1) The skin develops from surface ectoderm and underlying mesoderm. Key stages include specification, morphogenesis, and differentiation as the epidermis stratifies and cornification occurs.
2) Specialized cells like melanocytes and Langerhans cells arise and mature according to defined timelines. Dermal components also develop from distinct embryonic origins.
3) Skin appendages form through epithelial-mesenchymal interactions, with hair follicles, sebaceous glands, nails, and sweat glands developing in parallel through gestation. The dermal-epidermal junction also acquires mature structures by 12 weeks.
12. Development of specialized cells within
epidermis
1.Melanocyte 2.Langerhans cell 3.Merkels cell
1st seen @ 50 days @40 days @8-12 wks
Dendritic morphology Dendritic morphology C.dense core granules
HMB45 Ab +ve r/n CD45,HLA DR,CD1c Cytokeratin 20
ATPase activity Neuropeptides
From neural crest Mesoderm cells Ectoderm
13. Melanocytes
•Derived from neural crest
•Migrate dorsolaterally and ventrally
•Also from schwann cell
precursor
•Becomes functional 3-4m
•Melanosome transfer- 5m
•Density towards birth
14. Active melanocytes in dermis during embryonic period
Migrate to epiderms / Apoptosis
Disappears by birth, may persist in
some areas(Presacral, dorsum of distal
extremities,head and neck)
Mongolian spots
15. Langerhans cell
• Density low in early gestation increases during 3rd
trimester.
Merkel cell
• Highly innervated neuroendocrine cells
• Involved in mechanoception.
• Found in basal layers of epidermis associated with
appendages & nerves.
16. Clinical relevance:
Waardenberg syndrome
• Due to failure of melanocyte
precursors.
• Causative genes
MITF,PAX3,SOX10,SNA12
• Also membrane receptors & ligands-
Endothelin 3,Endothelin B,KIT
17. Development of dermis & hypodermis.
• Neural crest- face & frontal scalp
• Paraxial mesoderm-somite-dermomyotome- dermis of
back
• Lateral plate mesoderm- dermis
of extremities & central trunk
• 6-8 wks –dermal fibroblasts
secrete collagen III & I (3:1)
18. • 9 wks-demarcation b/n dermis & subcutis
• 12 wks-demarcation b/n papillary & reticular
dermis, collagen assemble into fibers
• End of 2nd trimester-dermis shifts from scaring to non
scarring type
• Dermal vasculature-starts at13 wks,matures fully at
birth. Regulated by VEGF,Tie 1&2,Ang 1&2
• Dermal nerves-follows vascular pattern
• Hypodermis-starts during 2nd trimester,continues in 3rd
19. Clinical relevance
• EDS-dermal structural proteins are
defective
• Cutis laxa with severe pulmonary,GIT &
Genitourinary malformation-LTBP4
• Goltz syndrome-focal dermal hypoplasia
PORCN gene, effector of Wnt signalling pathway
Goltz syndrome
20. Development of dermo-epidermal junction
• Flat embryonic DE junction-L. densa & L. lucida
composed of molecules common to all BM.
• 8wks-skin specific components
• 12wks-structures of mature DEJ-
hemidesmosomes,anchoring filaments,BPAG etc.
• Finally acquires rete ridges & dermal papillae like
adult DEJ.
21. Development of skin appendages
• Epidermal & dermal components
• Signals sent back & forth b/n epidermis & dermis.
Hair follicle development
• Epidermal placodes (10-11 wks)
• Presumptive dermal papillae
• Hair germ (12-14 wks)
• Hair peg
27. • 8-10 wks-folds visible at dorsal digital tips
• 13wks-proximal nail folds
• Ventral to nail fold nail matrix cells produce nail
plate
• Preliminary nail is shed-hard nail plate 4th mth
• Nail completely covers nail bed 5th mth
30. Interfollicular eccrine glands
• Arise independently -5th mth
• Do not function in utero
• Begin functioning post nataly
Apocrine glands
• Upper portion of hair follicle-5th mth
• Clear cells & dark cells(mucin secreating)-7th mth
• Quiscent in neonates, starts functioning during puberty
31. Clinical relevance
• Hypohydrotic ectodermal dysplasia(HED)-
Ectodysplasin A
• Also from genes involved in epidermal development.
• Ankyloblepharon ectodermal dysplasia cleft lip/palate
(AEC)-P63
• Ectrodactyly ectodermal dysplasia(EEC)-P63
35. In a nutshell….
• Surface ectoderm gives rise to keratinocytes
& merkel cells,while Neurectoderm –
melanocytes & dermis of face & frontal scalp.
• Development of skin is conceptually divided into
specification , morphogenesis & differentiation.
• Basal cells of epidermis gives rise to periderm f/b
intermediate layer , finally epidermal stratification &
cornification leading onto sloughing of periderm.
36. In a
nutshell..
• Langerhans cells precursors are seen from 40 days, while
merkel cells are detected at 8-12 wks.
• Dermis of face & frontal scalp develop from neural crest,
while paraxial mesoderm gives rise to dermis of back,
whereas dermis of ventral trunk & extremities are from
lateral plate mesoderm.
• Melanocytes migrate from
neural crest following a
characteristic trajectory.
• They become functional by 3-4m & transfers melanosomes
to keratinocytes by 5th m.
37. In a nutshell…..
• The flat embryonic DEJ acquires skin specific
components by 8 wks,& all structures of mature
DEJ are in place by 12 wks.
• Skin appendages have both epidermal & dermal components
& reciprocal interactions b/n these two are central to their
development.
• Hair follicle progresses through the placode, presumptive
D.papillae, hair germ & hair peg stages to the mature follicle
while sebaceous gland development parallels hair follicle dev