The dermis is dense irregular connective tissue that supports epidermis and underlying structures. Blood vessels in this layer supply nutrients to the skin, remove toxins and regulate temperature.
Naked nerve endings in this layer detect different sensations like gentle pressure, heat and vibrations. The dermis also contains hair follicles and oil glands.
The Papillary Layer
The thin top layer of the dermis, called the papillary layer, is named for the fingerlike projections that protrude into the epidermis. These are known as the dermal papillae, and they contain capillaries, sensory touch receptors, and a few fat cells (adipocytes). The papillary layer is composed of loose areolar connective tissue and contains blood vessels and a few nerve fibers. It also contains phagocytes, which are defensive cells that can “patrol” the area to look for foreign invaders that may have breached the epidermis.
This loose connective tissue includes a gel-like substance that is made of proteins. It includes collagen fibers, which provide toughness, and elastin fibers, which give elasticity. In addition, this tissue includes a network of vascular capillaries that supply the epidermis with nutrients and blood.
The dermis also contains a few oil glands and hair follicles, as well as some muscle and bone tissue. It is a major site of cell repair, and it is also involved in the regulation of body temperature. The dermis has two layers: the papillary layer and the reticular layer. The reticular layer is thicker than the papillary layer, and it is composed of dense irregular connective tissue. This layer is well vascularized, and it has a large number of fibroblasts and other cells that are involved in the formation of the skin.
The Reticular Layer
The reticular layer forms the deeper, major portion of your dermis. It is composed of dense, irregular connective tissue and it strengthens skin, providing structure and elasticity. This layer is also home to most of the structures that make up the skin, including hair follicles and sweat glands.
It also contains the blood vessels that run through your dermis and provide nutrients to cells in the epidermis layer and to the layers within the dermis. These blood vessels can dilate or contract depending on your body temperature.
In this layer, there are specialized nerve cells that are important in the sense of touch and in thermoregulation. The reticular layer of your skin also includes the meissner’s corpuscles and Pacinian corpuscles, which are sensory receptors that respond to light touch, as well as a variety of other sensory receptors that can detect heat or cold, pressure, vibration, and electrical impulses.
In addition, the reticular layer of your dermis includes a network of fibers called the collagen fibers, which provide the strength and resilience of the skin. In places where the tendons and skeletal muscles pass through the dermis, these fibers help the skin stretch and move. In the reticular dermis, there are also fat cells that give your skin its fullness. The fatty cells also store the energy you use to perform physical activity, as well as act as a source of heat.
The Nervous Layer
The dermis has many important functions, including supporting epidermis, insulating the body from cold, protecting the skin from injury and providing elasticity. It also contains hair follicles, sebaceous glands (oil glands), sweat glands, lymphatic vessels and nerve fibers. Blood vessels provide nourishment to and discard cellular waste from both dermal and epidermal cells.
Fibroblasts in the dermis form collagen and elastic fibers to give the skin strength and elasticity. They are embedded in a gel-like substance called ground substance, which is made of a soluble mucus and consists of glycoproteins such as hyaluronic acid and chondroitin sulfates. This layer also contains a network of fat cells that help insulate and cushion the skin.
A specialized type of blood vessel, the arrector pili muscle, helps control skin permeability, and it is located in this layer. The sweat glands and apocrine glands are also found in this layer as well as hair follicles. The sebaceous glands secrete a waxy oil, called sebum, to keep the skin lubricated. The hair follicles grow and shed throughout your life, and the number of them varies by area of the body.
The papillary and reticular layers of the dermis merge at the base of the hypodermis, a subcutaneous layer of loose connective tissue containing fat cells. This layer connects the skin to the underlying fascia of the bones and muscles, but is not strictly considered part of the integument or skin.
The Oily Layer
Located below the stratum basale, this layer is 8-10 cell layers of cuboidal to columnar mitotically active keratinocytes that produce lipids and melanin. The cells are arranged in rows and connect to each other with hemidesmosomes, which interlock to strengthen the barrier. The layer is sometimes referred to as the “spiny” epidermis, but the spiny appearance is due to cellular structures called cell processes, which protrude from the cells and contact each other via a mechanism called desmosomes. This layer is the most superficial and dead part of your skin, and helps prevent the penetration of microorganisms and water loss. It is also responsible for the greasy, yellowish appearance of your hands and feet. The cells in this layer are densely packed with a clear protein called eleiden, which helps the skin resist dehydration. The top of the epidermis is further protected from microorganisms by a lipid film called keratin.
The middle layer of your skin is the dermis (say: DUR-mis). It houses hair follicles, sebaceous glands, sweat glands, capillaries (small blood vessels), and nerve endings that allow you to feel heat, cold, touch, and pain.
The dermis varies in thickness across your body, from 0.6 millimeters over your eyelids to 4 millimeters on the back. The skin also contains fat, which is found primarily in the subcutis layer, or hypodermis. This fat provides insulation, conserves body heat, and acts as a cushion to protect your underlying muscles and tissues.