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Anatomy, physiology, and histology of the skin
Published in Michael Parker, Charlie James, Fundamentals for Cosmetic Practice, 2022
This layer is so named due to the “cornification” of the keratinocytes in this layer, a process in which dead keratinocytes form a tough, protective barrier to protect the soft tissues deep to it. It is the most superficial layer of the epidermis and consists of dead corneocytes that slough off and are replaced by newer ones. This process is called desquamation and occurs as desmocytes (connective tissue cells) are degraded. In this way, the stratum corneum physically protects the more delicate underlying layers as well as provide chemical and immunological defence against external pathogens through both its hardy exterior and the shedding of dead skin cells on which they reside.
Disorders of keratinization and other genodermatoses
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
The keratinocytes transform from metabolically active, cuboidal basal cells (stratum basale) to polyhedral cells of stratum spinosum to terminally differentiated, flattened, dehydrated, and dead corneocytes (stratum corneum) that are programmed to be shed off (desquamation). This complex and finely regulated process of differentiation is called keratinization. A human keratinocyte takes about 14 days to transit from the basal layer to stratum corneum. During this transit, the cell progressively loses its organelles and water content; there is polymerization and deposition of keratin filaments and filaggrin in the cytoplasm just beneath the plasma membrane and dissolution of the nucleus in the terminal stage. The end result, the stratum corneum, is a chemically and mechanically resistant barrier composed of stacks of protein-rich, anucleate, dead cells in a continuous matrix of extracellular lipid. Further, 14 days are required by these corneocytes to traverse the layers of stratum corneum and subsequently desquamate (Figure 15.1). Desquamation normally leads to inconspicuous shedding of individual corneocytes and is a controlled process involving degradation of corneodesmosomes by various lytic enzymes.
Evaluation of the Dermal Irritancy of Chemicals
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
Holzle and Plewig65 investigated the effects of increased or decreased epidermal turnover on the morphology of human corneocytes. The desquamating portion of the stratum corneum was sampled with a detergent scrub technique using Triton® X-100, and cells evaluated for quantity, size, shape, nuclear inclusions, and trabeculae. Corneocytes from skin of patients with allergic contact dermatitis differed from those of normal skin in that they were smaller, of irregular shape, and had asymmetrical trabeculae; more cells were nucleated and greater numbers of cells were collected. Topically applied steroids greatly improved all parameters. The authors believed such a bioassay permitted sensitive measurements of corneocyte morphology in conditions with altered epidermal cellular kinetics, and provided a method to evaluate the effects of corticosteroids on these parameters.
Iontophoresis for the cutaneous delivery of nanoentraped drugs
Published in Expert Opinion on Drug Delivery, 2023
Jayanaraian F. M. Andrade, Marcilio Cunha-Filho, Guilherme M. Gelfuso, Tais Gratieri
The skin is an attractive route for local and systemic drug administration due to its large surface area, ease of accessibility, and multiple pathways for drug absorption, such as transcellular, intercellular, and appendage routes [1]. In addition, transdermal drug delivery presents advantages over other conventional routes, like escaping from first-pass hepatic metabolism, reduced adverse events, noninvasiveness, and controlled drug release [2,3]. However, the complex structure of the stratum corneum (SC), the outermost skin layer, represents a barrier to be circumvented. Corneocytes composing SC are keratin-filled cells, densely compacted and embedded in a lipidic bilayer lamella. Under normal circumstances, the SC organization and composition limit the penetration of molecules to a weight of up to 500 Da and suitable lipophilicity, i.e. log P = 1 to 3 [4,5].
Anti-ageing peptides and proteins for topical applications: a review
Published in Pharmaceutical Development and Technology, 2022
Mengyang Liu, Shuo Chen, Zhiwen Zhang, Hongyu Li, Guiju Sun, Naibo Yin, Jingyuan Wen
The stratum corneum (SC) is the outermost epidermal layer of the skin with a thickness of approximately 15 μm. It mainly consists of 10 to 15 layers of dead keratinocytes, comprising 5 to 20% of water, 40% of keratinized protein, and 15% of lipid materials (Olsztyńska-Janus et al. 2018; Wang and Klauda 2019). Dead keratinocytes, also known as corneocytes, are in the last stage of their differentiation with the loss of nucleus and metabolic activity. Due to the combination of lipids with corneocytes, a moist waterproof barrier is formed, which helps to minimize the trans-epidermal water loss (TEWL) to keep the skin pliable and soft, and therefore to stop transferring of chemicals and microorganisms into the body (Gunnarsson et al. 2021). The first barrier to the penetration of the active ingredients is the stratum corneum (Liu, Wen et al. 2020).
Nanomaterial and advanced technologies in transdermal drug delivery
Published in Journal of Drug Targeting, 2020
Morteza Rabiei, Soheila Kashanian, Seyedeh Sabereh Samavati, Shahriar Jamasb, Steven J. P. McInnes
Drug delivery to skin permits improved treatment through site-specific delivery, reduction of side effects, and is more readily accepted by the patients. In addition to treating skin diseases such as alopecia, dermatitis, psoriasis, acne vulgaris, vitiligo and skin cancer [1], the transdermal method may also be used for other diseases such as diabetes, osteoporosis, rheumatoid, Alzheimer’s and Parkinson’s disease. In transdermal methods of delivery, the drug traverses the skin layers and then enters the general blood circulation, subsequently reaching the target organ. The main barrier of drug traversing the skin is the outermost layer of skin known as the stratum corneum (SC). This layer includes corneocytes or dead skin cells. These cells are located in multi-layered lipids, which describe as a ‘bricks and mortar’ model. Overcoming this barrier is the major challenge faced by researchers in formulating drugs and tools of drug delivery to the skin [1–3]. Among the different methods for drug delivery to the skin, nano-sized systems have attracted attention as drug carriers for transdermal drug delivery (TDD) [4]. Also, skin patches have enjoyed more commercial success as compared with ointment, creams and lotion.