Architecture Of The Skin
( Originally Published 1927 )
In this modern age, when so much attention is devoted to the care of the skin, exact knowledge of the proper measures for the preservation of its youth, vigor and health is interesting and valuable.
No eruption on the skin should be considered so unimportant as to be completely ignored. True, there are a number of trivial skin conditions caused by mechanical irritations, germs or parasites, but there are many that result from disorders of the internal organs, which not only have a bearing on the general health, but are the forerunners of serious and lingering illnesses. As the average person cannot know the ultimate outcome, or realize the seriousness of a skin eruption, it is urged that competent advice be sought early, for only in this way can one rest assured that no serious or fatal illness threatens.
The "skin" is the term applied to the outer covering of the body. Its thickness varies in different parts as well as in different persons and races. The average thickness of the skin of the eyelids, for example, is about two-tenths of an inch, while that of the palms and soles is about three-tenths of an inch.
It is really difficult for the average person to appreciate the intricate character of the skin with its various component parts. As a result of scientific investigation and study, certain definite facts have been established relative to the skin architecture.
Formation of the Skin. Let us begin our study by tracing the development of the skin.
The earliest sign of what is destined to become the top skin (epiderm) appears between the first and second months after conception. At this period only three layers of very tiny cells (microscopic in size) are visible. In the course of five or six months these cells have greatly increased in size and in number, and display various shapes. By the seventh month many of them have become so modified that the top layer of the skin can be readily identified.
Simultaneously with these changes, another portion of the skin, the true skin, is developing, but in a somewhat different manner, for the bundles of tissue and the cells which enter into its formation increase from within outward. The blood vessels of the true skin (corium) appear about the third month and the glands and hair are formed between the fifth and the eighth month. Thus you see that the fully developed skin consists probably of several different parts. In reality, there are three distinct layers. The outermost layer, that in contact with the air, is named the epidermis; the middle layer, the true skin or corium; and the innermost layer, the subcutaneous tissue.
STRUCTURE OF THE SKIN
The Epidermis. Even this early in our study it is very apparent that although the structural arrangement of these layers varies, there exists a very close relationship which insures unity of ac-. tion. Especially remarkable is the union between the outer layer and the true skin, for they are held together both by an adhesive-like substance and by a series of finger-like elevations and depressions which fit snugly into each other. Every living organ of the body must have blood, yet this part of the skin (the epidermis) is without blood vessels.
Then what provision has Nature made for nourishing it? This layer is nourished by a special fluid (lymph). derived from the blood, an arrangement made possible through the intimate relationship between this layer and the true skin, whereby this special fluid passes from the blood channels of the true skin into the epidermis. This lymph then circulates in canal-like spaces formed by its cells.
To further clarify the wonderful work of Nature, we must delve a little deeper. The epiderm is composed of several layers of cells. Those in the deeper portion, in close contact with the source of the lymph supply, are the most nourished and are therefore soft, spongy, and reproductive. As these age they are replaced by those younger, and as they migrate upwards away from the source of nourishment, they become less delicate and more firm. Finally, when contact with the outside world is established, these cells are hard, horny, and life-less, not only because of the complete cutting off of their nutrition, but also through the deposit of granular materials, both of which serve to prepare them for their special task as protectors of the more delicate parts of the human machinery. You will now understand how the living cells of this upper-most layer are gradually transformed into hard, horny structures and the marvelous mechanisms operative in continuing this process of life. The pigment allotted to the normal skin of the white race is located in the deeper portion of the epidermis.
The True Skin.—The true skin (the corium) consists of fine, threadlike fibers, arranged in alternating finger-like elevations and depressions,
Which interlock with similar parts of the epidermis. These fibers are placed so as to give the skin a certain degree of stretching power. The great importance of this layer is due to the many structures that reside or pass through it. They include the hair and hair sacs, the oil glands, the sweat glands, bundles of muscle tissue, also nerves and nerve endings for the appreciation of various sensations. Let us now study them.
Hair.—Hair consists essentially of two parts, that within the skin termed the root, and that above called the shaft. The lowest portion of the root surrounds a small elevation, known as the papilla, and this is the only living part of the hair. This papilla, with its contained blood vessel, nourishes the hair and upon the integrity of this structure largely depends the very life of the hair. Hair grows from within, upwards, and when it attains a certain length, it appears on the skin surface. Each hair is housed in a slender, cylinder-like sac termed the hair follicle.
The growth and health of the hair depend upon three factors: a normal blood supply, proper oiling, and an intimate union with its hair sac. The 41 oil is furnished by oil glands, so situated as to empty their secretions into the hair sacs. The source of the blood supply has already been de- , scribed. Hair fall is often encouraged by an impoverished blood supply, the result of prolonged fevers, nervous conditions, and other serious illnesses. There are times when hair fall is expedient and this is accomplished, largely, by loosening the interlocking contact between the hair and its sac. A mild electric current is used for this purpose and the process is known as electrolysis. This condition will be more fully discussed under the heading of excessive hair growth. The color of the hair depends upon the quantity of coloring matter and air within it.
Immediately after birth, hair grows quickly upon the scalp. During the change from childhood to adolescence, hair appears upon the face, the armpits, etc., especially in the male. In women, during and following the change of life, increased hairiness is often seen. Throughout life, hair constantly falls and is replaced by new growth.
Sweat Glands.— The sweat glands are located in the deepest part of the true skin. They are most numerous in the armpits, the groin, and upon the palms and soles. They consist of long tubes with an opening upon the skin. It is estimated that there are between two and three million sweat glands. They secrete perspiration or sweat. Under normal conditions, an adult may lose about two pounds of sweat a day. A close relationship exists between the amount of sweat given off and the character and quantity of urine voided. In winter, a small amount of sweat is secreted and the urine is almost colorless and abundant; in summer, perspiration is excessive while the urine is diminished and of darker color. Exercise and hot baths stimulate the sweat glands to increased secretion of perspiration.
Oil Glands.—The oil glands also inhabit the true skin. They are chiefly found in connection with the hair and the hair sacs, but may occur in-dependently of these. They resemble, in shape, bunches of grapes on their vines. They furnish fatty material which lubricates the skin and the hair. Oil glands consist of one or more pouches, which empty into a tubelike structure known as the duct.
Muscles.—The most important muscle group of the skin is the so-called "arrectores pilorum" (erectors of the hair) muscles, usually found in connection with the hair sacs. They originate in the true skin and terminate in the region of several adjacent hair follicles. Sudden contraction of these muscles produces the familiar phenomenon of "goose flesh." The relationship between these, "arrectores" muscles and the hair sacs aids in the expulsion of the oily secretion from the oil glands and in the raising of the hair.
Nails.—The nail is composed of a special variety of "epidermal cells." The visible part of the nail is comparatively lifeless; that portion upon which the nail rests is living and highly sensitive. The nail is held in place by a fold of the skin and by a special interlocking arrangement. The white crescent area, popularly known as the "moon," is termed the lunula. White spots on the nails are supposedly due to the presence of air between the layers of the nail structure. About one hundred to one hundred and sixty days are necessary for the regrowth of the finger nail, and about three times that period for that of the toenail.
The Subcutaneous Tissue.—The third layer of the skin, the subcutaneous tissue, consists mainly of masses of fat. It contains some hair. and many of the sweat glands and serves to convey the blood vessels to the true skin. The fat is largely responsible for the natural outlines of the body. When a person is emaciated, this fat deposit is greatly reduced.