The dermis is the innermost and much thicker of the two main layers of the skin of a vertebrate, the outer being the epidermis. The dermis (also known as the corium) is 1.5 to 4 mm thick and makes up approximately 90 percent of the thickness of the skin. Below the dermis lies the hypodermis.
The dermis is responsible for the tensile strength of skin. Its main functions 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.
The dermis contains most of the skin's specialized cells and structures, including:
· Apocrine glands are specialized sweat glands that can be found only in the armpits and pubic region. These glands secrete a milky sweat that encourages the growth of the bacteria responsible for body odor.
· Eccrine glands are the true sweat glands. Found over the entire body, these glands regulate body temperature by bringing water via the pores to the surface of the skin, where it evaporates and reduces skin temperature. These glands can produce up to two liters of sweat an hour, however, they secrete mostly water, which doesn't encourage the growth of odor-producing bacteria.
The dermis layer is made up of two sublayers:
The upper, papillary layer, contains a thin arrangement of collagen fibers. The papillary layer supplies nutrients to select layers of the epidermis and regulates temperature. Both of these functions are accomplished with a thin, extensive vascular system that operates similarly to other vascular systems in the body. Constriction and expansion control the amount of blood that flows through the skin and dictate whether body heat is dispelled when the skin is hot or conserved when it is cold.
The lower, reticular layer, is thicker and made of thick collagen fibers that are arranged in parallel to the surface of the skin. The reticular layer is denser than the papillary dermis, and it strengthens the skin, providing structure and elasticity. It also supports other components of the skin, such as hair follicles, sweat glands, and sebaceous glands.