Functions and pathologies of sweat and sebaceous glands. Sweat glands of the skin. Sebaceous glands of the skin
Human skin has appendages - sebaceous and sweat glands... They serve to ensure, from damage and excretion from the human body urea, ammonia, uric acid, that is, metabolic products.
The glandular epithelium is 600 times the surface of the epidermis.
Sebaceous glands under a microscope
The full development of the sebaceous glands occurs during the period of human puberty. They are located mainly on the face, head and upper back... But on the soles and palms they are not at all.
The sebaceous glands secrete sebum, which plays the role of a fatty lubricant for the epidermis and hair. Thanks to sebum, the skin softens, retains its elasticity, does not allow the development of microorganisms and reduces the effect of friction between the skin areas in contact with each other. In a day, the sebaceous glands are able to produce on average twenty grams of sebum.
They are located rather superficially - in the papillary and reticular layers. Up to three sebaceous glands are located next to each hair. Their ducts usually lead to the hair follicle and only in areas without hair release their secretion to the surface of the skin. When the function of the glands increases, the hair and skin are excessively oily. And when they are blocked acne may occur... If the functions of the sebaceous glands, on the contrary, are reduced, then the skin becomes dry.
These glands are simple in structure. alveolar having branched end sections. The secretion is allocated by holocrine type... The structure of the end sections includes two types sebocyte cells... The first type is low-specialized cells capable of mitotic division. The second type is cells that are at various stages of fatty degeneration.
The first type of cells is the upper layer of the terminal section, while inside there are cells that produce fat drops in the cytoplasm. When a lot of fat is formed, they begin to gradually shift towards the excretory duct, die and, disintegrating, turn into sebum, which then enters the hair funnel.
Another appendages of the skin - sweat glands play an equally important role in the protection of the body. Their main task is sweating.... It evaporates from the surface of the skin, thereby causing it to cool. The secretions of these glands are odorless. So the body is saved from overheating on hot days. This is the function eccrine sweat glands that are found on the skin all over the place.
There are still apocrine sweat glands that give a person his own scent. They are located in specific areas where hair is present. They are v armpits, anus, genitals and forehead.
The second function of the sweat glands is excretion of excess unnecessary substances from the body... They greatly facilitate the work of the kidneys, removing a fairly large amount of minerals through the skin. This function is performed mainly by the apocrine glands.
In structure, they are simple tubular, consist of a tubular excretory duct and the same rather long end section, which is twisted in the form of a glomerulus. These glomeruli are located deep in the reticular layer of the dermis, and the excretory ducts exit to the surface of the skin in the form of sweat pores.
Eccrine secretory cells are dark and light. Dark cells secrete organic macromolecules, while light cells predominantly release metal ions and water.
Have apocrine glands a slightly different function, it is mainly associated with the work of the gonads.
The appendages of the skin include nails, hair, sebaceous and sweat glands. The very term "appendages" should not mislead anyone, since these appendages are as important to humans as other organs.
Sebaceous glands
The sebaceous glands are located on all areas of human skin, except for the feet and palms. The structure of the sebaceous glands can be compared to grapes. The sebaceous glands are located in the upper layers of the dermis (the dermis is a dense connective tissue, which consists of strong intertwining connective tissue fibers that can contract and lengthen, which provides the skin with extensibility, strength, elasticity and elasticity). Most of the excretory ducts of the sebaceous glands open into hair follicles. Each hair, in turn, is supplied with several sebaceous glands.
In places where hair does not grow, the excretory ducts of the sebaceous glands open on the surface of the skin with a special sebaceous pore (for example, the genital area, breast nipples, nasolabial folds).
On the entire surface of human skin, there are approximately 80,000-100,000 sebaceous glands. The largest sebaceous glands are located in the mid-face, nose, chin, chest, navel, and genitals.
Sweat glands
The sweat gland is outwardly a thin tube, the inner end of which is twisted into a ball, which is located in the dermis. In this tangle, with the help of jelly cells, sweat is produced, which is removed through the excretory duct (outer end of the tube) to the surface of the skin.
There are several million sweat glands on the human body, but they are unevenly located. The maximum concentration of sweat glands is located in the armpits, groin, genitals, palms, feet, on the chest, around the navel.
Sweat glands are divided into small and large.
Small sweat glands the most numerous (up to 5 million). They are located in the deepest layers of the dermis. Their excretory ducts pass through the dermis, then the walls of the excretory canals merge with the basal layer of the epidermis. Sweat comes out in the upper stratum corneum, where the duct looks like a slit.
Large sweat glands (apocrine) also called aromatic, as they emit a secret that has a specific odor. The locations of the apocrine glands are concentrated in the armpits, genitals, nipples, anus, external auditory canal and eyelids. It is very important to keep these points in mind when caring for your skin.
Hair
Hair, as appendages of the skin, is of the most direct importance to the skin itself. The attractive appearance and health of hair is highly dependent on the condition of the person (both health status and general hygiene).
Hair has a great variety in its shape, color, length, location on the body. They are repeatedly replaced throughout a person's life. So, infant vellus hair with age is replaced by thicker hair, which is well pigmented and can acquire a completely different color (not the same as in childhood).
The hair color range (from dark black to bright white) is determined using two pigments: black-brown and yellow-red, as well as their combination, which determines the color of the hair of an adult.
The human body can grow from 30 to 150 thousand hairs. Each hair is equipped with a small muscle, which, in very low humidity (dryness), begins to contract, which causes the hair to rise (bulge). Scientists call this an atavism; this reflex is characteristic of animals.
The outer layer of the hair consists of several thinner layers, which are superimposed scales (these scales protect the inner layers of the hair from external influences).
However, the medulla plays the most important role in the structure of the hair. By the way, the fact that white hair is very thin is due to the fact that, as a rule, there is no medulla in it. Brunettes and redheads have the most brain matter in their hair. For this reason, these hairs are much thicker.
There are three types of hair in humans:
- vellus hair- their length is up to 14 mm; cover the entire body except lips, palms and soles;
- bristly hair- eyebrows, eyelashes, nose hairs, in older people in the inner ear;
- long hair- on the head, chin, armpits, pubis.
Hair has the ability to contract and stretch, it is resilient and durable, and can absorb moisture. The strength of the hair is influenced by both the general condition of the body and the environment (sunlight, hair dyeing or bleaching, perm).
Throughout a person's life, hair is in three states:
From the moment of birth to 14 years - the period of formation;
- from 15 to 50 years old - an active life of hair;
- from 50 years of age and older - hair changes occur, which can be caused by hereditary factors, human health conditions, improper hair care.
The lifespan of scalp hair can range from a few months to several years. During this period, the hair is constantly changing. Every day, a person can normally lose up to 100 hairs. Note that, subject to the normal state of human health and his environment, how much hair falls out, the same amount of hair grows again on the same day.
Hair grows more slowly during the day than at night.
Bristly hairs in the eyelashes, eyebrows, nose and ear canal have a lifespan of approximately 150 days.
Intensive hair renewal is also seasonal: in autumn - September-October; in spring - March-April.
Unfortunately, hair growth cannot be accelerated. Most hair, reaching a certain length, slows down the intensity of its growth by almost 2 times.
There is also a misconception that short hair cutting speeds up hair growth. This is not true. The hair shaft is the part of the hair that protrudes from the surface of the skin and does not have the ability to grow.
Nails
Nails are arranged according to the principle of hair. For example, if a hair is cut in half, its structure is fully consistent with the structure of the nail. Even the matrix of the nail completely matches the hair follicle.
Why does a person need nails? The main function of nails is to support the sensitive part of the fingers and protect them from mechanical damage. The structure of nails is determined by heredity, but this structure can change as a result of external factors (from the quality of nail care, the type of activity of a particular person, etc.).
Growth of nails occurs due to the division (reproduction) of root cells. The average growth of fingernails is 1-5 mm per week; on the legs -1-5mm per month.
Note that the fastest nail growth is observed on the middle fingers of the dominant hand (right-handed - on the right hand, left-handed - on the left). By the way, in men, nails grow faster than in women.
Warm weather, vigorous physical activity (playing the piano, typing on the keyboard, etc.), pregnancy (in women) stimulate the growth of nails.
Nails grow more slowly at night, in winter, during breastfeeding, with an unbalanced diet.
Scientists have not come to a single conclusion as to how the process of nail formation occurs. Most likely, the nails are formed from the epidermis, which covers part of the phalanges of the fingers. As a result of this process, which begins in the ninth week of embryonic development of the baby's fetus, the nail bed develops. Part of this bed forms the matrix from which the nail plate begins to grow.
The middle layer is freely located under the epidermis. dermis. I don’t know who gave the name to whom: dermis dermatologists or dermatologists dermis, but the connection between them is obvious.
Actually, the thickness of the dermis is from 0.5 to 5 mm, and the composition is the fibers of the connective tissue. It is this layer of the skin that is responsible for its firmness and elasticity, determines its appearance. And the most active part in this is taken by collagen fibers which are able to accumulate moisture in young skin. Over the years and under the influence of the harmful effects of the surrounding world (first of all, from the excess of ultraviolet radiation) collagen fibers become fragile, the layer of connective tissue saturated with moisture "dries up" and wrinkles appear on the skin. Therefore, it is the dermis that is the "homeland" of deep wrinkles.
Thanks to the dermis, a constant body temperature is also maintained - about 37 degrees. The dermis is full of blood and lymphatic vessels, sensitive nerve endings (receptors), which are responsible for the perception of temperature, tactile (in the form of touch) and pain. There are sebaceous and sweat glands, as well as hair roots. And around all this, smooth muscle cells are located, in places forming small bundles. Some of these bundles braid hair follicles (bags from which hair grows, like a palm tree from a tub) and are proudly called the muscles "lifting hair". Other bundles are located on the skin of the neck, forehead, dorsum of the hands and feet. In the cold, their reduction causes the appearance of "goose bumps", reducing blood flow and thereby regulating the heat transfer of the body.
But when the body overheats or physical work sweat glands are taken very diligently to excrete sweat, and in especially extreme cases, this sweat can be released about ten liters per day! It protrudes to the surface of the skin and evaporates there. The body makes a big U-F-f-f-f, the skin cools and protects our body from overheating. About 600 ml of water is excreted daily with sweat through the skin.
Unlike sweats, sebaceous glands absent in the skin of the palms and soles of the feet, because there is no hair, although ... maybe someone has hairy palms .... ;). So, near each hair follicle there are one or two sebaceous glands that secrete sebum directly into the hair follicle, which lubricates the surface of the skin and hair. These are a kind of internal "jars of cream" for lubricating the skin and it is thanks to the resulting thin fatty film that the skin is perceived as tender and soft.
Another important task of the dermis is to supply the epidermis with nutrients such as oxygen, proteins, amino acids, vitamins, minerals and trace elements. This is because the epidermis itself does not have blood vessels, and the dermis is all permeated with many tiny capillaries and therefore its nutrients are simply heaps of. Both layers are closely related to each other, but as the body ages, this connection gradually breaks down and, as a result, the epidermis does not receive enough
Sweat glands... They develop in the 3rd month of embryogenesis from the epidermis of the skin, which grows into the subepithelial mesenchyme in the form of epithelial cords. Sweat glands are subdivided into eccrine (merocrine) and apocrine. The largest number of sweat glands is located in the area of the palmar surface of the hands, face, forehead, inguinal folds, armpits, and back.
Eccrine glands are simple tubular glands. Their end sections are located deep in the reticular layer and are rolled into balls. The end sections of the eccrine glands are lined with a single-layer epithelium, which has a prismatic shape before secretion and cubic after secretion. The epithelial cells of the terminal sections are called spasmodiferocytes. Spasmodiferocytes are divided into dark and light. Dark spasmodic cells secrete organic components of sweat, light ones - electrolytes and water. The secret of sweat glands - sweat consists of 98% water, the rest is organic and inorganic solid substances. 500-600 ml of sweat is released per day. Together with sweat, bradykinin is released, which dilates the blood vessels of the skin and promotes heat transfer.
Between the basal end of spasmodiferocytes and the basement membrane, there are myoepithelial cells of a processional form. In their processes there are contractile filaments, with the contraction of which a secret is released from the spasmodiferocytes.
The excretory duct of the sweat gland, which runs in the dermis itself, is lined with two-layer cubic epithelium; when entering the epidermis, it is lined with flat epithelium, on the surface of the epidermis it opens with a sweat pore.
Apocrine sweat glands differ from merocrine in the following features; 1) finally develop during puberty; 2) functionally connected with the reproductive system (sweating increases during menstruation); 3) are located in certain places (in the area of the pubis, inguinal folds, armpits, anus, labia majora); 4) have a wide end section; 5) their excretory duct opens together with the duct of the sebaceous glands into the hair funnel; 6) secretes apocrine-type secret; 7) the secret contains more organic substances, so it has a sharper odor; 8) the cytoplasm of spasmodiferocytes is stained oxyphilically, does not contain alkaline phosphatase.
The functions of the sweat glands: 1) participation in water-salt metabolism; 2) the release of products of nitrogen metabolism, therefore, to some extent, they replace the function of the kidneys; 3) participation in thermoregulation.
Sebaceous glands... They are located near the hair root, with the exception of the outer zone of the transitional part of the lip, the glans penis, the labia minora and the nipples of the mammary glands. The sebaceous glands finally develop at the onset of puberty, belong to simple branched alveolar glands, secrete a holocrine-type secret. The terminal sections include undifferentiated, differentiating, and necrotic (disintegrating) cells. Undifferentiated cells lie on the basement membrane and are capable of mitotic division. Some of the daughter cells turn into differentiating cells, on the smooth EPS of which lipids are synthesized. As lipids are synthesized and accumulated, differentiating cells move to the excretory duct. Here they are destroyed under the influence of their own lysosomal enzymes and turn into a secret - fat. The excretory duct of the sebaceous gland is short, lined with stratified squamous epithelium, and opens into the hair funnel.
The functional significance of the sebaceous glands. During the day, the sebaceous glands of a person release about 20 g of fat, which softens the skin, facilitates friction of the contacting surfaces: when fat is broken down, fatty acids are formed that can kill microorganisms.
LESSON 1.
STRUCTURE AND FUNCTIONS OF THE SKIN.
As you know, our body consists of various organs and systems. The most superficial ORGAN is the SKIN. Yes, do not be surprised SKIN is what no real ORGAN is, the same as the heart, brain or liver. Moreover, it is the largest organ of the human body, because the total area of human skin is about two square meters, and the mass of the skin, together with subcutaneous fatty tissue, ranges from 7 to 11 kg. Behind the apparent simplicity of the skin, its complexity and multifunctionality is not immediately visible, however, in terms of the breadth of physiological functions and pathological processes that occur in the skin, it surpasses or, at least, is not inferior to other organs.
The skin is not just the border of our body with the outside world, its appearance betrays both the physical and mental state of a person. One can only admire the wisdom of nature, which created such a perfect material, because in the layers of the skin there are many different elements: cells, fibers, smooth muscles, pigments, sebaceous and sweat glands, nerve tissues with a large number of receptors, an extensive network of blood and lymphatic vessels. The skin is closely connected with all organs and systems of the body; it is an organ where all elements are constantly renewed.
The skin is made up of three layers:
These layers are shown schematically in Fig. 1.
Drawing. 1 Skin structure.
1 - epidermis, 2 - dermis, 3 - subcutaneous fatty tissue, 4 - hair, 5 - sebaceous gland, 6 - hair follicle, 7 - hair root, 8 - sweat gland, 9 - cutaneous artery, 10 - cutaneous vein, 11, 14 - nerve endings, 12 - a group of fat cells, 13 - loose connective tissue
Epidermis (cuticle).
The epidermis is composed of cells with different functions and tasks:
- keratin cells, or keratinocytes, which make up the bulk of epidermal cells,
- pigment cells, or melanocytes, which produce the pigment substance melanin in response to ultraviolet light irritation,
- immune cells that provide the body's own defenses.
All cells in the epidermis are arranged as if in layers or layers, and the thickness of these layers is not the same in different parts of the body: on the skin of the palms and soles, the layer of cells is the thickest, and on the genitals and skin of the eyelids - the thinnest. The epidermis consists of five layers: basal, prickly, granular, shiny, and horny.
The basal layer or germ layer is the deepest part of the epidermis, which is directly adjacent to the dermis. The germ layer consists of a single row of small cylindrical cells that divide vigorously and constantly, ensuring the reproduction of dying skin cells. During division, two cells are formed from one cell: one "mother" cell always remains in place, forming the basal layer itself, and the other "daughter" cell moves to more superficial layers. During migration, this cell changes significantly in shape and internal content. Having reached the thorny layer, the cell from the cylindrical one acquires a polygonal shape, thorns are formed on its surface, with the help of which the cells are connected to each other (hence the name thorny layer). Moving further, the cell flattens, its nucleus decreases in size and partially collapses, granules or grains containing a specific substance keratohyalin appear inside the cell - this is how a granular layer is formed. Keratohyalin plays the role of the cementitious base of this layer. Between the granular and stratum corneum on separate areas of the skin (palms, soles), a fifth shiny layer is observed. The cells of this layer contain a specific substance - eleidin, from which keratin, an insoluble protein, is subsequently formed.
As the cell moves from layer to layer, its gradual keratinization occurs. As a result, the uppermost layer of the epidermis is formed - the stratum corneum. It consists of horny plates or scales - completely keratinized, non-nucleated cells that constantly peel off and fall off. The scales are half composed of keratin and other water-insoluble proteins. It is due to them that the skin has a strong protective surface. The thickness of the stratum corneum depends on the rate of reproduction and advancement of keratinocytes in the vertical direction and the rate of rejection of the stratum corneum. The stratum corneum is most developed where the skin is exposed to the greatest mechanical stress (palms, soles).
The transit time of epidermal cells from the basal layer to the granular layer normally ranges from 26-42 days, and the transit time through the stratum corneum is about 14 days. The entire epidermis changes within 59-65 days. With age or under the influence of unfavorable factors, the cells of the basal layer begin to divide more slowly, as a result of which the number of new cells in the epidermis decreases, which leads to a decrease in the thickness of this layer and disruption of its functioning. In psoriasis, on the contrary, the transit time of cells from the basal layer to the stratum corneum is noticeably reduced, and therefore, on the surface of inflammatory plaques, we see abundant peeling with silvery scales.
In the epidermis, the pyrmis, in addition to keratinocytes, there are also other cells - pigment cells, or melanocytes, which, under the influence of ultraviolet rays, synthesize the pigment melanin as protection against them. Among the cells of the spiny layer, there are special cells of the immune system - macrophages. These are "guard cells" moving between the dermis and the epidermis, which are ready at any moment to absorb foreign substances that have fallen deep into the skin.
Derma (skin).
The dermis - the connective tissue part of the skin - consists of three main components:
- fibers,
- the main substance,
- few cells.
The dermis is a support for hair, nails, sweat and sebaceous glands, blood vessels and nerves. Its thickness varies from 0.3 to 3 mm. The dermis has two layers: papillary and reticular.
The upper papillary layer of the dermis protrudes into the epidermis in the form of papillae, inside which are blood and lymphatic vessels, capillaries and nerve endings. If you look closely, you can see many small grooves, ridges and lines on the surface of the skin, which, when connected, form triangles and diamonds of various sizes. All these combs and grooves are formed due to the protrusion of the skin papillae into the epidermis. This is best manifested on the palmar surface of the hand, where grooves and ridges are much more pronounced and form a complex pattern, and each person has his own individual pattern. It is this property of the papillary layer of the dermis that is used in fingerprinting (determination of fingerprints). The papillary layer consists of loose connective tissue and fine fibers. The thicker reticular layer extends from the base of the papillary layer to the subcutaneous fatty tissue, consisting mainly of bundles of thick connective tissue fibers located parallel to the skin surface. The strength of the skin depends mainly on the structure of the reticular layer, which is different in its thickness in different parts of the skin.
Subcutaneous adipose tissue (hypodermis).
Subcutaneous adipose tissue consists of loose connective tissue containing clumps of fat cells. The thickness of this layer ranges from 2 mm (on the skull) to 10 cm or more (on the buttocks). Adipose tissue plays an important role in heat regulation, being a poor conductor of heat, it protects the body from hypothermia. Subcutaneous adipose tissue contains a large amount of nutrients that are accumulated and consumed as needed. In places that have the greatest physical activity (soles and buttocks - after all, most often we walk or sit), the subcutaneous fat is thicker and resembles an elastic mat.
Appendages of the skin.
These include: nails, hair, sebaceous and sweat glands. In psoriasis, appendages of the skin are most often affected nail plates. The nail is a dense stratum corneum that well protects the underlying tissue of the nail bed from the effects of various environmental factors - mechanical, chemical, thermal, etc. The nail plate in healthy people is smooth, colorless and largely transparent, therefore, due to the translucence of superficially located small vessels (capillaries) of the nail bed, it appears pink. The nail can change color for various diseases. So, in psoriasis, the nail plate often either resembles the surface of a thimble, or is almost completely destroyed (as with a fungal infection), but in this case due to the localization of psoriatic papules under the nail bed.
Sweat glands located in the deepest layer of the dermis. They look like glomeruli, the inner walls of which are lined with glandular cells that secrete sweat. The long outlet ducts of the sweat glands open onto the surface of the skin. Together with sweat, products of mineral and protein metabolism are excreted from the body. The sweat glands are also involved in the regulation of body temperature.
Sebaceous glands are located in the skin itself and look like branched vesicles. The walls of the vesicles are composed of stratified epithelium. As the epithelium grows, its cells move closer to the lumen of the gland, undergo fatty degeneration and die. Unlike sweat glands, whose cells secrete secretions into the external environment without violating their integrity, the multilayer epithelium of the sebaceous glands is destroyed, resulting in the formation of sebum.
Hair are a kind of skin appendages and consist of two parts - a hair follicle and a hair shaft. The hair shaft is the visible part of the hair, located above the surface of the skin. The hair root is located in the dermis, in a special depression - the hair follicle. Together with the surrounding tissues, it forms a hair follicle (hair follicle). It should be noted that in patients with psoriasis, with the localization of the process on the scalp, premature hair loss may be observed, but this process is reversible. In psoriasis, inflammation on the scalp leads to trophic disorders, as a result of which hair can fall out, however, persistent atrophy of hair follicles is usually not observed and, when inflammation is stopped, hair begins to grow again.
Function of the skin.
The skin performs many important functions, without which the life of any organism would be impossible. The skin is a barrier between the human body and the environment, therefore one of the most important is protective.
Protection against mechanical stress provided by the dense stratum corneum of the epidermis, the elasticity of the skin, its elasticity and the shock-absorbing properties of the subcutaneous fat. Thanks to these qualities, the skin is able to resist mechanical stress - pressure, bruising, stretching, etc.
The skin largely protects the body from ultraviolet irradiation. Ultraviolet rays are partially blocked by the skin. Penetrating into the skin, they stimulate the production of a protective pigment - melanin, which absorbs these rays. Melanin makes the skin appear darker. Now it becomes clear why people living in hot countries have darker skin than people living in temperate climates, where sun exposure is much lower.
An important role in the protective function of the skin is played by water-fatty membrane or "mantle". It is an emulsion of oil in water or water in oil and covers the entire skin of the human body. The pH value of the water-fat mantle in different areas of the skin varies depending on the state of the sebaceous and sweat glands. Usually the "mantle" has an acidic reaction. Under the influence of various factors, the acidity of the water-fat mantle can change. The pH value is influenced by the state of the sebaceous and sweat glands, the predominance of fats or sweat on the skin surface. Humidity and air temperature also affect the water-fatty membrane. The stratum corneum and water-fat mantle are an effective barrier to various chemicals, including aggressive ones. The role of the water-lipid mantle in protection from microbes is also great.
On the surface of healthy human skin, there are usually from 115 thousand to 32 million microorganisms (bacteria, viruses and fungi) per 1 sq. see Healthy skin is impervious to germs. With the exfoliating corneous scales of the epidermis, sebum and sweat, various microorganisms and chemicals that get on the skin from the environment are removed from the skin surface. In addition, the acidic environment of the water-lipid mantle is unfavorable for the reproduction of various microbes and can contribute to the death of many of them. The ability of the skin to prevent the penetration of foreign microorganisms into the body is reduced under the influence of adverse environmental factors, with skin contamination, hypothermia, and certain diseases. If microbes enter the skin, a protective skin inflammatory response occurs in response.
In the process of vital activity of the body, heat energy is generated. At the same time, a constant temperature must be maintained in the body. The process of maintaining a constant body temperature is called thermoregulation. The skin occupies a special position in the implementation of this function of the body, because 80% of heat transfer is carried out through the skin through the emission of radiant heat energy, heat conduction and evaporation of sweat. The layer of subcutaneous fatty tissue of the skin is a poor conductor of heat, therefore it prevents excess heat or cold from coming in from the outside, and also prevents excessive loss of heat. When the ambient temperature rises, the blood vessels of the skin expand - the blood flow of the skin increases, sweating increases, the evaporation of sweat and the heat transfer of the skin to the environment increase. When the ambient temperature decreases, there is a reflex narrowing of the blood vessels of the skin, the activity of the sweat glands is inhibited, the heat transfer of the skin is noticeably reduced and the body is supercooled.
O respiratory function Skin doctors have known since the days of Leonardo da Vinci. Cutaneous respiration is carried out due to the work of sweat glands, blood vessels and nerve plexuses, which form a dense network in the dermis. Now we know that per day human skin at an ambient temperature of +30 degrees Celsius releases 7 - 9 g of carbon dioxide and absorbs 3 - 4 g of oxygen, which is about 2% of the total gas exchange in the body. A unit of skin surface absorbs more oxygen than a unit of lung tissue surface. Moreover, the skin, or rather the epidermis, completely provides itself with oxygen directly from the surrounding air.
Nerve fibers in the skin end in the form of specific formations, which are called receptors. They are designed to perceive sensations: pain, temperature, pressure. On average, 1 square centimeter of skin accounts for up to 5000 sensitive endings, 200 pain points, 12 cold points, 2 heat points and 25 pressure-sensitive points. Nerve receptors in the skin are unevenly distributed. They are especially numerous in the skin of the face, palms and fingers, and the external genitalia. The skin is a huge receptor field, millions of sensitive nerve endings of which constantly carry out direct and feedback connections with the central nervous system, playing a vital role in our perception of the world around us.
The role of the skin in metabolism , in it there is a constant exchange of carbohydrates, proteins, fats and vitamins, salts, water. These are complex processes as a result of which the body receives the nutrients it needs. In terms of the intensity of water, salt and carbon dioxide metabolism, the skin is almost as good as other organs.
Sun exposure in the epidermis Vitamin D is synthesized ... This vitamin is necessary for the absorption of calcium salts in the intestines and its absorption by the bones, which allows the body to grow and develop normally.
The skin, along with the kidneys, is a very important excretory organ that frees us from toxins and a number of harmful substances that poison the body. Excretory or excretory function the skin is carried out through the work of the sweat and sebaceous glands.
Sweating is carried out by the sweat glands and is controlled by the nervous system. The intensity of sweating depends on the ambient temperature, the general condition of the body. Sweating increases with increasing air temperature, with physical activity. Sweating decreases during sleep and rest.
An important role in the excretory function is played by the sebaceous glands, which produce sebum, which is 2/3 water, and 1/3 organic matter and some salts. Fatty and unsaponifiable organic acids and metabolic products of sex hormones are released with sebum. The maximum activity of the sebaceous glands of the skin begins at puberty and lasts until the age of 25; then the activity of the sebaceous glands decreases slightly.
Speaking about the excretory function of the skin, one cannot fail to mention that the skin secretes substances called pheromones ... These substances, through the sense of smell, are able to form sexual attraction in individuals of the opposite sex. This phenomenon is especially pronounced in animals during the mating season, however, humans also have glands capable of secreting pheromones, which plays an important role in the implementation sexual function ... In addition, there are specific nerve endings in the skin of the genitals - genital corpuscles, which also contribute to sexual sensation.