Stratification and Differentiation of the Developing Epidermis

Key concept

Two developmental pathways are proceeding simultaneously in the early epidermis, stratification and differentiation. As new keratinocyte layers are formed (stratification), the cells within those layers are also acquiring new properties characteristic of their location within the epidermis (differentiation). In the fully developed epidermis, the stratification developmental pathway is turned off; the only operating developmental pathway is that of differentiation, that is, the coordinated spatial and temporal maturation of keratinocytes as they pass upwards through the epidermis to the cornified cell layer.

Stratification (Bullet Summary)

• Week 2: precursor epidermis forms.
• Week 5: periderm forms over single keratinocyte layer.
• Week 9: first intermediate layer forms.
• Week 12: second intermediate layer forms.
• Week 15: hair follicle epidermis keratinizes.
• Week 24: interfollicular epidermis keratinizes.

To see how the pathways develop and to study the morphologic changes click on one of the buttons below:

Week 2
Week 5
Week 9
Week 12
Week 15
Week 24