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Human Body
both a mechanical and a chemical barrier between the body and the environment.
Structure of the Skin
Skin is a two-layered covering. The outer layer, the epidermis, is made from epithelial tissue. The thicker inner layer, the dermis is composed of connective tissue. The skin contains, sweat sebaceous glands and hair. It has been calculated that a single square inch (six square cms) of human skin contains an average of 20 blood vessels, 65 hairs, 100 sebaceous glands and 650 sweat glands, 28 nerves, 13 sense-receptors for cold, 78 for heat, 165 pressure and 1300 for pain.
The Epidermis
The outer layer of the skin is the portion of the body one presents to the view of the world. The innermost part of this layer is continually dividing and pushing towards the surface, during which time the nuclei degenerate and the cells die. The skin cells that are visible, therefore, are dead. This outer layer varies in thickness in different parts of the body. It is thickest on the palms and soles. There are neither blood vessels nor nerve endings in this layer.
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Some of the cells are specialized for the production of the dark pigment melamin, which is the major determinant of the skin colour. More melamin is produced among certain races than in others and this is the basis of colour difference among races.
Dermis
Dermis, the inner layer, is a thick layer of dense connective tissue. The structure of the dermis contributes great strength, toughness, distensibility and elasticity to the skin.
The dermis contains blood vessels, lymphotics, nerves and some structures derived from the epidermis (known as accessory organs). These are the sweat glands, hair, sebaceous glands and nails.
The upper layer of the dermis contains small projections. Since the epidermis is built on top of these projections, the order layer is also structured in a series of hollows and ridges which change the outer appearance of the skin.
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