Biomedical Engineering Reference
In-Depth Information
Embryonic
ectoderm
Periderm
Embryonic
basal layer
Primary
hair germ
Dermal papilla
anlage
Hair follicle
Adult epidermis
6.4
Development of the epithelial components of skin.
germs appear as invaginations of the embryonic basal layer directly above
aggregations of specialized mesenchymal cells, the anlage of dermal papillae.
From the primary hair germ the sebaceous gland, the hair follicle and the
apocrine gland will develop. The embryonic basal layer stratifies to form the
epidermis where dermal fibroblasts, rather than dermal papilla cells, exert their
influence.
Embryogenetically, the dermis comes from mesoderm which is brought into
contact with the inner surface of the epidermis during gastrulation. The mesoderm
is essential for inducing differentiation of the epidermal structures, as is classically
demonstrated in the feather germ of birds. In fact, the dermis remains instrumental
later during development in maintaining adult epidermis and this epithelial-
mesenchymal interaction is known to be dependent upon the interplay of many
factors synthesized by both the epidermis and the dermis.
At roughly the same time that a multi-layered epidermis forms, primitive hair
germs start developing. The first indication of a hair follicle is a crowding of
nuclei (termed primitive hair germ) in the basal layer of the epidermis. This
process is believed to be initiated by the specialized mesenchymal cell
