Anatomy and Physiology of the Skin
Domain 2 - Anatomy and Physiology of the Skin
Questions here test structure-to-function links: which layer a product can reach, which cell makes pigment, which gland makes oil, and what the acid mantle actually does.
Layers
- Epidermis - avascular, built of keratinocytes. Deep to surface: basale (cell division, melanocytes, Merkel cells), spinosum (Langerhans immune cells), granulosum, lucidum (palms and soles only), corneum (dead, keratinized, the barrier).
- Dermis - papillary layer with capillaries and nerve endings; reticular layer with collagen for strength, elastin for recoil, sebaceous and sudoriferous glands, follicles and arrector pili muscles.
- Hypodermis - subcutaneous fat for insulation, shock absorption and energy. No topical product reaches it.
Function and chemistry
Skin protects, senses, regulates heat, excretes, secretes and absorbs minimally. The acid mantle (roughly pH 4.5–5.5) is a film of sebum and sweat that inhibits bacteria and keeps enzymes working. Alkaline cleansers strip it, leaving skin tight and vulnerable.
Worked example
A client asks whether a firming serum will 'rebuild fat in the cheeks.' Fat sits in the hypodermis, cosmetic molecules are far too large, and the stratum corneum blocks them. The honest answer is no: the product can hydrate the corneum and temporarily plump fine lines, nothing more.
Traps
Sebaceous glands make oil; sudoriferous glands make sweat - exams swap these. Melanocytes sit in the basal layer, not the dermis. Pores do not open and close. Skin does not breathe through pores; oxygen arrives via the blood supply.