송도피부과 The middle layer of skin, dermis, plays an important role in protecting you from harm, feeling different sensations and producing sweat. It also contains hair follicles, sebaceous glands and nerve endings.
Your skin is full of blood vessels that bring nutrients and remove waste. They enlarge (dilate) when it’s hot and narrow (constrict) when it’s cold.
The epidermis is the outer layer of the skin and integument (natural coating) of plants and vertebrate animals. The epidermis protects the body from physical damage, viruses, fungi, bacteria and UV radiation. It also provides a barrier against some chemicals and pathogens.
The cells that comprise the epidermis are called keratinocytes, and they are continually replenishing themselves by dividing and then pushing old cells up toward the surface of the skin. This is the process known as mitosis. As the keratinocytes move upward, they become tougher and flatter. They are then shed and replaced by newer cells pushed up from below.
The innermost layer of the epidermis is the stratum basale. This is a cuboidal to columnar layer that has a direct connection to the basement membrane by means of hemidesmosomes. This layer contains melanocytes that produce the pigment that gives the skin its color. Melanocytes also help the skin to absorb UV light. The next layer is the stratum spinosum, a prickle cell layer with cellular projections that are sometimes described as spines. This is where the immunologically active Langerhans cells reside, as well as some other specialized epidermal cells.
Your skin’s middle layer, the dermis, is made of a tough, fibroelastic connective tissue that features elastic fibers of collagen and elastin. The fibres help your skin retain its shape. Your dermis also contains blood vessels, oil and sweat glands, hair follicles and nerves.
Like the epidermis, your dermis is a protective barrier against bacteria, parasites, viruses and the sun’s UV rays. It provides a sense of touch by allowing your nerves to detect temperature, pressure and vibration.
Your dermis consists of two layers — the papillary layer and the reticular layer. The former is thinner and contains areolar connective tissue, with fingerlike projections (dermal papillae) that extend into the epidermis. The latter is thicker and consists of densely woven collagen fibres, which provide strength and elasticity to the skin. The reticular dermis is rich in a clear, gel-like substance called hyaluronic acid, which has a high capacity for water binding and helps to maintain the skin’s moisture content. The reticular dermis contains hair follicles, arrector pili muscle and sebaceous glands (oil glands). The papillary and reticular layers are both connected to the hypodermis, a subcutaneous layer of loose fat cells.
The Papillary Dermis
The papillary dermis is composed of loose connective tissue and is highly vascular. It lies beneath the epidermis and is attached to it. It shows a network of fine elastic fibres and thin collagen fibrils. This layer is thinner and less dense than the reticular dermis.
This dermal layer contains the end of capillaries, lymph vessels and sensory neurons. These neurons sense things like temperature, touch and pressure. The capillaries bring nutrients to the skin, and they can contract or relax to increase or decrease blood flow to the skin. This regulates the temperature of the skin.
This layer also contains finger-like projections known as dermal papillae, which protrude into the epidermis. These help to increase the adhesion between the epidermis and dermis. They are more prominent in thick skin such as the palms and soles of the feet. The papillae are lined with fibroblasts, which help to maintain the integrity of the dermal tissue. They produce proteoglycans, which bind to other collagen fibres and help them to stay together. This gives the skin its strength and elasticity.
The Reticular Dermis
The dermis is tough connective tissue that provides the strength and elasticity of skin. It contains blood vessels, nerves and epidermal derivatives (hair follicles, sweat glands and the arrector pili muscle) embedded in an amorphous extracellular “ground substance” of glycosaminoglycans and glycoproteins bound with water. The dermis has two histologically distinct components: the papillary layer and the reticular layer.
The papillary layer lies just below the basement membrane zone and contains loose, thin-fibered connective tissue containing capillaries, elastic fibers and some collagen fibers. It has a number of finger-like projections called dermal papillae that extend into the epidermis and interdigitate with its rete pegs. These papillae give the skin its distinctive bumpy appearance and are responsible for the patterns visible on a person’s fingertips, palms and soles, which are known as fingerprints.
The reticular layer of the dermis is a thicker layer of dense, irregularly organized collagen and elastic fibers that support the skin. These fibers create the stretchy properties of skin. The reticular layer also contains nerve endings that sense pressure, vibration and touch. Meissner’s corpuscles and lamellar corpuscles are sensory receptors in the reticular layer of the dermis that can detect light touch, while Pacinian corpuscles sense vibration and pressure.
The subcutis, also known as the hypodermis is the layer of fat and connective tissue that resides under the dermis. It houses larger blood vessels and nerves and serves as an insulator to help regulate body temperature. It also functions as the main storage site for energy in the form of fatty cells (adipocytes). The thickness of this layer varies throughout the body and from one person to another.
This layer provides a strong connection between the dermis and the adjacent fasciae (see Fig. 6-4). It is also a major source of fluid that helps maintain skin tone and elasticity.
The subcutis connects the dermis layer to the muscles and bones of the body with specialized tissue. It also protects the bones, muscles and organs from physical damage. It insulates the body from cold and produces sweat to help regulate the body’s temperature. It also enables the skin to move smoothly over the bones and muscles without rubbing against them. Injections of medications into the subcutis are absorbed more slowly than when they are injected into a vein or muscle.