Ultrastructure of Developing Hair Tract and Hair Canal in the Human Fetus

Preparing the hair follicle canal for hair shaft emergence

“…Our observation that K79+ cells frequently undergo cell death postnatally aligns well with data from ultrastructural studies in human skin 11,12 and mice 25 . These studies have suggested that cells within the upper‐most region of the hair canal, at the level of the epidermis, are removed following keratinization and desquamation.…”

“…These studies have suggested that cells within the upper‐most region of the hair canal, at the level of the epidermis, are removed following keratinization and desquamation. For cells within the nascent infundibulum, both keratinization‐dependent 12 and ‐independent forms of cell death 11 have been proposed as mechanisms for creating a lumen. It is important to note that TUNEL+ cells in the developing hair follicle often do not exhibit typical morphological features of apoptosis, as previously noted by Magerl et al 25 , suggesting that K79+/TUNEL+ cells may be undergoing differentiation‐induced cell death 26 …”

“…9 In human skin, Maximow and Bloom simply noted that cells in the epidermis flatten and move aside to form the hair follicle opening. 10 Critically, ultrastructural studies by Hashimoto, 11 and later by Breathnach and Robins, 12 have suggested that the hair canal is comprised of adjoining epidermal and follicular compartments, and that interior cells become eliminated to create a lumen prior to the maturation of the hair shaft.…”