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Anatomy, physiology, and histology of the skin
Published in Michael Parker, Charlie James, Fundamentals for Cosmetic Practice, 2022
Deep to the dermis is the hypodermis, a layer of adipose tissue, macrophages and fibroblasts. Due to its significant number of adipose cells, the hypodermis is able to help regulate energy storage, thermal insulation and buoyancy of the skin. Fatty adipose cells at this layer are of key importance in the outward signs of ageing, as loss of these cells is one of the more prominent signs of older skin, such as volume loss and the prominence of wrinkles. From a pharmaceutical perspective, the dense vascularity of the hypodermis is frequently exploited as a method of introducing injected medications, such as insulin. This can, however, result in undesirable cosmetic outcomes such as focal lipodystrophy due to repeated subcutaneous injections at a particular site.
An introduction to skin and skin disease
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
It is difficult to understand abnormal skin and its vagaries without understanding the composition and function of normal skin. Although, at the first glance, the skin may appear quite complicated, a slightly deeper look shows that there is an elegant logic behind its architecture, which helps it perform several vital functions. The skin is composed of epithelial and adipose tissues. The epithelial tissue comprises the epidermis and the dermis. The adipose tissue, on the other hand, contains the hypodermis. The accessory structures include hairs, nails, sebaceous, sweat glands, sensory receptors, etc.
Neck and chest
Published in Jani van Loghem, Calcium Hydroxylapatite Soft Tissue Fillers, 2020
Yana A. Yutskovskaya, Anna Daniilovna Sergeeva
Aging of the skin occurs mainly due to atrophic changes in the dermis and hypodermis. The main substance is the redistribution of glycosaminoglycans, which undergo qualitative changes. The content of glycoproteins, in particular fibronectin, plays a role in the interaction of fibroblasts with collagen fibers. The fibers themselves atrophy and become looser. Collagen fibrils can lose periodic striation, and there is a delay in their maturation. Elastin fibers become coarse and partially fragmented. There are areas where they thicken, especially under the epidermis (senile elastosis). In this case, the hypodermis plays a major role, since it participates in the formation of granulation tissue—an important morphofunctional element of the regenerative process; there is a pool of undifferentiated, young and mature fibroblasts. The hypodermis also contains collagen, elastin, and reticular fibers [1].
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).
Injectable and adhesive hydrogels for dealing with wounds
Published in Expert Opinion on Biological Therapy, 2022
Parisa Ghandforoushan, Nasim Golafshan, Firoz Babu Kadumudi, Miguel Castilho, Alireza Dolatshahi-Pirouz, Gorka Orive
Human skin consists of a multilayered structure often categorized as epidermis, dermis, and hypodermis [17]. Each layer has distinctive features that are vital to its physiology. The epidermis, the outermost layer, contacts the environment directly and controls the release of water from the body. This layer also plays a protective role against UV radiation and pathogens. On the other side the dermis, consists of thick composite connective tissue of structural proteins and proteoglycans, and is located below the epidermis layer and exposed to the blood flow. The overall mechanical strength of the skin structure contributes to the dermis layer and provides an effective route to absorb drugs systemically. Besides these functions, dermis layer host many higher-order structures such as sebaceous and sweat glands, hair follicles, and arrector pili muscles, which together help to maintain essential cellular nutrition, by oxygen exchange and nerve signaling and ensures thermoregulation [18,19]. Finally, the hypodermis is the deepest layer (thickness of 10–20 µm) of the skin that ensures isolation and shock-adsorption. It is rich in collagen and fat, act as a reservoir of energy and connects the skin with the underlying muscles and bones [20].
Influence of physiochemical properties on the subcutaneous absorption and bioavailability of monoclonal antibodies
Published in mAbs, 2020
Amita Datta-Mannan, Selina Estwick, Chen Zhou, Hiuwan Choi, Nicole E. Douglass, Derrick R. Witcher, Jirong Lu, Catherine Beidler, Rohn Millican
The SC matrix or hypodermis has been reviewed extensively.4,6,8 Briefly, the hypodermis is composed of connective tissue separated by fat lobules (adipose tissues) and cellular components, including adipose cells, fibroblast and macrophages. The fibroblasts are responsible for producing constituents of the extracellular matrix (ECM), including glycosaminoglycans (GAGs), elastin and collagen. GAGs are highly negatively charged polysaccharides; the most common GAG in the SC space is hyaluronic acid. The strong negatively charged GAGs control the interstitial fluid content and hydraulic conductivity or movement of endogenous and exogenous entities within the interstitium. The macrophage and dendritic cells within the hypodermis function as a host defense mechanism by facilitating catabolism and sequestration of foreign antigens/substrates before these entities proceed into the blood circulation. In terms of structure, the SC tissue milieu is somewhat vascularized with mostly small blood capillaries and lymphatic vessels, both of which can provide access to the general circulation.