Ch2 skin development and maintenance

Question 1

Embryonic origin of skin components

Answer 1

• Ectodermal cells: keratinocytes, melanocytes, Merkel cells, neurons
• Mesodermal: fibroblasts, haematopoietic cells such as Langerhans, endothelial cells
• Overview:
  
  • embryo implants end of first week
  • 3rd week: gastrulation –> endoderm, mesoderm, ectoderm
  • Ectodermal then divide into
    
    • surface ectodermal –> keratinocytes of the embryonic epidermis + merkel cells
    • or neuroectodermal –> invaginate to create the neural tube (neurulation) –> dorsal becomes neural crest –> melanocyte
• Dermis origin varied:
  
  • Face and frontal scalp –> neural crest
  • Dermis elsewhere –> mesoderm

Question 2

What age to healthy full term infants attain full skin barrier function

Answer 2

3 weeks of age

Question 3

Where do melanocytes arise from

Answer 3

• Melanocytes come from the dorsal neural tube - neural crest
  
  • they migrate away from the neural tube within the mesenchyme beneath the primitive epidermis
  • move dorsolaterally and ventrally around the trunk to the ventral midline, anteriorly over the scalp and face, and distally along the extremities
  • Cutaneous melanocytes also arise from Schwann cell/melanocyte precursor cells that migrate along nerves to the skin via a distinct ventral pathway
  • These are in the epidermis at Day 50
  • Density is high initially, and increases more as the epidermis stratifies, then the appendages begin to develop
  • later in gestation the density decreases again

Question 4

Epidermal melanin production occurs at what gestation

Answer 4

3-4 months

Question 5

Melanosome transfer to keratinocytes occurs at what gestation

Answer 5

5 months

Question 6

Are melanocytes in the dermis during gestation and are they gone at birth

Answer 6

Melanocytes are also in the dermis during embryonic development, and then eventually move to the epidermis or undergo apoptosis
By birth dermal melanocytes have disappeared except for the head and neck, dorsal aspect of the distal extremities, and sacrococcygeal area –> these are the most common locations for blue naei and mongolian spots

Question 7

Piebaldism and Warrden burg pathogenesis

Answer 7

achromic patches of skin on the central forehead, abdomen and extremities –> failure of melanocyte precursors to survive, proliferate or travel to distal points of their embryonic migration pathway

Question 8

Prenatal diagnosis of genodermatoses

Answer 8

• CVS: 10-12 weeks
• Amniocentesis: 14-16 weeks
• The above have largely replaced foetal skin biopsy
• Can also do preimplantation genetic diagnosis –> more expensive, technically more challenging, low rate of completed pregnancies –> the cellular DNA is amplified using PCR