The skin is one of the largest organs, as well as one of the heaviest, weighing as much as 4-5 kilograms. The skin covers the entire outer surface of the body and thus represents a defense against external factors. It is composed of three layers. The outermost layer, which is in contact with the external environment, is called the epidermis. Next comes the middle layer, which is called the dermis. The innermost layer is called the hypodermis. All three layers differ greatly in their anatomy and function.

The skin has more functions than you might think

The main task of the skin is to protect us from external factors. It represents the first line of defense and thus also protects our organs. The skin represents mechanical protection, meaning that it protects us from the penetration of bacteria and viruses, from UV radiation and from the penetration of chemicals into the body. It also has a barrier function. The barrier function of the skin protects us primarily from water evaporation.

We also sense pressure, touch, pain, itching and temperature through the skin. The skin also participates in thermoregulation. The skin helps regulate body temperature, which helps to warm or cool the body. It is a reservoir of water and an energy reservoir in the form of fat, which is found in the subcutaneous tissue. Harmful substances are also eliminated from the body through the skin, through sweat.

The epidermis is composed of several layers

The epidermis is the top layer of the skin, which has a protective function and protects us from external factors. The epidermis consists of 4 layers: the basal layer (stratum corneum), the thorny layer (stratum granulosum), the granular layer (stratum spinosum) and the horny layer (stratum basale). The topmost layer, also called the horny layer or stratum corneum, consists of 20-30 layers of thin, flat cells that act as a barrier. Glycolipids are formed in the granular layer, which are secreted onto the surface of the cells and act as glue, so that the cells stick together. In the lowest, horny layer, new skin cells (keratinocytes) are formed, which allow skin renewal.

The epidermis renews itself every 28 days.

This is another interesting feature of our skin, namely that the epidermis renews itself every 28 days. In this process, the top layer of dead cells (corneocytes) is sloughed off, and living cells (keratinocytes) come to the surface. Quite similar to molting in snakes, only not as obvious.

Skin pH has a significant impact on barrier function

Our skin also has a certain pH, which is important for its normal functioning. The pH increases rapidly from the surface of the skin towards the lower layers of the epidermis (there it is equal to the physiological pH, which is 7.4). The pH on the surface of the skin usually ranges between 4 and 5.5, in intact skin. The pH of the skin is influenced by sebum, sweat and phospholipids. The acidic protective layer on the skin affects the barrier function of the epidermis and the antimicrobial protection of the skin.

On the surface of the skin we find the ducts of the sebaceous and sweat glands, as well as hair. Due to the ducts of the sebaceous glands on the epidermis, we also have fats present on it, which allow the skin to be flexible and prevent the formation of scales and cracks. Fats on the skin come from two sources, namely epidermal lipids, which maintain the barrier function of the skin, and secretions of the sebaceous glands or sebum.

The dermis is important for the mechanical strength of the skin

The dermis is a layer of connective tissue located between the epidermis and the subcutaneous tissue. The dermis is a fibrous structure composed of collagen, elastin, nerve endings, hair follicles, and glands. The dermis plays an important role in supporting and protecting the skin and deeper layers, and also helps with thermoregulation. The dermis is mainly made up of cells called fibroblasts. These cells are involved in the synthesis of new collagen tissues. The dermis also contains immune and fat cells, which also play an important role in maintaining the normal structure and function of the dermis.

Collagen is the most abundant protein in the dermis. It plays an important role in providing the skin with mechanical strength. Type I and type III collagen are found in the dermis. Collagen is also found in muscles, bones, teeth, cartilage, and the walls of all body organs. Elastin also plays an important structural role in the dermis.

Interesting fact: sebaceous glands and one type of sweat gland only become active during puberty

The dermis also contains all the skin appendages – hair follicles, sebaceous glands, and sweat glands. Sebaceous glands are not active in childhood, they only begin to function during puberty, due to the influence of hormones. They are densely present on the face, behind the ears, upper chest, and back. In oily skin, the sebaceous glands are larger than in dry skin. Sebum, which consists of triglycerides, squalene, and sterols, is secreted through the sebaceous glands. In the dermis, there are two types of sebaceous glands, one is called apocrine sweat glands, and the other is called eccrine sweat glands. Eccrine sweat glands participate in thermoregulation, and eccrine sweat consists of 99% water and 1% salt. Apocrine sweat glands only become active during puberty. Apocrine sweat has a characteristic odor and is composed of cholesterol, triglycerides, and fatty acids.

Subcutaneous

The subcutaneous tissue is the largest and thickest part of the skin, consisting mainly of fat. The subcutaneous tissue accounts for 10% of body weight, so the next time you weigh yourself, you can confidently subtract that 10%. Jokes aside. The subcutaneous tissue mechanically protects our internal organs. Due to its high fat content, it provides excellent thermal insulation for our vital organs and is a store of energy. Numerous hormones are synthesized in the subcutaneous tissue.

The blog was created in collaboration with Cosmedoc.si