Come Let's Get Sun Burnt: basale, spinosum, granulosum, lucidum, corneum
Mnemonic
“Come, Let’s Get Sun Burned”, from the surface down:
- C - stratum Corneum
- L - stratum Lucidum
- G - stratum Granulosum
- S - stratum Spinosum
- B - stratum Basale
Only palms and soles have a stratum lucidum, which is why the four layer version is quoted for the rest of the body.
Cells are born at the bottom and die at the top: mitosis occurs in the basale, keratohyalin granules appear in the granulosum, and the corneum is anucleate dead keratin. Transit takes about 28 days, and it is roughly 4 days in psoriasis, which is why the scale is so thick and immature.
Desmosomes are attacked in pemphigus (intraepidermal, flaccid blisters, Nikolsky positive), while hemidesmosomes at the basement membrane are attacked in pemphigoid (subepidermal, tense blisters).
Expansion
From deep to superficial (Come Let’s Get Sun Burnt):
- Stratum basale (germinativum): the dividing layer, containing stem cells, melanocytes, and Merkel cells
- Stratum spinosum: desmosomes give the prickle cell appearance; contains Langerhans cells
- Stratum granulosum: keratohyalin granules; the cells begin to die
- Stratum lucidum: only in thick skin of palms and soles
- Stratum corneum: anucleate corneocytes in a lipid matrix, the barrier layer
Transit time from basale to corneum is about 28 days, shortened to about 4 days in psoriasis, which is why the cells retain nuclei (parakeratosis) and the stratum corneum thickens.
Non-keratinocyte residents
- Melanocytes (basal layer, neural crest origin): transfer melanin in melanosomes to keratinocytes. Racial variation reflects melanosome size and distribution, not melanocyte number
- Langerhans cells (spinosum): dendritic antigen-presenting cells, containing Birbeck granules
- Merkel cells (basal): mechanoreceptors
Blistering diseases separate at different levels: pemphigus intraepidermally, pemphigoid subepidermally.