What skin structures perform the secretory function. The role of subcutaneous tissue

This complex and important organ plays a huge role in the human body. Without healthy skin unimaginably good health and appearance. What are the functions of the skin and what is its purpose, read further in the article.

What are the functions of the skin?

Main functions of the skin:

providing a protective barrier between the body and the environment, including protection from mechanical damage, radiation, chemical irritants, bacteria,

as well as the immune function of the skin,

receptor,

thermoregulatory function of the skin,

metabolic function of the skin,

resorption,

secretory,

excretory function of the skin,

respiratory.

Protective function skin

Protective function of the skin includes mechanical protection from external influences.

Mechanical protection of the skin from pressure, bruises, tears, stretching, etc. is due to the density of the epidermis capable of repair, the elasticity and mechanical stability of the fibrous structures of the connective tissue of the dermis, as well as the buffering properties of subcutaneous fatty tissue. The most important role in the implementation of the protective function of the skin belongs to the epidermis. The strength of its important component - the stratum corneum - is ensured by proteins and lipids, and elasticity - by proteins, lipids and low molecular weight products of the breakdown of keratohyalin, which bind and retain stratum corneum water. In contrast, the dermal-epidermal junction in human skin is relatively weak point. This explains the slight damage to the surface collagen of the papillary dermis in bullous dermatoses. The skin's resistance to rupture in response to blunt force is primarily associated with the dermis. In this case, the elasticity of the skin is due to the straightening of collagen fibers along the tension axis, and the return to its original state is due to elastic fibers. Violation of the structure of collagen fibers and skin function leads to excessive extensibility of the skin. The ability of the skin to compress with the formation of a pit when pressed into the skin small item is caused by the outflow of intercellular adhesive substance between the collagen fibers of the dermis.

The skin is protected from radiation exposure primarily by the stratum corneum, which blocks infrared rays completely and ultraviolet rays partially. Depending on the wavelength and biological effect on the body, they are distinguished: UV-A (320–400 nm), UV-B (290–320 nm) and UV-C (200–290 nm). UVB acts predominantly at the level of the epidermis and is the main cause sunburn, premature aging of the skin, and subsequently – precancer and skin cancer. UVA can penetrate deep into the dermis, have the least erythematogenous ability, but can provoke increased sensitivity to the sun, and also play an important role in skin aging.

Protective function of the skin and its barriers

The protective function of the skin has two barriers that prevent the damaging effects of UV radiation:

melanin barrier in the epidermis

proteoglycan barrier concentrated in the stratum corneum.

The action of each of them is aimed at reducing its absorption by DNA and other cell components. Melanin is a large polymer capable of absorbing light in a wide range of waves from 200 to 2400 nm and thereby protecting cells from the harmful effects of excessive insolation. Melanin is synthesized by melanocytes in the basal layer of the epidermis and transferred to adjacent keratinocytes in melanosomes. The synthesis of melanin is also influenced by the melanostimulating hormone of the pituitary gland. The protective function of tanning is associated with an increase in the number of functional melanocytes, an increase in the number of synthesized melanosomes and the rate of transfer of melanosomes to keratinocytes, as well as with the transition of the product of histidine metabolism in the epidermis - urocanic acid from the trans-isomer to the cis-isomer. Chronic exposure to sunlight over time leads to thickening of the epidermis, the development of solar elastosis and keratosis, precancer or skin cancer.

The normal stratum corneum of the skin provides protection from chemical irritants mainly through keratin. Only chemicals that destroy the stratum corneum, as well as those soluble in the lipids of the epidermis, gain access to the deeper layers of the skin and then can spread throughout the body through the lymphatic and blood vessels.

Human skin serves as a natural and permanent habitat for numerous microorganisms: bacteria (Staphylococcus epidermidis diphteroidus, Propionbacterium acnes, Pityrosporum, etc.), fungi and viruses, since its surface contains many fatty and protein ingredients that create favorable conditions for their livelihoods. At the same time, it is impermeable to a variety of bacteria and pathogenic microorganisms, which are especially rare on its surface.

Bactericidal function of the skin

The bactericidal function of the skin, which gives it the ability to resist microbial invasion, is due to the acidic reaction of keratin, the unique chemical composition of sebum and sweat, and the presence on its surface of a protective water-lipid mantle with a high concentration of hydrogen ions (pH 3.5–6.7). The low molecular weight fatty acids it contains, primarily glycophospholipids and free fatty acids, have a bacteriostatic effect that is selective for pathogenic microorganisms. A mechanical obstacle to the invasion of pathogenic microorganisms into the skin, in addition to the integrity of the stratum corneum, is ensured by their removal with scales, secretions of the sebaceous and sweat glands. Per 1 cm2 of skin healthy person There are from 115 thousand to 32 million different microorganisms, most of which belong to the permanent bacterial flora, which plays an important role in the antimicrobial protection of the skin and mucous membranes from pathogenic microorganisms. The skin's ability to resist microbial invasion decreases when the skin is traumatized. Moreover, the same microorganisms different nature injuries can cause different pathological processes. Thus, group A streptococci cause erysipelas after mechanical trauma to the epidermis or disruption of its integrity due to the intertriginous form of mycosis of the feet, while streptococcal impetigo usually occurs at the site of scratching in atonic dermatitis.

The bactericidal functions of the skin are also reduced under the influence of skin pollution, hypothermia, overwork of the body, and insufficiency of the gonads; they are also reduced in patients with skin diseases and in children. In particular, in children infancy this is due to the tenderness and looseness of the stratum corneum of the epidermis, the morphological inferiority of elastic and collagen fibers, as a result of which children's skin is easily exposed to mechanical, radiation, thermal and chemical irritations. The survival of pathogenic microbial flora on the surface of the skin is also facilitated by the slightly alkaline or neutral environment of the water-lipid mantle with an insufficient amount of low molecular weight free fatty acids. The penetration of microbes through the upper layers of the epidermis is accompanied by the migration of leukocytes from the vessels and their penetration into the dermis and epidermis with the formation of a protective inflammatory reaction.

Secretory function of the skin

Secretory function carried out by the sebaceous and sweat glands Sebum is a complex fatty substance of semi-liquid consistency, which contains free lower and higher fatty acids, bound fatty acids in the form of cholesterol esters and other stearins and high molecular weight aliphatic alcohols and glycerin, small amounts of hydrocarbons, free cholesterol , traces of nitrogen and phosphorus compounds. The sterilizing functions of sebum are due to its significant content of free fatty acids. The function of the sebaceous glands is regulated by the nervous system, as well as hormones of the endocrine glands (genital, pituitary and adrenal cortex). On the surface of the skin, sebum, mixing with sweat, forms a thin film of water-fat emulsion, which plays an important role in maintaining normal physiological state skin.

Excretory function of the skin

Excretory function combined with the secretory function of the skin and is carried out by the secretion of sweat and sebaceous glands. The amount of organic and inorganic substances, mineral metabolism products, carbohydrates, vitamins, hormones, enzymes, microelements and water they secrete depends on gender, age, and topographical features of the skin. With insufficient liver or kidney function, the excretion through the skin of substances that are usually removed in the urine (acetone, bile pigments, etc.) increases.

Respiratory function of the skin

The respiratory function of the skin is to absorb oxygen from the air and release carbon dioxide. Skin respiration increases with increasing ambient temperature, during physical work, during digestion, development of acute inflammatory processes in the skin, etc.; it is closely related to redox processes and is controlled by enzymes and the activity of sweat glands rich in blood vessels and nerve fibers.

Deficiency of skin functions

Skin dysfunction is a condition associated with severe loss or impairment of skin function (similar to failure of other systems - cardiovascular, respiratory, renal, hepatic, etc.). Skin failure consists of loss of normal control over thermoregulation, water-electrolyte and protein balance of the body, loss of mechanical, chemical and microbial barriers. Insufficiency of skin functions requires special treatment as an emergency condition and, in addition to thermal burns, can occur with Lyell and Stevens-Johnson syndromes, pustular psoriasis, erythroderma, pemphigus vulgaris, graft-versus-host disease, and epidermolysis bullosa.

The skin performs many functions, the main of which are the following: protective, immune, receptor, thermoregulatory, metabolic, resorption, secretory, excretory, respiratory.

Protective function of the skin represents protection of the skin from mechanical external influences: pressure, bruises, ruptures, stretching, radiation exposure, chemical irritants, etc. The epidermis protects the skin from mechanical damage, and the degree of protection depends on the thickness and strength of its stratum corneum. Collagen and elastic fibers protect the skin from injuries with blunt objects, the first of which stretch along the tension axis, and the second return the skin to its original state. Excessive skin elasticity is caused by a violation of the structure of collagen fibers. The epidermis also protects the skin from radiation exposure, completely blocking infrared rays and partially blocking ultraviolet rays. There are two “protective” barriers in the epidermis: the melanin barrier, which is responsible for increasing the number of functional melanocytes and, as a consequence, the appearance of tanning during prolonged insolation, and the protein barrier located in the stratum corneum of the epidermis. A healthy stratum corneum of the epidermis protects the skin from many chemical irritants, with the exception of those that can destroy the stratum corneum or dissolve in the lipids of the epidermis, gaining access to the deeper layers of the skin. The skin protects the body from the penetration of bacteria due to the unique chemical composition of sebum and sweat, the presence of a protective water-lipid mantle on its surface, as well as the presence of microorganisms that belong to the permanent bacterial flora and prevent the penetration of pathogenic microorganisms. Accordingly, when the skin is injured, hypothermia, overwork of the body, etc., its ability to resist the penetration of microbes is impaired.

Immune function of the skin . T lymphocytes present in the skin recognize exogenous and endogenous antigens; Largehans cells deliver antigens to the lymph nodes, where they are neutralized.

Receptor function of the skin – the ability of the skin to perceive pain, tactile and temperature stimulation. The following types of functional units that transmit nerve impulses are distinguished: mechanoreceptors, thermoreceptors. There are also pain receptors, but they respond only to stimulation (thermal, mechanical, chemical), the degree of which exceeds the pain threshold.

Stimulation of cold receptors occurs when exposed to temperatures 1-20 degrees lower than normal skin temperature (34 degrees); thermal - at a temperature of 32-35 degrees. Temperatures above 45 degrees are outside the limits pain threshold human and is therefore perceived not by thermal receptors, but by nociceptors. Nociceptors are responsible for the perception of pain and itch; Among them, mechanical, temperature and polymodal (i.e., perceiving several types of stimuli) nociceptors are distinguished.

Thermoregulatory function of the skin lies in its ability to absorb and release heat. Increased heat transfer occurs due to the expansion of skin vessels along various reasons(for example, an increase in ambient temperature), and a decrease in heat transfer, respectively, with a narrowing of blood vessels. Heat is generated by radiation, conduction, convection and evaporation, with heat loss through sweat generated by the skin being the most effective method.

Metabolic function of the skin combines a group of private functions: secretory, excretory, resorption and respiratory activity. Resorption function is the ability of the skin to absorb various substances, including medications. This is the advantage of local medications over oral ones, because the use of the former does not depend on side factors (for example, the acidity of the environment and the contents of the stomach), and there is no possibility of overdose. The secretory function is carried out by the sebaceous and sweat glands of the skin, secreting sebum and sweat, which, when mixed, form a thin film of water-fat emulsion on the surface of the skin. This film plays an important role in maintaining the physiologically normal condition of the skin. The excretory function is closely related to the secretory function and is carried out by the secretion of sweat and sebaceous glands, secreting organic and inorganic substances, mineral metabolism products, carbohydrates, hormones, enzymes, etc. Respiratory function is the ability of the skin to absorb oxygen and release carbon dioxide, which increases with increasing ambient temperature, during physical work, during digestion, and the development of inflammatory processes in the skin.

Some skin diseases can cause impairment of some skin function (so-called “skin deficiency”), this is an emergency condition and requires special treatment. To such possible violations include loss of normal control over thermoregulation, water-salt and protein balance of the body, loss of mechanical, chemical and microbial barriers.

The secretory function of the skin is carried out by the sebaceous and sweat glands. Through the release of sweat, heat is transferred to the external environment. Heat environment, increased muscle work contribute to an increase in sweating, which, however, can increase at normal temperatures under the influence of neuropsychic factors (excitement, fear, etc.).

Increased sweating can be caused by certain medicinal substances (pilocarpine), stimulating the endings of the secretory nerves; other substances (atropine) reduce sweating.

There is a certain relationship between urination and sweating: sweating to a certain extent can compensate for insufficient kidney function.

Sweat- liquid with a density of 1.004 - 1.008, similar in composition to urine. The sweat reaction is usually slightly acidic, but in some skin diseases it can become alkaline. Sweat secreted by apocrine glands is alkaline.

Sweat consists of 98% water and 2% dense residue, consisting of small quantities table salt, urea, uric acid and other substances (creatinine, cholesterol, acetic acid and etc.). Medicinal substances (mercury, bromine, arsenic, etc.) can be released with sweat.

Sebaceous glands secrete sebum, which serves to lubricate the stratum corneum, maintaining its integrity and impermeability to water. Sebum also prevents penetration through the skin chemical substances and microorganisms. During the day, about 20 - 30 g of sebum is secreted. It contains fats, fatty acids, soaps, cholesterol, phosphates and chlorides.

The skin of the face, back, chest, and scalp produces more sebum than other areas; therefore, in skin diseases associated with impaired sebum secretion, lesions often appear in these places.

Sebum secretion is to a certain extent associated with sexual function and occurs more intensely during the period of greatest sexual activity, significantly decreasing in old age. Functional status nervous system has a great influence on the intensity of sweat and sebum secretion, reducing or enhancing the activity of the corresponding glands.

Resorption function of the skin

The ability of intact healthy skin to absorb, i.e. the resorption function of the skin, is small.

Aqueous solutions of various substances do not penetrate the skin, but substances soluble in fats ( salicylic acid, sulfur, etc.), can penetrate through intact epidermis. Various types of damage to the epidermis - mechanical, chemical, as well as inflammatory conditions of the skin in skin diseases increase the skin's ability to absorb various substances used for medicinal purposes (salicylic acid, tar, chrysarobin, etc.), which should be kept in mind when prescribing these drugs to patients .

Respiratory function of the skin

The skin plays some part in respiratory function, or in the exchange of gases, although to a much lesser extent than the lungs. The human body receives 1/180 of the oxygen it absorbs through the skin and releases 1/90 of carbon dioxide. Gas exchange through the skin thus accounts for only 1% of gas exchange in the entire body. Water vapor is released through the skin 2-3 times more than through the lungs.

Metabolic function of the skin

Skin plays big role in the body’s metabolism, which primarily relates to water, mineral (potassium, sodium, calcium, etc.) and carbohydrate metabolism. It is known that the water content in the skin reaches 70%.

In the regulation of general, including water, metabolism, the skin belongs special role. A significant amount of sodium chloride, calcium chloride, etc. can be deposited in the skin. The skin also takes part in nitrogen metabolism. Metabolic processes in the skin are regulated primarily by the neuroendocrine system. Violations of vitamin metabolism in the body often manifest themselves in the form of various pathological skin conditions.

"Skin and venereal diseases"
A.A.Studnitsin, B.G.Stoyanov

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Leather- This is one of the human organs that perform a protective role and a number of biological functions. Skin covers the entire human body, and depending on height and weight, its area ranges from 1.5 to 2 m2, and its weight ranges from 4 to 6% of a person’s weight (excluding the hypodermis).

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

Skin functions

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

Main functions of the skin:

• mechanical protection- skin prevents soft fabrics from mechanical impact, radiation, microbes and bacteria, penetration of foreign bodies into tissues.
• UV protection- under the influence of solar treatment, melanin is formed in the skin as a protective reaction to external adverse effects (during prolonged exposure to the sun). Melanin causes the skin to become temporarily darker dark color. A temporary increase in the amount of melanin in the skin increases its ability to block ultraviolet radiation (retains more than 90% of radiation) and helps neutralize free radicals formed in the skin when exposed to the sun (acts as an antioxidant).

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

Skin structure

The skin consists of three main layers:

• epidermis(epidermis)
• dermis(corium)
• hypodermis(subcutis) or subcutaneous fatty tissue

In turn, each layer of skin consists of its own individual structures and cells. Let's look at the structure of each layer in more detail.

Epidermis

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

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

The epidermis does not contain blood vessels, so the intake nutrients from the inner layers of the skin to the epidermis is happening due to diffusion(penetration of one substance into another) tissue(intercellular) liquids from the dermis layer into the layers of the epidermis.

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

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

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

Skin acidity pH is 3.8-5.6.

How do human skin cells grow?

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

The entire process from the birth of a cell to its exfoliation from the surface of the skin takes an average of 2-4 weeks.

Skin permeability

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

Color of the skin

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

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

The effect of cosmetics on the skin

All cosmetical tools and procedures, intended for skin care, act mainly only on the top layer of skin - epidermis.

Dermis

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

The dermis consists of two layers:

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

Hypodermis (subcutaneous fat tissue)

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

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

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

Cellulite occurs during inflammatory processes in the hypodermis that occur during certain diseases.

Video: Skin structure

• Total area skin adult 1.5 - 2 m2
• One square centimeter of skin contains:

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

• Under active load or high external temperature, the skin through the sweat glands can secrete more than 3 liters of sweat per day
• Thanks to the constant renewal of cells, we lose about 10 billion cells per day, this is a continuous process. During our lifetime, we shed about 18 kilograms of skin with dead cells.

Skin cells and their function

Skin consists of large number various cells. To understand the processes occurring in the skin, it is good to have a general understanding of the cells themselves. Let's look at what different structures are responsible for (organelles) in a cage:

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

• cytoplasm- a semi-liquid substance that fills the internal space of the cell. Cellular metabolic processes occur in the cytoplasm
• ribosomes- necessary for the synthesis of proteins from amino acids according to a given matrix based on genetic information embedded in RNA (ribonucleic acid)
• vesicle- small structures (containers) inside the cell in which nutrients are stored or transported
• Golgi apparatus (complex)- this is a complex structure that is involved in the synthesis, modification, accumulation, and sorting of various substances inside the cell. It also performs the functions of transporting substances synthesized in the cell through the cell membrane and beyond its boundaries.
• mitochondria- the energy station of the cell, in which the oxidation of organic compounds occurs and the release of energy during their decay. Generates electrical energy in the human body. Important component cells, changes in activity over time lead to aging of the body.
• lysosomes- necessary for the digestion of nutrients inside the cell
• intercellular fluid filling the space between cells and containing nutrients

Accessory apparatus – glands: sweat, sebaceous, mammary

The skin is rich in glands. According to the nature of the secretion they secrete, they are divided into sweat, sebaceous and milky. The number of sweat glands is about 2-2.5 million; they are simple tubular glands. They lie in the deepest layer of the skin itself, their end sections curl, forming glomeruli. A long excretory duct passes between or through the papillae and penetrates the epidermis. There are two types of sweat glands: apocrine (develop only during puberty) and merocrine. The secretion of the sweat glands - sweat - consists of 98% water and 2% organic and inorganic substances (mineral salts, urea, uric acid). The sebaceous glands are simple alveolar glands, located on the border between the papillary and reticular layers of the dermis. The gland consists of an alveolar terminal section with a diameter of 0.2-2.0 mm and a short excretory duct that opens into the hair follicle. The terminal sections are formed by poorly differentiated dividing cells in a state of fatty degeneration. Poorly differentiated cells located on the basement membrane divide and, gradually enriched with droplets of fat, move towards the excretory duct. Cells saturated with fat die, forming sebum, which, being bactericidal, not only lubricates the hair and epidermis, but also protects it from microbes. The mammary (mammary) gland (tatta) is located on the anterior surface of the large pectoral muscle. In the center of the gland there is a pigmented nipple (10-15 milk pores open on its surface), surrounded by a pigmented isola. There are many myocytes in the skin of the nipple and areola, and when they contract, the nipple tenses. The mammary gland is altered sweat gland. In an adult woman, it consists of 15-20 lobes, between which there is fatty and loose fibrous connective tissue. Each lobe is a complex alveolar gland, the excretory flow of which is directed radically to the nipple. Before reaching the nipple, the duct expands and forms the lacteal sinus.

In humans, breathing through the skin is insignificant. At rest, a person absorbs 3-6.5 g of oxygen per day through the skin and releases 7.0-28.0 g of carbon dioxide. Skin respiration increases with rising air temperature, increasing oxygen content in the air, during muscle work and digestion. At an air temperature of 40 C, oxygen absorption through the skin is 2.5-3 times greater than at normal temperature. During muscular work at an air temperature of 18-20 C, oxygen absorption through the skin is 1.5-2 times greater than at rest. The more you sweat and the faster blood circulates through the skin, the more intense the skin gas exchange. Thickening of the epidermis reduces gas exchange. Breathing through the skin different areas It varies in different areas of the skin: on the torso and head it is more intense than on the arms and legs. The skin protects the body from harmful effects various external stimuli. The stratum corneum significantly reduces pressure, friction and impact. In areas of the body that are repeatedly irritated, the stratum corneum becomes thicker and calluses appear. On defense internal organs Subcutaneous tissue plays a large role in protecting the body from pressure and bruises due to its mobility and elasticity. The role of skin collagen fibers, which resist tearing 43 times more than elastic fibers, is especially important in the mechanical protection of the body. The skin pigment melanin plays a significant role in protecting the skin from electromagnetic waves. Melanin synthesis is activated by ultraviolet and x-rays. This pigment strongly absorbs ultraviolet rays, so the skin pigmentation protects against harmful action on the body of sun rays. The skin has a significantly greater resistance to electric current than the tissues located underneath it; the stratum corneum has the greatest resistance due to the air content between its cells. The skin is damaged by acids, alkalis, salts and poisons in sufficient concentration; It resists the action of acids much more than alkalis. The ability of the skin to neutralize alkalis depends on the intensity of the functions of the sebaceous and sweat glands. Protection against alkalis also depends on the degree of permeability of the stratum corneum. Keratin protein, located in the stratum corneum, is insoluble in alcohol and ether, resistant to alkalis and acids, and protects the body well from many chemicals. The skin also has sterilizing and bactericidal properties - the ability to destroy microbes. The bactericidal properties of the skin depend on the intensity of metabolism, the content of lactic and free fatty acids in sebum and sweat.

Animal ethology is one of the areas in the study of animal behavior, dealing mainly with the analysis of genetically determined (hereditary, instinctive) components of behavior and problems of its evolution. The term was introduced into biology in 1859 by the French zoologist I. Geoffroy Saint-Hilaire and indicates that biology deals with species-specific characteristics of animal behavior.

Development of E. The study of holistic animal behavior in natural conditions has a long history. In the works of naturalists of the 18th-19th centuries. huge descriptive (German scientist G. Reimarus, French scientists J. L. Buffon and J. A. Fabre) and partly experimental (French zoologist F. Cuvier) material was collected, which made it possible to identify and clearly define the category of instinctive behavior (See Instinctive behavior ). The development of ecology was directly influenced by the works of Charles Darwin. The numerous facts he collected about animal behavior in natural conditions made it possible to distinguish the main categories of behavior - Instinct , learning ability and basic reasoning ability. Darwin also pointed out that the signs of an animal's behavior, like the signs of its structure, are characterized by heredity and variability. Using instincts as an example, Darwin showed possible ways of forming behavioral traits in the process of natural selection. The formation of ethological ideas was directly influenced by the studies of the English scientist D. Spalding, the American scientist C. O. Whitman and the German scientist O. Heinroth, in which it was experimentally shown that some forms of behavior have an innate basis, constancy of expression and species specificity. As an independent scientific direction, different from the physiological and psychological schools of behavior research (Zoopsychology, Behaviorism, etc.), ecology took shape in the 30s. 20th century Its recognized founders are the Austrian zoologist K. Lorenz and the Dutch zoologist N. Tinbergen. The theoretical works of Lorenz (1931-37) summarized the main views of his predecessors - the American scientists C. Whitman and W. Craig, the German scientists J. Uexküll and O. Heinroth and a number of scientists of other directions (the French scientist J. Loeb, the American scientists G. Jennings, W. McDougall, etc.). In the works of Lorenz, Tinbergen and their followers (the Dutch scientist G. Behrends, the German scientists W. Wikler and P. Leyhausen, and many others), the foundations of the theory of instinctive behavior were laid. The period of flourishing and recognition of the ideas of classical psychology continued (mainly in Europe ) from the mid-30s. until the end of the 50s. 20th century In the USA, ethological concepts initially provoked quite strong opposition from animal psychologists and behaviorists. The further evolution of ethological views occurred, on the one hand, under the influence of criticism from physiologists and psychologists, and on the other hand, due to the active perception by the new generation of ethologists of the advanced ideas of ecology, neurophysiology and a number of other sciences. As a result, in the 60-70s. There is a tendency towards transformation of the original concepts of the Lorenz-Tinbergen school and towards their synthesis with the provisions of other behavioral and biological disciplines. E. gradually loses the character of an isolated discipline and becomes part of the emerging synthetic science of behavior. E. arose mainly on the basis of field zoology (mainly ornithology) and evolutionary studies and has close and constantly growing contacts with physiology, ecology, population genetics, and behavioral genetics. E's connections are strengthening. with experimental psychology. The traditional object of study for E. is the behavior of an animal in its natural environment. Full description species-specific behavior of animals (using objective methods of recording - filming, tape recordings, timing) is the basis for compiling a list (ethogram) of behavioral acts characteristic of the species. Ethograms of animals of different species are subjected to comparative analysis, which underlies the study of the evolutionary aspects of their behavior. For this purpose, ethologists use a wide variety of species from invertebrates to apes. Some ethologists began to apply these methods to the study of human behavior. When studying the behavior of animals in the process of individual development of the organism, ethologists also use laboratory methods. One of them is raising an animal in isolation from the action of certain environmental factors. This method was a necessary step in the study of the ontogenesis of behavior. In Russia, starting from the end of the last century, various studies of animal behavior were carried out, some of which were close to E. in their ideas and methods (V. A. Vagner, A. N. Promptov). Despite this, the views of the traditional ethological school did not receive timely recognition and development in the USSR. This situation changed in the 60s. 20th century, which was greatly facilitated by the translation of books by foreign ethologists. In the USSR in several scientific centers Ethological research is being developed based on a synthesis of ecological-physiological and physiological-genetic methods. At the Institute of Evolutionary and Ecological Morphology of Animals named after. A. N. Severtsov conducted various studies of the behavior of mammals and birds in terms of elucidating the features of ontogenesis, the structure of community mechanisms of communication, mainly acoustic and chemical (V. E. Sokolov and others). At Moscow University, along with research into the structure of communities and acoustic signaling (N.P. Naumov and others), research is being conducted on the elementary rational activity of animals (L.V. Krushinsky). The centers for studying the genetics of animal behavior are Leningrad University and the Institute of Physiology named after. I. P. Pavlova (work started by M. E. Lobashov and others), Institute of Cytology and Genetics of the Siberian Branch of the USSR Academy of Sciences (D. K. Belyaev and others). Research into animal behavior is carried out in a number of other institutions, including nature reserves.

Basic provisions of traditional E. The basis for the concept developed by ethologists was data on the peculiarities of the formation of a number of behavioral acts in ontogenesis. Some of them represent a fixed stereotypical sequence of actions, and usually they are characteristic of all individuals of a given species and are routinely performed in a certain period of ontogenesis without special training. Such acts of behavior were called by Lorenz innate instinctive movements, or hereditarily coordinated acts. Many instinctive movements appear only in response to certain stimuli, called key (or releasers); these stimuli are recognized by animals even at the first presentation without any individual experience. For example, a red spot on the abdomen of a male stickleback triggers an aggressive response from other males of the same species. The mechanism that ensures the execution of a motor reaction under the action of the corresponding key stimulus was called the “innate implementing mechanism.” A special group consists of stimuli, the recognition of which requires a specific type of learning - Imprinting. IN in this case the stimulus will be effective for an adult animal only if it was presented to this animal during a certain “sensitive” period of early postnatal (after birth) ontogenesis. Subsequently, it was shown that such “sensitive” periods are characteristic of certain types of learning, for example, during the formation of song in birds. The study of key stimuli and imprinting has played an important role in understanding the mechanisms of animal communication (See Animal Communication). It was shown what in means. to a certain extent, it is ensured due to key stimuli - certain features of external appearance and coloring, characteristic ritual body movements (see Ritual) and species-specific sound signals, which, without any preliminary training, cause appropriate reactions from other individuals. These ideas were reflected in the hypothesis proposed by Lorenz and then detailed by Tinbergen about the internal mechanisms of an instinctive behavioral act, according to which, under the influence of a number of external and internal factors (hormones, temperature, etc.), “action energy” accumulates in the corresponding nerve centers , specific to a certain impulse (hunger, thirst, etc.). Its increase above a certain level leads to the manifestation of the search phase of the behavioral act, which is characterized by wide variability in execution both in a given individual and in different representatives one type. It consists of an active search for stimuli, the action of which can satisfy the impulse that has arisen in the animal. When the appropriate stimuli are found, the innate realizing mechanism is activated and the final act is carried out. With increased accumulation of “energy of action,” the final act can be carried out “spontaneously,” i.e., without key stimuli (“idle” reaction). This second phase is characterized by species specificity, stability of execution and a high degree of genetic determination. This is what the so-called innate instinctive actions, or hereditary coordination. In general, this Lorenz-Tinbergen hypothesis is largely outdated, but its development and testing served as the basis for the contact of E. with physiology. The identification of the category of innate instinctive actions made it possible to apply the comparative method to the study of animal behavior and move on to the study of the evolutionary aspects of their behavior. Availability or absence data common features in representatives of different systematic groups made it possible to assess the degree of their phylogenetic relationship and clarify the systematic position of individual species. For example, not a single morphological feature characterizes representatives of the order Pigeonidae so clearly as the sucking movements they make when drinking. In addition, comparative studies have made it possible to get an idea of ​​the evolution of various types of behavior, the adaptive significance of individual acts of behavior and the factors under the influence of which they were formed in the process of evolution. Ethologists of the Tinbergen school made a great contribution to the study of the evolutionary aspects of animal behavior. Their studies made it possible to describe the patterns of the action of natural selection on behavioral traits. A comparison of instinctive actions in representatives of closely related species, as well as the study of intraspecific variability of behavior, formed the basis for studying its role in microevolutionary processes. Lorenz was one of the first to compare the behavior of various representatives of the duck family. Long-term studies of the role of behavior in the differentiation of a population have shown that it influences its group composition and thereby the fate of the genotypic changes that occur in it. This indicates that behavior is one of significant factors microevolutionary processes. The identification of the category of instinctive actions as elementary units of behavior opened up the possibility of considering the question of the genotypic foundations of behavior, the combination and correlation of environmental influences and Genotype in the ontogenesis of individual behavioral traits. The concept “innate” was used in economics to designate acts of behavior, the development of which is completely determined genotypically and does not require special education or training for its formation, in contrast to traits “acquired” in the process of development under the influence of certain environmental factors. Ethologists viewed a holistic behavioral act as a complex interweaving of congenital and acquired components. The current state and problems of ecology. The main areas in which traditional ethological views remain of paramount importance are comparative ecology, as well as the field of studying methods of organizing communities and communication of animals (the so-called . socioethology). When studying the organization of animal communities, the attention of many scientists is drawn to questions of animal population dynamics, factors controlling the formation, structure and number of groups of individuals in different species, the evolution of methods of organizing communities, their evolutionary continuity and interconnection. One of the areas of modern economics is the study of human behavior (Tinbergen, the German scientist J. Eibl-Eibesfeldt, the English scientist J. Crook, and others); These studies are a direct continuation and development of the ideas of Darwin, who in his work “The Expression of Emotions in Man and Animals” laid the foundation for the study of the biological foundations of human behavior. At the same time, ethologists consider the main task to be the objective registration and accurate description of certain instinctive actions and reactions of a person to biologically significant stimuli using methods and approaches that have been successfully tested in ecology in the study of animal behavior. These studies represent an important stage in the development of evolutionary ideas, since they contribute to the destruction of idealistic ideas about the barrier separating humans as a biological species from animals. The development of ethological research is of great importance for many aspects of human activity. For example, due to the increasing anthropogenic impact on the environment, an in-depth study of animal behavior in a natural environment is necessary to successfully solve problems of protection, reconstruction and rational use of fauna. Knowledge of animal behavior is of great importance for a number of areas Agriculture. As the work of the Soviet scientist D.K. Belyaev and his colleagues showed, the selection of fur-bearing animals based on behavioral traits can have a profound impact on a number of economically important traits. Studying the specifics of group behavior in agriculture. acquires animals special meaning in connection with the introduction of industrial methods of keeping and breeding into livestock farming.