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An introduction to skin and skin disease
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
The tissues of the dermis beneath the epidermis are important in giving mechanical protection to the underlying body parts and in binding together all the superficial structures. It is composed primarily of tough, fibrous collagen and a network of fibres of elastic tissue, as well as the vascular channels and nerve fibres of the skin. The dermis is thinnest in the eyelids and thickest on the back. It contributes to 15–20% of the total body weight. There are about 20 different types of collagen, but the adult dermis is made up mainly of types I and III, whereas type IV is a major constituent of the basal lamina of the dermoepidermal junction. Type V collagen is found in papillary dermis and periadnexal areas. Type VI collagen is present throughout the dermis and interfibrillar spaces. Type VII collagen is present in the anchoring fibrils of the dermoepidermal junction. Between the fibres of collagen is a matrix composed mainly of proteoglycan in which there are scattered fibroblasts that synthesize all the dermal components. Collagen bundles are composed of polypeptide chains arranged in a triple-helix format, in which hydroxyproline forms an important constituent amino acid. The important cells of the dermis are fibroblasts, monocytes, macrophages, dendrocytes, and mast cells.
Comparative Anatomy, Physiology, and Biochemistry of Mammalian Skin
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The dermis can be divided into two anatomical layers; an outer papillary and an inner reticular layer. The papillary layer is the thinnest and consists of loose connective tissue, while the reticular layer is thicker and consists of dense connective tissue.197–199
Development of Topical and Transdermal Dosage Forms
Published in Tapash K. Ghosh, Dermal Drug Delivery, 2020
While seen as a continuous membrane, the skin is in a dynamic equilibrium. On an average every two weeks the stratum corneum is replaced in a process of “flaking off.” In support of this remodeling process the dermis plays the key role in supporting the flexibility of the skin as it contains the elastin and collagen fibers that give skin its strength and resilience. The dermis also contains the sensory nerve fibers for pain, touch and temperature. This organization, notably the lack of nerve endings in the stratum corneum, has been utilized for drug delivery of otherwise impenetrable products by the use of microneedles which penetrate and pierce the stratum corneum and the epidermis yet remain above the sensory nerve endings. In doing so, microneedles present a viable route for the delivery of proteins, vaccines and other macromolecules or small molecule drugs that have either solubility or charge properties that hinder their penetration2. Microneedles also represent a flexible route of delivery as the depth of penetration is related to needle length and can be developed to only penetrate the stratum corneum or deeper to the dermis. They also come in a variety of presentations from a hand-held roller for cosmetic use3 to transdermal systems using coated, dissolvable, hydrogel or hollow, microneedles that provide access to a reservoir of drugs4.
Transport of hydrocortisone in targeted layers of the skin by multi-lamellar liposomes
Published in Journal of Liposome Research, 2023
Antoine Bernasqué, Muriel Cario, Stéphanie Krisa, Sophie Lecomte, Chrystel Faure
Strat-M® is an artificial membrane designed to mimic human skin. It has been well described in the literature (Haq et al.2018, Uchida et al.2015). From top to bottom, Strat-M® is composed of three layers of polyethersulfone of increasing porosity, and a very porous layer of non-woven polyolefin. The first layer is a very dense and thin polyethersulfone layer that mimics the stratum corneum. It also contains ceramides, cholesterol and free fatty acids in proportions comparable to those of the human SC to mimic its hydrophobicity. The next two layers represent the living epidermis and dermis. Lipids are also found in these layers. The highly hydrophobic polyethersulfone layer is meant to represent the hypodermis. Strat-M® was chosen for Raman imaging since in our previous study (Touti et al.2020), we showed that comparable results were found on an excised animal skin.
Transdermal delivery of inflammatory factors regulated drugs for rheumatoid arthritis
Published in Drug Delivery, 2022
Yanyan Zhang, Zhaoju Gao, Shushu Chao, Wenjuan Lu, Pingping Zhang
As the largest organ in the human body, skin is a natural barrier to protect the body from external invasion. The skin area is about 1.5–2.0 m2, accounting for 15% of the total weight of adults (Dąbrowska et al., 2018). Transdermal drug delivery first crosses the skin barrier. The skin consists of three layers: epidermis, dermis, and subcutaneous hypodermis (Figure 2) (Kalluri & Banga, 2011). The epidermis includes the upper layer of non-viable stratum corneum and the lower layer of viable epidermis. The stratum corneum (10–20 μm) is composed of 10–15 layers of inanimate keratinocytes, which are closely arranged so that drug molecules have difficulty in penetrating (Andrews et al., 2013). In addition, the non-viable stratum corneum contains multiple lipid bilayers, which form an enormous barrier to the penetration of hydrophilic molecules. The viable epidermal layer does not contain blood vessels, so it also has a blocking effect on drug absorption (Pan et al., 2020). The dermis is located in the lower part of the epidermis, which contains fibroblasts, adipocytes, blood vessels, and lymphatic capillaries, as well as a large number of hair follicles, sebaceous glands, and sweat glands. Drugs are mainly absorbed in the dermis (Romgens et al., 2015). The hypodermis, below the dermis, is mainly composed of loose connective tissue and fat, which has the function of preventing heat dissipation and storing energy (Wong et al., 2016).
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).