๐ ็ธฝ็ฎ้ ๏ฝ ๐ ่ฑๆๅๆ๏ผๆฌ็ฏ๏ผ ๏ฝ ๐ ๅฎๆด็ฟป่ญฏ ๏ฝ โญ ็ฒพ่ฏ็ญ่จ
Introduction
Biology of Hair and Nails 68
Etienne C.E. Wang, David de Berker and Angela M. Christiano
Key features
ยThe pilosebaceous unit and nail apparatus are epidermal deriva- tives that produce two of the hardest epithelial structures in mammalian biology
ยThe hair follicle is the only continuously cycling organ in mammals, while the nail exhibits uninterrupted growth
ยHair and nails serve multiple functions, including protection, sensation, and social communication
ยHair shafts and nail plates largely consist of dead, terminally differ- entiated keratinocytes (trichocytes and onychocytes, respectively) whose durability is based on the presence of abundant keratin intermediate filaments
ยThe hair cycle includes phases of growth (anagen), regression
(catagen), resting (telogen), and hair shaft shedding (exogen/ teloptosis)
ยThe hair follicle is a site of immune privilege and a major reservoir for epithelial and melanocyte stem cells; immune privilege and stem cells within the nail unit are also becoming recognized
ยThe nail apparatus consists of the fully cornified nail plate, which is produced by the nail matrix, and other specialized epithelial tissues such as the nail bed and nail folds