Structure of the Skin

 Perspiration

There are from 2 to 3 million sweat glands in the human body. They are most plentiful in the armpits, on the hands and feet, and on the forehead. These tiny coils extract water and some other substances such as salt and urea from the blood flowing through the capil­lary vessels in the true skin. The extracted water (i.e. sweat or perspiration! is then re­leased to the surface of the skin through the minute tubules or openings which we call body pores.

The quantity of perspiration released daily varies greatly and depends on many factors. The sweat glands are never entirely idle. The body, even though it does not feel wet, is con­stantly releasing some water through the skin. This so-called insensible perspiration may amount to a quart a day.

Loss of body heat through perspiration, both visible and invisible, involves not the blood vessels but the sweat glands. The per­spiration that exudes from the pores is re­moved from the surface of the skin by evapo­ration. A stream of warm, dry air speeds evaporation. That is why the warm breeze from an electric fan on a hot day still pro­duces the sensation of cooling.

Underneath the true skin is a layer of sub­cutaneous tissue which is usually largely in­filtrated with fatty tissue. This layer gives the body its more delicate curves and con­tours. It serves as a cushion between the tegumentary covering of the body and the underlying muscles and permits the free rip­pling of the skin during muscular activity.

The Functions of the Skin

The skin serves many vital functions for the body. It is, first of all, a protective covering, a barrier against the invasion of pathogenic bacteria. Second, it is the impor­tant regulator of body temperature and is provided with the mechanism with which to perform this task. Third it is an organ of sensation that provides warning against some of the threats to life or health, found in the im­mediate external environment.

 Fourth, it concerns itself with those reactions which heighten the body's immunity to disease. And, finally, it is an organ of expression, a mirror if you will, of many disorders, both Infection and psychic, which may affect the body.

Bacterial resistance on the part of the skin is high. This applies also to the mucous mem­branes of the lips, mouth, and other parts of the body. So long as the skin is clean, it very quickly gets rid of unwelcome bacteria that may come to lodge upon it. The mechanism of this repellent action is not altogether clear. Unless the skin is cut, broken, punctured (as by an insect), or abraded, harmful bacteria have a difficult time getting through its horny layer. Of course some bacteria always lie on the surface of the skin, just as some are al­ways to be found in the mouth.

Skin blemishes such as blackheads, pim­ples, sores, and scabs should not be picked at anywhere on the body, but this warning should be doubly observed concerning the area that is called "the danger triangle of the face." This area is bounded by the bridge of the nose and the corners of the mouth. Be­cause of the peculiar arrangement of veins and arteries feeding this area, bacterial in­fections originating here may be carried di­rectly into the brain and set up a possibly fatal inflammation.

Structure of the Skin

The structure of the skin is far more complex than appears on first glance. Most aston­ishing, perhaps, is the fact that the outer skin, the visible surface of the body, is composed of dead rather than living tissue. This same fact is true of the fingernails and toenails and the hair. They grow, obviously from the inside out. The cells thus appearing on the outer surface of the body are no longer alive. They have turned into a highly insoluble form of protein, called keratin, which is also found in the horns and hooves of lower animals.

The outer layer of the skin, composed of dry, dead cells, which are more or less flat­tened out and overlap each other somewhat like shingles on a roof, is sometimes called its "horny layer." These cells are constantly being shed and replaced by new cells, which take their origin in the germinative layer of the skin. This growing layer is made up of what are called Malpighian cells, named after Malpighi, the Italian anatomist, who first identified them.

The pigments which largely, though not altogether, determine the color of the skin are found in the Malpighian layer of cells. The color differences among the races of man­kind,  and  many of the social implications which follow, are thus crucially determined by the amount of skin pigment in the Mal pighian cells.

The outer layers of the skin are called the epidermis. Beneath is the dermis or true skin, also called the corium. This is tough, fibrous living tissue with undulating surfaces that pentrate into the epidermis above and into the subcutaneous tissue below. These undu­lations form series of ridges which are evident on epidermis, especially on the hands and feet. They create the unique pattern of the individual's fingerprints.

The dermis is well supplied with blood ves­sels, small capillaries which can greatly ex­pand and contract under nerve impulses and thus help control body temperature. Blushing is the phenomenon that occurs when the blood vessels expand. In the true skin layer are also to be found lymph vessels, nerve endings, sweat glands, sebaceous glands, and hair follicles.

The sensory nerve endings in the skin are capable of reporting a variety of sensations to the brain as we have already pointed out.

The hair follicles are tiny tubes which harbor the hair roots, one hair to a follicle. As long as the follicle is not atrophied (worn out), injured, or diseased, the hair continues to grow.

The sebaceous glands usually lie close to the hair follicles. Their function is to secrete an oily substance, called sebum, which helps to keep the hair lustrous and the skin soft. An excessive secretion of sebum will produce such appearances as the shiny nose and may be responsible for acne. The glands of the outer ear canal, which secrete ear wax, are