Anatomy and Physiology of the Nail and Skin
Anatomy and physiology items ask you to name the structures you touch and explain why technique matters. The exam favors the nail unit, growth rates, and the difference between living and dead tissue at the cuticle.
The nail unit
- Nail plate - the hard keratin structure; it has no nerves or blood vessels, which is why filing does not hurt.
- Nail matrix - where the plate is produced; the visible portion is the lunula. Matrix injury produces permanent grooves or distortion, so never file or cut into it.
- Nail bed - skin under the plate, rich in nerves and blood vessels; separation here is onycholysis.
- Eponychium - the living skin fold at the base; the cuticle is the dead tissue it sheds onto the plate. Only dead cuticle is removed.
- Hyponychium - the seal beneath the free edge that keeps pathogens out.
- Lateral folds and grooves - sidewalls that guide plate growth; the perionychium is all soft tissue around the nail.
Growth and composition
- The plate is compact keratin with about 15–18% water; more water means flexibility, too little means brittleness.
- Fingernails grow about 0.1 mm per day, roughly 3 mm (1/8 inch) per month; toenails about 1 mm per month.
- Full replacement takes 4–6 months on fingers and 9–12 months on toes. Growth slows with age, illness and poor circulation.
Skin and underlying structures
- Epidermis (outermost stratum corneum), dermis (vessels, nerves, glands), subcutaneous layer.
- The nail sits over the distal phalanx; digital arteries and nerves run along the sides, so nipping deep at the sidewalls risks injury and bleeding.
Worked example
A client's cuticles have been pushed back hard and the eponychium is torn. Reasoning: the eponychium is living tissue forming a seal over the matrix; tearing it opens a portal for bacteria, producing redness, swelling and pain (paronychia). Correct technique softens with cuticle remover, pushes gently with a rubber or plastic pusher, and nips only loose dead skin.
Traps that cost marks
- Saying nails 'breathe' or that the plate contains blood vessels.
- Confusing the lunula with the free edge, or the matrix with the nail bed.
- Calling the whole proximal fold 'cuticle' and cutting it.
- Applying fingernail growth rates to toenails.