Structure and Function of Human Skin
Marc B. Brown, Adrian C. Williams in The Art and Science of Dermal Formulation Development, 2019
Overlying the dermis, the epidermis is a complex multiply layered membrane which varies in thickness from around 0.06 mm on the eyelids to around 0.8 mm on the load-bearing palms and soles of the feet. The epidermis contains five histologically distinct layers, which, from the inside to the outside, are the stratum basale (also called the stratum germinativum, or simply the basal layer), stratum spinosum, stratum granulosum, stratum lucidum, and the stratum corneum (Figure 1.2). The stratum corneum, comprising anucleate (dead) cells, provides the main barrier to transdermal delivery of drugs and hence is often treated as a separate membrane by workers within the field. The term “viable epidermis” is often used to describe the underlying four distinct layers, although the viability of cells within, for example, the stratum granulosum is questionable, as the cell components degrade during differentiation.
Actions of Dopamine on the Skin and the Skeleton
Nira Ben-Jonathan in Dopamine, 2020
The epidermis has a 5- to100-μm thickness, depending upon its location, and is composed of stratified squamous epithelium devoid of blood or nerve supplies. Keratinocytes are the major cell type, constituting 95% of the epidermis, which also contains melanocytes. The deepest section of the epidermis, the stratum basale (basal layer or BL), is the reproductive layer of the epidermis. Its cells constantly divide and provide a continuous supply of new cells to the upper strata. This layer also contains neuroendocrine mechanoreceptors (Merkel cells). The proliferating keratinocytes are pushed upward to form the stratum spinosum (spinous layer or SL). The SL consists of about 10 rows of cells that fit closely together and are connected by desmosomes, or specialized structures for cell-to-cell adhesion. Also found in the SL are bone marrow-derived sentinel cells of the immune system called Langerhans’ cells, which are the antigen-presenting cells of the skin and play a role in immunological reactions such as allergic contact dermatitis. As they move upward toward the skin surface, keratinocytes gradually flatten and become part of the stratum granulosum, where the nondividing keratinocytes produce of a protein called keratinohyalin. The next layer, stratum lucidum, is present only in the thick skin of palms and soles.
Biology of the Hair and Skin
Randy Schueller, Perry Romanowski in Conditioning Agents for Hair and Skin, 2020
The skin develops at 30 to 40 days gestation and consists of two primary layers: the epidermis and dermis (8,9). The epidermis represents the external layer of skin and is composed mainly of keratinocytes, named for their primaiy proteinaceous component, known as keratin. The keratinocytes are held together by cellular attachments or desmosomes. The epidermis also contains melanocytes, which produce a pigment known as melanin, and specialized immune cells, known as Langerhans cells. It is divided into several distinct functional layers: the basal cell layer (stratum germinativum), from which all new cells are derived; the spinous layer.(stratum spinosum); the granular cell layer (stratum granulosum); and the horny cell layer (stratum corneum) (10). The stratum corneum is the outermost layer of the epidermis, comprised of 15 to 20 cell layers, functioning to protect the underlying tissues and nerves from damage. Products aimed at conditioning the skin must have significant impact on the stratum corneum.
Nanocrystal: a novel approach to overcome skin barriers for improved topical drug delivery
Published in Expert Opinion on Drug Delivery, 2018
Viral Patel, Om Prakash Sharma, Tejal Mehta
Skin consists of different layers which are broadly classified into the epidermis and dermis layers. The epidermis consists of different layers: stratum germinativum, stratum spinosum, stratum granulosum, and stratum corneum. While the dermis consists of the connective tissues. Various factors contribute toward low bioavailability of drugs upon topical application, the major being the barrier property of stratum corneum. For a drug to permeate across the skin, it can follow trans-epidermal route or via the appendages. Drug nanocrystals reach the targeted site via the appendageal route. Due to increased saturation solubility of the drug nanocrystals, it creates a concentration gradient between the skin and the formulation which results in increased absorption of the drug. There are good evidences suggesting that the particles within the size range of 300–600 nm penetrate significantly deeper into the hair follicles and diffuse based on the concentration gradient into the skin layers [17–19].
Higher degree of keratinization correlated with severe bone destruction in acquired Cholesteatoma
Published in Acta Oto-Laryngologica, 2023
Yisi Feng, Zhuohao Li, Wuhui He, Ying Xiong, Yu Si, Zhigang Zhang
NIS element software (Nikon) was used to examine cathepsin K-positive osteoclasts, which were counted via Image-Pro Plus 6.0 software (Media Cybernetics, USA). Measurement of the area ratio (the bone resorption area divided by the grafted skin area) was performed according to the procedures previously put forward by Jiang et al. [9]. The stratum corneum thickness of mouse skin and human cholesteatoma samples was measured by ImageJ software according to McCoombe et al. [10]. Two experienced microscopists performed the examinations of stratum corneumthickness on HE-stained slides. The distance from the outermost surface to the start of the stratum granulosum was used to define the stratum corneum thickness. ImageJ was used to measure such distance. Three microscopic fields of each sample were randomly selected and the maximum thickness was recorded and the average SC thickness was calculated.
Exposure to the anti-microbial chemical triclosan disrupts keratinocyte function and skin integrity in a model of reconstructed human epidermis
Published in Journal of Immunotoxicology, 2023
Rachel Baur, Michael Kashon, Ewa Lukomska, Lisa M. Weatherly, Hillary L. Shane, Stacey E. Anderson
The skin, comprised of the epidermis and dermis, is the first line of defense against environmental exposures and influences immune responses. Distinct features of the physical skin barrier, such as lipids, cornified envelopes in the stratum corneum, and tight junctions in the stratum granulosum, limit or prevent the passage of certain molecules, such as high molecular weight proteins, through the skin (Goleva et al. 2019). When barrier integrity or permeability are disrupted, chemicals and/or proteins are more likely to be absorbed through the skin (Rietz Liljedahl et al. 2021), and may lead to increased allergic sensitization. Additionally, in children, elevated levels of transepidermal water loss or mutations in the skin barrier gene filaggrin are a risk factor for development of atopic dermatitis or food allergy (Kelleher et al. 2015, 2016). Due to the use of triclosan in skin products, the skin is a primary route of exposure through which triclosan can be absorbed (MacIsaac et al. 2014). Thus, investigating the skin barrier integrity and response of keratinocytes, the most abundant cell type in the epidermis, to triclosan exposure is critical to understanding the effects on the immune system and associations with increased sensitization potential.
Related Knowledge Centers
- Epidermis
- Keratinocyte
- Keratohyalin
- Protein
- Stratum Lucidum
- Stratum Spinosum
- Cell Nucleus
- Lipid
- Stratum Corneum
- Lamellar Bodies