구월동피부과 The skin is the largest organ in your body. It protects you from harm, including ultraviolet (UV) radiation, bacteria, viruses, fungi, parasites and chemicals.
It also regulates body temperature. The vascular system of the epidermis allows blood to bypass the epidermis, diverting heat elsewhere. It includes cells called melanocytes that produce the pigment melanin that gives your skin color.
The simplest layer of the epidermis is called the basal cell layer (stratum basale). In this layer, cells continually divide and move up to the layers above. As they move upward, the new cells replace older ones, creating a continuous skin barrier that prevents evaporation of water from the outer surface. Cells in this layer have many desmosomes that connect them to neighbouring cells. They also have thick tufts of intermediate filaments, which look like prickles and give these cells their name: prickle cells or granulocytes.
The next layer, the stratum spinosum, is made up of keratinocytes that have accumulated and stored a tough protein called keratin. This gives the hair, nails and skin their hardness and water-resistance properties. The keratinocytes in this layer are dead and regularly slough away, being replaced by cells from the stratum basale.
The stratum lucidum is found in the thick skin of the palms and soles. This layer contains a clear substance called eleiden, which makes the cells in this layer look translucent. This layer also contains pigment cells that produce the brown and black pigment melanin, which gives skin its colour.
The tough, outer layer of the epidermis is known as the stratum corneum. This layer is composed of 10 to 30 thin layers of dead keratinocyte cells that are continually being sloughed off and replaced. This process is called keratinization. This layer helps to prevent the penetration of microorganisms, hydrates the underlying skin and provides protection from mechanical abrasion.
The keratinocytes of the stratum granulosum have a diamond-like shape and accumulate granules made of keratin in the spaces between them. The granules are mixed with intermediate-associated proteins, filaggrin and trichohyalin, which help aggregate the keratin filaments. Once these granules are mixed together they become flattened and shaped into cornified cells, which is the process of keratinization. The granules also lose their nuclei and organelles.
This outermost skin layer does not have direct blood supply, but depends on the underlying dermis for nutrients and waste disposal. It is protected from the sun by a natural barrier of lipids and peptides. Cleansing the skin too often or with harsh exfoliants can damage this layer, so using gentle soap and moisturizing regularly are recommended.
The Stratum Basale is the deepest single-layer of cells in the epidermis. It is composed of cuboidal basal keratinocytes that directly abut and attach to the dermis. Cells of this layer are constantly undergoing mitosis to produce new cells, and these push older cells up into the higher layers of the epidermis.
The uppermost layer of the epidermis is called the Stratum Corneum or horny scales (Figure 2). It consists of 20-30 layers of dead keratinocytes that form a dry, hard keratinous barrier against water penetration, microbes and dehydration of the underlying cellular tissue.
The keratinocytes in this layer are responsible for making a lipid bilayer that forms an effective waterproof barrier, and they also secrete a protein called keratohyalin. The squamous cells are also home to Langerhans cells that can recognize foreign materials and trigger an immune response to defend against the penetration of pathogens. They are also home to melanocytes that make the pigment melanin that gives skin its color. Melanocytes can also metastasize, or spread, to other parts of the body, where they can cause cancer.
The stratum spinosum, also known as the prickle layer, is located on the outside of your skin and is most exposed to the environment. It contains 15 to 30 layers of tough, dead, keratin-filled cells. This outer layer helps to prevent bacteria, viruses, and fungi from penetrating underlying tissues. It also helps to prevent dehydration of underlying tissues and protects against mechanical abrasion.
Stratum spinosum cells (keratinocytes) have bundles of tonofilaments (part of the cytoskeleton) that give them strength and they are tightly packed together. The cells are also filled with granules made of glycolipids (keratin protein) called eleiden. The granules help the cells adhere to one another.
The keratinocytes in this layer are mostly flattened and are filled with granules. These granules contain the keratin precursors that eventually fuse to form the keratin filaments in the next layer, the stratum granulosum. The granules also contain lamellar granules that generate the glycolipids eleidin which act as a glue to keep the keratin filaments in place. This outer layer is shed and replaced with cells pushed up from the stratum basale in a process that takes about four weeks.
The cells in this layer are very spiny and have dark clumps of cytoplasmic material (parts of the cell minus the nucleus) that give it its name. As the keratinocytes of this layer move up toward the surface, they become flatter, their cell membranes thicken and they generate large amounts of the proteins keratin and keratohyalin that give this layer its grainy appearance. The keratinocytes in this layer also release a lipid rich secretion called lamellar granules that bathe the stratum lucidum and stratum corneum with important fatty acids.
This layer is most prominent in the palms of your hands and soles of your feet and it protects the underlying layers from abrasion, friction, water and pathogens. In thick skin, a fifth layer can be seen between the stratum granulosum and stratum corneum, which is called the stratum lucidum.
This layer is also home to Merkel cells, oval shaped modified epidermal cells that function as mechanoreceptors of light touch and can be found in the fingertips, genitals, lips, oral and gastrointestinal tracts. These cells are bound to adjacent keratinocytes by desmosomes and interlock with free nerve endings in the skin to communicate sensations of light touch.