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Integumentary DevelopmentThis chapter will introduce our foray into organogenesis as we examine the development of the integumentary system. This is an important organ system that forms about 8% of the total body mass and has a surface area in an average sized person of approximately 2.2 square meters. Prior to the lecture you should be able to:

• Describe all the anatomy of the integumentary system covered in the anatomy course.

After this lecture you should be able to:• List all the embryonic germ layers that contribute to the formation of

the integument.• Describe the processes that account for the development of the layers

of the skin and their substrata.• Explain the developmental processes that account for the

development of the glands and hair follicles.• Clearly describe tooth development and emergence.

The skin is largely ignored by the student in the dissecting room, just being incised, reflected, and cast aside as something which hides more interesting things underneath. Yet, it is that part of the body in which, par excellence, can be demonstrated, at all levels of observation, the relation between structure and function in biological organization.

Gray’ Anatomy, 38th British Edition

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Anatomy ReviewRemember the key anatomical aspects of the integument and dental anatomy

Layers and substrataEpidermis

Stratum basale

Stratum spinosum

Stratum granulosum

Stratum lucidum

Stratum corneum

DermisStratum papillare

Stratum reticulare

HypodermisAdipose layer

Fibrous layer

Anatomy of the epidermal appendagesHair follicle

Dermal papilla

Hair

Arrector pili muscle

GlandsSebaceous gland

Sweat glands

Tooth AnatomyEnamel

Dentin

Cement

Pulp cavity

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I n t e g u m e n t a r y D e v e l o p m e n t

Development of the Integumentary LayersGerm layers of originBody ectoderm

Epidermal keratinocytes

Neural crest ectodermEpidermal melanocytes

Epidermal Merkel cells (mechanoreceptors)

Dermal tissues of head

MesodermEpidermal Langerhans cells (macrophages)

Dermis

Hypodermis

Epidermal developmentBody ectoderm – 4 weeks

Periderm – 5 to 10 weeksFormation of the vernix caseosa cheesy varnish

Migration of neural crest cells below the developing epidermis

Differentiation into melanoblasts

Timeline

4 weeksto

6 weeks

7 weeksto

10 weeks

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Stratified epithelium – 11 weeks to 21 weeksPeriderm

Intermediate layer

Basal layer Epidermal ridges

Melanoblasts migrate into epidermis to become melanocytes

Cornified layer replaces periderm - 22 weeksFormation of stratum corneum

Melanocyte activity

Mature EpidermisStratum basale

Stratum spinosum

Stratum granulosum

Stratum lucidum and corneum

Timeline

11 weeksto

21 weeks

22 weeksto

Neonate

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I n t e g u m e n t a r y D e v e l o p m e n t

Dermal developmentMesenchyme beneath the body ectoderm

Lateral mesoderm

Dermatome of the somite

Head ectomesenchyme - neural crest

Vessel formation - begins in 5th weekCapillaries

Larger vessels

Fibrocyte development during the 11th week

Formation of ridges

Formation of dermal strataStratum papillare

Stratum reticulare

Timeline

11 weeksto

21 weeks

22 weeksto

Neonate

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Hypodermis developmentSubdivision of the dermal development

Lateral mesodem

Glandular DevelopmentInvagination of epidermal cells

Sweat glandsEpidermal bud

Epidermal cell column

Basal coilSecretory cells

Lumen formation

Myoepithelial cells

Timeline

20 weeks

28 weeks

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I n t e g u m e n t a r y D e v e l o p m e n t

Development of the Pilosebaceous UnitInvagination of epidermal cells

Sebaceous glandsOutgrowth of follicular wall

Secretory cell development

Hair follicle and hairHair bud

Hair bulbGerminal matrix

Hair papilla

Epidermal root sheath

Dermal root sheath

Hair shaftLanugo hairs

Arrector pili muscle

Timeline

12 weeks

14 weeks

16 weeks

23 weeksto

28 weeks

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Mammary Gland DevelopmentMammary crests

Typical glandular formationInvagination process

Primary mammary bud

Secondary mammary buds

Mammary pit appears

Mammary glands emerge

Lactiferous duct

Areola of breast

Nipple formation

Timeline

12 weeks

20 weeks

30 weeks

Birth

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I n t e g u m e n t a r y D e v e l o p m e n t

Nail DevelopmentNail structureNail plate

Hyponychium

Proximal foldSuperficial epidermal layer

Deep epidermal layer

Dermal core

Eponychium (cuticle)

Germinal matrix

Ventral sterile matrix or nail bed

Process of epidermal cornificationNail field

Fingers

Toes

Nail folds

Nail plate

Timeline

10 weeksor

14 weeks

32 weeks

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Development of the TeethContributors to tooth developmentOral ectoderm

Mesoderm

Neural crest

Initiation of tooth developmentDental laminae – 6th week

What are they?

Formation induced by:

Tooth buds for deciduous teeth

Tooth buds for permanent teethRelated to deciduous teeth

No deciduous precursor

Cap stage of tooth developmentTooth germ

Enamel organ

Dental papilla

Timeline

6 weeks

6 weeks

end of 6 weeks

8 weeks

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Bell stage of tooth developmentTooth germ

Enamel organ

Outer enamel epithelium

Inner enamel epithelium

Enamel reticulum

Dental papilla

Dental sac

Formation of odontoblastsPredentin

Dentin

Formation of ameloblastsPrisms of enamel

Progression of deposition

Formation of the root of the toothEpithelial root sheath

Odontoblast activity

Cementoblasts from dental sac

Cementoenamel junction

Final activity of the dental sac

Timeline

10 weeks

14 weeks

28 weeks

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Timeline

6 monthspostnatal

18 monthspostnatal

Tooth eruptionDeciduous teeth

Permanent teeth