Norman Allan
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Fingernails: growth of...



Nails are composed of a protein called keratin. (Skin, hair, horn, hoofs are also made out of keratin.)

The nail grows from the "nail matrix". The nail matrix is the "moon" (or lunula). Further along the nail, the matrix ends and we come to the "nail bed"

"The nail can be considered to resemble a flattened, cubist-like, hair follicle." (Barnhill: Textbook of Dermotopatholgy)

"The nail plate moves distally entirely by growth pressure arising from the matrix. The nail bed epithelium plays a passive roll in this movement. Nails grow about 0.1 mm per day on average with growth faster in the summer than the winter, and fingernails faster than toenails."

"Regarding the dynamics of migration of the nail components, every layer of the nail unit moves forward alongside the plate in unison. Thus the plate does not glide over the bed epithelium but is firmly attached to it in a parellel course."

"Nails grow at an average rate of 0.1mm a day (1 cm every 100 days) Fingernails require 4 to 6 months to regrow completely. Toenails require 12 to 18 months. Actual growth rate is dependent upon age, season, exercise level, and hereditary factors." (wikipedia)



While we are advised to look at nails more as modified hair, than as modified skin...



Let's look first at the growth of skin.

Cells of the epidermis are generated in the stratum germinativum (SG). These cells become filed withthe protein keratin (in the picture to the right the keratin is stained red) until in the stratum corneum(SC) the "keratinocyte" are little more than packets of keratin. The keratinocytes gradually "migate" to the surface and are sloughed off in a process called desquamation. (images taken from Loyola University's site and wikipedia)

I want to explain how this one protein, ketatin, can be many things - skin, nails, horn, hoofs - but I haven't yet found good sources, so instead I'm going to tell you how another structural protein, collagin, can be tendon or cartilage or bone. Click here to read about these various arrangements of collagin..