Advanced Skin Sciences: Histology, Microbiology, and Anatomy
Histology
The epidermis has five strata. The stratum basale holds mitotic keratinocytes and melanocytes, roughly one melanocyte to every ten basal cells, with skin of color having more active melanocytes rather than more of them. The stratum spinosum hosts Langerhans cells, the granulosum produces keratohyalin and lamellar bodies, the lucidum exists only on palms and soles, and the corneum is the barrier. Turnover averages about 28 days, faster in youth, slower with age and photoaging. The dermis has a papillary layer with capillaries and Meissner corpuscles plus a reticular layer of collagen I and III, elastin, and fibroblasts. The acid mantle sits near pH 4.5 to 5.5, built from ceramides, cholesterol, and fatty acids.
Microbiology
Distinguish resident flora from transient organisms. Questions commonly test Staphylococcus aureus, Pseudomonas aeruginosa folliculitis from poorly maintained whirlpool or water systems, Cutibacterium acnes, Candida, dermatophytes, HPV, herpes simplex, hepatitis B, and HIV. Blood and body fluids require barrier precautions and proper handling of contaminated waste.
Anatomy
Name the muscles of expression and mastication - frontalis, corrugator, procerus, orbicularis oculi and oris, zygomaticus major and minor, levator labii, buccinator, masseter, temporalis, mentalis, platysma. The facial nerve, cranial nerve VII, is motor; the trigeminal, cranial nerve V, is sensory, with ophthalmic, maxillary, and mandibular divisions. Lymph drains to preauricular, parotid, submandibular, and cervical nodes, generally downward and toward the clavicle.
Traps: placing the stratum lucidum everywhere; claiming only dark skin has melanocytes; calling the trigeminal a motor nerve; working over the thyroid or carotid sinus. Rule of thumb: motor equals facial nerve, sensation equals trigeminal.