Anatomy and Physiology of Skin, Hair and Nails
This domain tests the structure and function of the three tissues you work on: skin, hair and nails. Questions ask you to name layers and structures, link structure to function, and explain why a technique is safe or unsafe.
Skin
- Epidermis: avascular keratinised layers - stratum corneum, lucidum (palms and soles), granulosum, spinosum, basale. The stratum corneum is thickest on soles and palms.
- Dermis: papillary and reticular layers, containing collagen, elastin, blood vessels, nerves, hair follicles and glands.
- Hypodermis: fat and connective tissue for insulation and cushioning.
- Cells: keratinocytes, melanocytes (pigment), Langerhans cells (immunity), Merkel cells (touch).
- Functions: protection, sensation, thermoregulation, secretion, excretion, absorption and vitamin D synthesis.
Hair
Shaft and root sit in a follicle with a sebaceous gland and arrector pili muscle. The shaft has cuticle (protective scales), cortex (keratin, melanin, bonds) and medulla (may be absent in fine hair). Growth cycles: anagen 2–7 years, catagen about 2–3 weeks, telogen about 3 months.
Nails
Nail plate, nail bed, matrix, lunula, eponychium, cuticle, hyponychium, lateral folds and free edge. The matrix produces the plate; fingernails grow about 3 mm per month, toenails about 1 mm.
Worked example
A client's cuticles are pushed back hard and the next week the nail fold is red and swollen. Reasoning: the cuticle and eponychium seal the nail pocket. Breaching that seal lets bacteria and yeast enter, causing paronychia. Damage to the matrix from aggressive tools can cause permanent ridges. Therefore soften with water, push gently with a rubber-tipped pusher, and never cut living tissue.
Traps that cost marks
- Calling the hair shaft or nail plate living tissue; only the follicle and matrix are living.
- Saying nails grow from the lunula rather than the matrix.
- Claiming all hair has a medulla.
- Confusing the dermis with the epidermis when explaining absorption or bleeding.