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Integumentary systemMin-Chuan Huang
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Integumentary system
Skin:
Epidermis
Dermis
Skin appendages
Sebaceous glands
Sweat glands
Mammary glands
Hair
Arrector pili muscles
Nails
Teeth
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• Embryonic skin: begins from embryo of 4-5 weeks
• Epidermis: surface ectoderm
Dermis: mesoderm
Development of skin: overview4 weeks
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: primordial
skin from surface
ectoderm
• 7 weeks:
●Periderm: single layer of
squamous epithelium- Continue keratinization,
desquamation
- Exfoliated cells form part of
vernix caseosa
●Basal layer: proliferation
4 weeks
7 weeks
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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
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Development of epidermis: 21st week
forward
• Stratum corneum: originally periderm
• Appearance of stratum lucidum, granulosum, spinosum Melanocytes fail to produce melanin:
1. Generalized albinism
2. Localized albinism (piebaldism)
(periderm disappears)
ichthyosis: severe keratinization
Newborn
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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 fibers
• Dermal papillae: with capillary loops & sensory nerve
endings
• Capillary-like vessels: derived from mesenchyme
(vasculogenesis), begin at the end of 5th week
11 weeks
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Development of
hair (1/2)
•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
Week 9-12
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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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Nature. 2007Hypertrichosis
Alopecia
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Folliculogenesis Hair cycling
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Stem Cells 2005;23:150–165
Hair follicle stem cells in bulge region
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Hair follicle stem cells
• Hair follicles
• Schwann cells
• Neurons
• Glial cells
• Keratinocytes/sebaceous glands
• Smooth muscle cells
• Blood vessels
• Adipocytes
• Hematopoietic cells
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Development of
sebaceous glands
Week 16 Week 20
• 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 peridermalcells (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
• Begin to function after birth20 weeks
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Development of apocrine sweat glands
• Axilla, pubic, perineal regions, areolae of the nipples
• Downgrowths of stratum germinativumgiving rise to hair follicles
• Open into the upper part of hair folliclessuperficial to the openings of sebaceous glands
• Secrete during puberty
• Pheromone / body odor
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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
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Supernumerary nipples
1% of the female
5.6%
Supernumerary breasts
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Development of mammary glands
Flat or inverted nipples (10-20%)
• 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)