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.
Adverse Effects to the Skin and Subcutaneous Tissue
Tiziana Rancati, Claudio Fiorino in Modelling Radiotherapy Side Effects, 2019
The two main layers of the skin are the epidermis, which is the outer shell, and the dermis, the inner one. The epidemis is 30 to 300 µm thick, the deepest layer is the stratum basale, a proliferative basal cell monolayer whose cells divide to form the keratinocytes of the epidermal cells. The outermost layer of the epidermis is the stratum corneum, made of flattened dead cells. The epidermal shell is bonded through the basement membrane to the dermal shell, which is 1–3 mm thick. The upper portion is the papillary layer, which contains the microvessels supplying the epidermis. The remaining dermis, the rete dermis, consisting of collagen bundles, scattered fibroblasts, and single microvessels, is bonded to the subcutaneous fat layer, which may be several centimeters thick. The subcutaneous tissue contains predominantly fat cells, but also a network of arteries, veins, and lymphatics (Archambeau et al. 1995).
The skin
C. Simon Herrington in Muir's Textbook of Pathology, 2020
The outermost layer of the skin, the epidermis, is a constantly self-renewing structure composed primarily of keratinocytes along with melanocytes, Langerhans cells, and Merkel cells. Keratinocytes are cells that produce keratin, a polymer of intermediate filaments that forms the intracellular cytoskeleton, providing structural integrity. The process of keratinization is a highly regulated process that results in terminally differentiated, anucleate, largely impermeable keratinocytes on the skin surface. The epidermal keratinocytes are organized into 4 distinct layers from bottom to the top: (a) the basal layer (stratum basale), (b) the spinous/squamous/prickle cell layer (stratum spinosum), (c) the granular layer (stratum granulosum), and (d) the cornified layer (stratum corneum) (Figure 19.1B).
Therapy for prevention and treatment of skin ionizing radiation damage: a review
Published in International Journal of Radiation Biology, 2019
José L. Soriano, Ana C. Calpena, Eliana B. Souto, Beatriz Clares
Figure 3 schematizes the main layers of skin. Dermis and epidermis are the two main layers of skin, which are separated by a dermal-epidermal junction protein thin layer called basement membrane. The epidermis is the outer region of human skin, which comes from the embryotic ectoderm and contains no blood vessels. It consists of stratified squamous epithelium primarily composed of keratinocytes and other types of cells such as melanocytes, Langerhans cells, and Merkel cells. The lowest portion of the epidermis is the basal layer, which is in contact with the basement membrane (Larcher et al. 2007). The basal layer contains proliferating cells undergoing continuous division and provides a source of cells that move up through suprabasal layers of the epidermis. Beneath the basement membrane is the dermis. The dermis, which is derived from mesoderm, is an underlying connective tissue that contains nerve and vascular networks, lymphatics, as well as epidermal appendages such as glands (sebaceous, endocrine and apocrine), hair follicles and nails. In both cases, in sebaceous glands and hair follicles, proliferation takes place. The former is in the basal layer of the sebaceous gland, and the latter is in the matrix cells of the hair bulb. Other types of cells in the dermis are fibroblasts, macrophages, and mast cells. Finally, the hypodermis is the connective and adipose tissue underlying the skin and located below the dermis. However, it is not actually considered as a part of skin.
Permeation enhancer nanovesicles mediated topical delivery of curcumin for the treatment of hyperpigmentation
Published in Journal of Liposome Research, 2022
Raziya Khatoon Farooqui, Monika Kaurav, Manoj Kumar, M. S. Sudheesh, Ravi Shankar Pandey
The pigment of the skin melanin and hairs are produced in the melanocytes of the basal layer of the epidermis by the melanogenesis pathway which is controlled by the crucial regulator enzyme tyrosinase (Sanchez-Ferrer et al.1995, Slominski et al.2004). It plays a photo-protectant function against the ultraviolet (UV) induced damage (Brenner and Hearing, 2008). However, excessive production and accumulation of melanin cause hyperpigmentation and related problems such as inflammation, redness, dark spots, uneven skin coloration, lentigo, freckles, and premature aging (Kumar et al.2013, Ko et al.2014). It is also associated with facial hyperpigmentation or melasma, one of the most common dermatological problems (Shrotriya et al.2018). Hyperpigmentation is mainly caused because of genetic predisposition, long skin exposure to UV rays, hormonal imbalance, steroid therapy, aging, side effects of certain drugs, and sometimes during pregnancy (Hridya et al.2016). Commercially available agents used in the treatment of hyperpigmentation such as hydroquinone, antihistaminic, topical corticosteroids, and kojic acid, although found to be effective; their long-term use may induce many side effects such as itching, contact dermatitis, cytotoxicity, and even carcinogenicity (Hengge et al.2006, Draelos, 2007, Chang, 2009). Therefore, there is demand for a safe and effective alternative for better patient compliance along with enhanced hypopigmentation efficacy.
Chronic cholestasis is associated with hypogonadism and premature ovarian failure in adult rats (cholestasis causes ovarian hypogonadism)
Published in Ultrastructural Pathology, 2018
Transmission electron microscopy: Ultrastructural assessment revealed that the ovaries of Sham-operated rats showed no morphological defects. The ovarian surface epithelium consisted of a single layer of cuboidal cells resting on a basal lamina. These cells contained apical microvilli, numerous mitochondria, and large oval and indented nuclei (Figure 4a). Early antral follicles had distinct structural components including the theca externa, theca interna, granulosa cells, and an oocyte. The thecal cells were relatively thin, displaying flattened cells that had elongated spindle-shaped nuclei (Figure 4b). Granulosa cells were arranged in several layers. The basal layer was composed of tall cells resting on a basal lamina (Figure 4b). Other granulosa cells appeared cuboidal with abundant mitochondria, relatively thin cytoplasm and centrally located, ovoid in shape but often indented, euchromatic nucleus (Figure 4c). The inner layer of granulosa cells has thick prolongations that penetrate a smooth and relatively wide zona pellucida. The membrane of the oocyte showed numerous microvilli also penetrating the zona pellucida (Figure 4d). The ooplasm was populated with loosely clustered organelles. Mitochondria appear round or oval, rather dark with small numbers of shelf-like cristae. Cytoplasmic lamellae and electron-lucent vesicular bodies were dispersed throughout the cytoplasm (Figure 4e).