Stratum basale (germinativum)
Epidermis · Layer 1 (deepest) K5/K14 Only mitotic layer
Single layer of keratinocytes sitting on the basement membrane; the only epidermal layer that divides, so every corneocyte at the surface began here. It also houses the melanocytes and Merkel cells.
Detail
- Cells
- Mitotically active keratinocytes and keratinocyte stem cells, plus melanocytes and Merkel cells scattered between them
- Keratins
- K5 and K14; the differentiation switch to K1/K10 occurs on leaving this layer
- Attachment
- Hemidesmosomes bind the basal cell to the lamina lucida; desmosomes bind it laterally and above to its neighbours
- Turnover
- About 28 days from basal mitosis to desquamation; roughly 4 days in psoriasis, which is why scale accumulates
- Vitamin D
- Holds 7-dehydrocholesterol, converted by UVB (290-315 nm) to previtamin D3
- Blood supply
- None — the whole epidermis is avascular and is fed by diffusion from the papillary dermal capillary loops
When it goes wrong
Chronic UV damage to basal keratinocytes and follicular stem cells
Basal cell carcinoma: the commonest skin cancer, on sun-exposed head and neck, locally invasive but almost never metastasises; hedgehog pathway (PTCH1) driven
K5 or K14 mutation (epidermolysis bullosa simplex)
Basal keratinocytes lyse under mechanical stress: intraepidermal blistering of hands and feet from birth, worse with heat and friction
Anti-desmoglein 3 IgG (pemphigus vulgaris)
Split immediately above the basal layer, which stays anchored to the basement membrane while the rest of the epidermis lifts off
Practise this structure
16 questions in the bank tagged Skin.
A 45-year-old woman presents with a painful, swollen, red area on her right forearm that developed over the past two days. She reports a minor cut from gardenin…
Mechanisms of disease · common
A 45-year-old woman with diabetes mellitus presents with a painful, rapidly expanding area of redness on her thigh. She has a fever of 39°C (102.2°F) and hypote…
Mechanisms of disease · middle twist
A 65-year-old man presents with purple spots on his forearms and hands that appeared over the past few days. He denies pain, itching, or trauma. His medical his…
Mechanisms of disease · middle twist
A biopsy of the tracheal epithelium shows a single layer of cells with nuclei at different levels, cilia, and mucus-secreting goblet cells. Which of the followi…
Foundations · common
Which of the following is TRUE about stratified columnar epithelium?
Foundations · niche
Which function is performed by stratified cuboidal epithelium?
Foundations · common