The dermis is located beneath the epidermis and is the thickest of the three layers of the skin (1.5 mm to 4 mm thick), making up approximately 90 percent of the thickness of the skin. The main functions of the dermis are to regulate temperature and to supply the epidermis with nutrient-saturated blood. Much of the body’s water supply is stored within the dermis. This layer contains most of the skins' specialized cells and structures, including:
- Blood vessels: The blood vessels supply nutrients and oxygen to the skin and take away cell waste and cell products. The blood vessels also transport the vitamin D produced in the skin back to the rest of the body.
- Lymph vessels: The lymph vessels bathe the tissues of the skin with lymph, a milky substance that contains the infection-fighting cells of the immune system. These cells work to destroy any infection or invading organisms as the lymph circulates to the lymph nodes.
- Hair follicles: The hair follicle is a tube-shaped sheath that surrounds the part of the hair that is under the skin and nourishes the hair.
- Nerve endings: The dermis layer also contains pain and touch receptors that transmit sensations of pain, itch, and pressure, as well as information regarding temperature to the brain for interpretation. If necessary, shivering (involuntary contraction and relaxation of muscles) is triggered, generating body heat.
- Collagen and elastin: The dermis is held together by a protein called collagen, made by fibroblasts. Fibroblasts are skin cells that give the skin its strength and resilience. Collagen is a tough, insoluble protein found throughout the body in the connective tissues that hold muscles and organs in place. In the skin, collagen supports the epidermis, lending it its durability. Elastin, a similar protein, is the substance that allows the skin to spring back into place when stretched and keeps the skin flexible.
- Sweat and sebaceous glands: The dermal layer contains specialized glands that produce sweat and oil to cool and lubricate skin.
The image shows the various structures found in the dermis.