Structure and Function of the Nails

Revision for “Structure and Function of the Nails” created on August 31, 2017 @ 02:31:17

Title
Structure and Function of the Nails
Content
Nail is a plate made of hard keratin that covers the dorsal tip of the digits. The nail is a highly specialised keratinised appendage of the skin – it is a “horny dead” product. Thickness normally varies from 0.05 to 1mm. Develops during ninth embryonic week Function: • protection of distal phalanx helps in manual dexterity defensive tool • enhance tactile discrimination aesthetic functions (finger nails) • contribute to foot biomechanics (hallux nail provide counter pressure to the pulp of toe during propulsion) Hardness of nail is due to low water content compared to skin (<5% of nail weight); 9% of nail weight is cystine (composed of sulphur)  assumed to contribute to hardness Nail structures: Nail plate: • keratinised structure that results from maturation of the nail matrix’s epithelium • firmly attached to nail bed, which also contributes to its formation • proximal and lateral borders surrounded by nail folds • separates from hyponychium at distal edge • shape of distal phalanx influences gross shape of nail plate – usually curved in longitudinal and transverse axes • transversely the plate has 3 sections – dorsal nail plate, intermediate nail plate and ventral nail plate. Dorsal and intermediate are produced by nail matrix; ventral is produced by nail bed Nail matrix: • specialised epithelial structure that produces the nail plate; lies above mid-portion of distal phalanx • extends proximally from nail fold up to 10mm; wedge shaped on transverse section; has a dorsal (proximal) and distal (ventral) portions. visible portion called the lunula Lunula: • semicircular white region at proximal end • represents junction between nail matrix and nail bed Nail bed: • extends from distal margin of lunula to onychodermal band; visible through nail plate • nail bed epithelium is very adherent to nail plate (remains attached to nail plate if the nail is avulsed); epithelium is thin (2 to 5 cell layers) – its longitudinally orientated rete pegs interdigitate with underlying dermis • keratinisation of nail bed  forms ventral nail plate (contributes about 1/5th of thickness and mass of nail Hyponychium: • anatomic area between nail bed and the distal groove – where nail plate detaches • normally covered by nail plate Nail Folds: - on the proximal and lateral sides of nail for support - rim of connective tissue covered with skin Circulation: • derived from two digital arteries that run alongside sides of digit  branches to matrix and proximal nail fold  abundant blood supply to nail apparatus Nerve supply: • cutaneous sensory nerves from dorsal branches of paired digital nerves Nail Growth: Grows continuously throughout life; fingernails grow faster than toenails; mean of toenail growth is 1mm/month
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