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Monday, May 23, 2011

Accessory Organs Of The Skin - - Lesson 245

In this post we would learn about ‘accessory organs of the skin’. Then in our mind one question may arise? What are the accessory organs of the skin?
1. Hair: A fiber of hair is composed or consisted of a tightly fused meshwork of horny cells filled with the hard protein also called keratin. The growth of hair is similar to the growth of the epidermal layer of the skin. Deep-lying cells in the hair root which produce horny cells that move upwards or to the top through the hair follicles (shafts or sacs that hold the hair fibers). At the root of the hair follicle, melanocytes are located and they support the melanin pigment for the horny cells of the hair fiber. Whenever the melanocytes stop producing melanin, hair turns gray. Out of the five million hairs on the body, about 100,000 are on the head. They grow about a half inch (1.3cm) a month, and cutting the hair has no effect on its rate of growth.

2. Nails: Nails are hard, the plates called keratin plates covering the dorsal surface of the last bone of each toe and finger. They are composed of horny cells that are cemented together tightly and can extend indefinitely unless cut or broken. As a result of division of cells in the region of the nail root, a nail grows in thickness and length, which is at the base or proximal portion of the nail plate. Mostly nails grow about one mm a week, which means that the re-growth of fingernails may occur in 3-5 months. Toenails which grow more slowly than fingernails, it takes 12-18 months for toenails to be replaced completely.

The ‘lunula’ is a semilunar(half-moon), white region of the base of the nail plate, and it is normally found in the thumbnail of most people and in differing degrees in other fingers. Air mixed in with keratin and cells rich in nuclei give the lunula its whitish color. The cuticle, a narrow band of epidermis(layer of keratin), is at the base and sides of the nail plate. The growth of the nail and appearance are frequently altered during systemic disease. For example, grooves in nails may occur with high fevers and serious illness, and spoon nails(flattening of the nail plate) occurs in iron deficiency anemia.                                                                                             

In the next post we would learn about ‘glands’.

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