Nail

The nail is a specialized skin appendage located on the dorsal aspect of the distal digits of hands and toes. The nail unit consists of several distinct components:

• Nail plate: A hard, laminated, keratinized structure that forms the visible part of the nail. It is produced primarily by the nail matrix and lies atop the nail bed. The plate is composed of dorsal, intermediate, and ventral layers, each with distinct keratin organization, contributing to its rigidity and mechanical properties.

• Nail matrix: The germinative epithelium located beneath the proximal nail fold, responsible for generating the bulk of the nail plate. The matrix extends distally to form the lunula, the visible half-moon area at the base of some nails.

• Nail bed: The tissue directly beneath the nail plate, extending from the distal edge of the lunula to the hyponychium. It is firmly attached to the plate and provides support and vascular supply, contributing to the pink color of the nail.

• Hyponychium: The distal barrier at the free edge of the nail plate, marking the transition from nail bed to fingertip skin. It serves as a protective seal against pathogens.

• Eponychium (cuticle): The thin layer of stratum corneum derived from the proximal nail fold, adherent to the nail plate, and providing a seal to protect the matrix from external insults.

• Nail folds: The proximal and lateral folds of skin that frame and protect the emerging nail plate.

• Connective tissue components: The nail unit is anchored to the distal phalanx by specialized dermal and ligamentous structures, with a rich vascular and sensory innervation.