Anatomy and Physiology of the Hand, Nail, and Skin
Domain 2 tests the structures of the hand, nail unit, and skin well enough to recognize normal variation and avoid damaging living tissue.
Core rules
- Nail unit: matrix (growth site), nail plate, nail bed, cuticle, eponychium, hyponychium, lunula, lateral folds, free edge.
- Fingernails grow about 3–4 mm per month; toenails grow more slowly. Complete replacement can take 4–6 months for fingernails and 12–18 months for toenails.
- The nail plate is keratinized and avascular; the matrix is living and determines thickness and shape. Injury to the matrix can cause permanent grooves or distortion.
- Skin layers: epidermis, dermis, subcutaneous layer. The cuticle is dead keratinized tissue; the eponychium is living tissue at the proximal fold. Do not cut living tissue.
- Nerves and blood vessels sit in the dermis and nail bed; the plate itself has no nerve endings.
Worked example
A client has a small white spot on the nail plate. It is not proof of calcium or zinc deficiency. Leukonychia often follows minor matrix trauma and grows out. You should not diagnose a systemic disease; note it, avoid aggressive buffing, and refer if it is new, painful, or spreading.
Traps
Confusing cuticle with eponychium; cutting the eponychium; assuming lunula size indicates health; treating the plate as living tissue; and describing normal ridges as disease.