A summary of the major events of the hair cycle, and known …

• Introduction
• Morphogenesis
• Anagen
• Anagen-to-catagen transition
• Catagen
• Telogen
• The follicle stem cell compartment
• Telogen-to-anagen transition
• References
• Figure

Biology Articles » Anatomy & Physiology » The hair cycle » Anagen

Anagen

- The hair cycle

Histologically, anagen follicles are long and very straight,but the follicles are angled to permit the hair coat to lieflat along the body surface. The proliferating matrix cellshave a cell-cycle length of approximately 18 hours (Lavker etal., 2003). Daughter cells move upwards, adopting one of sixlineages of the IRS and HS; from outermost to innermost, thelayers include Henley, Huxley and cuticle layers of the IRS,and the cuticle, cortex and medulla layers of the HS. As HScells terminally differentiate, they extrude their organellesand become tightly packed with bundles of 10-nm filaments assembledfrom cysteine-rich hair keratins, which become physically cross-linkedto give the hair shaft high tensile strength and flexibility.The IRS also keratinizes so that it can rigidly support andguide the hair shaft during its differentiation process, butits dead cells degenerate as they reach the upper follicle,thereby releasing the HS that continues through the skin surface.The duration of anagen determines the length of the hair andis dependent upon continued proliferation and differentiationof matrix cells at the follicle base.