Anatomy and Physiology of the Hands, Feet, and Nails
Nail Structure
Know each part and its function. The nail plate is the hard keratinized structure; the nail bed is the skin beneath it, rich in blood vessels, which gives the pink color. The matrix extends beneath the proximal nail fold and produces the plate - damage here causes permanent deformity. The lunula is the visible whitish half-moon, the front edge of the matrix. The cuticle (eponychium) is the dead tissue seal at the base; the nail folds are the skin borders; the hyponychium is the seal under the free edge; the free edge extends past the fingertip; lateral nail grooves are the side channels the plate slides along.
Bones, Muscles, and Circulation
The hand has 27 bones including carpals, metacarpals, and phalanges; the foot has 26 bones plus two sesamoids under the first metatarsal. Muscles of the forearm move the fingers through tendons; the intrinsic muscles fine-tune grip. Arteries supply the nail bed and matrix, which is why trauma causes bruising and why a nail can be lost after injury. Nerves carry sensation - important because a client who cannot feel pain may not report injury.
Growth and Variation
Fingernails grow roughly 3 mm per month, toenails slower (about 1 mm per month). Growth speeds up in summer, during pregnancy, and after injury, and slows with age and poor circulation. Nail plate thickness, curvature, and color vary naturally.
Traps and Rule of Thumb
Trap: calling the cuticle "living skin" - the eponychium is living tissue, but the cuticle itself is dead and may be gently pushed, never cut aggressively. Trap: confusing lunula with matrix. Trap: assuming toenail growth equals fingernail growth.
Rule of thumb: anything that injures the matrix risks permanent nail changes; treat the base of the nail as the most protected zone.