Anatomy and Physiology of the Nail and Skin
This domain tests structure and function together: not only where the matrix sits, but why over-filing it ruins the plate and why a diseased nail must be referred rather than serviced. Precision with terminology is what separates the passing answers.
The nail unit, layer by layer
- Nail plate: the visible hard keratin, roughly 100 layers of flattened cells, with no nerve endings and no blood supply.
- Nail bed: skin beneath the plate, pink from capillaries and supplied with nerves, so pressure is felt here rather than in the plate.
- Matrix: the generative area under the proximal fold that builds the plate; its length and curve determine thickness, shape and the free edge. Injury here leaves a permanent groove or ridge.
- Lunula: the visible portion of the matrix, pale and half-moon shaped, and not visible on every toe.
- Cuticle (eponychium): the dead tissue seal at the base. The living fold behind it is the proximal nail fold. Cuticle equals seal; fold equals living tissue.
- Hyponychium, lateral folds, nail grooves, nail mantle and nail root complete the unit.
Growth facts examiners like
Fingernails grow about 3 mm (1/8 inch) per month and are replaced in 4 to 6 months; toenails grow about 1 mm per month and take 9 to 12 months. Growth is faster in summer, on the dominant hand, in children and during pregnancy, and slows with age and poor circulation.
Skin you work across
Epidermis, with melanocytes in the basal layer; dermis, carrying nerves, blood vessels, sebaceous and sudoriferous glands; and subcutaneous tissue. The palms have no sebaceous glands, which is one reason hands dry and crack.
Disorders you recognize but never treat
Paronychia, onychocryptosis, onychomycosis, onycholysis, onychorrhexis, koilonychia, onychauxis, pterygium, nail hematoma and periungual warts are all referral findings, not service opportunities.
Worked example
A client shows a deep horizontal groove across both thumbnails. Reasoning: a groove across the plate is a Beau line, formed when matrix growth was interrupted months earlier by illness or trauma. It is not a filing error and will not buff out. Note it, explain it, recommend a physician if it is unexplained or recurring, and continue with a gentle manicure.
Traps
Swapping cuticle and eponychium; claiming the matrix is visible; saying the plate has nerve endings; and servicing a nail that should have been referred.