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Nanomaterials in the Work Environment
Published in Małgorzata Pośniak, Emerging Chemical Risks in the Work Environment, 2020
Lidia Zapór, Przemysław Oberbek
Skin is the largest human organ, with a surface area of about 1.5–2 m2. As shown in Figure 2.3, it is composed of three layers, from the outermost layer: the epidermis, dermis, and subcutaneous tissues. The epidermis is composed of five layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale. The stratum corneum is composed of tightly connected terminally differentiated cells (corneocytes) and is a natural barrier of the body. This barrier can be easily weakened by, for example, mechanical damage (abrasions), inflammation, exposure to UV radiation, or microbial colonization. Experimental studies to date show that only very small particles, below 4 nm, are capable of entering the surface channels between corneocytes and pass through undamaged skin. Flexible ENMs, such as liposomes and micelles, are an exception, as they are capable of penetrating undamaged skin even with sizes above 4 nm. The most likely way of nanoparticle absorption is through the hair follicles, sebaceous glands, and sweat glands. This is the most effective way of absorption for particles in the 4–20 nm range. The penetration of particles in the 20–45 nm range has only been observed when the skin is damaged, while non-soluble particles above 45 nm did not even pass through damaged skin [Larese Filon et al. 2015; 2016; Wang et al. 2018].
Tissue Structure and Function
Published in Joseph W. Freeman, Debabrata Banerjee, Building Tissues, 2018
Joseph W. Freeman, Debabrata Banerjee
In skin, the epidermis can be further subdivided into the following layers: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and stratum basale (Figure 4.17). The cells in the epidermis travel from the bottom to the surface, which means cells are formed at the basal layer. The cells move up the strata, changing shape and composition as they die because of isolation from their blood source. As they die, the cytoplasm is released, and the protein keratin is inserted. Cells eventually reach the corneum and slough off (desquamation). This process is called keratinization and takes place within about 30 days. This keratinized layer of skin is responsible for keeping water in the body and keeping other harmful chemicals and pathogens out. It makes skin a natural barrier to infection.
Biological Effects: Why We Care About Laser Exposure
Published in Ken Barat, Laser Safety Management, 2017
The epidermis is the outer layer of skin. The thickness of the epidermis varies in different types of skin. It is the thinnest on the eyelids, at .05 mm, and the thickest on the palms and soles of the feet, at 1.5 mm. The epidermis is made up of five layers. From bottom to top the layers are stratum basale, stratum spinosum, stratum granulosum, stratum licidum, and stratum corneum. The bottom layer, the stratum basale, has cells that are shaped like columns. In this layer the cells divide and push already formed cells into higher layers. As the cells move into the higher layers, they flatten and eventually die. The top layer of the epidermis, the stratum corneum, is made of dead, flat skin cells that shed about every 2 weeks. There are three types of specialized cells in the epidermis. The melanocyte produces pigment (melanin), the Langerhans cell is the frontline defense of the immune system in the skin, and the Merkel cell’s function is not clearly known.
Polymeric biomaterials for wound healing applications: a comprehensive review
Published in Journal of Biomaterials Science, Polymer Edition, 2022
Ahmed Olanrewaju Ijaola, Damilola O. Akamo, Fouad Damiri, Cletus John Akisin, Emmanuel Anuoluwa Bamidele, Emmanuel Gboyega Ajiboye, Mohammed Berrada, Victor Onyebuchukwu Onyenokwe, Shang-You Yang, Eylem Asmatulu
Human skin is the largest organ in the body, consisting of roughly 8% of its mass and enclosing its external surface. The outer area of the skin depends on the body’s weight and height, with skin thickness ranging from 1.5 to 4.0 mm [1]. Human skin performs several functions including fluid homeostasis, sensory detection, a barrier against microbial invasion, self-repair, self-renewal, selective permeability, and protection against external forces such as chemical, osmotic, thermal, and mechanical damages [2, 3]. Anatomically, skin is made up of three vital layers—epidermis, dermis, and hypodermis. The epidermis is the superficial layer of the skin that has a thin and highly cellular structure; it is the peripheral layer with high impermeability that controls water loss and protects against external harmful stimuli. From deep to superficial, the epidermis consists mainly of four layers as follows: stratum basale, stratum spinosum, stratum granulosum, and stratum corneum. On the palms and soles, a pale clear to pink layer, the stratum lucidium, is noted just above the granular layer. Stratum basale or stratum germinativum is the deepest layer of the epidermis (closest to the dermis) and the only layer where cells divide and move to the upper layers [4]. The adult epidermis is made up of mainly three cellular components the keratinocytes, melanocytes and Langerhans cells amidst other cells like basal and merkel cells and some non-cellular components. The keratinocytes produce keratin critical for normal functioning of the epidermis, the melanocytes produce melanosomes the pigment that determines the racial difference in skin color while the Langerhans cells are mainly for immune responses. The non-cellular components including keratin, desmosomes, hemidesmosomes, collagens, laminin granules, tonofibrils and vitamin D3, interacts with the cellular component to provide epidermis structural integrity, prevent water loss, up-regulate antimicrobial peptide synthesis for immune system and binds the dermis to the epidermis. Below the epidermis is the dermis, which consists of elastin, glycosaminoglycan (GAG), fibroblasts, and the collagen (COL)-rich extracellular matrix (ECM) [5]. The dermis performs the following functions: physical strength to the skin, support for nerve bundles, extensive vasculature, lymphatic system, and inflammatory and immune response [2]. The hypodermis, the layer underneath the dermis, is composed of a very large amount of vascularized adipose tissue, and is associated with the skin’s mechanical and thermoregulatory properties [6].