Anatomy and Physiology of Skin, Hair, Nails and Related Structures
What this domain covers
This domain tests the structure and function of skin, hair and nails, plus the facial bones and muscles you must know before massage, waxing or make-up.
Skin
- Epidermis: avascular; keratinocytes harden into the stratum corneum; melanocytes in the basal layer make melanin.
- Dermis: collagen and elastin from fibroblasts, blood vessels, nerve endings, sebaceous and sweat glands, hair follicles.
- Hypodermis: fat and connective tissue for insulation and shock absorption.
- Functions: protection, sensation, thermoregulation, excretion, secretion, vitamin D synthesis and limited absorption.
Hair
The shaft has cuticle, cortex and medulla; the follicle has a bulb and papilla fed by blood vessels. Growth cycle: anagen (2-7 years, active growth), catagen (2-3 weeks, transition), telogen (about 3 months, resting and shedding). This explains the 3-4 week waxing interval and the need for roughly 6 mm of growth to grip.
Nails
The plate sits on the nail bed, the matrix produces it, the lunula is the visible matrix, and the cuticle seals the nail fold. Fingernails grow about 0.1 mm a day, faster than toenails.
Bones and muscles
Facial bones: frontal, parietal, temporal, occipital, zygomatic, maxilla, mandible. Muscles: frontalis, temporalis, masseter, orbicularis oculi, orbicularis oris, zygomaticus, buccinator, platysma.
Worked example
A client says her hair stops growing after waxing. Answer: hair grows in cycles, so at any moment some follicles are in telogen and invisible; waxing removes the anagen hair only, and the rest appear over the following weeks. Reasoning links the cycle to the appointment interval.
Traps
- Saying the epidermis contains blood vessels.
- Placing melanocytes in the dermis.
- Confusing the lunula with the cuticle.