	Page 36 -- SPECIAL SKIN STRUCTURES (continued)

Hairs

Most of the skin is covered in fine hairs called vellus hairs, which are attached to tiny muscles in the dermis. When the air temperature falls, these muscles contract. When they do so the area in the skin to which they are attached is depressed and the skin around the hair 'stands up' - this produces 'goose bumps'. The process is of little or no value in helping us to keep warm.

Section through a hair follicle buried deep in the subcutaneous fat of the scalp. When hair is about to fall out naturally this rises to the surface.

    hair follicle
A hair growing from a follicle below the skin's surface.


Fine vellus hairs grow all over the body except the palms
and soles.



'Goose bumps' are due to depression of the skin as tiny
muscles tighten and raise the hairs.

   In babies and children longer, darker and thicker hairs, called terminal hairs, grow on the scalp, eyelids and eyebrows, though nowhere else. In the teens, however, the body starts to produce sex hormones. Both sexes produce some male hormones, and it is these that cause terminal hairs to develop in many other areas such as the beard area, chest, arms and legs. They do not replace the fine vellus hairs - they are still there as well.

Lips

The lips are prominent facial features. They can be divided into three different regions. There is skin on their outer surfaces and a thin smooth lining (mucosa) on the inner surfaces. Between these two tissues lies the vermilion zone (or red zone). It is this zone which people commonly call 'the lips'.

    The vermilion zone forms the transitional zone between the mucosa of the mouth and facial skin. It shares some features with the facial skin that surrounds it, but also has some noticeable differences.
   The skin of the lips, like skin elsewhere, has a dermis and an epidermis. The epidermis of the lips functions in a similar manner to the epidermis on other parts of the body: it provides a self-renewing barrier, protected from the outer world by a continually exfoliating stratum corneum. The characteristic red color of the lips is unique to humans and comes from the blood vessels in the dermis. The many rete pegs (papillae) are long and narrow, and contain loops full of blood vessels. The closeness of these vessels to the surface, combined with a thin, almost transparent epidermis, gives rise to the red appearance of the lips. In cold weather when the blood vessels close down and the circulation becomes sluggish, the lips look blue.
   The ridged appearance of the lips results from a highly folded dermis, which is not found in the skin of other parts of the body.

Chapped lips

There are no hair follicles and sweat glands in the dermis of the lips - this is one of the most marked differences from other parts of the skin. The absence of these features within the lip dermis means that the lubricating effects of sebum are not present in the lips. As a result the lips can easily become dry and chapped. The stratum corneum of the lips is thinner than that of the rest of the skin, worsening this effect. The lips require constant re-hydration keep them healthy and to prevent drying, with the accompanying deterioration in appearance. As everyone has found, licking dry, chapped lips just makes the dryness worse. Only a product like a lip salve can help, because only this can ensure that water molecules accumulate effectively in the stratum corneum. Modern lipsticks can help to protect the lips.