9.11:
Accessory Structures of the Skin: Nails
A nail is a hard, transparent protective plate. It is present on the dorsal surface of the distal portion of a finger or toe.
Its visible part is called the nail body or plate composed of densely packed dead keratinocytes. Blood flow in the dermal capillaries of the nail bed — an epidermal layer below the nail, makes the nail body look pink, especially in light-skinned people.
The nail body extends at the distal end as a free edge. It is white-colored due to the absence of underlying capillaries. Beneath the free edge is the thickened skin region called the hyponychium.
The whitish crescent-shaped lunula or the little moon is near the proximal end of the nail body.
Skin folds onto the proximal end of the nail body forming the Eponychium or the cuticle.
The nail root is buried in the skin, and proximal to it is the nail matrix consisting of mitotically active cells responsible for nail growth.
9.11:
Accessory Structures of the Skin: Nails
Nails are one of the important accessory structures of the skin. They are hard, protective structures that cover the dorsal surface of the distal phalanges of fingers and toes. Nails are composed of specialized keratinized cells and serve various functions, including protection, sensation, and manual dexterity.
The main components of a nail include the following.
Nail Plate: The nail plate is the visible portion of the nail that extends beyond the fingertips or toes. It is a hard, translucent structure that appears pink due to the blood vessels underneath. The nail plate is composed of layers of flattened, hardened keratinocytes that are continuously produced by specialized cells called matrix cells.
Nail Bed: The nail bed is the layer of skin beneath the nail plate. It provides a supportive base for the nail plate and contains blood vessels that give the nail its pinkish color. The nail bed also has a rich nerve supply, which contributes to the sense of touch in the fingertips. The nail bed is a specialized structure of the epidermis that is found at the tips of our fingers and toes.
Lunula: The lunula is the crescent-shaped area at the base of the nail plate, visible through the nail. It appears whitish because the cells in this area are not fully keratinized. The lunula represents the visible portion of the matrix, where new nail cells are formed.
Cuticle: The cuticle, also known as the eponychium, is a narrow band of tissue at the base of the nail plate. It consists of a thin layer of dead skin cells that overlap the proximal nail fold, helping to seal and protect the nail matrix.
Nail changes, such as discoloration, thickening, or deformities, may indicate underlying health conditions and should be evaluated by a healthcare professional.
This text is adapted from Openstax, Anatomy and Physiology 2e, Section 5.2: Accessary structures of skin.