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The Naked (N) Mutation, Chromosome 15
Published in John P. Sundberg, Handbook of Mouse Mutations with Skin and Hair Abnormalities, 2020
Homozygous (N/N) mice have follicles of noticeably smaller size than normal. Once the follicles are fully formed, Huxley’s layer may be poorly keratinized, the cuticle of the inner root sheath may be absent, the hair cuticle is usually absent, the hair cortical elements are reduced, the medulla may be reduced, and the amount of pigment is reduced. The dermal papilla is normal. Growth of the hair shaft results in coiling in the piliary canal. Sebaceous glands are uninvolved. Arrector pilorum muscles are reported to be in an abnormal position, possibly due to distortion of the follicles by the coiled hair shafts.
H
Published in Anton Sebastian, A Dictionary of the History of Medicine, 2018
Hair [Anglo-Saxon: haer, hair] Hippocrates (460–377 BC) believed that the shape of the body revealed the personality, and Aristotle (384–322 BC) studied the nose, limbs, hair and other parts of the body to characterize people. Paul of Aegina (AD 625–690) recommended fig leaves to stimulate hair growth in skin or scalp affected by burns. One of the earliest classification of human races according to the nature of hair was published by Franz Pruner-Bey (1808–1882) of Paris in 1865. The inner layer of the root sheath of the hair follicle (Huxley Layer) in human hair was discovered by Thomas Henry Huxley (1825–1895) while a medical student at Charing Cross Hospital, London. See depilatories, dyeing of hair.
How to diagnose the patient with hair loss
Published in Jerry Shapiro, Nina Otberg, Hair Loss and Restoration, 2015
The IRS is composed of three layers (Figure 1.7). None of these layers contains melanin, and all keratinize with trichohyalin granule formation. These granules stain eosinophilic, in contrast to the basophilic keratohyalin granules of the epidermis. The cuticle of the IRS consists of one layer of flattened overlapping cells that point downward in the direction of the hair bulb. Because the cuticle cells of the hair shaft point upward, these two types of cells interlock tightly. Trichohyalin granules are few in the IRS cuticle. Huxley’s layer is two cell layers thick and develops numerous trichohyalin granules. Henle’s layer is only one cell layer thick and already shows numerous trichohyalin granules as it emerges from the matrix. Just before the isthmus, the IRS becomes fully keratinized. However, at the level of the isthmus the IRS disintegrates and loses its tight connection to the hair shaft cuticle. The IRS cuticle cells therefore do not contribute to emerging hair but serve as a hard molding scaffold up to the arrector pili muscle.
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.