Anatomy and Physiology of the Hands, Arms, and Nails
This domain tests the structures you work around and the growth facts that explain nail shape, thickness, and service limits. Expect questions on the matrix, nail bed, cuticle, blood supply, and normal growth rates.
Core structures
- The nail plate is keratinized cells; it rests on the nail bed and is produced by the matrix. Matrix damage can permanently alter width, thickness, or shape.
- The lunula is the visible portion of the matrix. The cuticle seals the proximal nail fold; the eponychium is the living fold, and the hyponychium is the seal under the free edge.
- Lateral nail folds and grooves guide the plate. The free edge extends beyond the bed.
- Fingernails grow about 3-4 mm per month; toenails grow more slowly, often one-third to one-half that rate. Full fingernail replacement commonly takes 4-6 months, toenails 9-12 months.
- The hand and arm receive blood from the radial and ulnar arteries; tendons, nerves, and phalanges underlie the service area.
Worked example
A client has a horizontal groove on every fingernail after a severe illness two months ago. Reasoning: a temporary interruption in matrix activity produces Beau lines, which grow out with the plate. The pattern is not an infection. If the lines are new, painful, or accompanied by other symptoms, refer rather than treat.
Traps
Calling the lunula a health meter, cutting the eponychium, or assuming the nail plate is bone are common mistakes. Do not describe the cuticle as the matrix; the matrix lies beneath the proximal fold and is not visible along the entire nail.