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Comparative Anatomy, Physiology, and Biochemistry of Mammalian Skin
Published in David W. Hobson, Dermal and Ocular Toxicology, 2020
The hair follicle is composed of three primary layers: inner root sheath, outer root sheath, and connective tissue sheath. The first is composed of scale-like keratinized cells which interlock with cuticle cells of the hair. The second is continuous with the epidermis. Structurally, it resembles epidermis but also has glycogen in it. The third layer, the connective tissue sheath layer, is continuous with the papillary layer of the dermis and with the dermal papilla of the hair follicle. At the base of the hair follicle, termed the bulb, the dermal papilla and hair matrix are located. The matrix is composed of the germinative epithelial cells which give rise to the hair proper, and is the region responsible for biochemical regulation of hair growth. They are also the target cells for toxicants directly affecting hair growth.
Hair Follicle Stem Cells
Published in John P. Sundberg, Handbook of Mouse Mutations with Skin and Hair Abnormalities, 2020
Robert M. Lavker, Tung-Tien Sun, John P. Sundberg
When hair follicle keratinocytes were appraised using the above features as predictors, a subpopulation of outer root sheath cells, located at the insertion site of the arrector pili muscle, fulfilled several important requirements for epithelial stem cells.6 For example, they were experimentally identified as the so-called “label-retaining cells” and are thus slow-cycling — one of the most important criteria needed to be fulfilled. They had a large nuclear-to-cytoplasmic ratio and a relatively “undifferentiated” ultrastructure, features consistent with a “primitive” cell. Finally, bulge cells were shown to proliferate in response to topically applied tumor promoter.
Geriatric hair and scalp disorders
Published in Robert A. Norman, Geriatric Dermatology, 2020
Hair shafts and root sheaths are of ectodermal derivation. The dermal papillae that nourish the follicles are mesodermal in origin. Because hair follicles are self-renewing, they contain a population of slow-cycling stem cells. The stem cells of hair follicles are thought to be located at the ‘bulge’ region in the outer root sheath near the insertion of the arrector pili muscle16. Cotsarelis and colleagues suggested that the anagen phase is initiated when stem cells are activated by signals from the dermal papilla16. This has implications in scarring versus non-scarring hair conditions, which will be addressed in the following sections.
Low-frequency electromagnetic fields promote hair follicles regeneration by injection a mixture of epidermal stem cells and dermal papilla cells
Published in Electromagnetic Biology and Medicine, 2020
Xinping Li, Yan Ye, Xiaohan Liu, Liming Bai, Pin Zhao, Wenfang Bai, Mingsheng Zhang
None of the mice had visible hair generation when DP cells were injected alone (Nilforoushzadeh et al. 2017), and the mixture of ESCs and DP cells induced new hair follicle formation was investigated in this experiment (Figure 1). After the injection of the mixtures into nude mice for 14 days, the hairs were seen emerging from the dorsal skin (Figure 1B). Comparing to the control group, the hairs erupted at a higher density in the EMF group. Then we next analyzed the feature of the new hair follicle. Results of H&E staining showed that the new hair formed the correct structure comprising hair matrix, hair shaft, and inner root sheath, outer root sheath, and DP (Figure 1C). Comparing with the characteristics of new hair bulbs in the control group, EMF exposure induced a higher density of hair bulbs formation (Figure 2).
Recent advances in follicular drug delivery of nanoparticles
Published in Expert Opinion on Drug Delivery, 2020
Alexa Patzelt, Juergen Lademann
The permanent part of the hair follicle combines the infundibulum, the isthmus and the bulge region. The infundibulum is described as the part of the hair follicle between the skin surface and the sebaceous gland, and provides an intact keratinized epidermis in the upper part. In the lower infundibulum, the differentiation pattern changes from epidermal to trichilemmal with reduced barrier function in the region of the outer root sheath [48]. Especially in this region, a close network of capillaries and dendritic cells surrounds the hair follicle. It can be suggested that substances or xenobiotics that are able to pass the follicular barrier in this region can be immediately recognized by the immune system and evacuated by the blood system. In porcine anagen hair follicles, a continuous tight junction barrier was found from the infundibulum down to the upper suprabulbar region. In the infundibulum, the barrier was found in the stratum granulosum. In the isthmus, bulge and suprabulbar region, the tight junction barrier was localized in the outer root sheath. Additional tight junction barriers were observed between Henle’s and Huxley’s layer of the upper suprabulbar region. In the region of the hair bulb, no barrier can be detected [49,50]. The barrier properties of the hair follicle are schematically presented in Figure 3.
Hair growth potential of Salvia plebeia extract and its associated mechanisms
Published in Pharmaceutical Biology, 2020
Guang-Ri Jin, Yi-Lin Zhang, Jonathan Yap, William A. Boisvert, Bog-Hieu Lee
The hair follicle, distributed over the human body, is one of the most complex mini-organs waiting to be explored. The mature hair follicle is composed of different concentric cylinders of epithelial cells, inner outer root sheaths, which are surrounding the hair shaft (Enshell-Seijffers et al. 2010). Mature hair follicles also contain dermal papilla which are derived from the mesenchymal cells. Each hair follicle consists of epithelial and mesenchymal parts and the interactions between them are essential for postnatal hair growth (Yang and Cotsarelis 2010). Dermal papilla cells (DPC), a group of dermal cells encapsulated by the epithelial matrix cells, are believed to generate signal factors that mediate the behaviour of keratinocytes in the follicle, thereby playing an essential function in hair cycling and growth (Kishimoto et al. 2000; Botchkarev and Kishimoto 2003). During the anagen phase, growth factors released from the DPC such as hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), and insulin-like growth factor-1 (IGF-1) are believed to modulate the proliferation and differentiation of epithelial cells to form the hair shaft (Taylor et al. 2000; Oshima et al. 2001; Botchkarev and Kishimoto 2003; Enshell-Seijffers et al. 2010). Additionally, many studies have shown that transforming growth factor-β1/2 (TGF-β1/2) secreted by DPC results in apoptotic cell death of epithelial cells as well as anagen-to-catagen transition of hair follicle cycle (Inui et al. 2002; Soma et al. 2002).