Nails

	Hair, Nails and Mucous Membranes

		Nails Nails are plates of keratinized epithelial cells on the dorsal surface of each distal phalanx. Function Components Nail Plate Composition Nail Growth and Development A. Function: protects distal phalanx from trauma helps in picking up small objects aids in the appreciation of fine touch used for scratching aesthetic organ in animals, nails are used for locomotion (hoof) or as a prehensile organ (claw) B. Components of the human nail: nail plate nail unit: (a) nail fold, (b) nail matrix, (c) nail bed Nail Plate horny end product of the nail matrix; 0.5 mm thick; covers fingertip like a watch glass corneocytes are flattened, anuclear and devoid of organelles Nail Unit Nail fold: angle between the nail plate and the dorsum of the digit skin is Lovibond's angle. Proximal nail fold is an extension of the dorsal skin of the digits as a fold lying superficial to the matrix; it is the site where abnormal capillary patterns can be directly visualized in certain disease states (SLE, systemic sclerosis). Ventral epidermis of the proximal nail fold, also known as the eponychium, lies in direct contact with dorsal nail plate. Cuticle is the extension of the horny layer of the eponychium onto the dorsum of the nail plate and serves to protect the structures at the base of the nail. Nail matrix: melanocytes may be present, contributing to pigmentation of the nail plate. Lunula is the most distal part of the matrix. Nail bed: pink in color due to enriched vascular network. Epidermis is very thin, horny layer scant, granular layer absent. Nail Plate Composition main chemical component consists of hard keratin which is high in sulphur compared to keratins of skin high glycine-tyrosine rich matrix protein 18% water, lipid content <5%. rigidity depends upon arrangement of cells, their adhesions and the orientation of the keratin fibres. It is independent of chemical composition or calcium content Nail Growth and Development nail growth is continuous throughout life 0.5-1.2 mm/week the longer the finger, the more rapid the growth toenails grow at 33%-50% the rate of fingernails regeneration of a fingernail after avulsion is 160 days; 40 days to emerge from the nail fold and another 120 days for growth to the fingertips