Skin



The living barrier
"A layer of skin, usually less than one-fourth of an inch (5mm) thick, is the only barrier between the body's interior, with its delicate cells and finely blanched fluids, and the harsh, changing conditions of the outside world. Yet we rarely give our skin a second thought-unless it becomes bruised, cut, burned or otherwise damaged." -- The Body's Surface

Skin is pretty amazing, if you stop to think about it. The average adult has two square yards of it, constituting 15 percent of their total body weight. Each square inch contains an average of 625 sweat glands, 65 hair follicles and 19,000 sensory glands. At its thinnest, the eyelid, it protects the delicate cornea and at its thickest, the bottom of the feet it cushions the skeleton, making movement possible.

The skin is the largest organ of the human body. It covers a person completely from head to toe. Skin is waterproof and tough enough to protect someone from germs and dirt. Skin is elastic and flexible, it regulates fluid loss and body temperature. Skin contains nerves which send the brain messages about the texture or surface of things that we touch. The skin gives a person his/her identity by defining the color and shape a person sees in a mirror.

Epidermis
Microscopic view of the skin on the palm of the hand.

The skin has two layers. The epidermis is the thin, outer layer of the skin. Oil that is secreted through glands make the skin waterproof. The outermost layer of the epidermis is made up of dead skin cells. These dead skin cells are replaced by new cells that grow underneath. The skin grows new cells constantly.

Dermis
Microscopic view of a sweat gland.

The second inner layer of the skin is called the dermis. The dermis is filled with blood vessels, nerves, hair follicles and sweat glands. The blood vessels feed the skin growth cells and carry away waste. They are able to open wide to bring more blood to the surface of the body or they can close a little to keep the warm blood deep inside the body. These blood vessels also help control or regulate the body temperature to keep it between 79 degrees and 99 degrees Fahrenheit (normal body temperature).

Microscopic view of a dead skin cell.

Each year, up to nine pounds (four kg) of your skin wears away and flakes off your body's surface. The skin that falls from your body collects as dust, which you can find around the house. You do not lose this amount of weight, because your skin is constantly renewing itself. This renewal takes place in the skin's outer layer, the epidermis.

Cells in the lower part of the epidermis are always multiplying. Their "offspring" pass upward, gradually becoming filled with a tough fibrous substance called keratin. By the time they reach the surface, the cells are hard, flat and dead - ready to be worn away. This continual cell sacrifice in the epidermis protects the lower layer, the dermis, which contains delicate blood vessels, nerves and touch sensors.