Anatomy and Physiology of Skin, Hair, and Nails
Domain 3 tests basic anatomy and physiology so you can explain why a technique is safe or unsafe. Expect labelling of skin layers, hair structures and nail parts, and questions on growth.
Core rules
- Skin has three main layers: epidermis (outer, avascular, keratinising), dermis (nerves, blood vessels, glands, collagen) and hypodermis (fat, insulation). It protects, senses, regulates temperature, excretes and makes vitamin D.
- Hair grows from a follicle. The bulb contains the matrix and papilla; sebaceous glands and arrector pili attach to the follicle. The shaft has cuticle, cortex and medulla. Growth cycle: anagen (growth, years), catagen (transition, weeks), telogen (rest, months).
- The nail unit includes nail plate, matrix, bed, lunula, proximal and lateral folds, cuticle and free edge. The matrix produces the plate; the plate is dead keratin, the matrix is living.
- Blood and lymph supply skin, hair and nails; this is why cuts, infections and allergic reactions can spread.
Worked example
A client asks you to cut the cuticle deeply to make the nail look longer. Reasoning: the cuticle (eponychium) seals the gap between skin and nail plate. Cutting living tissue creates a portal for bacteria and fungi, causing paronychia. The correct action is to soften with cuticle remover, gently push back, and trim only loose dead tags with a disinfected nipper.
Traps that cost marks
- Saying hair grows from the shaft or that the nail grows from the cuticle.
- Confusing the nail plate with the matrix.
- Describing the epidermis as having blood vessels.
- Ignoring the growth cycle when explaining hair loss or shedding.