WHAT IS OUR SKIN?

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The main functions of the skin are to protect the body from mechanical impacts, pathogens and excessive water loss. It also serves as thermal insulation, temperature regulation, and as a receptor for part of the senses.

The skin is made up of two main layers - the epidermis and the dermis. Below the dermis is another inner layer - subcutaneous tissue (hypodermis), composed mainly of fat cells and in different parts of the body is of different thickness. The epidermis is composed of 2 layers - germinal (in it the cells are constantly dividing) and horny (composed of dead cells). At the base of the epidermis are pigment cells containing melanin, which gives skin color.

The dermis and epidermis contain a number of nerve endings through which the human body is constantly receiving information about changes in the external environment.

Collagen fibers are grouped in thick bundles. The subcutaneous tissue is composed of loose fibrous connective tissue. It also contains a lot of fatty tissue. Collagen and elastic fibers decrease significantly with age. This leads to a loss of elasticity and smoothness of the skin.

The epidermis is the outermost layer of the skin and is made up of a multilayered squamous corneal epithelium. Its thickness in different parts of the body is different.
The epidermis consists of different cells: keratinocytes (about 95%), melanocytes, Langerhans cells, Merkel cells and undifferentiated dendritic cells. Based on the differences in the number, size, shape and morphology of keratinocytes, there are 4 main layers - from the dermis to the surface, these layers are basal, spiny, granular and horny. Its deepest layer is formed by cells that are constantly dividing. The new cells, whose number is constantly increasing, push the old ones into the upper layers. In this layer there are cells (melanocytes) that produce the dark pigment melanin. It absorbs harmful ultraviolet rays from sunlight and thus protects cells in the deeper layers of the skin. Proof of its action is the fact that in the summer during a long stay at sea or in the mountains, the amount of this pigment increases.

The dermis represents about 15-20% of the total mass of the whole body. It is located under the epidermis and is composed mainly of connective tissue. It provides nourishment to the epidermis and determines the strength of the skin. Its thickness varies from 5 mm on the skin of the back to 1 mm on the skin of the eyelids.

The dermis is richly supplied with blood, about 10% of the total blood flow passes through it. This is of great importance for the thermoregulatory function of the skin, as well as for its role as a blood depot. Blood passes through it much more slowly than through other tissues and can reach up to 1 liter. Immediately below the epidermis, the dermis forms protrusions called papillae. They are most pronounced on the palms and fingers and form a strictly individual pattern. This feature is used in forensic medicine and forensics. Sweat and fat cells, as well as skin appendages, are located in different parts of the dermis. This layer consists of two sublayers - papillary and reticular.

The skin has a number of important functions:

protective - the skin covers the whole body and protects it from microorganisms, protects it from the harmful effects of ultraviolet rays, water loss and more.
sensory - in the skin there are receptors for the perception of external stimuli (heat and cold, touch, pressure, vibration), which are important for the overall senses. In visually impaired people, this skin function is highly developed.
secretory - through the sweat secreted by the sweat glands, the final products of metabolism are released. When the kidneys are damaged, their function is partially complemented by the skin - sweat releases more substances, and diabetes mellitus, the thermoregulatory function of the skin is carried out mainly by sweating and evaporation of substances.
storage - acts as a center for storage of lipids and water.
absorbent - oxygen, nitrogen and carbon dioxide can be absorbed into the epidermis in small amounts. In humans, the cells located at the outermost 0.25 - 0.40 mm of the skin are almost entirely nourished by external oxygen.
evaporation control - the skin provides a relatively dry and semi-permeable barrier to reduce fluid loss.
water resistance - the skin acts as a waterproof barrier so that essential nutrients are not washed out of the body

Tags: skin

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