The skin is made up of many layers. Among these layers are the Dermis, Epidermis, Stratum corneum, and Stratum lucidum. Let’s take a closer look at each layer and their role in skin development. The dermis is the outermost layer of the skin.
Dermis
The dermis is a layer of skin under the epidermis. It contains sweat glands, hair roots, blood, and lymphatic vessels. The dermis can vary in thickness from 0.6 mm in the eyelids to three millimeters on the back. The thickness of the dermis varies between individuals and varies from region to region.
The dermis is produced from various sources including the somites and the lateral plate mesoderm. These mesenchymal tissues are descendants of the cranial neural crest ectoderm. The development of the dermis begins around E12.5 and continues to E14.
The dermis is composed of a papillary layer and a thick reticular layer. Its functions include providing elasticity to the skin and providing the sense of touch and heat. It also contains sebaceous glands, hair roots, and nerves. The dermis also contains a protective layer of fat called the hypodermis.
The dermis contains three major types of cells, including fibroblasts, mast cells, and macrophages. It also contains a number of sublayers, including the papillary layer and the hypodermis. There are also small nipple-like extensions of the dermis that extend into the epidermis. These extensions of the dermis are referred to as dermal papillae. They also function in regulating blood flow and dermal repair.
Epidermis
The epidermis is the top layer of your skin. It is around 20 to 30 cells thick and contains keratinocytes. Keratinocytes are the cells that make your skin’s surface smooth. They divide in a process known as mitosis to produce millions of new ones every day. The process changes the cell’s shape and chemical composition, giving the epidermis its unique properties. About 95% of the cells in the epidermis are keratinocytes, although other cells like melanocytes, Langerhans cells, and Merkel cells are also found in this layer. In addition to keratinocytes, the epidermis contains a layer of cells known as basal keratinocytes, which are stem cells and migrate superficially.
The epidermis lacks a direct blood supply, so it depends on the underlying dermis for nutrients. The epidermis is connected to the dermis by a layer known as the dermo-epidermal junction. It also has an active role in the immune system’s communication and defense against harmful agents.
The epidermis is made up of different types of cells and forms four layers. These layers protect the body by making the skin waterproof. The epidermis also contains vitamin D, which makes it a vital part of skin health. The deeper epidermis contains keratinocytes, which are living cells.
Stratum corneum
The stratum corneum is the outermost barrier of mammalian skin. It consists of layers of cornified keratinocytes sealed by lipids. It has previously been considered a homogenous barrier, but recent studies have found that there are three distinct layers. For instance, the middle layer contains a high concentration of arginine, which may help explain how the skin maintains hydration. Moreover, topical application of metal ions revealed distinct barrier properties and a passive influx of metal ions.
The stratum corneum is the outermost layer of the epidermis, and is exposed to the atmosphere. It is composed of 15-30 layers of cells, and plays a protective role by preventing penetration of bacteria, fungi, and viruses. The stratum corneum also protects the skin from abrasion. This is why dry skin feels rough.
The stratum corneum is the most superficial layer of the skin. It consists of about twenty layers of flat keratinized cells without nuclei or organelles, and are filled with a keratin-based tonofibril complex. In the stratum corneum, cells further away from the skin surface have desmosomes, and assume a polygonal shape. These cells also contain a dense material lined by lamellae. This material is, known as the cornified cell envelope, which reinforces the cell membrane.
The dermis, or middle layer of the skin, lies between the stratum corneum and the hypodermis. The dermis contains collagen, elastin, and nerve endings. It also has sweat glands, oil glands, and hair follicles. These layers are also responsible for skin hydration.
Stratum lucidum
The first layer is the stratum granulosum. It contains three to five layers of keratinocytes. These cells divide in order to produce keratin. These cells also have thick plasma membranes and degenerated organs. The stratum granulosum also has a lipid-rich secretion. This substance helps regulate water entry and exit.
The outermost layer is the stratum lucidum. This layer is not present on all parts of the body, but it is, found on the palms. It contains dead keratinocytes and eleidin, a lipid that adds elasticity and protects the epidermis from water and other substances. It also helps maintain the skin’s elasticity.
The epidermis consists of four to five layers of cells. The outermost layer, the stratum lucidum, is not vascular. The second, the stratum corneum, contains 20 to 30 layers of keratin and dead keratinocytes. These cells make defensins, which protect the body from bacteria and other infections. The dermis contains numerous sections of blood vessels.
The layers of skin are very different. In addition to being thin, they are also thick. The palms and soles of the feet have thick skin that protects them from external elements. However, these areas do not have hair follicles.
Stratum granulosum
Stratum granulosum is an extracellular matrix, found in the topmost layer of skin. It is a layer of cells, composed of keratin. It is about 10 to 20 um thick and protects the lower layers of skin from harmful environmental insults and physiologically important components. This layer also contains 15 layers of corneocytes and a special type of multilamellar lipid sheet. It is, also known as the brick wall of the skin.
The stratum granulosum is one of the five layers of the skin. It contains irregular, diamond-shaped cells and lamellar granules containing glycolipids. These granules act as glue for the cells and help them adhere to each other. In thicker skin, the stratum granulosum is, covered with a fatty layer called eleidin.
The top layer of skin is the epidermis, which is, directly exposed to the environment and most susceptible to damage. The layers below are constantly replenishing themselves, replacing damaged cells with new ones. The layers of skin are, divided into different types according to their function.
The outermost layer of skin is, called the stratum spinosum. It has protruding cell processes that connect to one another via a desmosome. Desmosomes strengthen the bonds between cells and are responsible for the “spiny” appearance. The outermost layer of skin is, composed of eight to 10 layers of keratinocytes. This layer is, connected to the lower epidermis via a papillary layer. Finally, the reticular layer consists of bundles of collagen fibers.
Stratum basale
The basement membrane zone of the epidermis separates the stratum basale from the dermis. This single layer of columnar cells contains predominantly keratinocytes. Keratinocytes continually divide to replace themselves, and their daughter cells move into the outer layers of the epidermis and shed as dead horny cells. The basal keratinocytes are highly heterogeneous; some have proliferative functions while others serve an anchoring function.
The basal cell layer is the deepest layer of the epidermis. This layer is, made up of column-shaped cells that continually divide and are, pushed toward the surface. These cells are also home to melanocytes, which produce melanin. When exposed to sunlight, melanocytes produce more melanin. If these cells begin to grow abnormally, this can lead to melanoma, a type of cancer.
In the stratum basale, millions of new cells are, produced each day. As new cells grow, they push the old ones up the layers to make way for the new ones. This process occurs in two to four weeks. While the stratum basale is the deepest layer, it is also the most functional layer. It contains cuboidal keratinocytes that are rapidly dividing. Stratum basale cells also contain Merkel’s cells, oval-shaped modified epidermal cells.
The stratum basale contains cells that undergo mitosis and give rise to cells in the layers above. They also interact with the basement membrane. The cells of the stratum basale have a prickly appearance, have intercellular connections that do not retract when fixating tissue, and have prominent nucleoli, which indicate metabolic activity.
