What is the dermis?
The primary function of the dermis is to sustain and support the epidermis. The dermis is a more complex structure and is composed of 2 layers, the more superficial papillary dermis, and the deeper reticular dermis. These are formed by interlacing collagen and elastic fibers. These fibers produce skin tone as well as providing resilience and strength for the skin. The skin is characterized by deepening lines as we age, these are a consequence of the direction of collagen forming in a specific region, creating tension lines (cleavage lines) and wrinkling of the skin.
The papillary dermis is thinner, consisting of loose connective tissue containing capillaries, elastic fibers, reticular fibers, and some collagen. The reticular dermis consists of a thicker layer of dense connective tissue containing larger blood vessels, closely interlaced elastic fibers, and coarse bundles of collagen fibers arranged in layers parallel to the surface.
The reticular layer also contains fibroblasts, mast cells, lymphatics, epidermal appendages, and nerve endings, which provide signals responsible for sensations such as; touch, temperature, and pain. Moreover, only a few nerves penetrate the epidermis.
Encasing these components of the dermis is a gel-like ground substance, composed of mucopolysaccharides (primarily hyaluronic acid), chondroitin sulfates, and glycoproteins. The deep surface of the dermis is highly irregular and borders the subcutaneous layer, the ‘panniculus adiposus,’ which acts as a cushion for the skin.
The fibroblast is a key cell type of the dermis. These cells produce and secrete procollagen and elastic fibers. Procollagen is divided by proteolytic enzymes into collagen that begins to form and become cross-linked. These tightly cross-linked collagen fibers provide tensile strength and resistance against shear and other mechanical forces. Collagen makes up 70% of the weight of the dermis, primarily Type I (85% of the total collagen) and Type III (15% of the total collagen). Elastic fibers constitute less than 1% of the weight of the dermis, but they play an enormous functional role by resisting deformational forces and returning the skin to its resting shape.