Chemical Warfare Agent Decontamination from Skin *
Brian J. Lukey, James A. Romano, Salem Harry in Chemical Warfare Agents, 2019
The outermost layer of the skin is the epidermis. It is made up of an outer layer of dead cells providing protection to the underlying layers. The cells of the epidermis are called keratinocytes. As keratinocytes go through maturation, they lose their nucleus and become “keratinized” to form the dead protective layer, the stratum corneum. The barrier function is provided by this uppermost layer of dead, cornified (keratinized) cells. The cornified, or horny, layer ranges from three to 20 cell layers at very thick areas such as the soles and palms. The cells (corneocytes) are surrounded by a mixture of lipids in a “bricks and mortar” arrangement. The lipids are a unique mixture of oil-like compounds enriched in cholesterol that are adapted to protect the host against water loss. Additionally, varying degrees of skin oil (sebum) is deposited from sebaceous glands onto the skin surface, which provides an additional barrier layer and possibly contributes to the maintenance of skin hydration. The bottom layer of the epidermis, the basal cell layer, is normally one to two cells deep. This is the self-replicating layer, which replaces the epidermis approximately every 30 days and averages about 100 µm in thickness. The epidermis as a whole and specifically the stratum corneum serve to protect not only against excessive water loss but also against ingress of water, microbes, and toxic substances.
The Cause of Pressure Sores
J G Webster in Prevention of Pressure Sores, 2019
The epidermis is the outer layer. It is avascular and consists of many layers of cells, making this tissue relatively thick in regions that are often stressed. It can be up to 1.4 mm thick in the palms of callused hands and feet; however, it is usually much thinner averaging from 70 to 120 μm for most regions. The epidermis can be differentiated into five distinct layers. The outermost layer, the stratum comium, has about 70% less water than the innermost layer, the stratum germinativum. New cells originate in the stratum germinativum. With time they are pushed further and further outward as newer cells replace them. As they move outward they become flattened and accumulate a protein called keratin. This process, called keratinization, which causes the cells to become hardened and to die, gives the epidermis its characteristics.
Synthetic Compounds vs. Phytochemicals for the Treatment of Human Cutaneous Malignant Melanoma
Namrita Lall in Medicinal Plants for Cosmetics, Health and Diseases, 2022
The skin is composed of three main layers: the epidermis, dermis and hypodermis. The epidermis is the outer layer of the skin that serves as a physical and biological barrier to the external environment, e.g. protection from ultraviolet radiation and allergens. The epidermis is made up of five layers, namely the stratum corneum, stratum lucidum (found where the skin is the thickest i.e. palms and soles of feet), stratum granulosum, stratum spinosum and stratum basale. The dermis, which is thicker than the epidermis, sustains and supports the epidermis, while the hypodermis consists mainly of fat that supports the skin and insulates the body from cold and shock (Lawton, 2019). Melanocytes are distributed in the stratum basale layer of the epidermis and melanin (produced by melanocytes) displays photoprotective effects through the absorption of UV radiation. However, the exposure of the skin to excessive UV radiation, especially UVB radiation (280–315 nm), which cannot be absorbed by melanin, results in mutagenesis in melanocytes leading to HCMM (Lawton, 2019).
Effect of ultraviolet radiation on the Nrf2 signaling pathway in skin cells
Published in International Journal of Radiation Biology, 2021
Alena Ryšavá, Jitka Vostálová, Alena Rajnochová Svobodová
Skin is the largest human organ with an area, weight and thickness of approximately 1.5–2.0 m2, 3.0–4.5 kg and 0.1–4.0 mm, respectively (Kanitakis 2002). Skin tissue is a poorly water-permeable barrier with a slightly acidic hydrophilic film of pH 4–6. It consists of three layers: epidermis, dermis and hypodermis (Ali and Yosipovitch 2013). The outermost layer, the epidermis, is an epithelial self-renewing layer of ectodermal origin whose surface is in direct contact with the environment. It is separated from the adjacent dermis by the basement membrane. The dermis is a layer of mesenchymal connective tissue rich in collagen, elastin and various cell types. The hypodermis, the lowermost layer, is derived from the mesoderm and is largely composed of adipose cells and macrophages (McLafferty et al. 2012).
Shedding light on key pharmacological knowledge and strategies for pediatric atopic dermatitis
Published in Expert Review of Clinical Pharmacology, 2023
Ariana Moreno, Yael Renert-Yuval, Emma Guttman-Yassky
The epidermis plays a critical role in both physical and chemical barrier. A pathognomonic finding in AD is a disrupted epidermal barrier resulting in increased trans epidermal water loss (TEWL) [1]. AD-related barrier defects include terminal differentiation abnormalities (e.g. decreased levels of filaggrin/FLG and loricrin/LOR), claudin defects (e.g. downregulation of CLDN1 and CLDN5), and aberrant lipid metabolism in the stratum corneum (e.g. lower levels of very long chain fatty acids protein 3/ELOVL3 and fatty acid 2-hydroxylate /FA2H), in both adult and pediatric AD [6,9,10]. However, infant AD presents greater alterations in lipid genes related with the epidermal barrier, while adult AD presents more extensive downregulations of terminal differentiation genes in skin biopsies, among other variations detected across various age-groups [10].
Embryonic skin development and repair
Published in Organogenesis, 2018
Michael S. Hu, Mimi R. Borrelli, Wan Xing Hong, Samir Malhotra, Alexander T. M. Cheung, Ryan C. Ransom, Robert C. Rennert, Shane D. Morrison, H. Peter Lorenz, Michael T. Longaker
The adult epidermis has important barrier and protective functions. It is formed from the embryonic ectoderm via a multi-step process, involving distinct signaling patterns, and constant communication with the underlying dermis. In order to fulfill its important functions and maintain tissue homeostasis, stem cells in the basal layer of the epidermis continually reproduce to replace cell loss during turnover or after trauma. Adult skin is able to repair itself but through a process of fibrosis which results in scarring and loss of dermal appendages. The fetal epidermis has a unique ability to heal without scarring, and differences in extracellular proteins, signaling, and inflammatory and cell responses underlie this different healing capacity in fetal and adult skin. A greater understanding of the fetal tissue regeneration process has stimulated a variety of tissue engineering approaches to recapitulate this environment. However, more high-quality randomized controlled trials are required to demonstrate the clinical efficacy of many of the therapies in development for effectiveness in reducing or preventing scarring in human skin.