occurs. A new hair follicle is made and the old hair follicle falls out, repeating the cycle. About 50 hairs are lost and replaced every day but this can increase because of hormonal or dietary changes. Aging and certain hormones can influence the hair cycles and can cause increased hair loss. Figure 28 shows the different stages of hair growth.
In the hair papilla, there are melanocytes that give hair its color. This is genetically determined. The amount of melanin in the hair shaft declines with age, causing the hair to look white or gray.
THE NAILS The nail consists of a nail bed that is actually a specialized epidermal structure seen only on the tips of the toes and fingers. The nail body is formed upon the nail bed and protect the most distal parts of the body, which receive the most mechanical stress. The nail body is also helpful in picking up small objects with the fingers; it is made from packed keratinocytes that are dead. The source of the nail body is the nail root, which has its own matrix of proliferating cells originating from the stratum basale. The nails grow continually from this matrix. The nail fold or nail groove is on the sides of the nail and help anchor it. The proximal end of the nail body is the nail cuticle. The nail cuticle is also known as the eponychium. The lunula is the pale part at the base of the nail; it is pale because the epidermis is thicker there. The hyponychium is the most distally-connected part of the nail bed—made from a thick stratum corneum layer. Figure 29 shows what the anatomy of the nail looks like:
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