Structure and function of the epidermis related to barrier properties. Baroni A, Buommino E, De Gregorio V, Ruocco E, Ruocco V, Wolf R.Synthesis of proteins and ceramides important for the skin barrierĪcquired or genetic disturbances in any of the above barrier functions can result in skin disease or systemic disruption.Vitamins required for some skin barrier functions Vitamin The table below summarises some roles vitamins play in skin barrier function. Deficiencies and toxicities can disturb the skin barrier function. The role of vitamins in skin barrier functionĪdequate levels of micronutrients such as vitamins are important to maintain the integrity of the skin barrier. Numerous immune cell types are located in the dermis and include dermal dendritic cells, mast cells, and lymphocytes ( T cells, B cells, NK cells). The key epidermal immune cells are the keratinocytes and Langerhans cells. Immune cells are found in both the epidermis and dermis. The skin has elements of both the innate (nonspecific) and adaptive (specific) immune systems. Skin elements with immune barrier functions Antimicrobial peptidesĪntimicrobial peptides synthesised in the skin by keratinocytes, sebocytes, and sweat glands, have antimicrobial and immunomodulatory effects. Melanosomes are transferred to keratinocytes where they protect the epidermal cell nucleus against DNA damage by ultraviolet radiation. Melanin is the pigment produced by melanocytes in the basal layer of the epidermis and stored in melanosomes. Urocanic acid, another breakdown product of filaggrin, is important in protection from UV radiation damage. Natural moisturising factors (NMF) are degradation products of filaggrin which contribute to the water-holding capacity and acidic pH of the stratum corneum. It aggregates keratin filaments inside the corneocytes and helps form the cornified cell envelope outside corneocytes. Filaggrinįilaggrin is a specialised structural ‘ filament-aggregating protein’ responsible for the structural and mechanical integrity of the stratum corneum. The acidic skin surface, together with an intact stratum corneum, prevents colonisation with pathogens, and supports the normal skin microbiome. The acid pH also restricts the activity of kallikrein (KLK)-5 and -7, which cleave the extracellular corneodesmosomal proteins important in corneocyte adhesion. Enzymes in the stratum corneum including β-glucocerebrosidase and acid sphingomyelinase, function optimally in an acidic environment, and are responsible for the production of ceramides and free fatty acids which affect diffusion through the epidermis. The human skin surface has a normal pH range of 4.5 to 5.5, and the acidity is important in the skin permeability barrier. Skin (bio)chemistry with barrier functions pH The subcutis also acts as a mechanical barrier by absorbing mechanical shocks applied to the skin (such as a punch), protecting deeper structures including bone. Adipose tissue is responsible for heat production and forms an insulating layer, thereby playing a critical role in thermoregulation. The subcutis is composed predominantly of fat cells ( adipocytes). Prevents the growth of certain bacteria.Dense hair can protect the epidermis from sun exposure.Is an early-warning detection system on the scalp to prevent minor skin trauma.Holds a layer of warm air against the skin to minimise heat loss.The cuticle between the proximal nail fold and the nail plate provides a waterproof barrier against chemical and microbial entry. The diffusion path length which is determined by the thickness of the stratum corneum, numbers of layers of corneocytes, their size, and their cohesion.The unique lamellar organisation of the lipid matrix and its interaction with protein components of keratinocytes, including tight junctions and scaffolding proteins.The rate of diffusion across the stratum corneum is influenced by: Diffusion through the epidermis can be via one of two routes: intracellular through the epidermal lipid matrix, or transcellular across the corneocytes. A key barrier function of the epidermis is to control diffusion of molecules across the skin transepidermal water loss (TEWL) from inside to outside, and chemicals from the outside environment to inside.
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