Stratum spinosum
Epidermis · Layer 2 K1/K10 Langerhans cells
The thickest epidermal layer, where keratinocytes leaving the basal layer are joined to one another by abundant desmosomes and begin building the keratin and lipid machinery of the barrier.
Detail
- Adhesion
- Densest desmosome population in the epidermis, anchoring K1/K10 intermediate filaments cell to cell
- Residents
- Langerhans cells sit mainly at this level as the epidermal antigen-presenting network
- Synthesis
- Lamellar (Odland) bodies are assembled here, loaded with ceramides, cholesterol and free fatty acids for later discharge
- Vitamin D
- With the basal layer, the site where UVB converts 7-dehydrocholesterol to previtamin D3, which isomerises thermally to cholecalciferol; 25-hydroxylation follows in the liver and 1-alpha-hydroxylation in the kidney
When it goes wrong
Cumulative UV mutation of squamous keratinocytes
Actinic keratosis progressing to squamous cell carcinoma; unlike basal cell carcinoma it does metastasise, and does so more readily on the lip, ear and in immunosuppressed transplant recipients
Intercellular oedema separating keratinocytes (acute eczema, allergic contact dermatitis)
Vesicles within the spinous layer; itch and weeping rather than the flaccid erosions of an acantholytic disease
Prolonged sun avoidance, dark skin at high latitude, or covering clothing
Reduced cutaneous cholecalciferol synthesis, low 25-hydroxyvitamin D, and in children rickets with bowing and widened metaphyses
Practise this structure
1 question in the bank tagged Vitamin D.