The skin is the largest organ, the mass of which is about three times that of the liver. Reflecting harmful environmental factors, the skin is a protective barrier to the body, and also participates in the processes of thermoregulation, metabolism, respiration. The histological structure of the human skin is difficult enough, therefore we will consider it in the most simplified kind.
Skin layers
The human skin is represented by three layers:
- epidermis, which in turn consists of five layers;
- dermis - a two-layer connective tissue;
- hypodermis or subcutaneous fat.
The upper (outer) layer is the epidermis, the thickness of which differs in different parts of the body. Depending on this, the skin is classified into thick (on the soles, palms) and thin (on the remaining parts of the body).
The skin is supplemented by its derivatives (appendages):
- nails;
- hair;
- sweat glands;
- sebaceous glands.
Epidermis
In the epidermis there are no blood vessels - cells are fed through the intercellular space.
Layers of the epidermis:
- horny - outer layer, consisting of keratinizing epithelium; its cells are filled with protein keratin and, in fact, are already dead;
- shiny - filled with a special protein substance that refracts light;
- granular - represented by 1-5 rows of flattened cells;
- spiny - consists of 3-8 rows of cells with cytoplasmic outgrowths;
- basal - the lowest layer, which rests on the basal membrane, bordering on the dermis, and consists of a prismatic epithelium.
The cells of the stratum corneum constantly peel off, they are replaced by new ones, migrating from deeper layers.
Dermis and hypodermis
The structure of the dermis (actually the skin) is represented by two layers.
In the papillary layer are smooth muscle cells, connected with hair bulbs, nerve endings and capillaries. Below the papillary is a reticular layer, represented by elastic, smooth muscle and collagen fibers, due to which the skin is firm and elastic.
Subcutaneous fat or hypoderma consists of bundles of fat accumulations and connective tissue. Here, nutrients are accumulated and stored.
Skin on the face
The structure of human skin is somewhat different in certain areas of the body.
In the facial area is the least amount of sebaceous glands - this also determines the peculiarity of the structure of the skin of the face. Depending on the amount of secretion secreted by the glands, it is customary to classify the skin into a fat, normal, dry and combination type. Around the eyes and on the eyelids is the zone of the thinnest epidermal layer. The skin of the face is most susceptible to the influence of weather and environmental influences, therefore it needs systematic care.
Skin of hands
On the palms (as well as on the soles of the feet) there are no gun hair and sebaceous glands, but the sweat glands in these areas are the most - due to the substance released by them, the hands do not slip when moving. The structure of the skin of the palms of the hands differs more rigidly with the subcutaneous tissues. On the back of the palms, the skin is very elastic, soft and delicate - thanks to these features a person can squeeze fingers.
Skin of head
Features of the structure of the scalp are due to the presence of hair papillae, formed by the seizure of connective tissue onion, which is located in the sac follicle. The narrow end of the bulb is called the root, the hair itself grows from it. The part located above the epidermis is called the hair shaft, around it are the conclusions of the sebaceous and sweat glands. To the papilla, nerve endings and capillaries that feed the bulb and hair growth are suitable.
Skin Functions
The composition and structure of the skin determine its importance and the main functions:
- Protective (from chemical influences, UV-rays, loss of moisture);
- thermoregulatory (thanks to the evaporation of sweat and heat radiation);
- excretory (excretion of salts, metabolic products, drugs with sweat);
- endocrine and metabolic (synthesis of hormones, accumulation of vitamin D);
- receptor (due to nerve endings);
- immune (participation in the formation of an immune response).