Skin

           The skin is a thin layer that covers your whole entire body.  It's almost like a "wrapper" that holds your body together, but does many more things.  It is practically your primary line of defense for your body.  It protects your inner tissues from drying out and also provides you with a sense of touch, grows hair and nails, and even keeps pathogenic microorganisms out of your body. 
            To the right a simple diagram of human skin is shown, also the structure of hair.  The skin is composed of two basic layers, the top is the epidermis, the inner is the dermis, and below the dermis is the hypodermis.  The hypodermis binds the skin to the outer lying tissues.
            The top layer of the epidermis is a layer of dead cells and the inner layer is of living cells.  The living cells are constantly reproducing in this layer of skin.  The dead cells in the epidermis are firm and sturdy and this is what mainly protects your body from pathogenic organisms because it is hard for them to penetrate through.
            Your skin also has hair.  About the only place your skin does not produce hair is in such areas as the palms of your hands and the soles of your feet.  Hair comes from a structure known as a hair follicle which are like tiny pits in the epidermis.  The lowest part of the hair follicle is called the matrix which have cells that rapidly reproduce.  When you get cold, the muscle that controls your hair automatically contracts pulling the hair straight up.  This causes a little bump and keeps in the warm which is usually called a goose pimple.
             Your hair also has sensation so that when your hair is moved or moving it sends signals to your brain telling you that something is touching your skin.  Since hair is so little even a gentle breeze sends off the sensation.
            Your skin also has sweat glands.  The sweat is produced in your sweat glands, travels up through the dermis in the sweat duct, and then pours out onto your skin through your sweat pores cooling you down.  Sweat also feed helpful bacteria and fungi that live on your skin.
            Have you ever wondered why people have different colors of skin?  It depends on how much of a chemical called melanin they have. This chemical is called a pigment because it tends to give off color to whatever it's on.  The more melanin someone has, the darker the skin they have but if someone has a less amount of melanin, they will have lighter skin.
            In the same way, hair's color depends on melanin too.  Dark hair has a lot of melanin in it, whereas, light hair has very little.  Red hair has a mixture of melanin and red pigment.  Without any melanin, the hair is white.