it protects the body from external influences, performs through a variety of nerve endings the role of the receptor unit of the skin analyzer of the external environment (tactile, pain, temperature sensitivity). Through many sweat and sebaceous glands, it secretes a number of metabolic products, through the mouths of hair sacs, skin glands, the surface of the skin can absorb a small amount of solutions. The blood vessels in the skin can hold up to 10% of a dog's blood. Reduction and dilation of blood vessels are essential in the regulation of body temperature. The skin contains provitamins. Under the influence of ultraviolet light, vitamin D is formed.

In the skin covered with hair, the following layers are distinguished.
1. The cuticle (epidermis) is the outer layer. This layer determines the color of the skin, and keratinized cells are exfoliated, thereby removing dirt, microorganisms, etc. from the skin surface. Hair grows here: 3 or more guard hairs (thick and long) and 6-12 short and delicate undercoat hairs.

2. Dermis (skin itself):
pilar layer, which contains sebaceous and sweat glands, hair roots in hair follicles, muscles - hair lifters, many blood and lymphatic vessels and nerve endings;
mesh layer, consisting of a plexus of collagen and a small amount of elastic fibers.
In the dermis, there are aromatic glands that give off a characteristic odor for each breed. On hairless areas (nose, crumbs of paws, scrotum in males and nipples of bitches), the skin forms patterns that have a pattern strictly individual for each pet.
3. Subcutaneous base (subcutaneous layer), represented by loose connective and adipose tissue.
This layer is attached to the superficial fascia covering the dog's body.
It stores reserve nutrients in the form of fat.

Rice. Scheme of the structure of the skin with hair:
1 - epidermis; 2 - dermis; 3 - subcutaneous layer; 4 - sebaceous glands; 5 - sweat gland; b - hair shaft; 7 - hair root; 8 - hair follicle; 9 - hair papilla; 10 - hair bag

Derivatives of the skin

Derivatives of the skin include the mammary, sweat and sebaceous glands, claws, crumbs, hair, and the nasal mirror of dogs.

Sebaceous glands... Their ducts open into the orifices of the hair follicles. The sebaceous glands secrete a sebaceous secretion, which lubricates the skin and hair, giving them softness and elasticity.

Sweat glands... Their excretory ducts open to the surface of the epidermis, through which a liquid secretion - sweat - is released. There are few sweat glands in dogs. They are located mainly in the area of ​​the crumbs on the paws and on the tongue. The dog does not sweat all over, only rapid breathing through an open mouth and evaporation of fluid from the oral cavity regulate its body temperature.

Mammary gland... They are multiple and arranged in two rows on the lower chest and abdominal wall, 4-6 pairs of hills in each row. In each hill there are several lobes of the gland that open with the nipple canals at the tip of the nipple. Each nipple contains 6-20 teat canals.

Hair... These are spindle-shaped filaments of stratified keratinized and keratinized epithelium. The part of the hair that rises above the surface of the skin is called the shaft, the part inside the skin is called the root. The root passes into the bulb, and inside the bulb is the hair papilla.

By structure, there are four main types of hair.
1. The integumentary is the longest, thickest, most resilient and rigid, almost straight or only slightly wavy. It grows in large numbers on the neck and along the spine, on the thighs and to a lesser extent on the sides. A large percentage of this type of hair is usually found in wire-haired dogs. In short-haired dogs, the top coat is missing or
located in a narrow strip along the back.
2. Covering (covering hair) - thinner and more delicate. It is longer than the undercoat, covers it tightly, thereby protecting it from getting wet and abrasion. In long-haired dogs, it is curved to varying degrees, which is why a distinction is made between straight, curved and curly hair.
3. Undercoat - the shortest and thinnest, very warm hair that fits the entire body of the dog and helps to reduce heat transfer from the body in the cold season. It is especially well developed in dogs kept outdoors during the cold season. Undercoat change (molt) occurs twice a year.
4. Vibrissa - sensitive hair. This type of hair is located on the skin around the lips, nostrils, chin and eyelids.
There are a large number of coat quality classifications.

By the presence of undercoat:
dogs lacking undercoat;
dogs with undercoat.

According to the identity of their coat, dogs are:
smooth-haired (bull terrier, doberman, dalmatian and others);
straight-haired (beagle, rottweiler, labrador and others);
short-haired with feathers (St. Bernard, many spaniels and others);
wire-haired (terriers, schnauzers and others);
medium-haired (collie, spitz, Pekingese and others);
long-haired (Yorkshire Terrier, Shih Tzu, Afghan Hound and others);
long-haired with corded hair (poodle, commander and others);
long-haired shaggy (Kerry Blue Terrier, Bichon Frize and others).

Hair color is determined by two pigments: yellow (red and brown) and black. The presence of the pigment in its pure form gives an absolutely monochromatic color. If the pigments are mixed, then other colors occur.

Most dogs molt twice a year: in the spring and fall. This phenomenon is called physiological molting. Spring molt is usually longer and more pronounced. Molting is the natural protection of the dog from the summer heat and replacing old hair with new ones. In the summer, dogs retain mainly guard hair, and the undercoat falls out. For the winter, on the contrary, a thick and warm undercoat grows. When kept at home, dogs have a longer molting period than those living outdoors.

Claws. These are horny curved tips covering the last, third, phalanges of the fingers. Under the influence of muscles, they can be drawn into the groove of the roller and pulled out of it. Such movements are well pronounced on the fingers of the thoracic extremities of dogs. Claws are involved in the function of defense and attack, and with their help the dog can hold food, dig the ground.

Myakishi. These are the support areas of the limbs. In addition to the supporting function, they are organs of touch. The cushion of the crumbs is formed by the subcutaneous layer of the skin. The dog has 6 crumbs on each thoracic limb, and 5 on each pelvic limb.

STRUCTURE OF THE SKIN AND ITS DERIVATIVES

SKIN STRUCTURE

Leather- corium - mammals mainly consists of: the scabbard, or epidermis, and the base of the skin, or dermis. Where the skin easily displaces and folds, there is a subcutaneous layer through which the skin connects to the underlying organs (Fig. 3).

Epidermis - epidermis - the outer layer of the skin (/). In mammals, the epidermis is formed by stratified squamous epithelium. In places where the skin is not covered with hair,
the epidermis usually accounts for about 1-2% of the entire thickness of the skin. Several layers can be distinguished in it. The deepest layers are basal and prickly. Basal layer is represented by one layer of tall, prismatic, vigorously multiplying cells, among which there are
pigment-containing melanocytes, which cause skin coloration. In places of contact with the underlying layers, the basal cells carry microvilli, which improve metabolic conditions. Prickly layer composed of several layers (about 10) cells,
which are formed from older prismatic cells that have lost contact with the basement membrane and are displaced here due to the pressure of young, vigorously growing basal cells. Spiny cells multiply less actively, come into contact with each other with the help of protoplasmic processes, together their meeting desmosomes lie, separated by a space filled with tissue fluid. Metabolism takes place through it, and due to the presence of viscous mucopolysaccharides, tissue fluid firmly binds cells to each other. In the cytoplasm of spiny cells, there are tonofibrils, which end in desmosomes; they give elasticity to the epidermis.

Granular layer(3) is formed by 2-4 layers of cells that are formed from spinous cells. These are living cells, in their cytoplasm there are large granules of keratohyalin, well stained with nuclear dyes. Granular cells are displaced to the surface of the skin, forming the next shiny layer of it.

Shiny layer(4) consists of 2-3 layers of already dead flattened cells devoid of nuclei. Their cytoplasm is displaced by eleidin, formed from the keratohyalin of granular cells. The boundaries of the cells in this layer are not visible. Changing, these cells are gradually shifted to the outermost stratum corneum of the skin.

Stratum corneum(5) is the thickest and consists of several tens of layers of completely dead cells that take the form of horny scales. Each scale has a shell, consisting of a real horny substance - keratin and a cavity filled with air or a fat-like mass. Due to this structure, the flakes have elasticity and low thermal conductivity. The superficial scales of the stratum corneum lose their connection with the deep-lying cells of the epidermis and are rejected from the skin, being replaced by newly emerging cells. Retardation of rejected cells in the hair
the cover of farm animals leads to a violation of the multifaceted function of the skin. Therefore, it is necessary to systematically clean and wash the skin of animals.

Where the skin is covered with hair, the epidermis is much thinner and consists only of the basal, prickly and stratum corneum (Fig. 4).

The base of the skin, or the skin itself - dermis, cutis, s. corium - develops from the mesoderm dermatome and consists of connective tissue. It distinguishes between papillary and reticular layers (Fig. 3-II-8, 9).

Papillary layer located under the basement membrane that separates the base of the skin from the epidermis. On its surface there are papillae (7) lying between the scallops of the epidermis. This layer consists of reticular and loose connective tissue. It contains individual bundles of smooth muscle tissue and pigment cells that determine skin color. In the skin bearing the hair, the papillary layer of the base of the skin either does not form papillae at all, or they are very insignificant, and then the border between
the epidermis and base of the skin appear as a straight or slightly wavy line. The papillary layer passes into the reticular layer without a sharp border.

Mesh layer(9) is composed of dense connective tissue. There are few cells in it, but there are many elastic fibers and powerful collagen bundles intertwined with each other in the form of a dense mesh. The dermis gives the skin its strength. It is from this layer that various leather products are made.

Subcutaneous base (fiber) -tela subcutanea - (Fig. 4-III) consists of loose connective or reticular tissue and contains a large number of fatty lobules (17). Due to this, the subcutaneous layer is the most important fat depot, softens mechanical stress and provides the possibility of skin displacement. In semi-salty pigs, the fat layer in the region of the 6-7th thoracic vertebra reaches a thickness of 4-5 cm, in sebaceous pigs it is over 7 cm and is called fat. In fat-tailed sheep, fat is deposited on the buttocks and at the root of the tail, forming a fat tail. In a camel, fat deposits form a hump.

A well-developed subcutaneous layer makes the skin more mobile. The absence or a small layer of the subcutaneous layer, on the contrary, leads to a tight connection of the base of the skin with the underlying parts of the animal's body, to the absence or very weak mobility of the skin.

The vessels of the skin in the reticular and papillary layers form plexuses, and the branches of the latter in each papilla form a dense capillary network, which diffusely nourishes the epidermis. There are anastomoses between the arteries and veins of the skin, which are involved in thermoregulation.

Lymphatic vessels are especially developed in the subcutaneous layer.

The nerves of the skin are represented by a large number of sensitive nerve endings and fibers. The latter form a dense plexus in the papillary dermis. The nerve endings are numerous and unevenly distributed. Thanks to them, the skin in the body plays the role of the organ of touch.

The skin forms a number of derivatives. The main ones are hair, sebaceous and sweat glands, as well as the mammary gland, digital crumbs, hoof, horns.

HAIR DEVELOPMENT AND STRUCTURE

Hair development and growth(pilus) begins with a thickening of the epithelium, then, due to the increased multiplication of cells, a rudiment is formed, which, in the form of a cell strand, increasing in size, plunges into
dermis of the skin (Fig. 5). A thickening forms at the end of the cell cord,
formative onion(five). A mesenchyme grows inside the bulb, forming hair papilla(nine). A protrusion is formed from the middle part of the epithelial anlage, giving rise to the sebaceous gland. In the area of ​​the bulb, cells multiply intensively and give rise to rod hair, which, pushing the cells of the epithelial cord, makes its way to the surface
skin.

Under the pressure of young cells continuously forming in the bulb, the stem continues to elongate. Epithelial cells located near the intradermal part of the rod form outward(8) and internal(7) root sheaths... From the surrounding mesenchyme, in addition to the papilla, a connective tissue bag of the hair develops around the hair root (10), as well as smooth muscles (12).

Hair structure. The folded hair consists of a shaft and a root.

Kernel(14) has a supercutaneous part (wool, or "hair") and a part hidden in the skin, which is part of the hair root. The cross section of the rod shows that it consists of the medulla and cortex, as well as the cuticle (15). Core, or medulla(17) is central to the core. It is a continuous or discontinuous longitudinal strand, consisting of one or more rows of polygonal (polygonal) living, partially keratinized cells of epithelial origin. In the cytoplasm of cells, keratohyalin is deposited, which, closer to the outer layer of the rod, turns into eleidin, and the latter into keratin. Air bubbles are found inside the cells and between them, so the hair has little thermal conductivity, protecting the animal's body from cooling. The core contains the pigment that gives the hair color. The most delicate sheep hair - fluff, hair of young animals and some others do not have a brain substance. On the contrary, in a deer it is highly developed. Cortical substance(16) - the main mass of the rod, which gives it mechanical strength, extensibility, flexibility and elasticity. Hair deprived
this layer (reindeer) are easily torn. In the root part, near the bulb, the stem consists of living cells with rounded nuclei and weak signs of keratinization. With distance from the bulb, the cells become elongated and more keratinized, and the corneous substance is formed immediately in the form of solid keratin, which determines the mechanical properties of the rod. In the supercutaneous part, the highly elongated cells of the cortical layer are usually already devoid of nuclei, but contain pigment. With age, the number of gas bubbles in the cortex increases, which causes the hair to turn gray. Hair cuticle(15) consists of flat, keratinized, overlapping one another, like a tile, or closely adjacent non-nuclear cells. The configuration of the boundaries of the cuticle cells determines the varied pattern of the hair, which is not the same in animals of different breeds. Cuticle protects hair from moisture, light, chemicals
and mechanical damage. The spinning qualities of wool depend on its properties.

Hair root consists of: the intradermal part of the rod, enveloping its hair follicle, the bulb with the hair papilla, as well as the sebaceous glands and muscles. Inside the skin, a part of the stem near the bulb consists of living, low-keratinized cells. Closer to the surface of the skin, it is constructed in the same way as the outer shaft.

Hair follicle envelops the intradermal part of the rod and, like the skin, consists of epithelium and connective tissue. The inner and outer root sheaths are formed from the epithelium, and the hair follicle is formed from the connective tissue. The inner root sheath (7) is adjacent to the shaft. It starts from the bulb and usually only reaches the confluence of the sebaceous glands. In cows, it reaches the surface of the skin and is a continuation of the stratum corneum. This vagina is composed of several layers of cells. The innermost layer is the cuticle of the vagina,
consisting of one row of keratinized cells, the next layer is granulo-containing epithelial, represented by 1-2 rows of light cells with a small amount of trichohyalin. This layer is followed by a pale epithelial layer, in which it is impossible to distinguish with the usual staining of the nucleus. The outer root sheath (8) is a direct continuation of the basal layer of the epidermis of the skin and is present throughout the hair root. The number of its constituent cells gradually decreases towards the bulb. The outermost, higher cells of the vagina are the producing cells. Thanks to them, the rest of the cells of the external vagina are formed.

Hair bag(10) is formed by connective tissue with well-defined internal circular and external longitudinal collagen and elastic fibers. The pouch is well developed in thick hair. From the hair follicle to the epidermis of the skin, bundles of smooth muscle cells are directed at an obtuse angle, which, by contracting, raise the hair, and also promote the elimination of the secretion of the sebaceous glands.

Hair follicle(5) is composed of living, rapidly multiplying epithelial cells. They provide material for the formation of the shaft and the inner root sheath.

Hair papilla(9) consists of connective tissue with a mass of blood vessels and nerves. The first ones deliver the nutrients necessary for the vital activity of the hair, and the nerves provide the connection between the hair and the body.

The root forms a certain angle with the skin surface, so the rod lies more or less parallel to the skin surface. If the hair follicle is curved in a zigzag manner, then the rod extending outward from it has more or less crimp. In fine-fleeced sheep, several rods can emerge from the cavity of the bag (Fig. 6-5), which are glued together by the secretion of the skin glands into pigtails, and the latter are combined into a staple.

Occurs periodically hair change... At the same time, the producing cells of the bulb begin to receive less nutrients from the papillae, they stop dividing, some of them become keratinized and, together with the stem, are separated from the living cells of the bulb. Once free, the stem, together with the bulb section, moves out of the hair

1-epidermis; 2 - sub-epidermal zone of the papillary layer; 3 - intermediate zone of the papillary layer; 4- reticular layer; 5 - bulb and papilla; 6-blood vessel; 7-secretory from affairs of the sweat glands; 8 - muscle; 9 - lobules of the sebaceous glands; 10 secondary follicles; 11th flute hair; 12 - fluff; 13th; 14 - primary follicle; 15-wool fibers; 16 follicle.

STRUCTURE OF THE SEAL AND FLOW GLANDS

Sebaceous glands- glandulae sebaceae - located mainly at the base of the skin; in structure, they belong to simple, often branched alveolar glands (Fig. 6 and 7-A, B). Secretory departments they have no cavities. Their outer cells are flat or cubic and are productive. Vigorously multiplying, they are gradually pushed back to the center of the alveoli. As they approach the center, all of them
more and more viscous fatty secretion accumulates. As a result, the nucleus and part of the cytoplasm are reduced, and such degenerated cells are secreted along the duct to the surface of the skin (sebum). Some cells of the wall of the alveoli are flattened, keratinized and mixed with the secretion in the form of scales.

Thus, by the type of secretion, these glands are typically holocrine glands. Duct sebaceous glands in most cases open into hair follicles and occasionally independent holes on the surface of the skin (for example, on the head of the male penis). The ducts are lined with stratified squamous epithelium. There are no sebaceous glands in the teat of the udder of a cow, in the skin of the nasal speculum of predators and small ruminants, on the crumbs, horns, hooves and some other parts of the animal's body.

Sweat glands- glandulae sudoriferae (Fig. 7-C, E) - participate in thermoregulation and excretion of the product of nitrogen metabolism - urea. They lie in the deep layers of the dermis, partially going into the subcutaneous layer (Fig. 4-6). By their structure, they belong to simple, sometimes branching, tubular glands, by the type of secretion - to merocrine glands, and the glands of certain parts of the body (for example, the groin region) - to apocrine glands. Secretory department the glands in the cow are weakly curved, in the horse and pig it does not branch, but it is very long and curled up into a ball
(Fig. 7-C, D, E). The walls of this section have two layers of cells: the outer one contains myoepithelial cells, and the inner one consists of cubic glandular cells. Output ducts of glands slightly convoluted and also have two layers of cells. In most cases, they open into the hair follicles, less often - near the hair funnels, and in some hairless places - right on the surface of the skin with sweat pores.

In addition to the sebaceous and sweat glands, other glands lie in some places of the skin of farm animals. So, in cattle there are serous glands in the nasolabial speculum, in a pig specific glands are located in the "patch", in a horse - in the digital crumb of the arrow gland, in a sheep - interdigital glands, etc.

UDDER STRUCTURE

Udder - uber-cattle (Fig. 8) simple, located in the pubic region between the thighs.

Outside, the udder is covered with skin, which is covered with hair in animals kept in the cold. The caudal surface of the udder with clearly protruding sheer folds of skin and noticeable linear hair flow is called milk mirror... Under the skin of the udder is superficial fascia(Figure 9-2), and below it - deep udder fascia(3), which is a continuation of the yellow abdominal fascia. The deep fascia, giving off two elastic sheets in the middle of the udder, extending from the white line of the abdomen to the base of the udder, divides the udder into right and left halves and supports it. These sheets of deep fascia make up suspension bundle udder (4). Transversely, between the nipples, the udder is conditionally divided into front and back halves, that is, it has four quarters, not sharply demarcated among themselves. Each quarter of the udder has its own excretory ducts(7) and separate nipple... Sometimes there are six nipples. More often, accessory teats are found on the back half of the udder. These nipples sometimes function.

Rice. 9. The structure of the udder of a cow: A-general scheme of the udder in section; B - terminal section of the gland; B-large excretory duct; 1- leather; 2 - superficial fascia; 3 - deep fascia; 4 - suspension ligament; 5 - stroma; 6 - end sections; 7 - small excretory ducts; 8 - milk passages; 9 - parenchyma; 10 - milk tank; 11 - nipple duct; 12 - smooth muscle cells around the nipple; 13- annular muscles that form the sphincter of the nipple canal; 14 - bundles of smooth muscles accompanying large excretory canals; / 5 - myoepithelium surrounding the end sections and excretory ducts; 16 - nerves; 16a - nerve endings; / 7 - artery and its branch, encircling the terminal section of the gland; 18-vein of the udder; 18a - venous plexus of the nipple; 19 - milk elements; 20 - myoepithelium; 21 - the epithelium of the excretory duct.

The glandular part of the udder - parenchyma(9) is built like a complex alveolar-tubular gland and is dressed in its own connective tissue capsule with an accumulation of fat cells and elastic fibers. A number of plates and strands are directed from the capsule into the udder, dividing it into separate glandular areas - udder wedges... From the interlobular connective tissue plates, delicate bundles go inside the lobule, braiding the final tubules and alveoli, or alv eolotubes glands. The connective tissue frame of the udder is called str my or interstitium. Vessels and nerves pass through it into the gland.

The wall of the milk alveoli consists of: a single-layer cubic epithelium, a layer of myoepithelial (basket) cells, a basement membrane and perialveolar connective tissue containing blood and lymphatic capillaries and nerve fibers. The mammary glands secrete according to the apocrine type, each secreting cell secretes all the constituent parts of milk at once.

Secreting cells have a cloudy cytoplasm and a rounded nucleus, and there are microvilli on the free surface.

From the alveolotubes (6) milk passes into the thinnest excretory ducts, lined with a single-layer cubic epithelium, which, connecting with each other, form visible to the naked eye milk channels(ducts) connecting in milk passages(in them, the epithelium becomes two-layer), which, expanding near the base of the nipple, open into the cavity - milk tank (10).

The excretory ducts and end sections of the mammary gland are densely intertwined with a network of blood capillaries (17, 18a) and nerve endings (16a).

Nipple has a milk cistern (10) and a teat duct (11). The inner layer of the milk cistern wall - the mucous membrane - consists of a two-layer prismatic epithelium, a layer of myoepithelium and its own membrane, outside of it there are bundles of smooth muscle fibers. The mucous membrane of the milk tank forms many longitudinal folds, which straighten out when the tank is filled with milk. The lower end of the milk tank narrows and becomes a short nipple duct(11), its walls are lined with squamous stratified epithelium. The smooth muscles of the nipple consists of four layers (12): longitudinal (deep), annular, mixed and radial (superficial).

The annular layer, strongly developing around the nipple canal, forms sphincter nipple (13). Outside, the nipple is covered with skin, there are no sebaceous, sweat glands, or hair in it, but there are a large number of nerve endings (16a).

Udder shape and nipples different animals are not the same. In certain cases, it is associated with the productivity of animals (Fig. 10). Have sheeps and goats the udder consists of right and left halves with one teat on each half (Fig. 11-A). Have cattle cattle in each half of the udder there are two teats with one hole in each teat (B). Udder horses has one teat on each half, but each teat has two cisterns and two holes (B). Breasts (multiple udders) pigs consist of 10-16, more often 12 hills with the same number of nipples. Each nipple contains one, usually two, milk cistern with nipple canals.

Changes in the glandular tissue of the udder at different periods of the life of cattle. The state of the glandular tissue of the udder of different animals and even in the same animal at different periods of its life, at different levels of feeding, is different (Fig. 12). Until puberty, the glandular tissue of the udder does not develop. The development of this tissue occurs in close relationship with the development of the connective tissue frame of the udder. At the same time, an increase in the parenchyma of the udder causes a relative decrease in its stroma, and, conversely, a decrease in the glandular tissue causes a slight increase in the connective tissue frame of the udder. At the onset of puberty of the animal, the blood vessels and nerves of the udder grow strongly and densely entwine the glandular elements. The glandular and connective tissues begin to develop rapidly. However, the udder stroma develops faster than the parenchymal elements, which are already taking the form of alveoli. Only with the onset of pregnancy, glandular
the tissue begins to overtake the connective tissue frame in development; in some parts of the gland, cavities appear at this time, their wall is formed; the structure of the gland is close to the state that ensures its function.

By the end of pregnancy, the mammary glands are fully developed and begin to produce colostrum.

The mammary glands reach their greatest development and highest functional activity during lactation. At this time, the lumens of the alveolotubes expand, fill with secretion, and their connective tissue skeleton is relatively reduced (A). By the end of the lactation period, the opposite phenomena are observed in the gland: the alveolotubes gradually stop their work, shrink, and the connective tissue skeleton grows, and with good nutrition of the animal, fatty deposits are formed in it (B).

With the onset of a new pregnancy, glandular tissue again begins to predominate in the udder.

In high-milk cows, the connective tissue skeleton is tender, and the tubules and alveoli are closely adjacent to each other, occupying most of the udder lobule. In unproductive cows, on the contrary, the stroma is highly developed, while the glandular formations are less pronounced and lie at a considerable distance from one another, separated by thick connective tissue layers.

In heifers and old cows, the stroma also predominates over the parenchyma (B). In well-fed animals, the stroma increases due to the deposition of fat (fatty udders) (D).

STRUCTURE OF POLES

Myakishi - pulvini - there are carpal (tarsal), metacarpal (metatarsal) and digital (Fig. 2). The horse's finger crumbs are of the greatest practical importance. Therefore, they are described in more detail.

Horse toe crumb- pulvinus digitalis (Fig. 13-I, III) - the shape of a triangle bifurcated at the base, wedging its apex into the sole of the hoof (II). Its back, more elastic part is crumb pillow(10), and a sharp, more elastic, with a massive stratum corneum - arrow(eleven). The sharp end of the arrow is called the apex (A-13). The horny ridges of the toe crumb protruding on the plantar surface are arrow legs(11), and the recess between them - intercutaneous groove(12). On the inner side of the stratum corneum of the crumb, the interfacial groove corresponds comb arrow.

The digital crumb, being a derivative of the skin, consists of three layers: the epidermis, the base of the skin and the subcutaneous layer of the crumb.

Rice. 13. The stratum corneum of the hoof sole and toe (A) and the base of the skin of the hoof sole and toe of a horse (B), the stratum corneum of the sole of the hoof and toe of cattle (C):

I - the stratum corneum of the digital crumb; II - stratum corneum of the hoof sole; III - the basis of the skin of the digital crumb; IV - the base of the skin of the hoof sole;1 - the angle of the hoof wall; 2- the back part of the hoof wall; 3- the back of the hoof wall; 4- lateral furrows; 5 - branches of the hoof sole; 6- lateral parts of the hoof wall;7 - the body of the hoof sole; 8- plantar edge of the hoof wall; 9- the hook part of the hoof wall; 10- crumb pillow; 11- arrow legs; 12- inter-pedicle groove; 13- the top of the arrow; 14- crumb pad skin base:15 - the basis of the skin of the bar of the hoof wall; 16- the basis of the skin of the arrow of the digital crumb;17 - hanging ( 2 and 5) fingers; 18- finger crumb; 19 - hoof sole; 20- hoof wall.

A - in a sagittal section; B - position of the lateral cartilage; I - hoof border; II - corolla of hoof; III - hoof wall; IV - hoof sole; one - epidermis; 2 - skin base; 3-subcutaneous layer; 4 - tendon end of the common digital extensor; 5 - subcutaneous hoof border and corolla layer; 6 - base of the skin of the hoof border and hoof corolla; 7 - epidermis of the hoof border and the direction in which descends stratum corneum (glaze) from the border on the whisk and wall; 8 - ungulate epidermis corolla; 9 - hoof wall glaze; 10 - tubular horn and the direction in which it descends from the rim to the hoof wall; 11 - lamellar horn of the hoof wall; 12 - lamellar layer of the base of the skin of the hoof wall; 13 - white line; 14 - stratum corneum of the hoof sole; 15 - base of the skin of the hoof sole; 16 - periosteum tsa; 17 - stratum corneum of the arrow of the digital crumb; 18 - the basis of the skin of the arrow of the digital crumb; 19 - stratum corneum of the cushion of the digital crumb; 20 - the basis of the skin of the cushion of the digital crumb;
21 - subcutaneous layer of the finger cushion pillow; 22 - crumb cartilage; a - fetlock bone; b - coronoid bone; c- the coffin bone.

Epidermis finger crumb - hairless, has horny, shiny, granular and sprout layers. It contains tubular, coiled glands that secrete a fatty secret (10-13). IN skin based papillary and reticular layers are well developed in the digital crumb (14-16). Subcutaneous layer The digital crumb differs from the subcutaneous layer of the skin in that it contains a large amount of fatty and elastic tissue. There is especially a lot of it in the crumb cushion, which performs mainly a spring function. Paired (lateral
and medial) lateral cartilage firmly fused with the crumb cushion. Their shape is in the form of convex plates and with one edge they adhere tightly to the coffin bone (Fig. 14-B-22). In older animals, especially in heavy draft animals, these cartilages sometimes ossify if they are used improperly. The pulp cartilage, covering the sides of the cushion of the crumb, reaches with the proximal edge almost to half of the coronary bone and is well palpated from the volar surface of the limb. Cartilage is connected to nearby bones (hoof, shuttle, coronary and fetal) by ligaments.

Have cattle and pigs finger crumbs do not have arrows, and their cushion pads are well expressed (Fig. 13-B-18). Otherwise, the digital crumbs of cattle and pigs have the same structure as those of a horse. Have dogs finger crumbs are found on each finger. They float strongly on the claw from the plantar side.

CONSTRUCTION OF THE HOOF AND HORN

Hoof - ungula - horses are divided into hoof border, hoof corolla, hoof wall and hoof sole (Fig. 14).

Hoof border in the form of a narrow strip, about 0.5 cm wide, forms the transition from the hairy skin of the limb to its hairless part (A-I). Hoof corolla about 1.5 cm wide, it is located in a semicircle below the hoof border, making up the proximal edge of the hairless surface of the hoof (A-II). On its stratum corneum on the inside there is coronal groove(Fig. 15-2), which, on the basis of the corolla skin, corresponds crown cushion(B-10). Hoof wall(Fig. 14-A-III) - the most massive part of the hoof. It forms the front and side surfaces of the hoof, partially extends over the plantar surface of the hoof and is divided into unpaired hook(rice.
13-A-9), paired lateral front (6),
lateral rear (3), bolt(2) parts and turning corners(one). On the hoof wall, reaching the distal end of the limb, they also distinguish plantar margin(eight). On the hoof sole(A-II), directly resting on the soil, distinguish body(7) and plantar branches(5), between which the toe cushion wedges, separating from the plantar branches and bars of the hoof wall lateral furrows.

Hoof histology has a lot in common with the structure of the skin, but there are some differences associated with their functional difference.

Hoof border (Fig. 14-A-I) consists of the epidermis, the base of the skin and the subcutaneous layer. Epidermis has horny, granular and germ layers. The stratum corneum is hairless. Dropping onto the hoof wall, it forms a thin, shiny layer - hoof wall glaze(A-9; 16-1). Skin base consists of papillary and reticular layers (Fig. 14-A-6). The papillae of the papillary layer are lowered downward. Subcutaneous layer the border is slightly developed (A-5).

Hoof corolla (A-II) also has the epidermis, the base of the skin, and the subcutaneous layer. Epidermis hairless and consists of stratum corneum, granular and germ layers. The stratum corneum is very thick, tubular in structure, the strongest in the hoof and almost impervious to water. It grows towards the sole of the hoof, forming tubular horn hoof walls (fig. 16-2).

There is a depression on the inner surface of the stratum corneum of the epidermis - coronal groove(fig. 15 - A - 2). Skin base hoof corolla (Fig. 14-A-6; 15-B-10) has papillary and reticular layers. The papillae in this part of the hoof are the longest, drooping downward, as a result of which the horny layer of the hoof corolla grows downward. At the base of the corolla skin, a huge number of vessels and nerves branch out, providing
excellent blood supply to the entire area and a good sense of unevenness in the ground on which the hoof steps. Subcutaneous layer corolla (Fig. 14-A-5) together with the base of the corolla skin forms crown cushion(fig. 15-B-10).

Hoof wall (Fig. 14-III) in structure is significantly different from the skin. Epidermis it is hairless and consists of the germ and stratum corneum. There are no grainy and shiny layers in it (S. N. Krever). The bulk of the epidermal growth layer is located in its proximal part, on the border with the corolla. The leaf-shaped horn produced by nm is leaf horn(Figure 16-4). In the growth layer of the epidermis of the hoof wall, there are not cylindrical cells, but cubic and horny leaves
are not their derivatives. It is assumed that cubic cells contribute to the downward sliding of the stratum corneum, which forms at the border of the corolla and the hoof wall. The color of the leaf horn is white. Its final section on the hoof sole, together with the inner layer of the tubular horn, forms white line... By its location, it is determined where, when forging an animal, it is necessary to hammer nails so that they go into the tubular horn (lateral from the white line), and not into the base of the skin of the hoof wall, rich in vessels and nerves. Thus, the hoof wall has three stratum corneum. The leaf horn (4) is located under the tubular horn extending from the hoof rim, and the tubular horn (2) is covered with glaze (1) descending from the hoof border. In this case, the glaze in old animals and in animals kept in poor conditions is usually destroyed, and then the outer layer of the hoof wall remains a tubular horn.

Skin base Instead of the papillary layer, the hoof wall has a lamellar layer (6), each leaf of which is, as it were, a fusion of a number of papillae. Between the leaves of the base of the skin of the hoof wall, the horny leaves of its epidermis move. On the surface of each leaf on both sides there is a row
smaller secondary leaflets. This increases the surface of all leaflets to one square meter, which ensures a strong connection of the lamellar layer of the base of the skin of the hoof wall with its lamellar horn. Mesh layer the base of the skin of the hoof wall (7) due to the absence of the subcutaneous layer is in direct contact with the coffin bone. Its inner surface, growing together with the bone, forms periosteal layer ungulate
walls. Such a strong connection of the base of the skin of the hoof wall with the coffin bone ensures, when muscles act on the coffin bone, its simultaneous and combined movement together with the hoof.

Subcutaneous layer the hoof wall does not. Skin base The hoof wall is rich in nerves and blood vessels. When forging an animal, nails should not fall into this layer.

Hoof sole(Fig. 13-A-II) also does not have a subcutaneous layer, which contributes to strong adhesion of the base of the skin of the foot sole to the coffin bone. Epidermis of the foot sole(Fig. 14-A-14), consisting of stratum corneum, granular and germ layers, without hair, but has a powerful tubular stratum corneum, in strength, however, inferior to the tubular horn of the hoof wall. Its surface layers represent a tiny mass, which gradually falls off, and if necessary, it is cleaned off. Skin base hoof sole (A-15) consists of papillary and reticular layers. The inner surface of the mesh layer forms periosteal layer, which has the same meaning as the corresponding layer of the hoof wall.

The stratum corneum of all parts of the hoof and toe is hornyshoe. The rest of the epidermis, as well as the base of the skin and subcutaneous layer of the toe and hoof, are not included in the stratum corneum. Various deviations in the keeping of animals are reflected in the growth of the horn shoe and cause its deformation.

Cattle hooves and pigs are similar to a horse's hoof, divided in half (Fig. 13-B), do not have bars, and their sole, especially in small ruminants, is more developed.

Horn structure. The horns are located on the bony horny processes of the frontal bones and consist of two layers - the base of the skin and the epidermis. The horns have a root, body and apex (Fig. 17). Skin base the horn grows together with the periosteum of the horny processes of the frontal bones. It has papillary and reticular layers. The papillary layer in different parts of it is expressed differently. At the base of the horn, the papillae are low and often located, then gradually rise, are located less often and obliquely to the apex of the horn, where the highest papillae are located. Epidermis the horn has the same layers as the hoof epidermis. Its germ layer produces a very strong tubular stratum corneum. The growth of the stratum corneum is reflected in various conditions of the animal's existence - increased or decreased feeding, healthy or painful state, normal or weakened function of the growth layer. The enhanced function of the germ layer leads to the appearance of special nodules, rings on the horns. Weakening in the development of the horn makes its walls thinner, forms an interception, or ring, on the horn. In cows, each pregnancy is accompanied by the appearance of such a ring. In many animals, the rings are expressed over the entire surface of the horn, in cattle, they are clearly visible only at the root of the horn. The top of the horn is usually smooth and sharp.

11 12 ..

11. Leather. Animal skin structure

The skin is a dense, strong and elastic outer shell of the animal's body, repeating the relief of muscles and bones. Three layers are distinguished in the skin: the superficial - the epidermis, the middle - the base of the skin, or the dermis, and the deep subcutaneous layer (Fig. 75).

The epidermis consists of a squamous stratified epithelium arranged in several layers. The deep layer of prismatic cells continuously multiplies and pigment is deposited in the cells. The stratum corneum or surface layer consists of flat keratinized anucleated cells, which gradually die off and slough off, forming scales.

The base of the skin is composed of papillary and reticular layers. The papillary layer lies under the epidermis from which it is separated by a membrane. The papillae contains a dense network of blood vessels and nerve endings. The papillary layer is built from elastic fibers, loose and reticular tissues. The reticular layer is formed by dense connective tissue with a predominance of collagen and elastic fibers. The dermis contains hair roots, sebaceous and sweat glands, as well as smooth muscles and pigment cells.

The subcutaneous layer consists of loose connective tissue, in the spaces between the fibers of which there is adipose tissue - subcutaneous adipose tissue. In pigs, after slaughter, subcutaneous fat (lard) is used as an independent product in sausage production.

The functions of the skin are very diverse. It is a receptor field that perceives irritation and thus establishes a connection between the body and the external environment. Blood vessels and capillaries of the skin regulate body temperature, cutaneous respiration and blood deposition.

The respiratory function of the skin is carried out due to the release of carbon dioxide and the flow of oxygen from the air into the blood.

The excretory function of the skin is carried out by the sweat, sebaceous and mammary glands.

Specific glands located in the skin perform a secretory function. The secretion of these glands is one of the sources of olfactory signals and determines the behavior of animals. With the help of smells, they can recognize the belonging of an individual to a certain species.

The skin protects the body from harmful effects, microorganisms, low and high temperatures, drying out.

The thickness of the skin depends on the age, sex, breed and performance of the animal. In young people it is thinner than in adults; in females it is thinner than in males, in dairy cattle it is thinner than in meat. The thickness of the subcutaneous layer in cattle reaches 15% of the total thickness of the skin, and in fattened animals, and especially pigs, it can be many times greater than the thickness of the skin.

The strength and thickness of the skin also depend on where it is located on the body of the animal. So on the back, lower back, sacrum, it is thicker and stronger than on the stomach; thicker on the outside of the limbs than on the inside. Thin skin lies behind the auricle, on the neck, under the armpit, in the knee (probe) and tail folds. In these places, it gathers well in folds and is palpable due to the developed subcutaneous layer of loose fiber.

The skin removed from the head is called the head, from the neck - the collar, from the limbs - paws, from the lower abdomen and chest - the floors, from the knee fold - the rear groin, from the back, lower back and sacrum - saddlecloth. In the saddlecloth, a croup is distinguished - the back-lumbar part, which occupies 85% of its front area. And the rump is the sacral part and the root of the tail, separated from the rump by a perpendicular line at the level of the groins. The pork croup includes the neck, back and rump. The lateral line runs along the carcass 16-20 cm higher from the nipples.

The skin only covers the outside of the body; it has many different functions. The skin protects the body from all kinds of harmful effects of the external environment (mechanical, temperature), from numerous pathogens and from drying out. Being strong and flexible, the skin protects deeper cells from mechanical damage caused by pressure, friction or impact. Until the integrity of the skin is broken, it is virtually impervious to microbes. The waterproofness of the skin protects the body from excessive loss of moisture, and in aquatic forms - from excessive penetration of water from the outside. The skin is able to protect the cells underneath from the harmful effects of ultraviolet rays thanks to the pigment that is synthesized in it.

The skin takes part in the metabolism; through it, water, mineral salts and some other metabolic products are removed from the body. In this way, the skin helps to maintain the constancy of the composition of the internal environment of the body. The skin regulates the release of heat from the body, helping to maintain a constant body temperature.

The skin is an organ of the senses... It contains many specialized receptors through which animals perceive pressure, temperature, pain, and other stimuli. Sweat and sebaceous glands are located in the skin. Sweat is released through the sweat glands. The sebaceous glands produce a lubricant that keeps the hair covering the skin moist and flexible, and the skin does not dry out or crack. Derivatives of the skin include the mammary glands of mammals. They produce milk. By the condition of the skin and the shine of the coat, one can almost infallibly judge the health of the animal.

Skin structure... The skin consists of the skin itself and its derivatives, hair, crumbs (pillow-like thickenings on the limbs), hooves, hooves, claws, horns, feathers, scales, sweat, sebaceous and mammary glands.

Three layers are distinguished in the skin: the outer layer is the cuticle, or the epidermis, the inner layer is the skin itself, or the dermis, under the skin itself there is a connective tissue layer, in which fat is deposited with good feeding of the animal. The third layer is called subcutaneous tissue.

The cuticle consists of squamous stratified epithelium. On its surface lie dead cells that have lost their nuclei, impregnated with a special horny substance. Thanks to the horny substance, the outer layers of cells acquire hardness, they protect the tissues lying under them from the harmful effects of the external environment.

Under the layer of horny cells is a deeper layer of the epidermis. It consists of living cells with nuclei. These cells are cylindrical in shape, capable of reproduction, and as they approach the surface layer, they become flat and lose nuclei.

By the condition of the skin and the shine of the coat, one can almost infallibly judge the health of the animal. The upper, horny, layer of the epidermis gradually separates from the skin in the form of dry dandruff flakes. If animals are poorly kept in unsanitary conditions, dry peeled off scales can stick together and clog the coat. At the same time, crusts form on the skin, which interfere with the normal functioning of the sweat and sebaceous glands. As a result, the health of the animal deteriorates, its productivity decreases. To prevent this, the skin of animals should be systematically cleaned and washed.

Special scrapers and brushes, which are used for this purpose, not only cleanse the skin, but also contribute to its better blood supply, hair growth, the activity of sweat and sebaceous glands. When a cow is well-groomed and her coat is shiny, there can be no doubt that she will give more milk than a cow with sticky dirty wool. Thorough care pays off with high productivity.

Hair is a keratinized, hard, elastic thread made up of epidermal cells. The part of the hair protruding above the surface of the skin is called the shaft, the part of the hair located in the skin is called the root. The hair root ends with an extension - a hair follicle, the cells of which, multiplying, provide hair growth and the appearance of new hair instead of the lost one. Hair follicles lie in the skin itself in hair follicles.

The hair root is almost always oblique to the skin surface; from the side, muscle fibers approach the hair roots, the contraction of which leads to the raising of the entire hair. When the body cools, the raised hair creates a kind of microclimate around the animal, protecting it from hypothermia. Due to the low thermal conductivity, the air between the individual raised hairs contributes to the preservation of heat by the body of the animal.

The skin itself, or dermis, is built of dense connective tissue, abundantly permeated with blood, lymphatic vessels and nerves. Tactile, cold, heat and pain receptors are located here, through which irritations from the external environment are perceived. The skin itself contains sweat and sebaceous glands and hair follicles. The outer layer of the dermis, consisting of densely interwoven connective tissue fibers, is the part from which leather is made by tanning.

The density of the skin is created by connective tissue bundles directed parallel or at an angle to the surface of the skin, and the elasticity of the skin is due to the presence of special fibers. The thickness of the skin depends mainly on the development of the connective tissue layer. On the back, the skin is thicker than on the abdomen, on the outer surfaces of the limbs is thicker than on the inner ones.

The dermis is thicker than that of pigs and horses, and significantly thicker than that of sheep. Older animals and males have thicker skin than young animals and females. High yielding dairy cows of the same breed have thinner skin than low yielding cows. Animals of hot countries have thinner skin than the same species living in northern latitudes.

The skin itself, removed from killed animals, along with the epidermis, is called a skin or skin, and sometimes skin. The mass of the skin depends not only on the species, breed, age, productivity, but also on the feeding and conditions of the animal. In cattle, the mass of the skin is 7% of the mass of the animal, in sheep - 5-7.3%.

The subcutaneous tissue is formed by loose connective tissue. The better this layer is developed, the more mobile the skin is. Fat cells accumulate in the subcutaneous layer, forming fat reserves, which protects animals from cold and overheating. This is subcutaneous fatty tissue. The fat layer is especially developed in pigs. In the subcutaneous layer, there are muscles that, with a sharp contraction, "shake" the skin, thereby removing dust, water, etc. from it.

Hair formation and structure... The hair of mammals, as well as the feathers of birds, are derived from the skin. Hair is located on the entire surface of the animal's body, except for hard skin formations.

Hair and feathers develop from a group of epithelial cells of the epidermis, which, as a result of invagination, penetrate into the dermis. The density and length of hair depends on the breed of the animal, its individual characteristics, and conditions of detention. On average, 1 cm 2 of skin has up to 700 hairs, in rabbits of the chinchilla breed - from 6,000 to 12,000, in Romanov sheep - up to 5,000, and in merino sheep - up to 8,000.

Hair growth is associated with protein nutrition, in particular with the content in food of the amino acid cystine, which is part of hair proteins. Improved feeding has a positive effect on wool density and length in sheep. Trimming increases the proliferation of cells in the hair follicles and accelerates hair growth.

Stimulates hair growth and irritation of nerve endings. Hair grows more intensively in young animals than in old ones. Hair growth also depends on the season of the year - it is more intense in summer than in winter. The hair of different animals has a different structure. Even the same animal has different hair. For example, in horses, there are short, covering hairs covering the whole body; long hair (mane, tail, brush, bangs), performing a protective role; sensitive, or tactile, hair growing on the lips.

In fine-fleeced sheep, the integumentary hair consists of thin, delicate twisted hairs glued together with grease into a continuous mass - fleece. Coarse-haired sheep in the rune, in addition to thin ones, also have coarse hair called awn. The awn retains the fur coat qualities of a sheepskin, preventing delicate downy hair from knocking into lumps. The color of the fur of animals and feathers of birds depends on the amount and type of pigment contained in the skin.

Bird feathers. The shaft of the feather, which is strengthened in the skin by its point, is equipped on both sides with fans, which consist of thin beards connected to each other. Feathers have evolved primarily as an adaptation to flight and combine lightness with good aerodynamic configuration. Flight feathers of the forelimbs form the wings of birds, the function of the tail feathers is clear from their name, the entire body is covered with contour feathers. Down feathers with a thin shaft and free barbs and down, in which tufts of the finest barbs extend from the end of a very short shaft, are of great importance for protecting the bird's body from cooling. Especially soft pillows and blankets are made of down.

The skin of dogs, like all mammals, consists of:

Epidermis,
... the skin itself - the dermis,
... subcutaneous adipose tissue.

The structure of the surface layer of the skin - the epidermis and its appendages is different in different classes of vertebrates, but they have common properties:

They consist of epithelial cells originating from the ectoderm, and under them is the dermis originating from the mesenchyme;

The skin develops from two embryonic primordia. From the ectoderm of the embryo, the outer layer of the skin develops - the epidermis.

The deep layers of the skin - the dermis and subcutaneous tissue - are formed by the mesenchyme.

The thickness of the skin in vertebrates varies. In addition, it can be different on different parts of the body of the same animal. The epidermis reaches its greatest thickness in places experiencing constant friction when walking and climbing; often calluses are formed here (For example - the soles of the paws, ischial calluses of some monkeys, calluses on the knees of camels, etc.)

In accordance with the species characteristics of animals, the skin is characterized by specific derivatives of the skin: the hooves of herbivores, the comb of a bird, horns, hair, mammary glands in mammals, feathers in birds.

The epidermis of the skin is represented by stratified squamous keratinizing epithelium. Its thickness and degree of keratinization are specific for each type of animal, body region and development of the hairline.

The epidermis of the skin is most fully represented in areas not covered with hair. The process of keratinization is associated with the accumulation of special proteins by cells - keratins and their transformation. There are no blood vessels in the epidermis. Nutrients and oxygen are supplied to it from the capillaries of the dermis, which forms a large area of ​​contact with the epidermis due to the abundance of papillae and a high degree of their development.

The skin is involved in metabolism, in the processes of heat regulation, excretion, synthesis of vitamins (vitamin D), etc. Skin coloration is caused by pigments, which are in the form of melanin grains, distributed in the cells of the growth layer, in the intercellular spaces and in special pigment cells.

The skin itself or the dermis is a derivative of the mesenchyme, consisting of a layer of cells and fibers of connective tissue, below which lies a layer of adipose tissue. Consists of two layers - outer - papillary and inner - reticular.

The blood vessels penetrate the dermis, the endings of the sensory nerves branch out, perceiving temperature and pain irritations. Since pigments are located mainly in the derivatives of the skin - scales, scutes, feathers or hairs - these derivatives are the main carriers of animal color. The skin itself is usually not dyed.

Myakishi.

Derivatives of the skin include crumbs. The crumb is a cushion-shaped thickening of the skin located in the area of ​​the hand and foot. The dog has carpal, metacarpal, metatarsal and digital cushions. Each crumb has a subcutaneous layer (especially yellow adipose tissue), the base of the skin and the epidermis.

In the skin of mammals, there are various glands that secrete various substances and perform different functions.

Skin glands.

Sebaceous glands distributed throughout the skin of mammals, absent only in the skin of the teats of the udder, a patch of pigs and crumbs of the extremities. The excretory ducts of the sebaceous glands open into the hair funnel. The cells of the sebaceous glands form a fatty secretion that lubricates the surface of the skin and hair, contributing to the maintenance of elasticity, and protects the skin from the penetration of microbes and fungi.

Sweat glands located in the deep zone of the dermis. With sweat, decay products are released, but the main function of the sweat glands is thermoregulatory: the sweat released during overheating evaporates, cooling the body. Sweat glands are abundant in primates and ungulates, relatively poorly developed in dogs, cats, lagomorphs and rodents, absent in cetaceans, sloths, and lizards.

Scent glands are modified sweat or, less often, sebaceous glands, and sometimes a combination of both. For example, the anal glands of many predators. The odorous secret of these glands serves primarily for marking the territory and for species identification, less often for self-defense (skunks).

Milky glands- modified sweat glands - develop in females of all mammals. These are specialized glands of the skin associated with hormonal regulation.

Subcutaneous tissue- a layer of loose connective tissue with a high content of fat cells. This layer is usually evenly distributed over the entire body of the animal, but it happens to be concentrated in certain places. The deposition of fat in the subcutaneous tissue of terrestrial animals is used as an energy reserve. Fat deposits are especially high in hibernating animals (marmots, ground squirrels, badgers, bears); they reach their maximum size in autumn.

In most animals, fat stores are not so noticeable and we are not even aware of its presence. Subcutaneous adipose tissue flexibly connects the skin with internal tissues: it provides mobility of the skin, sometimes it is so loosely attached to the body that the animal can practically turn around in it.

Functions of the skin.

The skin performs functions that are types of body responses:

• protective
• thermoregulating,
• receptor,
• excretory,
• respiratory
• suction

Protective function:

Mechanical protection the body's skin from external factors is provided by the dense stratum corneum of the epidermis, the elasticity of the skin, its elasticity and the shock-absorbing properties of the subcutaneous tissue. Thanks to these qualities, the skin is able to resist mechanical stress - pressure, bruising, stretching, etc.
The skin largely protects the body from radiation exposure... Infrared rays are almost entirely retained by the stratum corneum of the epidermis; UV rays are partially retained by the skin.
The skin protects the body from penetration into it chemical substances, incl. and aggressive.
Protection against microorganisms provided by the bactericidal property of the skin (the ability to kill microorganisms). Healthy skin is impervious to microorganisms. With the exfoliating horny scales of the epidermis, fat and sweat, microorganisms and various chemicals that get on the skin from the environment are removed from the skin surface. In addition, sebum and sweat create an acidic environment on the skin that is unfavorable for the reproduction of microorganisms. The bactericidal properties of the skin are reduced under the influence of unfavorable environmental factors - with skin contamination, hypothermia; the protective properties of the skin are reduced in some diseases. If microbes enter the skin, a protective inflammatory response of the skin occurs in response.
The skin takes part in immunity processes.

Respiratory function:

Skin respiration increases with an increase in ambient temperature, during physical exertion, during digestion, an increase in atmospheric pressure, and during inflammatory processes in the skin. Cutaneous respiration is closely related to the work of the sweat glands, which are rich in blood vessels and nerve endings.

Suction function:

There is practically no absorption of water and salts dissolved in it through the skin. A certain amount of water-soluble substances is absorbed through the sebaceous hair follicles and through the excretory ducts of the sweat glands during the period of absence of perspiration. Fat-soluble substances are absorbed through the outer layer of the skin - the epidermis. Gaseous substances (oxygen, carbon dioxide, etc.) are easily absorbed. Separate substances that dissolve fats (chloroform, ether) and some substances that dissolve in them (iodine) are also easily absorbed through the skin. Most of the poisonous gases do not penetrate through the skin, except for skin blisters - mustard gas, lewisite, etc. Medicines are absorbed through the skin in different ways. Morphine is absorbed easily, and antibiotics are in small quantities. The absorption capacity of the skin is enhanced after loosening and desquamation of the stratum corneum of the epidermis.

Excretory function:

The excretory function of the skin is carried out through the work of the sweat and sebaceous glands. With a number of diseases of the kidneys, liver, lungs, the excretion of substances that are usually removed by the kidneys (acetone, bile pigments, etc.) increases. Sweating is carried out by the sweat glands and is controlled by the nervous system. The intensity of sweating depends on the ambient temperature, the general condition of the body. Sweating increases with increasing air temperature, with physical activity. Sweating decreases during sleep and rest. Sebum is secreted by the sebaceous glands of the skin.

Thermoregulatory function:
In the process of vital activity of the organism, heat energy is generated. At the same time, the body maintains a constant body temperature necessary for the normal functioning of internal organs, regardless of fluctuations in external temperature. The process of maintaining a constant body temperature is called thermoregulation. The layer of subcutaneous adipose tissue, the fatty lubricant of the skin are a poor conductor of heat, therefore they prevent excess heat or cold from coming from outside, as well as excessive loss of heat. The thermal insulating function of the skin decreases when it is moisturized, which leads to a violation of thermoregulation. When the ambient temperature rises, the blood vessels of the skin expand - the blood flow of the skin increases. At the same time, sweating increases, followed by evaporation of sweat and the heat transfer of the skin to the environment increases. With a decrease in the ambient temperature, a reflex narrowing of the blood vessels of the skin occurs; the activity of the sweat glands is inhibited, the heat transfer of the skin is noticeably reduced. Thermoregulation of the skin is a complex physiological act. The nervous system, hormones of the endocrine glands of the body take part in it. The temperature of the skin depends on the time of day, the quality of nutrition, the physical condition of the body, the age of the person, and other factors.