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![Page 1: Development of the skin and its derivatives - Embryology · Development of the skin and its derivatives Dr Annemiek Beverdam – School of Medical Sciences, UNSW Wallace Wurth Building](https://reader031.fdocuments.us/reader031/viewer/2022022009/5ae811777f8b9a8b2b8f7880/html5/thumbnails/1.jpg)
Development of the skin and its derivatives
Dr Annemiek Beverdam – School of Medical Sciences, UNSW Wallace Wurth Building Room 234 – [email protected]
Resources: http://php.med.unsw.edu.au/embryology/ Larsen’s Human Embryology – Chapter 7
The Developing Human: Clinically Oriented Embryology
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Lecture overview Skin function and anatomy
Skin origins
Development of the overlying epidermis
Development of epidermal appendages:
Hair follicles Glands Nails Teeth
Development of melanocytes
Development of the Dermis
Dr Annemiek Beverdam – School of Medical Sciences, UNSW Wallace Wurth Building Room 234 – [email protected]
Resources: http://php.med.unsw.edu.au/embryology/ Larsen’s Human Embryology – Chapter 7
The Developing Human: Clinically Oriented Embryology
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Skin Function and Anatomy
Largest organ of our body Protects inner body from outside world (pathogens, water, sun) Thermoregulation Diverse: thick vs thin skin, scalp skin vs face skin, etc Consists of: - Overlying epidermis - Epidermal appendages:
- Hair follicles, - Glands: sebaceous, sweat, apocrine, mammary - Nails - Teeth
- Melanocytes - (Merkel Cells - Langerhans cells) - Dermis - Hypodermis
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Trilaminar embryo
Ectoderm (Neural crest) brain, spinal cord, eyes, peripheral nervous system
epidermis of skin and associated structures, melanocytes, cranial connective tissues (dermis)
Mesoderm musculo-skeletal system, limbs
connective tissue of skin and organs urogenital system, heart, blood cells
Endoderm epithelial linings of gastrointestinal and respiratory tracts
Skin origins
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Ectoderm Overlying epidermis, epidermal appendages,
nerve endings
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Neural Crest Melanocytes + Cranial Connective Tissue
Melanocytes
Cranial Connective Tissue
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Mesoderm Dermis, Hypodermis
Somitic mesoderm (yellow): dermomyotome -> dorsal dermis Somatic lateral plate mesoderm (purple) -> ventral dermis
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Page 342 S.F. Gilbert Developmental Biology 5th edition
Embryonic development:
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Epidermal development Surface ectoderm
Skin/Interfollicular epidermis: stratified squamous epithelium Appendages: Hair follicles Glands (sebaceous, sweat, apocrine, mammary, lacrimal, salivary) Nails Teeth
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Development of Skin/interfollicular epidermis (IFE)
Week 11
Week 4
Week 24
Onset of stratification
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Development of Skin/interfollicular epidermis (IFE)
Periderm formation: 4 weeks
Basal layer
Periderm
Basement membrane
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Intermediate layer
Development of Skin/interfollicular epidermis (IFE) Stratification
Week 11: intermediate layer
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Stratified skin/IFE
Keratin 5/14
Keratin 1/10
Involucrin Loricrin
integrins Junctions:
Envelope proteins Fillagrin
Regeneration, skin types
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Stratified skin/IFE
Thick skin
Thin skin
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Epidermal Appendages Surface ectoderm
- Hair follicles, - Glands: sebaceous, sweat, apocrine, mammary,
salivary, lacrimal - Nails - Teeth
Share common developmental mechanisms: Epithelial to mesenchymal signaling inducing formation of placode and mesenchymal condensations, invagination of epidermis into dermis.
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Hair follicle development and cycling Epidermal appendage
Involved in thermoregulation/sun protection
Month 2-4: Onset hair follicle development Hair follicles develop first in cranial region
Month 5: most hair follicles present ≈ 5,000,000 hair follicles Anatomy
Permanent Infundibulum
Cycling
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Hair follicle development
Mesenchymal condensate
Dermal papilla
Signaling events
Month 2 Birth: 5000,000
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Hair follicle development
Hair germ
Hair peg
Bulbous hair peg
Invasion of dermal cells
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Hair follicle development
Formation of: Arrector pili muscle Hair follicle bulge Germinal matrix Inner and outer root sheaths
Babies are born with first generation of fine un-pigmented hairs: lanugo
Permanent
Cycling Postnatal regeneration: Hair follicle cycling
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Postnatal hair follicle cycling
Telogen: rest Anagen: growth Catagen: regression
Ageing
germ peg bulbous peg
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Epidermal gland development Epidermal appendages: outgrowths from IFE or HF
Sebaceous glands: sebrum/vernix
Sweat glands Apocrine glands (pheromones)
Mammary glands Salivary glands Lacrimal glands
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Epidermal gland development Epidermal appendages
Sebaceous glands: develop from hair follicle (4 weeks +) Sweat glands: develop from basal layer IFE (20 weeks+)
Apocrine glands: develop in association with HFs, most lost late in fetal dev.
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Mammary gland development Epidermal appendage
4 weeks:
Postnatal regenerative growth
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Teeth
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Tooth development Ectoderm/cranial neural crest derived mesenchyme
Tucker and Sharpe, Nature Genetics 2004
Week 6: dental lamina
U-shaped ridge
Week 7: Mesenchyme condensation
Week 14: Epithelial cells: Ameloblasts: enamel
Mesenchymal cells: Odontoblasts: dentin
Week 8: Mesenchyme invades base tooth bud:
Dental papilla
enamel
dentin
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Tooth development Week 6: dental lamina forms
Week 7-8: formation of tooth buds: Bud stage
Week 8: formation of dental papilla: Cap and Bell Stage
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Tooth development Primary teeth
10 + 10 Adult teeth
16 + 16
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Nails
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Nail development Ectoderm
Week 10: epidermal thickening, nail field
http://discovery.lifemapsc.com/library/review-of-medical-embryology/chapter-75-development-of-the-nails
Week 11: nail anlagen moves proximally, nail folds, proximal hair fold: formation of formative zone
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Nail development Ectoderm
http://discovery.lifemapsc.com/library/review-of-medical-embryology/chapter-75-development-of-the-nails
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Melanocytes
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Melanocyte development Neural crest
Ernfors, Exp Cell Res 2010
Week 6
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Melanocyte development Neural crest
Millar, Plos Biology 2005
Active Proliferation
Migration into
epidermis
Migration into
Hair Pegs
Week 6/7 Week 10
Final destination: Bulge Matrix
Basal layer (Humans)
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Melanocyte development Neural crest
Djian-Zaouche, Pigment Cell Melanoma Res 2012
Before stratification
Onset stratification
Bulbous hair pegs
Anagen
Hair follicle Bulge
Matrix
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Dermis Connective tissue with:
Fibroblasts Blood vessels Nerve endings
Sensory receptors Muscle bundles
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Dermis development Somitic mesoderm -> trunk
Somatic lateral plate mesoderm -> trunk, limbs Cranial neural crest derived mesenchyme -> cranial region
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Dermis development 3 Months: formation of papillary layer (dermal papillae and epidermal ridges)
Inner dermis: reticular layer
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Lecture overview Skin
Skin origins
Development of the overlying epidermis
Development of epidermal appendages:
Hair follicles Glands
Mammary glands Nails Teeth
Development of Melanocytes
Development of the Dermis
Dr Annemiek Beverdam – School of Medical Sciences, UNSW Wallace Wurth Building Room 234 – [email protected]
Resources: http://php.med.unsw.edu.au/embryology/ Larsen’s Human Embryology – Chapter 7
The Developing Human: Clinically Oriented Embryology
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QUIZ
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1. Hair follicles develop from: A – the epidermis B – the dermis C – the hypodermis D – the melanocytes
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1. Hair follicles develop from: A – the epidermis B – the dermis C – the hypodermis D – the melanocytes
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2. Hair follicle development: A – is controlled by signaling exclusively from the mesenchyme B – is controlled by signaling exclusively from the surface ectoderm C – is controlled by signaling from mesenchyme and surface ectoderm D – is controlled by signaling from the melanocyte stem cells
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2. Hair follicle development: A – is controlled by signaling exclusively from the mesenchyme B – is controlled by signaling exclusively from the surface ectoderm C – is controlled by signaling from mesenchyme and surface ectoderm D – is controlled by signaling from the melanocyte stem cells
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3. The non-cranial dermis is derived from: A –ectoderm B – mesoderm C – neurectoderm D – endoderm
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3. The non-cranial dermis is derived from: A –ectoderm B – mesoderm C – neurectoderm D – endoderm
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4. Human melanocytes: A – are ectodermal in origin B – initially populate the dermis C – are eventually localized in the basal epidermal layer and hair follicle D – all of the above
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4. Human melanocytes: A – are ectodermal in origin B – initially populate the dermis C – are eventually localized in the basal epidermal layer and hair follicle D – all of the above
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5. Epidermal appendages are: A – nails B – mammary glands C – teeth D – all of the above
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5. Epidermal appendages are: A – nails B – mammary glands C – teeth D – all of the above