Dermatology: Embryology Flashcards
What does the epidermis originate from?
Ectoderm - single layered epithelium
Ectoderm proliferates to form layer of surface epithelium called periderm
Periderm covers the developing epidermis until cornified cell layer is formed
Label this image
When does the epidermis stratify?
Then what happens?
At approximatey 8 weeks EGA
Cornification (‘dead’ keratinocytes held together by proteins & lipids) until about 19 weeks EGA
What occurs at 19 weeks EGA?
Keratinisation - skin becomes impermable
Prior to 19 weeks - fetal skin highly permeable & amniotic fluid volume mostly determined by fetal surface area
What is the vernix caseosa?
Greasy coat; protects skin from amniotic fluid in utero
When differentiation completes, periderm detatches from epidermis and remnants form the vernix caseosa
When does the skin acquire full barrier function?
A few weeks after birth
Epidermis is more similar to adult skin from around mid 3rd trimester
How do melanocytes develop?
Develop from ectoderm
Migrate from neural tube to epidermis
Active melanocytes are present throughout dermis during embryonic development and most migrate to the epidermis or undergo apoptosis by birth
Melanocytes are not fully functional until 2nd trimester
How does congenital dermal melanocytosis develop?
When melanocytes fail to reach epidermis and are trapped in dermis at time of birth
Slowly resolves spontaneously with time
What is cutaneous mosaicism?
2 or more genetically different populations of cells exist side by side in skin
Typical patterns: V shaped (upper spine), S shaped (abdomen), linear (arms/legs), spiral (scalp), vertical (midface)
What are Blaschko’s lines?
A manifestation of cutaneous mosaicism
A distribution pattern often followed by skin conditions that result from genetic abnormalities in the epidermis and/or its appendages.
The pattern represents migration pathways of epidermal cells during embryonic development
What are these 4 patterns of cutaneous mosaicism? (with examples)
A - narrow bands of Blaschko
- incontinentia pigmenti,
- epithelial naevi e.g. inflammatory linear verrucous epidermal naevus
- hypomelanosis of Ito
B - large bands of Blaschko
-McCune-Albright syndrome
C - chequerboard pattern
- Becker naevus
- vascular malformation (Port wine stain)
D - Phylloid pattern
- Mosaic trisomy 13
What is an epidermal naevus?
Defect in ectoderm –> overgrowth of epidermal keratinocytes
Presents at birth (50%) or in early infancy: localised, linear, warty, hyperpigmented plaque
2 types: linear (majority) and systematised
What is hypomelanosis of Ito?
Naevoid hypopigmentation - hypopigmented streaks that follow Blaschko’s lines
Part of rare neurogenetic cutaneous syndrome due to defect in NEMO gene.
Typically presents in newborn with blisters that also follow Blaschko’s lines. Blisters then resolve and reveal hyperkeratotic, warty plaques, followed by increasing pigmentation at 2-6 months
Hyperpigmented brown streaks later fade into atrophic hypopigmented streaks in later childhood.
What is a sebaceous naevus?
Genetic: overgrowth of entire skin component (epidermis, sebaceous glands, hair follicles, apocrine glands and connective tissue).
Typically brown/orange hairless patch on scalp which becomes warty during puberty. Small risk of tumour in later life. Surgery recommended late adolesence.
What is aplasia cutis?
TBC
What is meant by ‘collodion baby’?
Born encased in taut, shiny, transparent membrane - formed by aberrant stratum corneum
Caused by global abnormal epidermal differentiation / barrier formation
Membrane shed over first 2-3 weeks of life
In majority, shedding will reveal ichythyosis (genetic cornification disorder –> persistent dry and scaly skin).
What is inflammatory linear verrucous epidermal naevus (ILVEN)?
Defect in ectoderm - overgrowth of epidermal keratinocytes - tends to follow Blaschko’s lines (like other types of epidermal naevus).
Warty / inflammed / itchy.
What is McCune-Albright syndrome?
TBC
What is incontinentia pigmenti?
TBC
What does the dermis originate from?
Depends on body site
Face & anterior scalp = neural crest ectoderm
Extremities & trunk = mesoderm
How does the dermis develop?
Dermal fibroblasts develop under the epidermis by 6-8 weeks EGA
These synthesise collagens and microfibrillar components
By 12-15 weeks, distinction between papillary dermis and reticular dermis
By end of 2nd trimester: dermis shifts from non scarring to scarring form of wound repair.
What does the dermal-epidermal junction (DEJ) do ?
Provides adhesion between the basal keratinocytes and the dermis as well as resistance against shearing forces on the skin
Rete pegs ensure attachment of the dermis to the epidermis via the basement membrane (the multilayered structure forming the DEJ).
Mutation in the genes that encode the components of the DEJ can result in skin fragility and blister formation.
What is epidermolysis bullosa?
Group of genetic disorders - mutation in genes encoding molecules in the DEJ.
Blisters on skin and mucous membranes, often at sites of friction and minor trauma e.g. hands/feet. Symptomatic treatment, to protect skin/prevent secondary infection/deformity.
What is an infantile haemangioma?
“Strawberry birthmark”
Proliferation of endothelial cells and mutations in genes that encode for VEGF (and other pathways affecting vascular development).
Usually present shortly after birth (where as vascular malformations usually present at birth).
Common in head/neck, usually proliferate in first 6-9 months. Then spontaneous involution over several years.
Treatment should be considered for lesions which are large with potential for disfigurement, ulcerating, threatening vital function e.g. vision/hearing/breathing/feeding or high-output cardiac failure.
Steroids were mainstay but now oral propranolol (non-selective beta blocker) is treatment of choice for complicated lesions.
