Skin Sciences: Anatomy, Physiology, and Histology
Organization
Skin is the largest organ: epidermis (avascular), dermis (vascular, with collagen, elastin, glands, follicles, and nerves), and subcutaneous layer (fat, insulation, shock absorption). Epidermis layers from deep to surface are basale, spinosum, granulosum, and corneum. Keratinocytes migrate upward and cornify; melanocytes in the basal layer produce melanin; Langerhans cells are immune; Merkel cells are sensory.
Physiology
Barrier function and the acid mantle limit water loss and microbial growth. Sebaceous glands connect to hair follicles and produce sebum; eccrine glands produce sweat; apocrine glands are in axillae and groin. Skin regulates temperature, synthesizes vitamin D, senses touch, and participates in immune response. Wound healing proceeds through inflammation, proliferation, and remodeling.
Traps
The epidermis has no blood vessels; bleeding means the dermis has been reached. Melanocytes are in the basal layer, not the corneum. Sebaceous glands are associated with follicles, so hair removal can affect sebum distribution. “Thick skin” refers to palms and soles-more stratum corneum, not more layers overall. The Fitzpatrick scale describes UV response, not skin type.
Worked example
A scrape that oozes clear fluid is epidermal; one that bleeds is dermal. That distinction guides whether a service is safe and whether a lesion needs referral.