The skin develops from two germ layers - the epidermis derives from surface ectoderm and the dermis derives from mesodermal mesenchyme. The epidermis forms from proliferating surface ectodermal cells that generate a basal layer and periderm. The periderm desquamates and is replaced by cells from the basal layer. The basal layer stratifies to form the epidermis and develops ridges determined genetically. The dermis develops from mesenchyme and projects ridges into the epidermis. Congenital skin anomalies can affect development, such as ectodermal dysplasia impacting ectodermal tissues.

1. Development of Skin
Handout for Medical Students
Prepared by: Melaku Geletu (M.Sc. in Anatomy)

2. Development of Skin
• Epidermis is derived from surface ectoderm
• Dermis is derived from mesodermal
mesenchyme

4. Epidermis
• Primordium of the epidermis is
a layer of surface ectodermal
cells
• These cells proliferate and
form:
– Periderm—a layer of squamous
epithelium
– A basal (germinative) layer

5. Epidermis
• Peridermal cells
– Continually undergo keratinization and
desquamation
– Replaced by cells arising from the basal layer
– Form part of the white greasy substance-vernix
caseosa

6. Epidermis
• Vernix caseosa
– Covers the fetal skin
– It contains epidermal cells, lanugo hair and sebum
– Protects the developing skin from constant
exposure to amniotic fluid
– It also facilitates birth of the fetus

7. Epidermis
• Basal layer becomes stratum
germinativum
• Stratum germinativum
– Produces new cells
– By 11 weeks, cells from it forms
an intermediate layer
– Epidermal ridges also forms.

8. Epidermis
• The type of pattern of epidermal ridges that
develops is determined genetically
• Abnormal chromosome complements affect
its development patterns
– E.g. Down syndrome

9. Epidermis
• Periderm disappears and the stratum
corneum forms at 21st
week

10. Epidermis
• Neural crest cells migrate into the developing
dermis and differentiate into melanoblasts
• Later melanoblasts migrate to the
dermo-epidermal junction and differentiate
into melanocytes
– This differentiation involves the formation of
pigment granules

11. Epidermis
• Melanin
– Begins to be produced and distributed before birth
by melanocytes
– Its amount increases in response to ultraviolet light
– Its relative content is responsible for different skin
colors
– Pigment formation can be observed prenatally in
epidermis

12. Epidermis
• Development of epidermis need inductive
interactions of dermis
• Skin is classified as thick or thin based on the
thickness of the epidermis

13. Dermis
• It develops from mesenchyme, which is derived from
the mesoderm
• Origin of the mesenchyme for the development of
dermis:
– Most from somatic layer of lateral mesoderm
– Some from dermatomes of the somites

14. Dermis
• Dermal ridges
– Formed by the projection of dermis into the
epidermis
– Capillary loops develop in some of it
– Sensory nerve endings form in others

15. Anomalies of the skin
Congenital Ectodermal Dysplasia
• A group of hereditary disorders involving
tissues that are ectodermal in origin
• Teeth are completely or partially absent
• Often the hairs, nails, and skin are also
severely affected

16. Anomalies of the skin
Ectrodactyly-Ectodermal Dysplasia-Clefting Syndrome
• It is a congenital skin condition that is inherited as an
autosomal dominant trait
• It involves both ectodermal and mesodermal tissues
• Consists of ectodermal dysplasia

17. Anomalies of the skin
Ectrodactyly-Ectodermal Dysplasia-Clefting Syndrome
• Associated with:
– Hypopigmentation of skin and hair
– Scanty hair and eyebrows
– Absence of eyelashes
– Nail dystrophy
– Hypodontia and microdontia
– Cleft lip and palate