Skin is the largest organ of human body, accounting for about 15% of body weight, and the body surface area of adults is 12-20 square feet. The chemical composition of skin includes 70% water, 25% protein and 2% lipid, as well as trace elements, nucleic acids, glycosaminoglycans, proteoglycans and a lot of other chemicals.
Extended data
Skin action
(1) barrier function: On the one hand, the skin protects various organs and tissues in the body from harmful factors such as machinery, physics, chemistry and biology in the external environment, on the other hand, it prevents the loss of various nutrients, electrolytes and water in the tissues. Therefore, skin plays an important role in maintaining the stability of the internal environment of the body. Without skin, it is hard to imagine how the organs in our bodies will function.
(2) Sensory function: Sensory nerve and motor nerve are distributed in the skin, and their nerve endings and special receptors are widely distributed in epidermis, dermis and subcutaneous tissue, which can sense stimulation, produce various senses such as touch, cold, temperature, pain, pressure and itching, and cause corresponding nerve reflex.
(3) Function of regulating body temperature: Body temperature is the expression of heat generated in the process of substance metabolism in the body, and it is also one of the indispensable conditions for various biochemical reactions and physiological activities of body cells. Skin is an important part of body heat dissipation. The body temperature can be adjusted by vasoconstriction, hair bristling, perspiration reduction and other forms, and heat can also be dissipated by physical means such as radiation, convection, conduction and evaporation.
(4) Absorption: The skin has the ability to absorb foreign substances through the stratum corneum, hair follicle sebaceous glands and sweat pores, which is called percutaneous absorption, permeation or infiltration. It is indispensable for maintaining health, and it is also the theoretical basis for the treatment of dermatoses with external drugs in modern dermatology.
(5) Secretion and excretion: The skin has certain functions of secretion and excretion, mainly through sweat secretion by sweat glands and sebum excretion by sebaceous glands. Sweating has the functions of cooling, caring skin, excreting drugs and replacing some functions of the kidney. Sebum has the function of forming lipid film on epidermis and lubricating hair and skin.
(6) Immune function: Both epidermis and dermis of skin contain cells involved in immune response, such as keratinocytes, Langerhans cells, lymphocytes and macrophages. Keratinocytes secrete cytokines such as interleukin-1, interleukin -2, interleukin -3 and interleukin -6, which participate in the regulation of skin immune function and can activate target cells. Langerhans cells can bind antigens and transmit antigen information to immunocompetent cells to start immune response.
(7) Metabolism: Like other tissues and organs of human body, skin has the same biochemical metabolism process. When the metabolism of the body is disturbed, it will also affect the normal metabolism of the skin, which will lead to the occurrence of capacitive dermatosis. On the contrary, when skin metabolism is disturbed, it will also affect the metabolism of the whole body. For example, 7- deoxycholesterol in epidermis can be synthesized into vitamin D3 after ultraviolet irradiation. When there is a problem in the process of this generation, it will affect the absorption of calcium by the human body and cause rickets.
Resource Skin _ Baidu Encyclopedia