Structure of the Dermis

The dermis serves as the structural support foundation of the brick wall that is the epidermis. The dermis is composed of a meshwork of collagen-rich fibrous connective tissue.  Collagen is the primary structural protein of the dermis.  Elastin, an elastic protein, is present in lesser amounts but contributes to flexibility of the dermis.  The structural proteins are interspersed with a gel-like ground substance composed of extracellular fluid and glycoaminoglycans.  In this way, the dermis is similar to a sponge where dynamic compression is possible.

The dermis is divided into two regions: the superficial, or papillary dermis, and the more substantial reticular dermis.  The functions of the dermis, in addition to providing structural and tensile strength, include thermoregulation (vasculature), support for adnexal structures, a focus of immune responses, and storage of fluid, electrolytes and nutrients.

Dermal cell populations

Dermal collagen, elastin and ground substance is produced by dermal fibroblasts, narrow spindloid mesenchymal cells uniformly but sparsely distributed throughout the dermis.  Dermal fibroblasts not only generate the structural proteins of the dermis, but also play a major role in dermal inflammation and wound healing.  In addition, the dermis contains low numbers of resident immune cells, including mast cells, macrophages, dendritic cells, and T cells.  These immune cells are critical in the development of both innate and adaptive immune responses in the skin.

Vasculature

The vascular supply for the epidermis and dermal adnexal structures is located within the dermis.  The vasculature is divided into three distinct layers:  subcutaneous/deep dermal, cutaneous plexus, and papillary plexus.  The largest blood supply, the subcutaneous/deep dermal supply, is composed of arteries and veins that branch superficially into the middermis to form the cutaneous plexus.  The cutaneous plexus is responsible for supplying blood to the adnexal structures of the dermis, including follicles and glands.  Finally, the cutaneous plexus branches superficially to form a fine network of capillaries and venules called the papillary plexus, which lies directly subjacent to and supplies blood to the epidermis.

Blood flow to the skin is dynamic, and factors such as environmental temperature, systemic disease and/or localized inflammation can readily induce shunting of blood to or from the skin.