Skin is the natural outer covering of the human body. It is considered the largest and most complete human organ. Its total area can reach two square meters. The main function of the skin is to protect against environmental influences, as well as in interaction with it.
Composition of the skin. Structure, functions and derivatives of human skin
In total, there are three main layers in the skin: epidermis, dermis and subcutaneous tissue. It is the dermis that is commonly called the skin or skin integument. Modern medicine distinguishes four different derivatives of human skin: sebaceous, sweat and mammary glands, as well as hair and nails. Each of the three types of glands is significantly different from the other two, both in terms of function and structure.
The mammary glands are complex and alveolar-tubular in structure. Sebaceous, in turn, are simple branched and alveolar. As for the sweat glands, their structure is simple tubular and unbranched. Schematically, the structure of the sweat glands can be depicted as a "snake".
Other derivatives of human skin -hair and nails - are formed directly in the epidermis, and are formed from already dead cells. These dead cells consist mainly of keratin proteins.
The number of derivatives of the skin in mammals is usually greater than in humans. The glands are represented by sebaceous, sweat, milk, milky and odorous. Also, crumbs, hooves, horns, claws and hair stand out among the derivatives. One type of hair is wool.
Functions and features of the sebaceous glands
The sebaceous glands have a holocrine type of secretion. The secret of this type of gland consists of sebum, the function of which is to lubricate the surface of the hair and skin, giving them elasticity and softness. Another function of the sebaceous glands as derivatives of the skin is considered to be protection against damage by microorganisms and the prevention of maceration of the skin by moist air and water.
Every day, the body secretes up to 20 grams of sebum through the sebaceous glands. Almost always, the concentration of this type of gland in a certain place can be associated with the presence of hair in it. The main part of the sebaceous glands is located on the head, face and upper back. There are no glands of this type on the soles and palms.
Structure and structure of the sebaceous glands
It is customary to include the excretory duct and the secretory end section in the composition of the sebaceous gland. The latter is located near the roots of the hairs in the superficial parts of the reticular layer of the dermis, and at the bottom of the hair funnels openexcretory ducts.
The secretory end section looks like a sac ranging in size from 0.2 to 2 mm and is surrounded by a basement membrane, which is located on the outer germinal layer of cells. These cells, otherwise called germ cells, are poorly differentiated cells of a cubic shape, have a well-defined nucleus and are capable of reproduction (proliferation). At the same time, the secretory terminal section consists of two types of sebocyte cells. The central zone of the terminal section has rather large polygonal cells with actively synthesizing lipids.
During the accumulation of fat inclusions, sebocytes move through the cytoplasm to the excretory ducts, and their nucleus undergoes decay and subsequent destruction. Gradually, new accumulations of sebaceous glands form from degenerated serocytes, the cells die and stand out on the surface of the epithelium layer, which is closest to the secretory section. This type of secretion is called holocrine. Stratified squamous epithelium forms the excretory duct of the gland. At the end, the duct acquires a cubic shape and passes into the outer growth layer of the secretory section.
Functions and features of sweat glands
The secret of the sweat glands consists of sweat, which consists of water (98%) and mineral s alts and organic compounds (2%). A person produces about 500 ml of sweat per day. The main function of the sweat glands as one of the derivatives of the skin is considered to be participation in water-s alt metabolism, as well as the secretion of urea, ammonia, uric acid and other metabolicslag.
No less important is the function of regulation of heat exchange processes in the human body. An adult has about 2.5 million sweat glands throughout the body. The above-mentioned function of heat exchange during the release and subsequent evaporation of sweat enhances heat transfer and lowers body temperature.
Structure and structure of sweat glands
The structural elements of the sweat glands are similar to those of the sebaceous glands. Here, too, there is a terminal secretory section and excretory ducts. The secretory department outwardly resembles a tube twisted like a ball with a diameter of 0.3 to 0.4 mm. Depending on the phase of the secretory cycle, cuboidal or columnar epitheliocytes can be found forming the wall of the tube.
There are dark and light types of secretory glands. The former are engaged in the release of organic macromolecules, and the latter in the secretion of mineral s alts and water. Outside, a layer of myoepithelial cells surrounds the secretory cells of the terminal sections in the glands. Thanks to their abbreviations, the secret stands out. The basement membrane serves as a separating element between the connective tissue of the reticular layer of the dermis and the epitheliocytes of the secretory sections of the sweat gland.
Through the reticular and papillary layers of the dermis, the excretory ducts of the glands pass in a spiral form. This spiral pierces absolutely all layers of the dermis and opens on the surface of the skin in the form of a sweat pore. The bilayer cuboidal epithelium forms the wall of the excretory duct, and in the epidermis this epithelium becomes squamous and stratified. The stratum corneum does not imply the presencewalls and channels. By themselves, the cells of the excretory duct in this type of gland do not have a strongly pronounced ability to secrete a secret.
Features of the mammary glands
These glands are essentially modified sweat glands and come from them. The gender factor plays a big role here. Men have underdeveloped mammary glands that do not function throughout their lives. In women, the mammary glands play the role of one of the most important derivatives of the epidermis and skin. The beginning of puberty marks the start of a very intensive development of this type of glands. This is due to hormonal changes. The period of menopause, which occurs in women after 50-55 years, is characterized by a partial withering of the functions of the mammary glands.
Changes visible to the naked eye occur during pregnancy and lactation. The tissue of the glands grows, and they increase in size, and the nipples and areolas around them acquire a darker shade. With the cessation of feeding, the glandular tissue returns to its previous size.
Pathologies are known in which men develop mammary glands according to the female type. This is called gynecomastia. In addition, in some cases, with polymastia, additional nipples appear, and sometimes additional mammary glands. The opposite situation is also possible, when one or both mammary glands in a sexually mature woman are underdeveloped.
Functions and features of hair
Hair is a derivative of the skin of animals and humans, playing for the most partcosmetic role. There are three types of hair in total:
- Long head hair. Located on the head, in the armpits and on the pubis. Men also have long hair in the beard and mustache area.
- Bristly hair of eyelashes and eyebrows.
- Vlulu hair. They are located almost throughout the body, their length is from 0.005 to 0.5 mm.
The differences between them are in strength, color, diameter and general structure. In total, an adult has about 20 thousand hairs throughout the body. However, hair of any kind is completely absent on the soles, palms, and partially absent on the genitals and the surface of the fingers.
Of the other functions of the hair, it is worth noting the protective one, thanks to which thermally insulating air cushions are created between individual hairs. Ear and nose hairs accumulate dust, dirt and small debris, preventing them from getting inside. Eyelashes contain foreign bodies, and eyebrows protect the eyes from another derivative of the skin - sweat glands and their secretions.
Structure and structure of hair
The formation of hair occurs due to the hair matrix. The shaft of each hair has a superficial cuticle on the outside and a cortex on the inside. The roots of long and bristle hairs have one more zone in addition to those listed - the inner brain. The cells of the medulla inside this zone move to the surface, provoking the processes of keratinization and the conversion of trichohyalin into melanin. Melanin pigments are initially located together with air bubbles and trichohyalin granulesin the medulla of the hair.
The root expands at the bottom of the hair and forms a hair follicle. It is the undifferentiated cells in these bulbs that are responsible for the processes of hair growth (regeneration). Below the hair follicle rests the hair papilla, which carries the vessels of the microcirculatory bed and provides nutrition to the hair. Hair follicles are formed from the inner and outer sheath of the hair. The smooth myocytes in the hair follicles are the same muscles that cause the hair to be perpendicular to the surface of the dermis.
Hair is a derivative of the skin that is able to reflect light in a he althy state, which can be seen externally by its luster. With the destruction of the scaly cover of the hair, they cease to reflect light, become split and dull.
Functions and features of nails
Nails are thickenings on the stratum corneum of the epidermis. In total, a person has twenty nails on the terminal phalanges of the fingers and toes, attached by connective tissue to the skin. According to the structure of skin derivatives, nails are the hardest formations, convex in shape and transparent.
The main function of nails is to protect the sensitive pads underneath. Also important is the support function and help in touch for the nerve endings of the fingertips. The absence of a nail significantly reduces the overall sense of touch in the finger. The removed nail grows back within 90 to 150 days.
Structure and structure of nails
The structure of the nails includes the root, the growth zone and the nail plate attached to the nail bed. Due to the powerful supply of blood and minerals, nails can grow by a millimeter in just a day. The edge of the nail and the sides pass through the skin fold, while the other edge remains free.
The epithelium in the nail bed is formed by the growth zone of the epidermis, while the nail is the stratum corneum of the epidermis. In the connective base of the nail bed (in its dermis) there are a large number of elastic and collagen fibers. The composition of the nail also includes hard keratin. Like other derivatives of the skin, nails have impressive regeneration capabilities and grow throughout a person's life.
