SKIN: GENERAL INFORMATION
The body is covered entirely with skin, from top to toe. This skin is in fact a very complex organ and has a totally different function than, for example, the skin of a cheese. A person's skin is responsible for many different functions. It is a mighty weapon, acting as a barrier against outside influences and has a vitally important role in maintaining a constant body temperature of 37 degrees Celsius. The skin also behaves like a third kidney, as in the control of perspiration: it filters out waste products and ensures that we do not dehydrate.
The skin is one of the biggest organs of the body and a man has roughly 1.5 square metres of skin, weighing about 4.5 kilogrammes with 10 kilogrammes of fat underneath. Contrary to the male, the skin of a female weighs about 3 kilogrammes and the fat underneath weighs 12 kilogrammes.
The skin is made up of two distinct layers. The outer or superficial layer is called the epidermis, while the deeper layer is known as the dermis. During the first month of pregnancy, an embryo is covered by a single layer of ectodermal cells. During the second month the periderm develops over the surface. By the end of the fourth month, four distinct layers of skin are evident. The basal layer is known as the germinative layer and is responsible for producing new skin cells. This latter layer forms into ridges and hollows which we see as fingerprints on the surface. Fingerprints form the basis of many genetic studies and, of course, are used in criminal investigations. During the third and fourth months the lower layer is formed. This is the dermis, and the inner layer is called the subcorium, while the outer layer is known as the corium. The skin glands form in the corium and the deeper layer, or subcorium, consists of fatty tissue. The epidermis is responsible for the growth of nails and hair, and the dermis contains arteries and nerves.
Depending on what is required from the skin, it can be thick and rough, or fine and supple. Hormonal secretions determine whether the skin is dry or oily.
The cells of the epidermis house a substance called keratin. These cells are very thin fibres on the top layer of the skin. Keratin strengthens the skin and also makes it impossible for water to permeate, thus making us waterproof. There are also glands which ensure that water cannot penetrate the skin, and they secrete a fatty substance which destroys bacteria on the surface. This network which also consists of small blood vessels or capillaries in the cutis, penetrates the epidermis and carries nourishment to the follicles and the skin glands.
The elastic and collagen fibres which surround this structure do a highly efficient job. When we see how quickly the skin regenerates after a little damage, we realise that it deserves to be treated with great respect. It is really wonderful to see how a small cut is healed by so many invisible helpers. There are few tissues in the body that work as effectively as the skin and yet, on the whole, we take little care of this valuable, protective layer.
Keratin is a very important substance and is the main ingredient of nails and hair. Nails start to grow after two months' growth of the embryo in the uterus, and after five months the nails are fully developed. While the total thickness of the skin is only a few millimetres, finger nails grow at a rate of about one millimetre a week.
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