Dermis  - Development and Stem Cells

Embryonic Development of the Dermis:

Dermis is formed approximately at E11 of mouse embryonic development. Various embryonic origins contribute to dermis at different regions of the body: dermis of the back skin - dorsal dermis - is derived from somitic dermatome, dermis of the ventral and flank regions is derived from lateral plate mesoderm and the head dermis originates from neural crest cells. Canonical ß-catenin signaling is responsible for dermis initiation in the embryo.

Anatomical Structure and Function of the Dermis:

The dermis is one of the two main layers of the skin. It is located under the epidermis and is connected to it via the basal membrane at the dermal-epidermal junction (DEJ). 

The main function of dermis is to protect the body from stress and strain. It produces extracellular matrix and communicates with neighboring cells to maintain normal skin physiology and acts as a signaling center enabling epidermal growth, proliferation, differentiation and wound healing. 

The main structural components of dermis are collagen, elastic fibers and the extrafibrillar matrix. Collagens provide resistance and strength, while elastin supports the elastic properties of the dermis.

Histologically, dermis contains two layers – papillary and reticular, each formed by papillary and reticular fibroblasts respectively.

The papillary dermis is the thinner layer lying adjacent to the basal membrane and is characterized by thin, non-organized collagen bundles of collagen types I and III. It includes structures such as the dermal papilla and vascular and neural components that support hair formation and growth. The border between the papillary and reticular dermis is defined by the vascular plexus, called rete subpapillare. The reticular dermis differs from the papillary layer in its well-organized fiber batches and lower collagen type III content. The lower border of the reticular dermis is defined by another vascular plexus, rete cutaneum, which separates it from the hypodermis.

The dermis also includes touch and heat receptors, sweat glands, sebaceous glands, apocrine glands, lymphatic and blood vessels.