What is skin histology. Histological structure of the skin

SKIN HISTOLOGY

The skin is made up of three layers: epidermis, dermis and hypodermis.

EPIDERMIS- the outer part of the skin, represented by stratified squamous keratinized epithelium. Its thickness varies from 0.05 mm on the eyelids to 1.5 mm on the palms. About 95% of the cells of the epidermis are keratinocytes (derivatives of the ectoderm), which, as they differentiate, move from the basement membrane towards the surface of the skin.

The epidermis consists of 5 layers: basal, spiny, granular, shiny and horny.

The basis of the epidermis is its innermost basal layer (stratum basale syn. germinativum), consisting of 1 row of small cylindrical cells located in the form of a palisade and called basal keratinocytes. They have large dark-colored basophilic nuclei and a dense cytoplasm containing many ribosomes and bundles of tonofilaments. Cells are connected to each other by intercellular bridges (desmosomes), and are attached to the basement membrane by hemi-desmosomes. Basal keratinocytes synthesize an insoluble protein, from which keratin filaments are formed, which form the cytoskeleton of keratinocytes and are part of desmosomes and hemidesmosomes. The mitotic activity of the cells of the basal layer (1 mitosis per 400 cells) ensures the formation of the overlying structures of the epidermis.

Immediately above the basal layer, keratinocytes increase in size and form a spiny layer (stratum spinosum), consisting of 3-6 (sometimes 15) rows of spiny keratinocytes, gradually flattening towards the surface of the skin. The cells of this layer have a polygonal shape and are also interconnected by desmosomes. In the cells of this layer, there are more tonofibrils than in basal keratinocytes; they are concentrically and densely located around the nuclei and are woven into desmosomes. In the cytoplasm of spiny cells there are numerous rounded vesicles of various diameters, tubules of the cytoplasmic reticulum, and melanosomes. The basal and spiny layers are called the Malpighi germ layer, since mitoses are found in them, and in the spiny one - only with extensive damage to the epidermis. Due to this, the formation and regeneration of the epidermis occurs.

The granular layer (stratum granulosum) consists of 2-3 rows of cells that have a cylindrical or cubic shape near the prickly layer, and diamond-shaped closer to the surface of the skin. Cell nuclei are distinguished by noticeable polymorphism, and inclusions are formed in the cytoplasm - keratohyalin grains. In the lower rows of the granular layer, the biosynthesis of filaggrin, the main protein of keratohyalin granules, occurs. It has the ability to cause the aggregation of keratin fibrils, thus forming the keratin of the horny scales. The second feature of the cells of the granular layer is the presence in their cytoplasm of keratinosomes, or Odland bodies, the contents of which (glycolipids, glycoproteins, free sterols, hydrolytic enzymes) are released into the intercellular spaces, where a lamellar cementing substance is formed from it.

The shiny layer (stratum lucidum) is visible in areas of the most developed epidermis, i.e., on the palms and soles, where it consists of 3-4 rows of elongated, poorly contoured cells containing eleidin, from which keratin is subsequently formed. There are no nuclei in the upper layers of cells.

The stratum corneum (stratum corneum) is formed by completely keratinized non-nuclear cells - corneocytes (horny plates), which contain the insoluble protein keratin. Corneocytes are connected to each other with the help of interpenetrating outgrowths of the membrane and keratinizing desmosomes. In the superficial zone of the stratum corneum, the desmosomes are destroyed and the stratum corneum is easily torn off. The thickness of the stratum corneum depends on the rate of reproduction and movement 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 subjected to the greatest mechanical stress (palms, soles).

The epithelium of the mucous membranes, with the exception of the back of the tongue and the hard palate, is devoid of the granular and stratum corneum. Keratinocytes in these areas in the process of migration from the basal layer to the surface of the skin initially appear vacuolated, mainly due to glycogen, and then decrease in size and eventually undergo desquamation. Keratinocytes of the oral mucosa have no a large number of well-developed desmosomes and many microvilli, the adhesion of cells to each other is carried out by means of an amorphous intercellular gluing substance, the dissolution of which leads to separation of cells.

Among the cells of the basal layer are melanocytes - dendritic cells that migrate in the embryonic period from the neural crest to the epidermis, epithelium of the mucous membranes, hair follicles, dermis, pia mater, inner ear and some other tissues. They synthesize the pigment melanin. Melanocyte processes spread between keratinocytes. Melanin accumulates in basal keratinocytes over the apical part of the nucleus, forming a protective shield against ultraviolet and radioactive radiation. In persons with dark skin, it also penetrates into the cells of the prickly, up to the granular, layer.

In humans, there are two main classes of melanins: eumelanins - produced by ellipsoid melanosomes (eumelanosomes), giving the skin and hair brown and black color; pheomelanins - produced by spherical melanosomes (pheomelanosomes) and causing hair color from yellow to red-brown. Skin color does not depend on the number of melanocytes, which is approximately constant in people of different races, but on the amount of melanin in one cell. Sunburn after ultraviolet irradiation is due to the acceleration of melanosome synthesis, melanization by melanosomes, transport of melanosomes into processes and transfer of melanosomes to keratinocytes. A decrease in the number and activity of follicular melanocytes with age leads to progressive graying of the hair.

In the lower part of the epidermis, there are white process Langerhans cells - intraepidermal macrophages that perform an antigen-presenting function for T-helpers. The antigen-presenting function of these cells is carried out by capturing antigens from the external environment, processing them and expressing them on their surface. In combination with their own HLA-DR molecules and interleukin (IL-1), antigens are presented to epidermal lymphocytes, mainly T-helpers, which produce IL-2, which in turn induces the proliferation of T-lymphocytes. Thus activated T cells are involved in the immune response.

In the basal and spiny layers of the epidermis, there are Greenstein cells - a type of tissue macrophages, which are antigen-presenting cells for T-suppressors.

The epidermis is separated from the dermis by a basement membrane, 40–50 nm thick, with uneven contours that follow the relief of the epidermal cords penetrating into the dermis. The basement membrane is an elastic support that not only firmly binds the epithelium to the collagen fibers of the dermis, but also prevents the growth of the epidermis into the dermis. It is formed from filaments and hemidesmosomes, as well as plexuses of reticular fibers that are part of the dermis, performs barrier, exchange and other functions, and consists of three layers.

DERMIS – connective tissue part of the skin three components: fibers, ground substance and a few cells.

The dermis is a support for the appendages of the skin (hair, nails, sweat and sebaceous glands), blood vessels and nerves. Its thickness varies from 0.3 to 3 mm. There are two layers in the dermis: papillary and reticular.

The thin upper papillary layer (stratum papillare), consisting of an amorphous structureless substance and thin connective tissue (collagen, elastic and reticular) fibers, forms papillae that lie between the epithelial ridges of spiny cells. A thicker mesh layer (stratum reticulare) extends from the base of the papillary layer to the subcutaneous fatty tissue; its stroma consists mainly of bundles of thick collagen fibers arranged parallel to the surface of the skin. The strength of the skin depends mainly on the structure of the mesh layer, which is different in its power in different areas. skin. The dermis is relatively poor in cells. In the papillary layer there are cellular elements characteristic of loose connective tissue, and in the reticular layer - fibrocytes. Small lymphohistiocytic infiltrates may occur around vessels and hairs in the dermis. In the dermis there are histiocytes, or sedentary macrophages, accumulating hemosiderin, melanin, and detritus that has arisen during inflammation, as well as mast cells or tissue basophils, localized mainly around blood vessels, synthesizing and releasing histamine and heparin. In some areas of the papillary layer, smooth muscle fibers are located, mainly associated with hair follicles (muscles that lift hair).

HYPODERMIS – subcutaneous adipose tissue. Consists of a loose network collagen, elastic and reticular fibers, in the loops of which the slices are located adipose tissue- accumulations of large fat cells containing large drops of fat.

The thickness of the hypodermis varies from 2 mm (on the skull) to 10 cm or more (on the buttocks). The hypodermis is thicker on the dorsal and extensor surfaces, thinner on the ventral and flexor surfaces of the limbs. In places (on the eyelids, under the nail plates, on the foreskin, labia minora and scrotum), it is absent.

Blood and lymphatic vessels of the skin. Arteries, having entered the dermis from a wide-loop fascial network, branching and anastomosing, form a deep (subdermal) and superficial (on the border between the epidermis and dermis) parallel networks. From the first depart terminal arterioles, going to the skin papillae (one for several papillae). In the papilla there is a capillary in the form of a lady's hairpin, rising to the top of the papilla with an arterial knee and passing into a thicker venous knee. From the capillary loops, blood flows into the venules, which form a superficial fine-loop network just below the papillae. A little deeper is the second subpapillary network of venules, parallel to the first. The third venous network is located in the reticular layer of the dermis. In the hypodermis there is a large-mesh deep venous network. It lies parallel to the deep arterial plexus, with which it is connected by many arterio-venular anastomoses, which play an important role in the regulation of blood flow, thermoregulation, sweating, etc.

In the dermis, there are two horizontal networks of lymphatic vessels: superficial and deep. Blind outgrowths (papillary sinuses) extend from the superficial network into the papillae of the dermis. From the deep network, lymphatic vessels originate, which, gradually becoming larger and anastomosing with each other, form plexuses at the border with subcutaneous fatty tissue.

Nervous apparatus of the skin is a large receptor field. Sensitive (afferent) nerve fibers come from skin receptors, are part of the cranial and spinal nerves. Perceiving irritations from the external environment, they are divided into mechano-, chemo-, thermo- and nocireceptors (pain).

There are free (branched) and encapsulated skin receptors. Free nerve endings are the most functionally important; they are represented in all parts of the dermis by short and long branches, accompanied by Schwann cells. The source of free nerve endings are unmyelinated nerve fibers. Most of these fibers are tactile Merkel cells. Unmyelinated nerve endings in the papillary dermis perceive sensations of pain, itching, and temperature. Encapsulated nerve endings, consisting of an inner bulb and a capsule surrounding it, perform specific functions. So, Krause flasks, which are mechanoreceptors, are found in the subpapillary zone of the dermis of the hands and shoulders. forearms, feet and legs; lamellar bodies of Vater-Pacini - in the smooth skin of mainly fingers, nipples of the mammary glands; tactile bodies of Meissner - in the skin of the palms, especially fingers, lips, eyelids, genitals, in the nipples of the mammary glands, in the papillae of the tongue.

Numerous autonomic nerve fibers enter the skin, innervating blood vessels, smooth muscles and glands. Moreover, pulpy and non-fleshy, sensitive and autonomic nerve fibers can be in the same trunk.

Large nerve trunks entering the dermis from the subcutaneous fatty tissue form a deep nerve plexus at the border with the subcutaneous fatty tissue and a superficial nerve plexus in the lower part of the papillary dermis. From here, individual nerve fibers and their small bundles are sent to the papillae of the dermis, blood vessels, skin appendages and the epidermis. Approaching the epidermis, thin nerve fibers lose their myelin sheath and penetrate into the intercellular tubules of the basal and spinous layers in the form of bare axial cylinders. Myelinated (pulp) nerve fibers (axons) are 5 times more common than unmyelinated (pulpless).

Skin appendages include sebaceous and sweat glands, hair and nails.

Sebaceous glands(glandulae sebaceae) are found all over the skin, with the exception of the palms and soles, and are usually in close contact with the hair follicles, where their ducts open. Only in the skin of the red border of the lips, the glans penis, the inner layer of the foreskin, the coronary sulcus (the glands of the foreskin are the tysonian glands), the labia minora, as well as in the nipple and areola of the mammary gland, along the edge of the eyelids (the glands of the cartilage of the eyelids are meibomian glands) sebaceous glands open directly on the surface of the skin. Each follicle has one or more sebaceous glands. Larger glands are observed in persons 17-25 years old and are located in the face (nose, cheeks), chest and back. By structure, the sebaceous glands belong to simple alveolar glands and have a holocrine type of secretion, in which the formation of a secret is associated with cell destruction.

Most sebaceous glands are spherical or ovoid in shape. Their secretory sections consist of 1-2 lobules surrounded by connective tissue. The lobules consist of acini or alveoli that open into a common duct. The acini of the sebaceous gland are devoid of gaps; they are compact formations consisting of concentrically located cells lying on the basement membrane. In the alveoli of the sebaceous gland there are poorly differentiated prismatic cells capable of mitotic division and constituting the outermost layer of the glandular epithelium, as well as cells at different stages of fatty degeneration. The cells that form the outer germ layer have large nuclei that occupy most of the cytoplasm. By mitosis, they form cells located inside the alveoli, having a round or polygonal shape and a cytoplasm with drops of fat. In fully differentiated cells, lipid droplets occupy the entire cytoplasm, and the nuclei shrivel, become hyperchromic, and die. As fat accumulates, the cells move towards the excretory duct and disintegrate. The short excretory duct of the sebaceous glands is lined with stratified epithelium, directly passing into the epithelium of the outer epithelial sheath of the hair follicle.

sweat glands(glandulae suboriferae) are simple tubular glands. Their number in human skin is very large (up to 3.5 million). They can be found in any part of the skin, with the exception of the skin of the glans penis, the inner leaf of the foreskin, the outer surface of the labia minora. Most of the human sweat glands belong to the eccrine (merocrine) glands, the secretion of which is not accompanied by even a partial death of the secerating cellular elements. Apocrine (holocrine) glands are found only in certain areas (in the armpits, around the anus, on the skin of the pubis and areola, as well as in the skin of the labia majora), the secretion of which is associated with partial cell death.

Eccrine (merocrine) sweat glands consist of a secretory section represented by a glomerulus surrounded by a basement membrane and lined with a single-layer epithelium, the cells of which, at rest and participating in secretion formation, are cylindrical in shape and contain secretory granules with a diameter of 1-2 microns, and after secretion they flatten . On the basement membrane, in addition to secretory, there are also myoepithelial cells containing a large number of myofilaments in the cytoplasm. contracting under the influence of nerve impulses, which is associated with secretion. The excretory duct of the eccrine sweat gland ends in the basal layer of the epidermis, and then continues in the form of a corkscrew-shaped tortuous fissure, opening on the surface of the skin with a sweat pore.

Apocrine (holocrine) sweat glands are deeper, have a large size, and their excretory ducts, similar to the excretory ducts of the eccrine sweat glands, flow into the sebaceous hair follicles.

Hair. Each hair (pilus) has two parts: the shaft and the root. The shaft is the part of the hair that protrudes above the surface of the skin. The hair root is embedded in the dermis and sometimes reaches the subcutaneous fatty tissue. The root is surrounded by epithelial root sheaths and is immersed in a connective tissue bag - the dermal sheath, which make up the hair follicle.

The hair follicle has a cylindrical shape and opens on the surface of the skin with a kind of extension - a funnel in which the hair shaft is placed. At the border of the upper and middle thirds of the follicle, the excretory duct of the sebaceous gland opens into it. The epithelial part of the hair follicle is formed in the 2-3rd month of intrauterine life by immersion in the connective tissue of the dermis of the processes of the integumentary epithelium. However, only in the region of the funnel, the epithelium retains all its layers. Below the funnel, the epithelium lining the follicle consists only of cells of the basal and spinous layers. This part of the epithelial wall of the follicle is called the outer root sheath. As it deepens and approaches the bulb, the outer root sheath passes into the growth layer of the epidermis and the cells acquire the ability to keratinize. The outer root sheath serves as a source of hair and follicle cells for hair regeneration and skin wound healing.

The connective tissue bag of the hair follicle consists of soft fibrous connective tissue with a large number of elastic and reticular fibers. The latter, on the border with the outer root sheath, form a basement membrane. Hair follicles are entwined with a large number of nerve fibers.

The deepest expanded part of the hair root is called hair follicle; Bottom part bulbs - matrix - consists of undifferentiated pluripotent cells, characterized by a very high mitotic activity and providing hair growth. Here are melanocytes capable of synthesizing melanin. At the base of the follicle, the hair (dermal) papilla protrudes into the hair follicle, containing vessels that feed the hair follicle.

The hair follicle consists of polygonal cells, constantly multiplying and containing a large amount of pigment. Bulb cells form both the hair itself and several rows of cells located between the hair root and the outer root sheath, forming an internal root sheath that is interrupted at the top of the follicle, usually at the level of the sebaceous gland duct. It consists of three layers: the cuticle of the internal vagina is located inside, the granular layer of Huxley and the pale layer of Henle lie outside of it.

In the hair root, the medulla, cortex, and cuticle can be distinguished. The medulla is determined only in long hair and consists of one or more layers of polygonal cells containing remnants of the nucleus and pigment. They originate from a stem cell located directly above the papilla and differentiate as they move upward. The cortical substance, representing the bulk of the hair, consists of one or more layers of cells that differentiate from the cambial cells of the bulb, located lateral to the cambial cells of the medulla: as they differentiate, these cells lengthen in the vertical direction; the cortical substance, formed from spindle-shaped horn elements, contains a large amount of pigment. The hair cuticle adjacent to the cortical substance consists of 6-10 layers of cells (horny plates), located in a tile-like manner and not containing pigment. The cuticle of the hair root, connecting with the cuticle of the inner root sheath, creates a strong bond between the hair and the walls of the hair follicle.

The hair root without a sharp boundary passes into its shaft, in which all processes of differentiation are completed. The shaft contains a cortical substance and a cuticle; the medulla in thick hair disappears at the level of the funnel. Approximately at the level of the middle of the follicle to the connective tissue bag under acute angle the muscle that raises the hair is attached. Its other end is woven into the fibrous framework of the dermis. When the muscle contracts, not only the erection of the hair occurs, but also the secretion of the sebaceous glands is squeezed out. The sebum that has fallen on the surface of the skin, having a low thermal conductivity, prevents heat loss.

Nails. Nail (unguis) is a horny plate covering the back surface of the distal phalanx of the fingers. It is located on the nail bed. Distinguish between the body and the root of the nail. The body of the nail - its visible part, has a pink color due to translucent capillary blood. Behind and from the sides, it is covered with skin folds - nail rollers.

The roller, arcuately covering the proximal part of the nail, forms a thin horny - supraungual plate (eponychium). The part of the body of the nail, adjacent to the root and having the appearance of a white-colored crescent, is called the hole of the nail. The free edge of the nail (margo liber) protrudes forward. The backmost part of the nail - the root of the nail (radix unguis) - goes deep under the nail fold. The epidermal cells of the proximal part of the nail bed, located under the root of the nail, are called the nail matrix. Due to the matrix, the nail grows in length. Matrix cells of epidermal origin, characterized by larger sizes and light homogeneous cytoplasm, are called onychoblasts. The lower cells of the matrix proliferate, due to which the nail grows and thickness; the upper cells of the matrix differentiate into the stratum corneum of the nail. The nail consists of a dense compact horny mass containing 89% solid keratin, 10% water and about 1% fat. The outer surface of the nail is smooth, the inner ~ uneven due to the formation of horny protrusions and grooves, due to which the nail is tightly adjacent to the nail bed. The growth rate of nails is on average 0.5-1 mm per week. Renewal of the entire nail plate occurs in 170-230 days. Nails grow faster on the hands than on the feet.

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Melanin is synthesized from tyrosine under the influence of catalytic enzymes - tyrosinase and DOPA oxidase and is transferred to the intercellular space through exocytosis, from where it is phagocytosed by keratinocytes. Melanogenesis with the help of melanocyte-stimulating hormone is controlled by the pituitary gland. Copper ions, vitamin C, adrenaline and norepinephrine, thyroid and gonadal hormones also participate in its process. The color of the skin and the degree of its protection from radiation depend on the amount of melanin in keratinocytes, and not on the amount of melanocytes themselves, the synthesis of melanin in which increases under the influence of ultraviolet radiation.

3. Merkel cells are tactile neuro-endocrine cells located in the basal and spiny layers of the epidermis, the outer layers of the epithelium of the hair follicle and some mucous membranes. They are somewhat larger than keratinocytes, have a rounded or elongated shape, contain an elongated and slightly segmented nucleus. In their cytoplasm, there are cytokeratin filaments and neuroendocrine granules specific for these cells with a diameter of 100-200 nm.

The granules contain a complex of neuropeptides (meth-inkephalin, nerve growth factor, vasointestinal polypeptide, bombesid, substance P, endorphins). Merkel cells connect with keratinocytes

are formed with the help of desmosomes, and with nerve endings in the zone of their lower pole, they form formations resembling synapses. In the area of these formations, neuroendocrine granules are concentrated in the cytoplasm, and there is a synaptic gap of 50 nm in size between the cell plasma membrane and nerve endings. Some Merkel cells are free and not associated with nerve fibers.

4. Langerhans cells- dendritic cells of monocytic origin. They belong to the system of phagocytic mononuclear cells and are tissue macrophages. These cells are located both in the basal and in the lower rows of the spinous layer of the epidermis. Their nuclei are segmented and have 1-2 medium-sized nucleoli. The cytoplasm of cells is light and contains many organelles, among which there are special structures - the so-called Birbeck granules in the form of a tennis racket, ranging in size from 30 nm in width to 200 nm in length. The role of these granules has not been fully established, but it is known that they accumulate epidermal chaylon, which suppresses the proliferation of keratinocytes. Langerhans cells have numerous processes, with the help of which they are connected to each other and to neighboring keratinocytes, forming a characteristic branching network. The processes of the lower layer of cells penetrate the dermis.

Discipline: Histology | comment

1. general characteristics skin. skin functions.
2. Embryonic sources of development of the skin and its derivatives.
3. Histological structure epidermis and dermis of the skin.
4. The structure of the glandular derivatives of the skin (sweat and sebaceous glands).
5. Blood supply and innervation of the skin. Nerve endings of the skin.

GENERAL CHARACTERISTICS OF THE SKIN AS AN ORGAN:
In humans, the surface area of the skin is about 1.5-2 m2 (depending on height, sex, age). The weight of the skin (without subcutaneous fat) is about 5% of the total body weight, and with subcutaneous fat - 16-17%.
The skin is a complex organ that is the outer covering of the body, and therefore primarily performs protective functions:
- protection against mechanical influences;
- protection against radiation effects (from infrared to UV light);
- protection against chemicals;
- protection against bacterial influences;
- participates in immune protection;
- possesses electroresistance;
- respiratory function (up to 2% of gas exchange - through the skin);
- absorption function (absorption of substances);
- excretory function (slags of nitrogen metabolism are partially excreted through the sweat glands; with kidney pathology, this function is enhanced;
- participation in thermoregulation (20% of heat is given off by sweat evaporation Õ surface cooling; heat release by radiation);
- participation in water-salt metabolism (through sweat glands; per day up to 500 ml in comfortable conditions, up to 10 liters in hot weather or physical activity);
- participation in fat metabolism (subcutaneous adipose tissue - fat depot);
- participation in vitamin metabolism (vitamin D synthesis under UV exposure;
- skin - a huge receptor field;
- is a blood depot (thanks to the rich vascular network, 1 liter is deposited).
Even a simple enumeration of functions shows the importance of this body. Therefore, it is not without reason that the doctor, when examining a patient, pays great attention to the skin (color, temperature, turgor, humidity, smell, etc.), because these signs can be used to judge the state of many internal organs and the body as a whole. For example: color (cyanosis indicates hypoxia, as a symptom of a disease of the cardiovascular system or respiratory system; pallor is a disease of the cardiovascular system or blood system; jaundice is a disease of the liver); puffiness is a disease of cardio-vascular system or kidney; smell (mouse smell - phenylketonuria; smell of acetone - in diabetes).

Embryonic sources of development.
The skin develops from 2 main sources:
1. Ectoderm ® epidermis (stratified squamous keratinized epithelium) and its glandular (sweat, sebaceous and mammary glands) and horny derivatives (hair and nails).
2. Dermatomes (part of somites) ® skin itself or skin dermis.
In addition to the ectoderm and dermatomes, mesenchyme is involved in the laying of the skin (participates in the laying of the skin dermis, vessels and muscles that raise the hair are formed) and evicted cells from the ganglionic plate, differentiating into skin melanocytes.

Histological structure of the skin.
In the skin, the surface part is distinguished - the epidermis and the dermis of the skin (skin itself) - the connective tissue basis of the skin.
The epidermis is a stratified squamous keratinized epithelium, in its composition contains 5 cellular differons:
- The main differon: differon of epitheliocytes (keratinocytes), consists of stem cells, mitotically dividing keratinocytes, keratinocytes accumulating keratohyalin, horny scales. In addition, keratinocytes under the influence of UV light synthesize vitamin D (antirachitic vitamin), which is involved in bone mineralization. ; Keratinocytes during their life cycle gradually move in the direction from the basement membrane to the surface of the epidermis, while multiplying, accumulating the horny substance keratin - they become keratinized and exfoliate from the surface of the epidermis. Keratinocytes derived from a common ancestral stem cell are arranged in a single vertical column and are called the epidermal proliferative unit (EPU). In the center of the EPE is a Langerhans cell surrounded by 20-50 keratinocytes located in all layers of the epidermis in one vertical column. In EPE, Langerhans cells regulate the proliferation and differentiation of keratinocytes with the help of chalons;
- Langerhans cells (synonymous - white process epitheliocytes), make up 3% of epidermal cells - irregular shape, process cells of hematogenous origin, have mitochondria and lysosomes, perform the immunological functions of epidermal macrophages (represent A-genes to lymphocytes), regulate the proliferation and differentiation of keratinocytes with the help of kalons, cleave the cementing substance with the help of lipolytic enzymes of lysosomes and promote desquamation of horny scales from the surface of the epidermis;
- melanocytes - pear-shaped cells with processes. The cytoplasm contains ribosomes, the Golgi lamellar complex, and melanosomes. In melanocytes, from the amino acid tyrosine, under the influence of the tyrosinase enzyme, DOPA (dihydrooxyphenylalanine) is formed, and from it, under the influence of the DOPA oxidase enzyme, the melanin pigment is formed, which protects the underlying tissues from UV radiation. Melanin synthesis is regulated by pituitary melanotropic hormone and is enhanced by UV exposure. A congenital inability to produce melanin is albinism.
- Merkel cells - large polygonal cells with short outgrowths. The dendrites of sensitive neurocytes of the spinal nodes approach the basal surface of these cells and form nerve endings - i.e. Merkel endings are formed, which are mechanoreceptors of the skin. In addition, Merkel cells are APUD cells and synthesize hormone-like substances (VIP, bombesin, histamine, enkephalins, etc.);
- lymphocytes, represented mainly by a subpopulation of T-lymphocytes; together with Langerhans cells provide immune protection.
The epidermis has 5 layers:
1. Basal layer - contains all 5 types of cells:
a) keratinocytes - up to 90% of the cells of the layer; prismatic cells, the cytoplasm is basophilic and contains keratin tonofilaments. Mitotic figures are often observed - they actively divide and provide renewal of the epithelium, daughter cells rise to the overlying layers. Among basal epitheliocytes there are stem cells;
b) melanocytes - up to 10% of the cells of the layer;
c) Langerhans cells;
d) Merkel cells;
e) lymphocytes.
2. Spiny layer - consists of keratinocytes (most of the cells of the layer), Langerhans cells (epidermal macrophages) and lymphocytes. Keratinocytes of this layer are polygonal cells with short outgrowths - spines; in the cytoplasm, the synthesis of keratin is enhanced, and from them tonofilaments are formed, which are collected in bundles - tonofibrils, which provide the elasticity and strength of the cell (cytoskeleton). These cells actively divide and participate in the regeneration of the epidermis. Langerhans cells and lymphocytes are found in the spinous layer - they provide immune protection.
3. Granular layer - consists of 3-4 rows of flattened keratinocytes that have lost the ability to divide. Keratin, filaggrin, involucrin and keratolinin are synthesized in the cells of the granular layer. Filaggrin in the form of an amorphous mass sticks together keratin tonofibrils, the decay products of the nuclei and organelles of keratinocytes are mixed with them - as a result, a complex compound keratohyalin is formed (in the preparation they look like large basophilic granules). Involucrin and keratolinin under the plasma membrane of cells form a protective protein layer.
4. Shiny layer - represented by 3-4 rows of flat dead cells. Cell boundaries are not visible, the nuclei are destroyed, the cytoplasm is completely filled with a mass (elaidin - the old name), consisting of longitudinally arranged keratin fibrils glued together with filaggrin. This mass (elaidin) strongly refracts and reflects light, so the layer shines - hence the name of the layer.
5. The stratum corneum - consists of horny keratin plates (scales), having the form of flat polyhedrons, arranged on top of each other in the form of coin columns or columns. The scales have a thick, durable shell of keratolinin protein, inside they are filled with longitudinally arranged keratin fibrils, interconnected by bisulfide bridges and glued together by an amorphous keratin matrix. The scales are interconnected by a cementing substance rich in lipids (gives hydrophobicity). The enzymes of lysosomes of Langerhans cells and keratosomes destroy the bonds between the scales and are exfoliated from the surface of the scales.
Topographic features of the structure of the epidermis of the skin.
1. The thickness of the epidermis differs in different parts of the skin - from 0.03 mm (on the head) to 1.5 mm (skin of the fingers).
2. The severity of individual layers of the epidermis differs, up to the absence of individual layers.
The nutrition of the epidermis is carried out diffusely, through the basement membrane due to the vessels of the dermis of the skin.
The dermis of the skin consists of 2 layers - papillary and reticular layers.
1. Papillary layer - in the form of papillae protrudes into the epidermis, which increases the surface area of contact with the epidermis. This makes it easier to get nutrients into the epidermis. The papillary layer determines the pattern on the surface of the skin. Moreover, this skin pattern is strictly individual and genetically encoded - which is used in forensic medicine and forensic science to identify a person (dactyloscopy). In addition, the genetic determinism of the skin pattern is used in the diagnosis of certain hereditary diseases (dermatoglyphics).
The papillary layer of the dermis histologically consists of loose fibrous connective tissue, contains many blood capillaries and nerve endings (mechano-, thermo- and pain receptors). The papillary layer provides nutrition to the epidermis, is the supporting basis of the epidermis.
The reticular layer of the dermis of the skin - histologically it is a dense, unformed fibrous connective tissue: there are many randomly arranged collagen fibers, between them there are fibroblasts and fibrocytes. The mesh layer provides mechanical strength to the skin.

Glandular derivatives of the skin - sweat, sebaceous and milky (see the lecture "Women's reproductive system”) glands.
The embryonic development of these glands is similar - epithelial strands grow from the ectoderm into the underlying mesenchyme: secretory sections are formed from the distal end of these strands, and excretory ducts form from the proximal part.
Sweat glands are simple, tubular, unbranched. They have a secretory (terminal) section and an excretory duct. The secretory section is located in the deep layers of the reticular layer of the dermis, it is a tube that twists strongly and forms a glomerulus. The wall of the secretory section consists of cuboidal or cylindrical secretory cells, which are externally covered by process myoepithelial cells. Myoepithelial cells have contractile proteins and help expel sweat into the excretory ducts. There are apocrine and merocrine (eccrine) sweat glands.
Morphofunctional differences between apocrine and merocrine sweat glands

	Apocrine sweat glands	Merocrine sweat glands
	The cytoplasm of the cells of the terminal section is oxyphilic	The cytoplasm of the epithelial cells of the terminal sections is weakly basophilic
	End sections larger 150-200 microns	End sections are smaller
	Type of secretion apocrine	Type of secretion merocrine
	Localized in the genital area, armpits	Localized in all other areas of the skin
	Start functioning at puberty	Functioning from birth
	Composition of sweat: water, salts and a significant amount of protein (when decomposed, they emit a specific smell)	Composition of sweat: water, salts and few proteins
	The excretory duct has a straight course and opens into the hair funnel	The excretory duct has a corkscrew-shaped course and opens independently from the hair
	Function: in animals - signal - to identify individuals of the opposite sex), in humans, the value has lost	Function: participation in thermoregulation, in water-salt metabolism, excretory, creates a bactericidal environment, neutralizes acids and alkalis

The sebaceous glands of the skin are simple alveolar branched in structure.
The secretory sections lie in comparison with the sweat glands more superficially - on the border of the papillary and reticular layers of the dermis; have the form of sacs - alveoli and consist: in the peripheral part there are stem and poorly differentiated cells with weakly basophilic cytoplasm. As they move towards the lumen of the secretory section, cells (sebocytes) lose their ability to divide, accumulate fat and die in the lumen of the end section, are destroyed, releasing accumulated sebum, i.e. secretion type - holocrine. The excretory duct of the sebaceous glands opens into the funnel of the hair. The function of the sebaceous glands is to secrete sebum for:
- grease for the epidermis and hair;
- softens the skin, gives elasticity;
- gives the skin hydrophobic (water-repellent) properties, protects against maceration with water;
- creates a bactericidal environment on the surface of the skin.
During puberty, under the influence of sex hormones, the secretion of the sebaceous glands increases, and sometimes so much that the fat does not have time to stand out on the surface of the skin and accumulates in the secretory sections. Stretching the walls of the alveoli. This is often accompanied by a local infection - the so-called acne is formed.

Skin blood supply. The skin is richly supplied with blood. There are 2 arterial plexuses:
1. Deep arterial plexus (on the border of the reticular layer of the dermis with subcutaneous adipose tissue), their branches provide nutrition to the subcutaneous adipose tissue and the reticular layer of the skin with sweat, sebaceous glands and hair roots.
2. Superficial arterial plexus (at the border of the reticular and papillary dermis), from this plexus branches extend towards the papillary layer, which break up into loop-type capillaries that feed the epidermis (diffusely, through the basement membrane) and participate in heat transfer.
Skin veins form 3 plexuses.
Thanks to such an abundant blood supply to the skin, it performs the functions of a blood depot (up to 1 liter), and participates in thermoregulation.

skin innervation. The skin receives both somatic and autonomic innervation. From the vegetative department nervous system sympathetic and parasympathetic nerve fibers enter the skin, which act as antagonists and jointly regulate the functions of skin vessels, smooth muscle cells and glands.
Somatic innervation in the skin is represented by the terminal sections of the dendrites of sensitive pseudo-unipolar neurocytes of the spinal nodes. The dendrites of these neurocytes form sensitive receptors in the skin. They are divided into 2 groups - free nerve endings and encapsulated nerve endings.
I. Free nerve endings - mainly formed from non-myelinated nerve fibers.
1. Free unmyelinated nerve endings. They lie in the papillary layer of the dermis, are receptors of 3 types:
a) mechanoreceptors (touch, pressure, vibration);
b) thermoreceptors;
c) pain receptors.
2. Part of the fibers pass through the basement membrane into the epidermis and form free thermo-, mechano- and pain receptors in the basal and spinous layers.
3. Some unmyelinated nerve fibers, after passing through the basement membrane of the epidermis, form the terminal disc on the basal surface of the Merkel cells. those. form Merkel endings - also mechanoreceptors.
II. encapsulated nerve endings.
1. Fater-Pacini bodies (or lamellar nerve endings) - according to their function, mechanoreceptors, they respond to pressure and vibration. Localized in the dermis and subcutaneous adipose tissue. In the body of Vater-Pacini, the axial cylinder of the nerve fiber ends with a club-shaped thickening and is surrounded by a "core" - flattened, modified lemmocytes concentrically surrounding the axial cylinder; the core is outside covered with a thin connective tissue capsule.
2. Meissner's bodies - are found in the skin of the fingers, palms and soles. Localized in the papillary dermis. In these bodies, the dendrite branches many times like a bush. The branches of the bush are in the form of a spiral; the bush is surrounded by concentrically located modified lemmocytes, outside there is a thin connective tissue capsule. Function - tactile receptors.
3. Ruffini bodies - located in the deep layers of the dermis and in the subcutaneous fatty tissue, especially in the skin of the sole. They are rounded formations, in the center of the bodies the sensitive nerve fiber branches many times in the form of a bush. The ramifications of the nerve fibers are surrounded and intertwined with collagen fibers, the connective tissue capsule is thin on the outside. Function - mechanoreceptor, react to tension and displacement of collagen fibers in the surrounding connective tissue.
4. Krause end flasks. In the center of the flask there are 1 or several nerve fibers ending in club-shaped thickenings, on the outside there is a weakly expressed connective tissue capsule. Function - mechanoreceptor.
Due to the abundance of sensitive receptors, we can consider the skin as a kind of sensory organ or a huge receptor field, through which the body receives operational information about the state environment and quickly adapts to these conditions. In addition, the skin is innervated according to the segmental type, i.e. each segment of the spinal cord simultaneously innervates certain internal organs and certain areas of the skin (Zakharyin-Ged zones), and within this segment there are connections between the nerve pathways innervating the internal organs and innervating the skin area. Therefore, acting on the skin with various stimuli, we can also affect the internal organs innervated from the same segment of the spinal cord. Many methods of reflexology are based on this, including oriental ones. unconventional methods treatment - acupuncture, moxibustion, acupressure.

LEATHER AND MPS

GENERAL COVER #1

General cover. Its morpho-functional characteristics. Sources of development. The structure of the skin and its derivatives - skin glands, hair, nails. Age-related sex characteristics of the skin.

General cover - leather,

Protective

Depot of blood

Reception

COVER COMPONENTS: epidermis, dermis and subcutaneous fat.

DEVELOPMENT:

STRUCTURE:

EPIDERMIS- Stratified squamous keratinized epithelium. At the heart of keratinization

LAYERS:

BASAL:
- Langerhans cells - intraepidermal macrophages.
- Lymphocytes - protection
- Melanocytes -
- Merkel cells -
- stem cells - regeneration (3-4 weeks
SPIKED - keratinocytes round shape, gradually lose their ability to replicate (synthesize) DNA, but they synthesize mRNA for the synthesis of keratins. Fibrils gather around the nucleus. Cells synthesize keratosomes - lipid structures limited by the membrane, which then undergo exocytosis, and after the granules are released outside the cell.
GRANULAR - keratinocytes lie in 3-4 rows, flattened, contain keratohyalin granules.

The composition of the granules:

Thin fibrillar mass - represented by a histidine-rich fraction of proteins
Amorphous component - corresponds to the cysteine-rich fraction

BRILLIANT: destruction of the nucleus and organelles occurs. The granules change: the amorphous component of the granules forms the peripheral layer, and the fibrillar component is located in the center of the cell.

HORN: Highly differentiated, flattened cells. It occupies an area equal to 9-10 cells of the basal layer, between the cells there are lipids that protect the skin from drying out. Keratinization - the transformation of living cells capable of dividing into dead horny scales.

DERMIS:

Papillary layer - formed by loose connective tissue, determines the pattern on the surface of the skin.
NET LAYER - dense irregular connective tissue, collagen fibers lie parallel and oblique to the surface of the skin, forming a network that gives the skin strength.

FEATURES: the presence of skin pigment - located in the dermis as part of dermal melanocytes; melanocytes in the epidermis itself are of neurogenic origin. The ratio of epithelial cells and melanocytes is 10:1.

SKIN GLANDS:

F-II:

thermoregulation
Protection
Selection

Sweat glands: divided into merocrine (eccrine) and apocrine (the secret is rich in proteins), as well as glands that secrete earwax (protection).

By structure: simple tubular

SEBALS: lie near the hair, open into the upper 1/3 of the hair. Simple alveolar branched.

HAIR: develops at the 3rd week of embryogenesis, when the epidermis grows into the dermis in the form of strands, forming hair follicles from which hair grows.

Hair types: long (head, beard, mustache), bristly (eyebrows, eyelashes), fluffy (others).

The hair root lies in the hair follicle, which consists of: the inner epithelial sheath (a derivative of the hair follicle), the outer epithelial sheath (develops from the germ layer of the epidermis), the hair follicle (loose connective tissue). The hair ends with a hair follicle, into which the hair papilla is embedded. The bulb is a matrix where cells divide and move upwards - keratinization.

Actually hair: medulla (cells of a polygonal shape, lie in the form of coin columns, contain pigment), cortical substance (keratinization processes proceed intensively and solid keratin is formed, consisting of horny scales), cuticle (cylindrical cells, then pass into horny scales, which do not contain pigment), muscle elevating hair.

NAILS: develop on the 3rd month of embryogenesis. First, the nail bed appears, and from it the nail, it is formed by the time of birth. The nail is a horny plate lying on the nail bed, which in turn is represented by the epithelium and the underlying connective tissue.

AGE AND GENDER FEATURES:

Men have thicker skin more hair and sweat and sebaceous glands. The skin of women contains a greater number of nerve endings (especially at the fingertips).

GENERAL COVER #2

Leather. Its structural components and functional significance. Sources of development. The structure of the skin of the soles and palms. The process of keratinization, the physiological regeneration of the epidermis of the skin. The receptor apparatus of the skin and communication of the skin with other body systems.

Skin - forms the outer cover of the body, the area of \u200b\u200bwhich in an adult is 1.5 - 2 sq.m. It is connected to the underlying parts of the body by a layer of adipose tissue - subcutaneous tissue (hypodeoma). Skin thickness varies from 0.5 to 5 mm.

Protective

Participates in water-salt and heat exchanges

Synthesis of vitamin D under the action of UV rays.

Depot of blood

Reception

Participation in immune reactions (recognizes antigen).

COVER COMPONENTS: epidermis, dermis and subcutaneous fat

DEVELOPMENT: develops from 2 main sources: ectoderm - epidermis, mesenchyme, evicted from the somite dermatome - dermis. Regularity: layers of epithelial cells slowly grow. Initially, the first layer is formed, then the second, by the third month it becomes multi-layered. At the same time, hair, glands and nails are laid.

Keratinization - the transformation of living cells capable of dividing into dead horny scales.

At the heart of keratinization- accumulation of specific proteins - keratins (in humans, ά - keratin, which consists of: fibrils - are high molecular weight proteins that are held together by marix - low molecular weight proteins.

On the palms and soles, the epidermis consists of many dozens of layers of cells, which are combined into 5 main layers: basal spiny, granular, shiny and horny. In other areas of the skin (head, thighs) there is no shiny layer. Contains 5 cell types:

Major epithelial cells keratinocytes (accumulate proteins - keratins) - high prismatic with sharply basophilic cytoplasm, actively divide by mitosis (synthesize DNA)

§ Langerhans cells - intraepidermal macrophages.

§ Lymphocytes - protection

§ Melanocytes - contain melanin that protects against UV rays

§ Merkel cells - lie in the sensory areas of the skin, together with the nerve endings form tactile mechanoreceptors.

§ stem cells - regeneration (3-4 weeks

The basis is keratinocytes, which are directly involved in the keratinization of the epidermis, they synthesize special proteins, are resistant to mechanical and chemical influences.

RECEPTOR APPARATUS - due to abundant innervation, the skin is a huge receptor field in which tactile, temperature and pain nerve endings are concentrated, which are abundantly concentrated around the hair roots and skin areas with increased sensitivity (palms, soles, face, genitals). These include free and non-free nerve endings: lamellar nerve corpuscles (Fattero-Pacini), terminal flasks, tactile bodies and tactile Merkel cells. The feeling of pain is transmitted along the free nerve endings that reach the granular layer, as well as along the nerve endings lying in the papillary dermis. These endings are also thermoreceptors. The feeling of pressure is associated with the Futter-Pacini bodies. Mechanoreceptors include terminal flasks.

Skin and integument #3

Leather. General morpho-functional characteristics. The structure of the mammary glands, features of the glands during lactation. Endocrine regulation of glands. Age changes.

Protective

Participates in water-salt and heat exchanges

Synthesis of vitamin D under the action of UV rays.

Depot of blood

Reception

Participation in immune reactions (recognizes antigen).

BREAST: develop in the embryo at 7-8 weeks from milk lines (seals of the epidermis). Milk points are formed from them, from which epithelial strands grow into the mesenchyme, forming the rudiments of the mammary glands.

STRUCTURE: 15-20 individual glands separated by layers of connective and adipose tissue. Complex alveolar, excretory ducts open at the top of the nipple. The excretory ducts pass into the milk sinuses (accumulate milk). Numerous branching milk ducts flow into the milk sinuses, ending before the onset of lactation with alveolar milk ducts, which during pregnancy give rise to numerous alveoli. The milk sinuses open at the top of the nipple, which is a thickening of the skin. Puberty stimulates the formation of excretory ducts.

Hormonal regulation: estrogens, somatostatin, prolactin, glucocorticoids, human chorionic somatomammotropin.

The first 3 days are colostrum (contains a lot of proteins, but few carbohydrates and fats). Later it is replaced by milk: fats (synthesized on smooth ER - apocrine secretion), casein (synthesized on granular ER and KG - merocrine secretion), ά-lactoalbumin, lactoderrin, serum albumin, lysozyme, water, salts, antibodies.

AGE CHANGES: in girls during puberty, intensive development of the mammary glands begins. Of the branched glandular tubes, secretory sections are differentiated - alveoli (acini). During the sexual cycle, secretory activity increases during ovulation and decreases during menstruation. With the onset of menopause, the mammary gland undergoes involution.

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Part I. General partCellular elements of the dermis

Chapter 1. Anatomy and histology (cellular structure) of the skin. Features of the anatomy and histology of the skin in children

Being the outer covering of the human body, the skin has a complex structure and performs several important functions. Most big organ human is the skin. The area of the skin depends on the age, weight and height of a person and is 1.5-2 m 2. The mass of the skin is approximately 4-6% of the total body weight, and if you take into account the subcutaneous fat, then 15-17%. The total number of skin cells is 9-12 billion, i.e. 6 million / cm 2. The thickness of the skin depends on age, skin color, gender, health status and localization. In different parts of the body, the skin has a different thickness: from 2.12 to 11.57 mm in men and from 2.07 to 10.4 mm in women (Table 1).

Table 1

Thickness of different layers of adult skin (in millimeters)

Older people and children have thinner skin than adults. In children of the first months of life, the average is 1 mm; at the age of 3 to 7 years - 1-1.5 mm; from 7 to 14 years - 1.5-2 mm, and only by the age of 20-25 it reaches 3 mm.

Skin around natural openings (nose, mouth, vagina, anus, urethra) passes into the mucous membrane.

The skin is made up of 3 layers:

1) upper - epidermal or epidermis;

2) the actual skin or dermis;

3) subcutaneous fat.

Epidermis represented by stratified squamous keratinized epithelium. Due to the ability to keratinize, or keratinization, the main cellular element of the epithelium is called a keratinocyte. Five layers of cells are distinguished in the epidermis, each of which represents a certain stage of differentiation (development) of keratinocytes.

The deepest layer basal or germinal layer, borders the dermis and consists of a single row of cells. In the cytoplasm of a keratinocyte, that is, intracellularly, there are granules of a dark brown or black pigment - melanin. In light-skinned people, the pigment melanin is found only in the cells of the basal layer. In dark-skinned individuals, it occurs both in the cells of the spinous layer and in the stratum corneum. Melanocytes are also located in the basal layer, which make up about 10-25% of the cells of the basal layer and produce melanin pigment. The ratio of melanocytes to keratinocytes in the epidermis is 1:36. In black people and in whites, the number of melanocytes is approximately the same. Melanin is involved in wound healing processes and protects body cells from the damaging effects of ultraviolet radiation.

Among the basal (basic) keratinocytes there are tactile cells - Merkel cells (Merkel discs). Especially a lot of Merkel cells in the basal layer on the fingertips, lips. Langerhans and Greenstein cells, or immune cells, are jointly involved in the regulation of immune responses in the skin. Langerhans cells are capable of phagocytosis: by capturing foreign antigens and holding them on the surface, they provide immunological memory. Langerhans cells can synthesize biologically active substances: γ‑interferon, interleukin‑1, etc. Langerhans cells secrete met‑enkephalin, an endogenous modulator (internal pathogen) of pain and a strong stimulant of the immune system. Above the basal layer is the spiny layer. Then there is a granular layer. On the palms and soles, the granular layer consists of 3-4 rows, in other areas this layer is represented by 1-2 rows of cells. The cells of the granular layer have lost the ability to divide.

Flattened, non-nuclear keratinocytes form shiny layer consisting of 3-4 rows of cells. The shiny layer is clearly visible on the skin of the palms, where there is a thick epithelium. The cells of the zona pellucida contain eleidin, glycogen, and oleic acid. The borders of the cells of the shiny layer are poorly visible.

The nuclear-free outer part of the epidermis is stratum corneum. The thickest stratum corneum is on the skin of the palms and soles, on the extensor surface of the limbs. Thinner - the stratum corneum on the abdomen, on the flexor surface of the limbs, on the lateral surfaces of the body, especially thin on the skin of the eyelids and external genitalia in men. The stratum corneum is represented by stratum corneum (scales, corneocytes) - cells that are at the final stage of keratinization (keratinization). Horny plates in the outer part of the epidermis are gradually rejected. This process is called desquamation of the epithelium. Horny scales are of two types: with loose and dense filling of keratin fibrils (fibers). Loose horny scales are located closer to the granular layer, they can reveal the remains of cellular structures (mitochondria, etc.); these scales are called T cells. Dense horny scales are located superficially. The thickness of the stratum corneum depends on:

1) on the rate of reproduction and movement in the vertical direction of keratinocytes;

2) on the rate of their rejection.

The whole process of skin renewal, i.e. the appearance, differentiation, maturation of a keratinocyte, takes about 26-27 days. The main characteristics of the epidermis are shown in Table 2.

table 2

Main characteristics of the epidermis

The structure of the skin as an integral unit consists of:

1) from epidermal vertical columns of cells that ensure the gradual growth and replacement of the upper layer of the skin, adequately responding to external environmental influences and the internal needs of the body;

2) from the dermo-epidermal junction;

3) the actual dermis;

4) subcutaneous fat.

Dermo-epidermal junction. The boundary between the epidermis and dermis is a wavy line of complex shape. The epidermis is attached to the dermis by a basal lamina, or membrane.

The dermis is composed of fibrous connective tissue (cellular elements and extracellular matrix). The thickness of the dermis is different: on the back, on the hips and chest is the thickest; in the skin of the external genitalia, palms and soles is thinner. In the dermis, there are two layers without clear boundaries:

1) subepithelial, or papillary;

2) mesh.

The papillary layer protrudes into the epithelium in the form of papillae, which causes the presence of small furrows on the surface of the skin that form a unique skin pattern. The papillary and reticular layers of the dermis are formed by:

a) various cells (histiocytes, fibrocytes, fibroblasts, mast cells or mast cells, plasma cells, etc.), which are less in the dermis than in the epidermis;

b) extracellular matrix (base), which contains polysaccharides and fibrillar proteins.

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Part I. General partCellular elements of the dermis

Private histology- this is the doctrine of tissues and the features of their development, structure, functions and inter-tissue interactions in the composition of organs and organ systems. Organogenesis proceeds on the basis of the interaction of histogenesis, during which the structural and functional units of the organ are formed. To designate the latter, a number of concepts have been proposed (functional elements, microdistricts, regions, modules, ensembles, histions, etc.). Since the structural and functional units of organs include cells of different tissue nature and different tissues, knowledge about tissue specificity, sources of their development, stages of histogenesis and regeneration is required.

Functions each organ are diverse. But there is always a leading one, which is carried out within the framework of the four main properties of the living, considered both in the course of cytology and general histology. The same principle is preserved in the course of private histology. All human organs can be combined into 4 leading functional systems, which include complexes of organs interconnected by a commonality of the leading function performed: this is the cover system of the body and derivatives, the system of organs of the internal environment associated with the performance of metabolic functions, the system of organs that provide reactive properties , human musculoskeletal system.

Organs are classified into a separate group. human reproductive system, which are discussed in the final section - "Human Embryogenesis".

Leather. skin functions.

body cover system body is the skin. Its total area in an adult is about 1.5-2 m2. The leading function of the skin is a barrier, protecting the deeper tissues and organs from mechanical, chemical, physical and other external influences. This function is carried out through various mechanisms. The acid reaction of the epidermis and the density of its stratum corneum prevent the penetration of microbes into the body.

Powerful stratum corneum makes it difficult for the body to absorb and lose fluid, which is extremely important for maintaining the physiological water and electrolyte balance (in case of skin damage with extensive burns, rapid dehydration of the body occurs). Substances soluble in lipids (chloroform, ether, phenol), as well as toxic substances of skin action (mustard gas, lewisite, etc.), on the contrary, penetrate the skin relatively easily, because they mix well with sebum covering the surface of the skin, and a lipid substance located between the horny scales of the epidermis. Due to the presence of melanocytes in the epidermis, the skin protects deeper tissues from adverse influence ultraviolet rays.

Protective function of the skin It also manifests itself in allergic reactions when foreign proteins - antigens - enter the body.

In addition to the leading barrier function, the skin is involved in protecting the body from hypo- and hyperthermia. About 82% of the body's total heat loss occurs through the skin surface by convection, radiation, and evaporation. In case of violation of the function of thermoregulation (for example, during prolonged work in rubber overalls), overheating of the body occurs (heat stroke). The skin is involved in the excretory function - together with sweat, about 500 ml of water is removed through the skin per day, as well as a number of metabolic products (proteins, chlorides, lactic acid, etc.). The excretory function of the skin is enhanced in diseases of the excretory system.

Availability in skin vascular networks allows it to play the role of a blood depot - the vessels of the dermis, if they expand, can hold up to 1 liter of blood. Skin takes Active participation in vitamin metabolism. Under the action of ultraviolet rays, vitamin D is synthesized in epitheliocytes, which prevents the development of rickets. The skin is a huge receptor field - in its individual areas per 1 cm2 there are about 200 pain, 25 tactile, 17 thermoreceptors.

For medicinal purposes uses the close relationship of various topographic areas of the skin with internal organs with physiotherapy, acupuncture, massage. For the same reason, in the pathology of various organs, hypersensitivity occurs in certain areas of the skin - the Zakharyin-Ged zones. Many skin and infectious diseases are accompanied by the appearance of characteristic rashes that are of great diagnostic value.

Leather and especially its derivatives(hair, mammary glands) are involved in the development of secondary sexual characteristics.

Leather forms derivatives, or appendages, in the form of glands (sweat, sebaceous, milk), hair and nails.
Skin in different areas of the body differs in thickness, color, surface relief, degree of hair development, content of sweat and sebaceous glands, microscopic structure of tissues. Distinguish between thick and thin skin. Thick skin covers only the palms and soles, the rest of the body is covered with thin skin. It should be noted that these concepts reflect only the thickness of the epidermis, and not the entire skin as a whole. On average, the thickness of the skin ranges from 0.5 mm to 4-5 mm.