SKIN

The skin, along with hair and nails, provides the body with a protective outer covering that shields it, for example, from harmful solar rays. It also provides our first line of defence against infection, helps control water loss from the body, plays an important role in TEMPERATURE CONTROL, and contains the receptors that provide the sense of touch.

STRUCTURES IN THE SKIN

Many different structures exist in the dermis, including blood vessels, nerves, hair follicles, and sweat glands. The nerve fibres terminate in free (uncovered) endings, in touch receptors, or in other types of receptors sensitive to pressure, vibration, or temperature change.

SKIN LAYERS

The skin has two main layers, called the epidermis and dermis. The epidermis consists of an upper layer of dead cells and a lower living layer, which replaces cells as they are lost from the upper layer. Beneath the epidermis is the thicker dermis, which overlies an insulating layer of fatty tissue.

HAIR FOLLICLE

Hair grows from follicles, pockets of epidermal tissue that extend down into the dermis. Hair has a cycle of growth, rest, and then loss, when the new hair pushes the old hair out of the follicle. About 100 hairs are lost and replaced in a person’s scalp every day.

FINGERNAIL

The ends of the fingers and toes are covered by nails. These plates of tough protective tissue are made mainly of keratin, a protein also found in hair and skin. Nails grow from a region of living cells called the germinal matrix, which lies underneath a fold of skin called the cuticle.

TEMPERATURE CONTROL

The blood vessels, hairs, and sweat glands of the skin work together to help control body temperature. If we get too hot, our sweat production increases and blood vessels widen to allow more blood to reach the skin’s surface, where it cools. If we get too cold, these processes go into reverse. In addition, tiny muscles attached to the hair follicles pull the hairs erect, trapping an insulating layer of air next to the skin.

SWEAT PORE

Sweat, a salty liquid, reaches the surface of the skin through pores. The pore is surrounded by dead epidermal cells. Sweat evaporates from the surface of the skin and so helps to lower the body temperature. Sweating also rids the body of excess water and some waste products.

Copyright © 2007 Dorling Kindersley

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