This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Anatomy of Skin, Subject name: Skin
[{'content': "'Growth Phase' of the hair? \nSelect and explain. \nA. Anagen, B. Metagen, C. Catagen, D. Telogen", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans. A. AnagenHair Growth CycleScalp hair-follicles have a four phase cycle.Anagen (growth), Catagen (transition), Telogen (resting) and Exogen (hair-shaft evacuation).The Anagen Phase (growing phase)- During the process of folliculo-regenesis, the follicle + epithelial sheath + new hair shaft is recreated.- During its growth (anagen) phase the hair shaft continues to gain length for a period of 2-7 years.- Approximately 80-85% of hair follicles are in anagen.- Hair growth rates range from 0.5cm-1.45cm per month.The Catagen phase (involutionary phase)- mitosis ceases, the follicle enters a period of degeneration.- Catagen accounts for approximately 3% of hair follicles.- The Epithelial sheath shrinks forming a minute "club root" at the proximal end of the hair shaft.- Catagen lasts for approximately 10-20 days.The Telogen Phase (resting or dying phase)- approximately 12-20% of hair shafts are in the amitotic (resting) phase.- Eventually (up to 3 months) the hair shaft vacates the follicle.The Exogen Phase- in which the hair-shaft is evacuated.', 'role': 'assistant'}]