Embryology Flashcards
What distinct layers is the skin divided into? -
- Epidermis
- Dermis
What cell lines are the layers of the skin derived from?
Ectoderm and mesoderm
What is the surface ectoderm?
The initial single layered epithelium that covers the developing embryo
What happens to the surface ectoderm?
It proliferates and forms a layer of surface epithelium, the periderm
What is the role of the periderm?
It covers the developing epidermis until the cornified cell layer is formed
When does the embyronic epidermis begin to stratify?
Around 8 weeks’ estimated gestational age
What is the stratification of the embryological epidermis followed by?
Cornification
What happens in cornification?
‘Dead’ keratinocytes are held together with proteins and lipids
Until when is the fetal skin highly permeable?
Week 19
What is amniotic fluid volume mostly determined by in early gestation?
Fetal surface area
What happens to the skin at 19 weeks?
Keratinisation occurs, and the skin becomes impermeable
What happens when differentiation of the skin is complete?
The periderm detaches from the underlying epidermis
What happens to the remnants of the periderm?
They form the vernix caseosa
What is the vernix caseosa?
The greasy coat that protects the skin in utero from amniotic fluid
When is the fetal epidermis morphologically similar to adult skin?
By the mid third trimester
When does the epidermis acquire full barrier function?
A few weeks after birth
What cell line are melanocytes derived from?
Ectoderm
Where do melanocytes migrate to and from?
From the neural tube to the epidermis
When are melanocytes fully functional?
The second trimester
What happens to active melanocytes present throughout the dermis during embryonic development?
Most migrate to the epidermis or undergo apoptosis by the time of birth
What happens if melanocytes fail to reach their proper location in the epidermis and are entrapped in the dermis at the time of birth?
It leads to the presentation of congenital dermal malnocytosis (Mongolian blue spot)
What happens to Mongolian blue spots?
They resolve spontaneously with time
What is often a feature of skin conditions that are a result of genetic abnormalities in the epidermis and/or its appendages?
They follow a distribution pattern
Why do skin conditions resulting from genetic abnormalities often follow a distribution pattern?
Represents migration patterns of epidermal cells during embyronic development
What is it called when skin conditions caused by genetic abnormalities follow a distribution pattern?
Blaschko’s lines
What do Blaschko’s lines represent?
A manifestation of cutaneous mosacism
When does cutaneous mosaicism occur?
When 2 or more genetically different populations of cells exist side by side within the skin
What are the typical patterns of cutaneous mosaicism?
- V-shaped on upper spine
- S-shaped on abdomen
- Linear on arms and legs
- Spiral on scalp
- Vertical in mid-face
Give 4 patterns of cutaneous mosaicism
- Narrow bands of Blaschko
- Large bands of Blaschko
- Chequerboard pattern
- Phylloid pattern (leaf-like)
What conditions cause narrow bands of Blaschko?
- Incontinentia pigmenti
- Epithelial naevi, e.g. inflammatory linear verrucous epidermal naevus, hypomelanosis of Ito
What condition can cause large bands of Blaschko?
McCune-Albright syndrome
What conditions can cause chequerboard pattern?
- Becker naevus
- Vascular malformation (port wine stain)
What condition can cause phylloid pattern?
Mosaic trisomy 13
