Epidermis
The epidermis is the outermost layer of the skin. It protects the body from the outside world such as Purity Skin Studio, as well as from pathogens. It also provides a protective shield against UV radiation and the effects of chemicals. When the epidermis is damaged, the skin can develop dark spots, a sign of skin cancer. A skin biopsy can be performed to detect skin diseases, such as psoriasis. Some medical conditions that affect the epidermis include essential fatty acid deficiency (EFAD), pemphigus Vulgaris, atopic dermatitis, and ichthyosis.
The epidermis is composed of various layers. The basal layer is the thinnest and contains keratinocytes, which produce melanin. Melanin is the pigment responsible for skin color. As the skin is exposed to sunlight, the production of melanin increases. Since keratinocytes die as they move toward the surface, the stratum corneum forms, which is the outermost layer of the epidermis.
In addition to providing a protective layer, the epidermis regulates temperature. This is done by allowing perspiration, which helps the body to cool down. Sebaceous glands play a role in this by secreting a hydrolipid film that acts as a barrier against bacteria and fungi. Another protective layer is the acid mantle, which protects the body from harmful alkaline-based chemicals. An essential component of the acid mantle is hyaluronic acid, a gel-like substance that provides the skin with volume and water-binding capacity.
Epidermis cells also contain lipids, which help form a barrier. These lipids are a mixture of free fatty acids, ceramides, cholesterol, and triglycerides. Fatty acids are the main components of sebum, which is the lipid-rich fluid produced by human sebaceous glands. Human sebum is mainly triglyceride-based, while cholesterol and wax esters comprise the rest.
The chemical/biochemical barrier consists of antimicrobial peptides, macrophages, and cell-cell junctions. Gap junctions, in particular, are essential for cell-cell communication. They are formed when connexons, transmembrane proteins, are found on the plasma membrane of keratinocytes and the adjacent cells. For example, E-cadherin, a protein found in the plasma membrane of keratinocytes, is an essential component of adherens junctions.
Other skin barrier components are the lipid-enriched intercellular domains and a physical barrier, mainly consisting of protein-enriched cells. However, the primary contributor to the wall is the stratum corneum.
Cell-cell adhesion is a crucial function of the epidermal barrier. This is achieved through synthesizing proteins called TJ. Desmosomes, which are the cellular domains in which TJ proteins are present, contribute to the skin barrier. However, TJ proteins are absent or reduced in some genetic disorders, leading to impaired barrier function.
Various cellular structures produce the skin’s physical barrier, including keratinocytes and dermal fibroblasts. These cells have a gel-like substance containing collagen and elastin fibers, giving skin strength. Additionally, fatty acids are also produced in the epidermis. By binding to moisture, these fatty acids form a protective barrier.
The horny layer, the outermost layer of the epidermis, forms a protective barrier against viruses, fungi, and other microorganisms. This layer also has pores that allow sweat to enter the body. Once the horny layer has been damaged, the skin becomes rough and cracks easily.
