The skin is the natural outer cover of the human body. It is considered the largest and most holistic organ of man. Its total area can reach two square meters. The main function of the skin is to protect it from environmental influences, as well as to interact with it.
The composition of the skin. The structure, functions and derivatives of human skin
In total, there are three main layers in the skin: the epidermis, dermis and subcutaneous tissue. It is the dermis that is commonly used to call skin or skin. 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 functional terms and in structure.
The mammary glands are complex and alveolar-tubular in structure. Sebaceous, in turn, simple branched and alveolar. As for the sweat glands, their structure is simple tubular and unbranched. Schematically, the structure of 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 dead cells. These dead cells are composed primarily of keratin proteins.
The amount of skin derivatives in mammalian animals is usually greater than in humans. The glands are represented by sebaceous, sweat, mammary, milky and odorous. Also among the derivatives stand crumbs, hooves, horns, claws and hair. One type of hair is the coat.
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 protection against microorganisms and the prevention of maceration of the skin with 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 glands 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 in the upper back. There are completely no glands of this type on the soles and palms.
The structure and structure of the sebaceous glands
The composition of the sebaceous gland is customary to include the excretory duct and the secretory end section. The latter is located near the roots of the hairs in the surface parts of the reticular layer of the dermis, and excretory ducts open at the bottom of the hair funnels.
The secretory end section looks like a pouch measuring 0.2 to 2 mm in size and is surrounded by a basement membrane that is located on the outer germinal layer of cells. These cells, otherwise called germ cells, are poorly differentiated cubic cells, have a well-defined nucleus and are capable of proliferation (proliferation). At the same time, two types of sebocyte cells make up the secretory terminal section. The central zone of the end section has rather large cells of a polygonal shape with actively synthesized lipids.
During the accumulation of fat inclusions, sebocytes move along the cytoplasm to the excretory ducts, and their nucleus undergoes decay and subsequent destruction. Gradually, new clusters of sebaceous glands form from degenerated serocytes, cells die and stand out on the surface of the epithelial layer, which is closest to the secretory section. This type of secretion is called holocrine. The stratified squamous epithelium forms the excretory duct of the gland. At the end, the duct takes a cubic shape and passes into the outer germ layer of the secretory department.
Functions and features of sweat glands
The secret of sweat glands consists of sweat, which is composed of water (98%) and mineral salts and organic compounds (2%). A person releases about 500 ml of sweat per day. The main function of the sweat glands as one of the derivatives of the skin is the participation in the water-salt metabolism, as well as the secretion of urea, ammonia, uric acid and other metabolic toxins.
Equally important is the function of regulating heat transfer processes in the human body. An adult has about 2.5 million sweat glands almost throughout the body. The heat exchange function mentioned above during the release and subsequent evaporation of sweat enhances heat transfer and lowers body temperature.
The structure and structure of sweat glands
The structural elements of the sweat glands are similar to those of the sebaceous. Here, too, there is an end secretory department and excretory ducts. The secretory section 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, cubic or cylindrical epithelial cells that form the tube wall can be detected.
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 salts and water. Outside, a layer of myoepithelial cells surrounds the secretory cells of the terminal sections in the glands. Thanks to their reductions, a secret stands out. The basement membrane serves as a separating element between the connective tissue of the reticular dermis and epithelial cells 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 sweat pores. The bilayer cubic epithelium forms the wall of the excretory duct, and in the epidermis this epithelium becomes flat and multilayered. The stratum corneum does not imply the presence of a wall and duct. By themselves, the cells of the excretory duct in this type of gland do not have very pronounced secretion secretion abilities.
Features of the mammary glands
These glands are inherently modified sweat and come from them. A major role is played by gender. Men have underdeveloped mammary glands that do not function throughout life. 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 gland. This is due to a change in the hormonal background. The period of menopause, which occurs in women after 50-55 years, is characterized by partial wilting of the functions of the mammary glands.
Changes noticeable to the naked eye occur during pregnancy and lactation. The tissue of the glands grows, and they increase in size, and the nipples and areoles around become darker. 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. A reverse situation is also possible when one or both mammary glands of an adult woman are underdeveloped.
Functions and features of hair
Hair is a derivative of the skin of animals and humans, playing for the most part a cosmetic role. There are three types of hair:
- Long hair of the head. Located on the head, in the armpits and on the pubis. In men, long hair is also found in the beard and mustache.
- Bristly hair of eyelashes and eyebrows.
- Fluffy hair. They are located almost throughout the body, their length is from 0.005 to 0.5 mm.
The differences between them are strength, color, diameter and overall structure. In total, an adult has about 20 thousand hair throughout his body. However, the hairline of any species 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, due to which thermally insulating air cushions are created between individual hairs. Ear and nasal hair accumulate dust, dirt and small debris, preventing them from getting inside. Eyelashes restrain foreign bodies, and eyebrows protect eyes from another derivative of the skin - sweat glands and their secret.
The structure and structure of hair
Hair formation occurs due to the hair matrix. The core of each hair has a superficial cuticle on the outside and a cortical substance inside. The roots of long and bristle hair have another zone besides the listed ones - the inner cerebral. The cells of the medulla within this zone move to the surface, provoking the processes of keratinization and the conversion of trichogialin into melanin. Melanin pigments are initially located together with air bubbles and trichogialin granules in the brain part of the hair.
The root expands at the bottom of the hair and forms the hair follicle. It is the poorly differentiated cells in these bulbs that are responsible for the processes of hair growth (regeneration). Below the hair bulb, the hair papilla abuts, which carries the vessels of the microvasculature and provides hair nutrition. Hair follicles are formed from the inner and outer vagina of the hair. Smooth myocytes in hair bags are the very muscles that cause 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 healthy state, which can be seen externally by their shine. When the scaly cover of the hair is destroyed, they cease to reflect light, become split and dull.
Functions and features of nails
Nails are thickenings on the keratinized layer of the epidermis. In total, a person has twenty nails attached to the skin on the terminal phalanges of the fingers and toes. According to the structure of leather derivatives, nails are the hardest formations, convex in shape and transparent.
The main function of nails is to protect sensitive pads under them. An important role is also played by supporting function and assistance in the sense of touch for the nerve endings of the fingertips. The absence of a nail significantly reduces the overall sense of touch on the finger. The removed nail grows in a period of 90 to 150 days.
The structure and structure of nails
The structure of the nails includes the root, the growth zone and the nail plate, which is attached to the nail bed. Due to the powerful replenishment 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 germinal zone of the epidermis, while the nail is the stratum corneum of the epidermis. In the connecting base of the nail bed (in its dermis) is 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.