Nail Anatomy & Terms
THE NAIL STRUCTURE
The nail plate is a hard keratin structure that protects the end of the finger. The condition and appearance of the nail plate is well recognized as being an indicator of the overall health. Nail cells are produced in the matrix (or nail root) and “nourished” from the underlying nail bed until the nail plate leaves the end of the finger. This “free” nail plate is the most challenged and exposed part of the nail unit and is often in the greatest need of cosmetic attention as it is prone to breakage and splitting. The nail plate itself is comprised of flattened corneocyte cells and has three distinct layers. The dorsal (uppermost) layer is 2-3 cell layers thick and contains the oldest, most damaged cells. The intermediate layer makes up about 3/4 of the nail material and the ventral (lower) region is 1-2 cells thick and contains the youngest, softest cells.
The keratin nail plate is highly cross linked containing approximately 10.5% cystine. This sulphur containing amino acid is responsible for holding the nail protein structure together and giving it the structural robustness it needs to perform its functions. This protein structure is porous and highly water absorbent - increasing water content results in increased flexibility.The composition of the nail includes 7–12% water. The nail plate also contains about 1% lipid, which is thought to reside between the corneocyte cells. When this is depleted, for example by solvents in nail polish removers, nail brittleness often results. The main mineral found in nails include Calcium, Zinc, and Magnesium. Their role has not been clearly established.
TERMS & DEFINITIONS
Cornification (kôr′nə-fĭ-kā′shən) The process by which squamous epithelial cells in vertebrate animals develop into tough protective layers or structures such as hair, hooves, and the outer layer of skin; the final stage of keratinization.
Dehydration (dēˌhīˈdrāSH(ə)n) The loss or removal of water from something. A harmful reduction in the amount of water in the body.
Cohesion [koh-hee-zhuh n] The act or state of cohering, uniting, or sticking together. To stick together; be united; hold fast, as parts of the same mass.
Thickness [thik-nis] The state or quality of being thick. The measure of the smallest dimension of a solid figure. The thick part or body of something. A layer, stratum, or ply.
Ridges [rij] Vertical ridges are furrows that run from the tip of your fingernail down to the cuticle. They are sometimes called longitudinal striations or bands.
Beau's lines are nail ridges that run horizontally across the fingernail. These ridges are often deep, and multiple lines may appear across the nail. Horizontal ridges are often a sign of an underlying condition that requires diagnosis and treatment.
Lipid [lip-id, lahy-pid] A any of a group of organic compounds that are oily to the touch, insoluble in water, and soluble in alcohol and ether (air): Lipids comprise the fats and other esters with similar properties and constitute, with proteins and carbohydrates, the chief structural components of living cells.
Lipids in nail consitute the intracellular cement.
Onychocyte [onґĭ-ko-sīt] One of the tightly packed keratinized cells arranged in layers to make up the nail plate.
Keratinization [ker·a·tin·i·za·tion] The process by which vertebrate epithelial cells become filled with keratin protein filaments, die, and form tough, resistant structures such as skin, nails, and feathers.
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