Stratum corneum
Epidermis · Layer 5 (surface) Corneocytes Permeability barrier
Fifteen to twenty layers of anucleate corneocytes embedded in a continuous intercellular lipid matrix. This is the permeability barrier: it limits water loss outwards and drug, allergen and microbe entry inwards.
Detail
- Lipid matrix
- Roughly 50% ceramides, 25% cholesterol and 10-15% free fatty acids, arranged in lamellae between the corneocytes
- Water loss
- Restricts insensible loss through skin to about 400-600 mL/day in an adult at rest; loss rises steeply when the layer is destroyed
- Desquamation
- Kallikrein-family serine proteases digest corneodesmosomes so cells shed individually; the process is balanced against basal mitosis
- Drug absorption
- The rate-limiting step in percutaneous absorption; thinnest on the eyelid, face, scrotum and flexures, thickest on palms and soles, which is how topical steroid potency is matched to site
When it goes wrong
Loss of the cornified layer over a large area (extensive burn, toxic epidermal necrolysis, erythroderma)
Massive evaporative water loss, hypothermia, hypovolaemia and high-output cardiac failure, plus a wide portal for Staphylococcus and Pseudomonas sepsis
Potent topical corticosteroid applied to the face or under occlusion
Enhanced absorption through thin corneum: skin atrophy, telangiectasia, perioral dermatitis and, over large areas in children, adrenal suppression
Practise this structure
16 questions in the bank tagged Skin.
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Foundations · common