The dermis is the connective tissue layer of your skin, sandwiched between epidermis and hypodermis. It is made up of two layers called the papillary and reticular dermis that blend into one another without a clear demarcation.
The thin, outer layer is the stratum papillare and contains elastic fibers and fine collagen bundles. The deeper, thicker layer is the stratum reticular and contains sebaceous glands, hair follicles, blood vessels, and nerves.
The Epidermis
The epidermis is the outermost layer of cells that forms your skin or integument, which is the protective covering that covers all other body tissues. The epidermis provides a barrier that protects against pathogens, mechanical injury and UV light. The epidermis contains many types of cells, but it is composed primarily of stacks of keratin-producing epithelial cells called keratinocytes.
The top layer of the epidermis is a tough, inert layer of dead keratinocytes known as the stratum corneum. This layer is impermeable to water and other substances, but it is still able to transmit some UV radiation through the cell walls of the keratinocytes themselves.
Below this layer is the stratum basale, where keratinocytes undergo mitosis, or cell division. These new cells slowly push old ones upward, creating a fresh layer of cells above the stratum granulosum. As these cells near the surface of the skin, they become tougher and flattened, with spiny cellular projections that help to hold them together. They also secrete a waxy substance that seals the intercellular junctions. This process of keratinization is called cornification.
There are no blood vessels in the epidermis, so these cells rely on diffusion to get oxygen and nutrients from the dermis below. Melanocytes within the epidermis produce and store the dark brown pigment melanin, which gives your skin its characteristic color.
The Papillary Dermis
The papillary dermis is the upper portion of the layer that reaches under the basement membrane zone and includes thin haphazardly arranged collagen fibres, thin elastic fibres and ground substance. It contains nerves, blood vessels and cellular infiltrations. This area also contains dermal papillae, which are finger-like extensions of the dermis into the epidermis. These structures increase the surface area for exchange of oxygen, nutrients and wastes between the epidermis and dermis, which reduces blister formation.
The dermis contains a large number of fibroblasts, which secrete the collagen, elastin and ground substance that make skin strong and flexible. It also contains reticulocytes, which produce granules to engulf and destroy bacteria and other foreign substances entering the skin. The granules then pass the debris to other cells for disposal or destruction.
The dermis consists of a superficial area that is attached to the epidermis and a deeper, thicker region known as the reticular dermis. The two dermal layers work together to keep the skin healthy and provide its elasticity and strength as well as the sense of touch. In addition, the dermal layer’s many blood vessels help regulate body temperature.
The Reticular Dermis
The dermis is a thick layer of connective tissue that provides your skin its strength, flexibility and ability to resist damage. It lies beneath your epidermis and is composed of two regions: the papillary layer and the reticular layer.
Like all connective tissue, the dermis contains cells in a matrix (like a scaffolding) of collagen and elastic fibers. The reticular dermis also contains blood vessels, hair follicles, glands and nerve endings.
Blood vessels in the papillary dermis dilate to release heat when your body temperature rises or constrict to preserve warmth on a cold day. This helps your skin maintain its moisture and prevents it from becoming irritated or dry. The reticular dermis contains the touch receptors (Meissner corpuscles) and nerve fibers that sense sensation, and it also contains a network of collagen and elastin fibres that support your skin and make it strong and flexible.
The reticular dermis contains glands such as your sweat glands and sebaceous (oil) glands. It also contains hair follicles and lymphatics that help your skin to fight infection. The reticular dermis also has blood vessels that carry nutrients and remove wastes from the dermal cells. It also contains fat cells that provide your skin with a layer of insulation that prevents your body from losing heat by convection, radiation or evaporation.
The Subcutis
The subcutis, also known as superficial fascia, hypodermis and the subcutaneous layer, is the deepest skin layer. It contains a thick layer of fat, which works alongside the blood vessels in the dermis to regulate body temperature and protect deeper structures from physical trauma. The fatty tissue in the subcutis is made up of fat cells called adipocytes that form lobules separated by connective tissue. The lobules in the subcutis can vary in size depending on where in the body they are located. The fat in the subcutis is thickest in the buttocks, palms of your hands and soles of your feet; it is thinner around your eyes, eardrums, clitoris and external genitalia.
The hypodermis lubricates the skin, helping it move smoothly over muscles and bones without rubbing against them. It is also responsible for insulating the body from cold temperatures and producing sweat to regulate your body’s temperature, protecting your skeletal system, organs and muscles.
The subcutis is home to hair follicles, deep pressure sensors (Ruffini and Paccinian corpuscles), and a plexus of blood vessels involved in control of local blood flow and thermoregulation. Free nerve endings that sense touch, temperature, pain and itching are also found in the subcutis. In addition, the subcutis supports the overlying skin layers by providing a cushion of tissue that is surrounded by blood vessels and nerves.