Anatomy and Physiology
Skin as an organ system
The skin is the body's largest organ. The epidermis is the outer avascular layer, with the stratum corneum (barrier), stratum granulosum, stratum spinosum, and stratum germinativum (basal layer where mitosis occurs). The dermis holds collagen and elastin fibers, blood vessels, nerves, glands, and hair follicles. The subcutaneous layer stores fat and insulates.
Appendages and glands
Sebaceous glands secrete sebum, most densely on the T-zone. Eccrine sweat glands regulate temperature; apocrine glands are associated with hair follicles in axillae and groin. The arrector pili muscle contracts with cold or emotion.
Systems that estheticians must reason about
- Circulatory: arteries carry oxygenated blood away from the heart; veins return deoxygenated blood. Lymph vessels drain interstitial fluid and are part of immune defense.
- Nervous: sensory receptors detect touch, pressure, heat, cold, and pain; motor nerves control muscles of facial expression.
- Skeletal/muscular: the skull, mandible, and facial muscles (frontalis, orbicularis oculi, orbicularis oris, masseter, zygomaticus) shape the face and inform massage and waxing technique.
Traps
Questions often ask which layer contains blood vessels (dermis, not epidermis), where new cells form (basal layer), or which gland is associated with acne (sebaceous). Another trap: confusing arteries and veins, or asking which layer is avascular.
Rule of thumb
"Epidermis = protection, no blood; dermis = structure and nourishment; subcutis = cushion and insulation." When a question mentions collagen, elastin, or blood supply, think dermis.