Biology The Skin
The skin is the largest organ of the body. The skin, including nails, hair, and sweat glands, is sometimes called the integumentary system. If the skin of a 150-pound (68-kilogram) person were spread out flat, it would cover approximately 20 square feet (1.9 square meters). Skin has two layers: the epidermis and the dermis. Subcutaneous tissue provide protection for the skin. The epidermis forms the outermost layer of the skin. It serves as a bar
The outer portion of the epidermis consists of tough, dead cells that prevent bacteria, chemicals, and other harmful substances from entering the body. They provide extra fuel for the body. When the body needs to give off heat, the blood vessels in the dermis expand and so increase heat loss. It also protects the body's inner tissues from the harsh rays of the sun and prevents the loss of water from these tissues. Nerve endings within the dermis respond to cold, heat, pain, pressure, and touch. Some of this heat escapes from the body through the blood vessels in the dermis. When the body needs to retain heat, these blood vessels narrow and so limit heat loss. As the sweat evaporates from the surface, it cools the body. The sweat glands, which come from the epidermis, also help control body temperature. rier between the outside world and the inner tissues of the body. The dermis also serves as an important sense organ. Subcutaneous tissues also help retain body heat and cushion the inner tissues against blows to the body. Subcutaneous tissues lie directly beneath the skin. The dermis helps keep the temperature of the body within its normal range.
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