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Skin, hair and nails

This is a cross-section through skin, greatly enlarged. Skin has two layers. The upper epidermis continually renews itself as its...Read More >>This is a cross-section through skin, greatly enlarged. Skin has two layers. The upper epidermis continually renews itself as its hard, dead outer surface is worn away by daily activity. The much thicker lower layer, the dermis, contains nerves, blood vessels, sweat glands and hair follicles.The body’s largest organ is the skin. It is a protective "overcoat" that covers the entire body. Tough, flexible and waterproof, skin protects the body from damage, filters out harmful rays in sunlight, prevents drying out, and stops micro-organisms that cause disease, such as bacteria, entering the body. The skin helps keep body temperature constant by reducing body temperature in hot conditions, through sweating and increased blood flow and raising it in cold conditions. The skin also contains millions of tiny nerve endings that provide the body’s sense of touch.



A micrograph (photo taken through a microscope) of a cross-section through skin, showing a sweat gland

Inside the skin

Skin has two layers. The upper layer, the epidermis, constantly renews itself. Dead skin flakes—flattened cells packed with tough, waterproof keratin—are worn away. Cells in the lower part of the epidermis divide constantly to produce new cells to replace lost skin flakes. Melanin, a dark pigment, colours the epidermis and filters out harmful rays in sunlight. 
The thicker, lower skin layer, the dermis, contains blood vessels, oil and sweat glands, hair follicles, and nerve endings that detect touch, heat, cold and pain.
Hairs and the epidermis are kept soft by oil from sebaceous glands. In hot conditions, sweat, a salty liquid, is released by the sweat glands. The sweat takes heat away from your skin as it evaporates and cools the body.

Of all mammals, only primates—the group that includes baboons, chimps and humans—have nails on their fingers and toes.

WHY IS THE SEA SALTY?


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