The lunula, or lunulae (pl.) (), is the crescent-shaped whitish area of the bed of a
fingernail or
toenail.
In humans, it appears by week 14 of
gestation
Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregna ...
, and has a primary structural role in defining the free edge of the distal nail plate (the part of the nail that grows outward).
Appearance
It is located at the end of the nail (that is closest to the skin of the finger), but it still lies under the nail. It is not actually white but only appears so when it is seen through the nail. Outlining the nail matrix, the lunula is a very delicate part of the nail structure. If one damages the lunula, the nail will be permanently deformed. Even when the totality of the nail is removed, the lunula remains in place and is similar in appearance to another smaller fingernail embedded in the
nail bed.
In most cases, it is half-moon-shaped and has unique
histologic
Histology,
also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures vis ...
features. Examinations concluded that the lunula is an area of loose dermis with lesser developed collagen bundles. It appears whitish because a thickened underlying
stratum basale obscures the underlying blood vessels.
The lunula is most noticeable on the thumb; however, not everyone's lunulae are visible. In some cases, the
eponychium
In human anatomy, the eponychium is the thickened layer of skin at the base of the fingernails and toenails. It can also be called the medial or proximal nail fold. The eponychium differs from the cuticle; the eponychium comprises live skin cells ...
may partially or completely cover the lunula.
Importance
The lunula’s location on the newest part of the nail allows assessments to be made about one’s health. In some cases, its absence may indicate an underlying health problem. Some examples of such problems are malnourishment, anemia, kidney failure, and heart disease.
See also
*
Nail disease
References
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Nail anatomy