Download Development of Dermis

Integumentary system
Min-Chuan Huang
台大醫學院解剖學暨細胞生物學研究所
黃敏銓
1
Integumentary system
Skin:
Epidermis
Dermis
Skin appendages
Sebaceous glands
Sweat glands
Mammary glands
Hair
Arrector pili muscles
Nails
Teeth
2
Development of skin: overview
4 weeks
• Embryonic skin: begins from embryo of 4-5 weeks
• Epidermis: surface ectoderm
Dermis: mesoderm
Mutual inductive mechanism for ectodermal/mesenchymal
interactions (epidermal / dermal interactions)
WNT, fibroblast growth factor (FGF), transforming growth factor-β (TGF-β),
sonic hedgehog (SHH)
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Development of epidermis: early stage
4 weeks
• 4 weeks: primordial
skin from surface
ectoderm
• 7 weeks:
● Periderm:
single layer of
squamous epithelium
7 weeks
- Continue keratinization,
desquamation
- Exfoliated cells form part of
vernix caseosa
● Basal
layer: proliferation
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Development of Epidermis at 11 weeks
• Stratum germinativum
–Epidermal ridges: begin at 10 weeks, permanently established at 19th
week; genetically determined (fingerprint), Dermatoglyphics 皮紋學
• Intermediate layer: from stratum germinativum
• Migration of neural crest cells to developing dermis
(melanoblasts), later melanocytes (as early as 40-50 days) in
stratum germinativum
11 weeks
5
Development of epidermis: 21st week
forward
(periderm disappears)
ichthyosis: severe keratinization
Newborn
• Stratum corneum: originally periderm
• Appearance of stratum lucidum, granulosum,
spinosum
Melanocytes fail to produce melanin:
1. Generalized albinism
2. Localized albinism (piebaldism)
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Development of Dermis
• Mesenchyme from mesoderm: (major) somatic layer of
lateral mesoderm & (minor) dermatomes of somites
• By 11 weeks: mesenchymal cells produce collagenous &
elastic connective tissues fibers
• Dermal ridge: with capillary loops & sensory nerve
endings
• Capillary-like vessels: derived from mesenchyme, begin
at the end of 5th week
11 weeks
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Week 16
Week 20
Development of
sebaceous glands
• Glandular buds from sides
of developing epidermal
root sheaths of hair
follicles, branch to form
primordia of alveoli &
ducts
• Central cells of alveoli:
break down, release into
hair follicle, mix with
desquamated peridermal
cells (vernix caseosa)
• Sebaceous glands
independent of hair
follicles: in external genital
organs
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Development of eccrine sweat glands
• Epidermal downgrowth into dermis by elongation, and coiling
• End: primordium of secretory part; (1) myoepithelial cells, (2)
secretory cells
• Epithelial attachment: primordium of duct, central cells
degenerate
• weeks
Begin to function after birth
20
9
Development of apocrine sweat glands
• Axilla, pubic, perineal regions, areolae of
the nipples
• Downgrowths of stratum germinativum
giving rise to hair follicles
• Open into the upper part of hair follicles
superficial to the openings of sebaceous
glands
• Secrete during puberty
• Pheromone
10
Development of
hair (1/2)
Week 9-12
• Hair follicle: stratum
germinativum into
dermis
• Hair bud
• Hair bulb (primordium of
hair root)
–Germinal matrix,
invaginated by
mesenchymal hair papilla
–Hair shaft: keratinized
portion
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Development
of hair (2/2)
• Epidermal root sheath:
from peripheral cells of
hair follicles
• Dermal root sheath: from
mesenchymal cells
• Lanugo: the first hair, end
of 12th week, replaced
during perinatal period
• Melanocyte in hair bulb
from migrating
melanoblast
• Arrector pili muscles from
mesenchyme, goose
bumps
Week 12
Week 20
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Hypertrichosis
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Hypertrichosis
Nature. 2007
Alopecia
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Folliculogenesis
Hair cycling
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Hair follicle stem cells in bulge region
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Stem Cells 2005;23:150–165
Hair follicle stem cells
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Hair follicles
Schwann cells
Neurons
Glial cells
Keratinocytes/sebaceous glands
Smooth muscle cells
Blood vessels
Adipocytes
Hematopoietic cells
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We need tissue regeneration
instead of scar formation
Nature. 2008. 453:314-21.
Myocardial infarction
Spinal cord injury
Liver cirrhosis
Lung fibrosis
Development of mammary glands
• Mammary ridges: 4th week; thickened strips of
ectoderm from axillary to inguinal regions
• Mammary buds: downgrowth of epidermis at 6th week
19
Supernumerary nipples
Supernumerary breasts
1% of the female
5.6%
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Development of mammary glands
• Mammary buds: primary bud → secondary buds → lactiferous
ducts/branches: canalization by placental sex hormones
• Mammary pits: depressed epidermis → nipples rise by proliferation of
connective tissues (areola)
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Flat or inverted nipples (10-20%)