Stratum granulosum
Epidermis · Layer 3 Filaggrin Barrier is made here
Three to five cell layers in which the keratinocyte dismantles itself: nucleus and organelles are lost, keratohyalin granules release filaggrin to aggregate keratin, and lamellar bodies discharge the intercellular lipid that becomes the permeability barrier.
Detail
- Keratohyalin granules
- Contain profilaggrin, cleaved to filaggrin, which bundles keratin filaments into the dense corneocyte core; its breakdown products form natural moisturising factor
- Lipid discharge
- Lamellar bodies empty ceramides, cholesterol and free fatty acids into the intercellular space at the granular-corneal interface, sealing the barrier
- Cornified envelope
- Involucrin and loricrin are cross-linked by transglutaminase 1 beneath the plasma membrane
- Adhesion
- Desmoglein 1 predominates from here upwards, so this is the level at which anti-Dsg1 antibodies and staphylococcal toxin cause splitting
When it goes wrong
Filaggrin (FLG) loss-of-function mutation
Ichthyosis vulgaris and the strongest known genetic risk factor for atopic dermatitis: a leaky barrier admits allergens and drives the atopic march to asthma and rhinitis
Staphylococcus aureus exfoliative toxin A or B cleaving desmoglein 1 (staphylococcal scalded skin syndrome, bullous impetigo)
Split at the granular layer, positive Nikolsky sign, mucous membranes spared because Dsg3 compensates there; blister fluid is sterile in scalded skin syndrome because the toxin is blood-borne
Transglutaminase 1 (TGM1) mutation
Lamellar ichthyosis, with a collodion membrane at birth and lifelong scaling from a defective cornified envelope
Practise this structure
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