RT Book, Section A1 Kobielak, Krzysztof A2 Kang, Sewon A2 Amagai, Masayuki A2 Bruckner, Anna L. A2 Enk, Alexander H. A2 Margolis, David J. A2 McMichael, Amy J. A2 Orringer, Jeffrey S. SR Print(0) ID 1161320878 T1 Nail T2 Fitzpatrick's Dermatology, 9e YR 2019 FD 2019 PB McGraw-Hill Education PP New York, NY SN 9780071837798 LK accessmedicine.mhmedical.com/content.aspx?aid=1161320878 RD 2024/03/29 AB AT-A-GLANCEThe nail appendage is composed of several layers that organize the nail organ:The eponychium creates a border between skin epidermis and nail organ at the dorsal limit of the nail proximal fold (NPF), forming a protective seal.The NPF forms after skin epidermis bends inward ventrally at the eponychium’s border and becomes the nail epidermis, creating the NPF, which localizes slow-cycling bifunctional nail proximal fold stem cells (NPFSCs). NPFSCs actively deliver progeny to the perinail epidermis and nail matrix along with differentiated nail plate upon nail regeneration.The matrix, a ventral continuation of the proximal fold after it bends dorsally and distally, is composed of actively proliferating cells called onychocytes. In the proximal nail matrix, fast-proliferating nail stem cells are located. Their differentiation is coupled directly with the ability to orchestrate digit regeneration.Nail matrix differentiates, forming the keratogenous zone, which finally deposit cells into the overlying nail plate.Hyponychium is the most distal part of the nail epithelium located peripherally to the nail bed, and beneath the nail plate at the junction between the free edge and the skin epidermis of the fingertip, it forms a seal that protects the nail bed.