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Sublamina densa anchoring fibrils (type VII collagen)

Adhesion & dermo-epidermal junction · Type VII collagen Dystrophic EB Salt-split floor

Loops of type VII collagen that leave the lamina densa, encircle the collagen I and III bundles of the papillary dermis and return, stapling the entire basement membrane to the dermis. Failure here splits below the lamina densa, so healing scars.

Traced from the start

  1. Stratum basale (germinativum)
  2. Sublamina densa anchoring fibrils (type VII collagen)

Detail

Molecule
Type VII collagen, encoded by COL7A1
Mechanics
Resists shear; the deepest and last line of dermo-epidermal attachment
Split level
Sublamina densa — the blister floor is dermis, so re-epithelialisation is accompanied by scarring and milia, unlike a lamina lucida split

When it goes wrong

COL7A1 mutation (dystrophic epidermolysis bullosa)

Blistering with scarring; the recessive form gives fusion of the digits, oesophageal strictures needing dilatation, anaemia, failure to thrive and aggressive squamous cell carcinoma in early adult life

Autoantibody to type VII collagen (epidermolysis bullosa acquisita)

Trauma-induced blistering on hands, elbows and knees healing with scars and milia; salt-split skin localises IgG to the dermal floor, separating it from bullous pemphigoid; associated with inflammatory bowel disease

Practise this structure

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