Anatomy and Physiology of Skin, Hair and Nails
Anatomy and Physiology of Skin, Hair and Nails
This domain tests the structure and function of skin, hair and nails so you can choose safe treatments and recognise contraindications.
Core rules
- Skin has three main layers: epidermis (avascular, keratinocytes, melanocytes, Langerhans cells, Merkel cells), dermis (collagen, elastin, blood vessels, nerves, glands) and hypodermis (fat, insulation).
- Skin functions: protection, sensation, thermoregulation, vitamin D synthesis, excretion and absorption. The barrier lies mainly in the stratum corneum.
- Hair has a shaft above the skin and a root in the follicle. The bulb contains the matrix and dermal papilla; sebaceous glands attach to the follicle; arrector pili muscle causes goosebumps.
- Hair growth cycles: anagen (growth), catagen (transition), telogen (rest). Hair does not grow continuously from the same fibre.
- Nail structures: nail plate, nail bed, matrix (makes plate), lunula, cuticle/eponychium, hyponychium, lateral nail folds. The matrix determines thickness and shape.
Worked example
A client wants cuticles cut deeply because they look 'ragged'. Reasoning: the cuticle seals the nail fold and blocks microbes. Cutting it creates an entry point for bacteria and can cause paronychia. The safe action is to soften with cuticle cream and push back gently, trimming only a loose hangnail with sterile nippers, not the sealed cuticle.
Traps
- Saying the epidermis contains blood vessels.
- Describing the nail cuticle as 'dead skin to be removed'.
- Confusing the nail matrix with the nail bed.
- Claiming hair grows from the shaft.
- Ignoring that the dermis contains nerve endings and glands.