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An introduction to skin and skin disease
Published in Rashmi Sarkar, Anupam Das, Sumit Sethi, Concise Dermatology, 2021
The hair shaft grows from highly active, modified epidermal tissue known as the hair matrix. The shaft traverses the hair follicle canal, which is made up of a series of investing epidermal sheaths, the most prominent of which is the external root sheath (Figure 1.5). The whole follicular structure is nourished by a small, indenting cellular and vascular connective tissue papilla, which pokes into the base of the matrix. The sebaceous gland secretes into the hair canal a lipid-rich substance known as sebum, whose function is to lubricate the hair. Sebum contains triglycerides, cholesterol esters, wax esters, and squalene. Hair growth and sebum secretion are mainly under the control of androgens, although other physiological variables may also influence these functions.
The Rex (Re), Wavy Coat (Rewc), and Denuded (Reden) Mutations, Chromosome 11
Published in John P. Sundberg, Handbook of Mouse Mutations with Skin and Hair Abnormalities, 2020
In all three alleles of the rex (Re) mutation, all hair types are present; however, the diameter of the hair shaft is irregular, and there are bends and twists in the hairs. Medullary structures within the hair shaft break down. Pigment remains aggregated around cortical ridges or is scattered within the medulla. These observations were confirmed in hairs plucked from the mice shown in Figure 2. The primary change from the control was a general distortion of the hair shaft. This distortion manifested from various shaft diameters with twisting of the hair (Figures 3 and 4). Both of these changes were subtle and appeared not to effect the integrity of the hair. Cuticle scales did appear slightly longer than in the normal. The defect has been reported to be due to abnormalities in all three layers of the inner root sheath that is irregular in shape and unable to support the hair shaft and control its diameter.9
Geriatric hair and scalp disorders
Published in Robert A. Norman, Geriatric Dermatology, 2020
There are several features of early involvement of the skin and follicles with follicular plugging, enlargement of the follicular ostium, follicular parakeratosis, mild acanthosis and irregular hyperkeratosis. The outer root sheath and hair matrix are not affected. Other common findings include sebaceous gland atrophy, reduction of follicular size and decrease in hair shaft diameter113. Scarring can occur in severe psoriasis caused by inflammatory destruction of the follicle104.
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.
Are hair follicle stem cells promising candidates for wound healing?
Published in Expert Opinion on Biological Therapy, 2019
Bingmin Li, Wenzhi Hu, Kui Ma, Cuiping Zhang, Xiaobing Fu
If HFSCs are intended for wound healing, they have to possess a powerful capability of regeneration. Abundant researches have described the multiple differentiation potential of HF cells. During homeostasis, bulge SCs maintain the outer root sheath (ORS), the inner root sheath (IRS), the hair matrix and the secondary hair germ, contributing to the regenerative cycling of the hair follicle and fueling hair growth [51]. The morphogenesis of hair follicles proceeds through the cycle of proliferation (anagen), destruction (catagen), and stasis (telogen) (Figure 1) [52,53]. In this process, the upper portion of the hair follicle (HF) is retained while the lower portion undergoes repeating degeneration and regeneration. At the onset of anagen, stem cell progenies in the secondary hair germ (sHG) are initially activated and launch the process of the telogen-anagen transition. Subsequently, bulge HFSCs begin to proliferate and give rise to the ORS, and then, they proliferate and migrate downward. In addition, the sHG, which is composed of abundant transient amplifying cells (TACs), develops into the matrix. TACs differentiate into the hair shaft and the IRS, fueling hair growth [54]. With the consumption of TACs, bulge HFSCs gradually return to quiescence [55]. Once catagen is initiated, the lower portion of the ORS and matrix cells die through apoptosis, while the cells of the upper and middle portions of the ORS migrate upward and form a new bulge [56,57].
Infrared thermography as control of handheld IPL device for home-use
Published in Journal of Cosmetic and Laser Therapy, 2018
Hrvoje Glavaš, Marko Vukobratović, Tomislav Keser
According to Mulholland et al. (18). for safe and effective hair shaft heating and surrounding cellular structure in the root sheath damage three conditions of selective photothermolysis need to be fulfilled: Absorption of hair shaft should be higher than the absorption in surrounding tissue which can be accomplished by using cut-off filters and broad spectral rangeLight penetration needs to reach hair follicle depth which is achieved through longer wavelengths and higher fluences usage along with larger spot sizes.The pulse duration should be less than the hair follicle thermal relaxation time.