Anatomy, Physiology, and Histology of Hair, Skin, and Nails
What this domain tests
This domain tests the structures and functions of hair, skin, and nails, including growth cycles and the layers that matter in salon services.
Core rules
- Hair grows from a follicle; the bulb contains the papilla, which supplies nutrients. The sebaceous gland lubricates hair, and the arrector pili muscle causes goose bumps.
- The hair shaft has three layers: medulla, cortex, and cuticle. The cortex contains melanin and gives strength and color; the cuticle is the outer protective layer.
- Growth cycles are anagen (active growth), catagen (transition), and telogen (resting/shedding).
- Skin layers are epidermis, dermis, and subcutaneous tissue. The dermis contains nerves, glands, and hair follicles.
- Nail structures include the matrix, plate, bed, cuticle, eponychium, hyponychium, and lunula.
Worked example
A client’s hair color looks lighter after sun exposure. The reasoning is that melanin in the cortex is altered and the cuticle may be damaged, increasing porosity. This explains why porous hair absorbs color quickly and can appear darker than expected.
Traps
Confusing cortex and cuticle; mixing up growth-cycle names; forgetting that the dermis contains the follicle; misidentifying nail structures.
Exam focus
Connect each structure to its function and to a visible salon effect.