The skin is the largest organ in the human body, the weight of the skin is about 15-20% of the total body weight. The surface area of the skin in an adult is approximately 1.5-2 m ².
The thickness of the upper layer of the skin (epidermis) in areas that are subjected to constant mechanical pressure (palms, soles) reaches 0.5-2.3 mm, in the rest it does not exceed 0.02-0.05 cm.
The thickness of the dermis is 1-2.5 mm.
The thickness of the hypoderm depends on nutrition, lifestyle, heredity.
Skin functions.
1. Protective function
Each skin layer takes a role in this function.
The epidermis is the uppermost layer of the skin, which is why it has to take on the "whole blow," and the degree of protection of the whole organism will depend on the thickness of the stratum corneum. Collagen and elastin fibers are located in the dermis, which help the skin stretch and recover. In the hypoderm are fat cells - adipocytes, collagen and elastin fibers, which give us good cushioning (when falling).
2. Thermal control function
Thanks to this function, our body can give away, hold and absorb excess heat. The temperature of our environment is constantly changing, which means that the amount of heat given by our body will also change. The temperature of the skin depends on the amount of blood that comes to it, the higher the blood flow, the higher the temperature. This leads to an increase in heat transfer.
Conversely, if the vessels narrow, the amount of incoming blood decreases and heat lingers in the body, which helps protect the body from hypothermia.
In hot weather, with physical exertion, so that there is no overheating of the body, heat transfer helps - by releasing sweat, since the released heat using vessels will not be sufficient. If the ambient air temperature is low, the vessels narrow and retain heat inside the body.
3. Respiratory function
Only 2% of the skin can absorb oxygen and release carbon dioxide. This happens when the temperature of the environment increases, during digestion, during physical activity.
4. Receptor function
There are a large number of sensitive nerve endings in the skin - receptors that are responsible for something specific: heat, cold, pain, touch. This helps the body avoid possible damage.
5. Secretory function
Sebal and sweat glands secrete sebum (sebum) and sweat, which, mixing on the surface of the skin, create a "certain film" - a hydrolipid mantle. Sebaceous glands secrete lipids (fat), and sweat glands - hydro (water). The hydrolipid mantle is a protective "film" for the skin.
6. Excretory function
It is associated with secretory, during the release of sweat and sebum (sebum), other substances are released on the skin surface: organic and inorganic origin, minerals, hormones, carbohydrates, enzymes.
7. Resorption function
This function is responsible for the penetration of drugs, cosmetics, ointment, lotion inside and affect the body from the inside. But thanks to the epidermis, it does not allow all formulations to penetrate deep.
8. Immune function
In some layers of the skin are cells that are responsible for immunity: keratinocytes, T-lymphocytes, Langerhans cells. If suddenly some antigen enters the human body: a virus, a microbe - immune cells immediately recognize it and the process of destroying this antigen begins. Immune cells create biologically active substances in the human body that kill this antigen.
