The Skin

The skin covers the outer surface of the body and is our interface with the natural environment. It is the body organ with the biggest area and the heaviest weight. The skin protects the inside of the body from physical, mechanical and thermal influences. It prevents fluid loss from the body and penetration by microorganisms into the body. The skin plays an important role in our immune defence system and acts as a filter against ultraviolet light. It also plays an important role in body temperature, electrolyte and water regulation. The pigment melanin and vitamin D are formed in the skin on exposure to sunlight.

The skin protects the body from the external environment, but also interacts with it through the nervous system. Free nerve endings and sensory organs detect pressure, vibration, heat, cold, pain and itching. This information is transmitted to the brain through the nerve paths.

At the body orifices (eyelids, nostrils, lips, urethral orifice, vaginal entrance, anus), the external skin changes and becomes the internal mucous membranes. So the body is covered on the outside by the skin, on the inside by the mucous membranes.

The skin has a surface area of about 1.5 to 2.0 m² and accounts for some 15 to 20 % of our body weight. It consists of three layers: the outer skin (epidermis), the true skin (dermis) and the underskin (subcutis). The epidermis has a thickness of 0.1 – 4.0 mm, the dermis of 1.0 – 5.0 mm. The skin is thinnest on the eyelids, relatively thin on the forehead, thicker on the back, and thickest on the palms of the hands and soles of the feet. This is to protect the hands and feet from the heavy mechanical stresses of grasping and walking.
Appendages of the skin:
The hair, nails, sebaceous, sweat and scent glands are termed adnexae of the skin and develop from the epidermis.
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