​the skin, in its whitening. In this case, you must immediately grind the whitened area in order to restore blood circulation in it. With severe frostbite, as with severe skin burns, it is necessary to cover the affected area of ​​\u200b\u200bthe skin and immediately contact a medical institution.

Alcohol violates the mechanisms of thermoregulation, which contributes to hypothermia of the body and the occurrence of colds and infectious diseases.

In addition to the entrance exam requirements

• Hardening of the body (based on the book: Laptev A.P. The ABC of hardening, M., FiS, 1986)

What is skin? This is a natural barrier that is located between the outer and the human skin performs a number of very important functions and tasks and ensures the smooth operation of the entire human body. In this article, we will find out what the value of human skin is, why it is needed, what diseases it can be exposed to.

Skin functions

• thermoregulation- This is a very important process that must regulate the temperature of the human body and maintain it constant, regardless of environmental conditions. More than 80% of heat transfer occurs through the skin.
• Receptor. Receptors are organs or cells that are able to translate external influences into nerve impulses and transmit signals of this influence to our nervous system. Pain and touch receptors are located here. Those that react to cold and heat. There are about 6 million cells per 1 square centimeter, and of these there will be 5 thousand receptors that are responsible for the perception of certain external signals.
• Protective- a very important function, since it is the human skin, the meaning of which is revealed in the article, that is a kind of barrier to the penetration of various infections through the surface of the body. Therefore, if there is any damage on the skin, they must be treated to prevent the penetration of harmful substances into the human body. In addition, sweat is released on the surface of the skin, which has an acidic reaction and kills most bacteria.
• Respiratory. Thanks to the skin, gas exchange occurs in the human body. Scientists are still arguing about the degree of importance of gas exchange for human skin. But it is known for sure that through the skin we receive a large amount of oxygen.

• excretory. Together with sweat, all those components that must be removed from the body for its proper functioning are released through the skin.
• exchange. Regulation of water-salt and temperature balance. All this happens due to the exchange of substances with the environment. As a result, regulation of many processes occurring in the human body is carried out.
• Synthetic. The essence of this function is that a special pigment melanin is synthesized in human skin, which allows you to neutralize the effects of ultraviolet radiation. Melanin is a good antioxidant. In addition, with its help, the human body receives vitamin D, which protects it from bacterial infections and is still considered one of the best means of combating a disease such as tuberculosis. This vitamin causes the formation of protective peptides in the body that activate the immune system and destroy the Koch's wand.
• Deposition of blood. In the blood vessels of the skin, about 1 liter of blood can linger, which is a kind of necessary when wounds occur.
• Self cleaning. The skin is constantly losing its cells due to contact with the environment, but thanks to regeneration, we hardly notice this.

All these features perfectly show how important human skin is.

Skin structure

Answering the question of what skin is, it is necessary to dwell in more detail on it consists of three layers. The outer layer is called the epidermis. It is he who is constantly in contact with the environment. The second layer is the skin itself, or the dermis, or it is also called the dermis. And the deepest layer is the subcutaneous fatty tissue, which in some people can reach a thickness of several centimeters. Let's take a look at these three layers in more detail.

Epidermis

Dermis

The dermis is made up of connective tissue. Its main component are collagen and elastic fibers. They are what give the skin its elasticity. Thanks to this property, we can painlessly move our limbs, while stretching the skin. In addition, the dermis contains receptors, thanks to which we feel touch, pain, cold and heat. Sweat and sebaceous are also located here, which will release substances from the human body into the environment. And finally, in the dermis are the hair follicles and a small number of muscles that affect them.

Let us dwell in more detail on the glands and follicles. The glands are divided into sebaceous and sweat. The sebaceous glands secrete a special secret called sebum, which prevents the penetration of water into the human body, as well as the loss of moisture from the body. A person will secrete about 20 g of sebaceous secretion during the day. Sweat glands look like twisted tubules with an excretory duct. Depending on the physique, the intensity of physical activity in a person, about half a liter of sweat can be released daily. Sweat plays an important role in the water-salt balance, controlling homeostasis as the constancy of the internal environment, and in the thermoregulation of the human body, since, evaporating from the surface of the body, it cools it.

Hair follicles are located deep in the dermis and underlie hair growth. They are approached by blood vessels that bring oxygen and essential nutrients, and nerves.

Subcutaneous adipose tissue

This is the deepest layer, consisting mainly of adipose tissue and fat cells. This fat performs a number of useful functions. Firstly, it is a place of energy storage and fat-soluble vitamins, thanks to which the human body can do without food for some time. Secondly, adipose tissue is an excellent heat-insulating material that protects the body from hypothermia. Thirdly, this layer of skin in a certain way protects a person from injuries and fractures.

We answered in detail the question of what skin is. Now let's turn to the diseases that the skin can be subjected to, as well as to the methods of treatment.

Diseases and treatment of the skin

What is skin? It is primarily an organ. And therefore, like any other human organ, it can get sick. What are the main problems associated with human skin?

Hives

Blisters on the skin, redness, itching - almost every one of us has encountered similar problems at least once in a lifetime, and some suffer from this all the time. Urticaria, and this is the name of this disease, can cause many reasons. This is malnutrition, and contact with synthetic materials, and, of course, allergies. Urticaria is easy to distinguish from other skin problems. It is characterized by blisters and itching. In addition, urticaria passes quickly enough (if we are not talking about a chronic disease). Blisters stay on the skin for no more than a day. Urticaria is usually treated with various antihistamines.

Fungal diseases. Rubromycosis

Despite the great preventive medical work, fungal diseases are still widespread. The most common is rubromycosis. It affects the skin of the feet and interdigital folds. With this disease, flour-like peeling and cracks appear. In the absence of timely treatment, the disease from the feet can spread further over the entire surface of the skin. With rubromycosis, antifungal ointments and keratolytic drugs are prescribed.

Epidermophytosis

The most common interdigital form of the disease. Cracks, loosening, weeping erosion appear. Most often, athletes and workers in hot shops suffer from this ailment. With timely access to a doctor, the disease can be easily cured with conventional antifungal drugs.

microsporia

Another disease of the scalp, which very often affects children. The fact is that the carriers of this disease are animals. Rounded foci with clear contours appear on the skin. Perhaps the appearance of pustules and peeling. When the disease spreads to the scalp, it is possible to break off the hair 4-6 mm from the surface of the skin. If you find such foci of the disease, you should consult a doctor. As a rule, a dermatologist prescribes antifungal ointments, and with an advanced disease, drugs that include a hormonal component.

The skin, photos of all its components are presented in the article, suffers from many influences and diseases. We have listed only the most important of them.

The skin, with its surface area of ​​1.5-2 square meters, is the largest organ of the human body. It performs numerous functions. Skin condition depends on age, nutrition and lifestyle. This is especially true for the skin of the face, because it is more affected by all the harmful effects of the environment. In addition, the face is the most exposed part of the skin and needs careful care.

Our skin is:
about 5 million hairs; - the total surface area of ​​the skin is 1.5-2 square meters;
contains 60% moisture, in children up to 90%;
one hundred pores per square centimeter;
two hundred receptors per square centimeter;
average skin thickness 1-2 mm;
the skin is slightly rougher and thicker on the soles, thinner and more transparent on the eyelids;
the weight of the skin without the hypodermis is 4-6% of the total body weight;
an average of 18 kg of keratinized and newly replaced skin throughout the life of an adult.

The skin has a very complex structure, it is penetrated by a huge number of vessels, nerves, ducts of the sebaceous and sweat glands.

In a very simplified way, the structure of the skin can be described as follows:
1. The outer layer of the skin is the epidermis, formed by epithelial cells lying on top of each other in several tens of layers. The upper part of the epidermis, which has direct contact with the external environment, is the stratum corneum. It consists of aged and keratinized cells, which are constantly exfoliated from the surface of the skin, and are replaced by young ones migrating from the deep layers of the epidermis. (The complete renewal of the epidermis, for example, on the sole lasts about a month, and on the elbow - 10 days).
We owe to the stratum corneum that our body does not dry out and foreign substances and pathogens do not penetrate inside. The so-called protective acid mantle (also called the hydro-lipid mantle), which covers the surface of the skin with a thin film, is of great help in this. It consists of the fat of the sebaceous glands, of sweat, and of the components of viscous substances that bind individual horny cells. The protective acid mantle can be considered as the skin's own cream. It is slightly acidic (compared to an alkaline environment, and therefore is called acidic) - a chemical environment in which bacteria and fungi usually die.
In the deepest layer of the epidermis are melanocytes - cells that produce the pigment melanin. The color of the skin depends on the amount of this pigment - the more it is, the darker it is. The formation of melanin is enhanced by the action of ultraviolet rays, it is he who causes sunburn.
2. The next layer - the dermis - is also heterogeneous. In its upper part, located directly under the epidermis, are the sebaceous glands. Their secretions, together with the secretion of sweat glands, form a thin film on the surface of the skin - a water-fat mantle that protects the skin from harmful effects and microorganisms. The underlying elastic fibers give the skin firmness, while the collagen fibers give strength.
3. And, finally, the third layer of the skin - the hypodermis (or subcutaneous tissue) - serves as a heat-insulating pad and softens the mechanical effects on the internal organs.

The skin itself consists of two layers - papillary and reticular. It contains collagen, elastic and reticular fibers that make up the frame of the skin.

In the papillary layer, the fibers are softer, thinner; in the reticulum they form denser bundles. To the touch, the skin is dense and elastic. These qualities depend on the presence of elastic fibers in the skin. The reticular layer of the skin contains sweat, sebaceous glands and hair. Subcutaneous fatty tissue in different parts of the body has an unequal thickness: on the abdomen, buttocks, palms, it is well developed; on the auricles of the red border of the lips, it is very weakly expressed. In obese people, the skin is inactive; in thin and emaciated people, it easily shifts. In the subcutaneous tissue, reserves of fat are deposited, which are consumed in case of illness or in other adverse cases. Subcutaneous tissue protects the body from bruises, hypothermia. In the skin itself and subcutaneous tissue are blood and lymphatic vessels, nerve endings, hair follicles, sweat and sebaceous glands, muscles.

How does the skin breathe and what does it eat?

Exactly a quarter of all blood circulates in the skin, supplying it with everything necessary for the formation of young cells and to support active ones: oxygen for skin “breathing” (more precisely, as fuel for skin metabolism), energy-supplying carbohydrates (for example, glycogen), peptides and amino acids for protein formation, fats (also called lipids), vitamins and trace elements.

Arterial vessels in the skin form superficial and deep networks. The first is located at the level of the base of the papillae of the skin; the second - on the border of the actual skin and subcutaneous tissue. The superficial arterial network connects to the deep one. Of great importance for coloring the skin is the distribution of blood vessels. The closer the vascular network to the surface of the skin, the brighter the blush.

The cells of the epidermis feed on lymph that penetrates from the skin itself. The skin has a large number of nerve endings. The nerves also form two networks in the skin, running parallel to the vascular networks; in the epidermis they end in nerve fibers and free endings. The sensitivity of the skin is very high, since, in addition to nerves, special nerve apparatuses are also located in the subcutaneous fatty tissue. They convey sensations of pressure, touch, cold and heat. The nerves and nervous apparatuses of the skin connect it with all internal organs and the brain.

In principle, the skin can do without external feeding. However, there is one subtlety here - at least in relation to the upper skin. Since the epidermis, unlike the lower layers, does not have its own blood vessels, it must be fed by capillaries in the papillary boundary layer of the dermis. The tight serration of the two layers of skin, which guarantees a good supply, becomes progressively flatter and weaker with age. This can lead to insufficient supply of oxygen and nutrients to the upper skin. To compensate for this deficiency is one of the most important tasks of cosmetics.

How skin is renewed

The germ layer is especially important because it is here that young cells constantly arise. Within 28 days, they move to the surface of the skin, while losing the cell nucleus. And already with flat, “dead” flakes of keratin, they finally form a visible surface layer of the skin, the so-called stratum corneum. Dead cells fall off in the process of daily friction during washing, wiping, etc. (two billion every day!) And are constantly replaced from below by others. This process is called regeneration. Within three to four weeks, the entire upper skin is completely renewed. If this cycle operates smoothly and without interference, the upper skin perfectly protects the lower layers - the dermis and subcutaneous. Above the dermis is a layer of the upper skin, which, in turn, is divided into five different layers. At the very bottom, the germ layer forms young keratin, pigment and immune cells. Within 28 days they move up and become more and more flat. And finally, in the form of dry peels without a nucleus, they form a protective stratum corneum about 0.03 mm thick.

The peeling process underlies many cosmetic procedures that contribute to increased rejection of the most superficial stratum corneum of the epidermis, for example, when removing freckles, age spots, etc.

The skin contains nerve endings and nerve apparatus that perceive temperature irritations. Cold is perceived faster than heat. However, both cold and heat are felt differently in different parts of the body. The skin of the face is the least sensitive to cold and heat, the skin of the extremities is the most sensitive. The sensitivity of the skin to temperature irritations is evidenced by the fact that the skin feels a difference in temperature by 0.5 ° C.

We owe to the skin that the body temperature of a healthy person remains constant at about 37 degrees - regardless of the ambient temperature. It regulates the exchange of heat between the body and the external environment. Thermoregulation depends on the nervous system. Irritation of the nerves causes expansion or constriction of blood vessels; when contracting, heat is retained in the body, when expanding, a greater heat transfer occurs.

However, this “vascular gymnastics” can lead to the appearance of red veins on the face, namely when the skin is tender and the connective tissues are too weak to support the thin walls of the vessels from the outside. Vessels remain dilated and appear through the skin.

Sweat glands play a significant role in heat transfer. On average, a person produces from 600 to 900 ml of sweat per day. Evaporation from the surface of the skin causes a decrease in body temperature. With a decrease in external temperature, heat transfer decreases, with an increase, it increases.

Although cosmetics is mainly concerned with the skin of the face, it is important to know the function of the skin as an organ for the health of the body as a whole. Moreover, the violation of its functions always affects the skin of the face.

The skin is closely connected with all organs and systems of the body. It performs a wide variety of metabolic functions. It removes toxins, participates in water-salt, carbohydrate and protein metabolism. Its great importance in the functioning of the immune system has been proven.

Skin is the organ of the fifth sense

Together with the eyes, ears, mouth and nose, the skin belongs to the five sense organs. It is not only the largest, but also the most sensitive organ among them. She instantly notifies us of hot, sharp and sharp. The skin owes its incredible sensitivity to tiny tactile bodies, pressure, cold and heat receptors, free nerve fibers and other sensors in the connective tissue and dermis. They are directly connected via nerve pathways to the brain and spinal cord. There, the delivered information is immediately evaluated, transforming into sensations, and, if necessary, into actions.

Skin - chemical laboratory

Under the influence of sunlight, the skin synthesizes vitamin D. It is responsible for ensuring that the body has enough calcium for bone formation, as well as for many other metabolic processes.
under the influence of light stimulation, other special cells convert amino acids until the coloring substance melanin appears. This pigment acts as a “natural umbrella” to protect the skin from ultraviolet radiation and its destructive effects on cells.
A further skill of the skin is the ability of some of its enzymes to activate the appropriate hormones. For example, cortisone in the skin is converted into an even more effective substance hydrocortisone, and the male sex hormone testosterone is converted into dihydro-testosterone. In this form, it sensitizes hair roots and sebaceous glands and can cause hair loss, oily skin, and acne (a disease called acne).

Cleoteca

Despite the outward simplicity, the human skin has a complex structure and performs a wide variety of functions. The properties of the skin are such that it successfully protects the bones, muscles and internal organs of a person from mechanical influences, external diseases, actively participates in the regulation of body temperature, and is an organ of touch.

The skin is an elastic, porous, durable, waterproof, sensitive tissue that is able to maintain the thermal balance of the body, protect against mechanical, chemical, physical influences, and keep out harmful viruses and microbes.

On one square centimeter there are about a thousand sensory points, millions of cells, hundreds of sweat and dozens of sebaceous ducts, which, thanks to a complex system of receptors, connect the skin with the cerebral cortex, providing detailed information about the external environment.

At the same time, it informs the brain about how well it is able to protect the body from external influences and cope with its other duties at the moment: the brain receives data on the slightest mechanical damage to the skin instantly.

The total area of ​​the human skin is about 2 m2, the thickness ranges from 1 to 4 mm (the thickest skin on the feet). It consists of several layers, each of which has its own properties and performs certain functions:

• The epidermis is the uppermost part of the skin and consists of five layers. At the very bottom, a skin cell is born by division, which immediately begins to move to the surface to replace the old and dead cell. Having reached the outer layer, it, in turn, dies, forming a stratum corneum with other cells similar to it, which provides a mechanical barrier against the penetration of bacteria into the body. After a while, the scale cell peels off and falls off. It is immediately replaced by another cell that does the same. This process is continuous and allows the skin to constantly renew itself and retain its properties.
• Dermis - located under the epidermis and consists of two layers. In the first, papillary, there is a huge number of outgrowths, inside of which are nerve fibers and capillaries. In the second, mesh, in addition to a developed network of nerve fibers, there are lymphatic and blood vessels, hair roots, sebaceous and sweat ducts, as well as elastic, smooth muscle and collagen fibers, due to which the skin is characterized by such mechanical properties as strength and elasticity.
• Subcutaneous fat - is a connective adipose tissue, which is unevenly distributed throughout the body. The main task of this layer is to accumulate and store vitamins and nutrients. In addition, it additionally protects the internal organs and, having heat-insulating properties, retains heat inside the body.

Diagram of human skin

Also, the skin contains the rudiments from which hair, nails, sweat, sebaceous develop, in women - the mammary glands that produce milk, and therefore are extremely important when feeding a baby.

Protective properties

The skin is the body's most powerful defense against harmful environmental factors. It successfully protects the internal organs from mechanical, physical, chemical, biological influences, from waterlogging or drying out.

This is greatly facilitated by such mechanical properties of the skin as elasticity (the ability to resist pressure) and elasticity - the ability of the epidermis to stretch under mechanical action and quickly return to its original state.

Due to the huge number of woven elastic fibers connecting with each other, the skin is able to painlessly endure severe mechanical damage: shocks, sprains, bruises, pressure.

The skin also successfully protects the human body from cold or excessive exposure to sunlight.

The upper, stratum corneum of the epidermis, due to its low level of acidity, is resistant to non-concentrated exposure to chemicals. Healthy skin, without breaks, successfully protects the body from the penetration of foreign substances and disease-causing bacteria into it, and thanks to the continuous exfoliation of dead cells, it gets rid of microbes, viruses, bacteria, fungi.

Self-cleaning properties

On the human skin there are a lot of substances that promote the growth of bacteria. Some species appear on the skin as soon as a person is born, and do not leave it until the end of life: it is impossible to completely remove them from the surface. These are mainly streptococci (live in the folds of the skin) and staphylococci (in the hair follicles). Other microbes live here temporarily: they got on the epidermis from the external environment and, after washing with soap, are removed without problems.

If a person's skin is healthy, it produces substances that prevent the reproduction of viruses, which is why those that are on it quickly die, and those that live permanently do not increase their number. This also contributes to a slight level of acidity of the skin.

Thermoregulating properties

Thanks to the skin, the body has the ability to regulate heat and maintain a constant temperature. An increase in temperature dilates blood vessels and relaxes the muscles of the skin, which causes an increase in the amount of blood flowing through the vessels, and its flow to the surface of the skin (blood gives off heat to the external environment). An important role here is assigned to the sweat glands, when, with an increase in temperature, the amount of sweat brought to the surface increases from 800 to 4 thousand cm3, and heat transfer also increases with it.

When cold, on the contrary, the muscles contract, the vessels narrow, which causes a decrease in the amount of blood passing through them, as well as a decrease in sweating, which leads to a decrease in the heat generated by the body.

Excretory and absorbent properties

Thanks to the sebaceous and sweat glands passing through the skin, the role of the skin in the metabolic processes that occur in the body is great, and in fact it performs the same role as the kidneys. Sweat glands rid the body of sodium chloride, potassium, urea, hydrogen sulfide and other substances produced by the body.

Through the sebaceous ducts, sebum and fatty acids come to the surface, which, mixing with the substances excreted by the sweat glands, form a waterproof and bactericidal film that protects the epidermis from the aggressive effects of the external environment.

Another interesting property of the human skin is that it can be called an auxiliary respiratory organ: oxygen enters the body through the pores, and excess water vapor and carbon dioxide are excreted.

Also, the skin is able to absorb fat-soluble substances - this feature of the epidermis is successfully used in medicine and cosmetology, rubbing creams, ointments, oils, lotions, etc.

organ of touch

One of the important properties of the skin is its ability, thanks to a developed network of nerve fibers, to perceive sensations (heat, cold, touch), determine the shape of objects, their mechanical properties and, by sending signals to the cerebral cortex, identify them and respond accordingly.

Disease ID

The human skin is inextricably linked with the internal organs, which makes it possible to judge how healthy the body is by its condition. Studies have shown that all human organs are reflected in different areas of the skin - on the face, body, feet, hands, ears.

If any organ becomes ill, changes for the worse appear on the skin in the area of ​​its projection: it begins to peel off, polyps form, spots appear, color changes, porosity increases. Therefore, you need to pay attention to such changes and consult a doctor so that he confirms or refutes the suspicions.

Timely treatment will not only save the body from the disease in time, but also give the skin the opportunity to successfully cope with its duties: the condition of the epidermis is influenced by external and internal factors, for example, the work of the circulatory, nervous, endocrine systems. Therefore, in order for it to function properly, the coordinated work of all its systems is necessary.