Hair cycle by aseem

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Hair cycle by aseem

  1. 1. THE HAIR CYCLE
  2. 2. Introduction • Hair follicles undergo a repetitive sequence of growth and rest known as the hair cycle • The timing of the phases of the hair cycle and its overall duration varies between body site, gender, species and races.
  3. 3. Stages of hair cycle • ANAGEN – Growth / Progression • CATAGEN – Involution / Regression • TELOGEN – Resting / Quiscent
  4. 4. • aa
  5. 5. •a
  6. 6. Anagen • Duration of anagen determines the final length of the hair • Length varies according to body site – Scalp hair – Legs – Arms – Eyelashes – Fingers 02-08 Y 05-07 M 02-03 M 01-06 M 01-03 M
  7. 7. Anagen • 90 to 93 percent of scalp follicles are in anagen at any given time. Growth rate : 01 cm / 28 days • Anagen can be divided into seven stages: – I : Mitotic Onset in Germ Cell Epithelium  Dermal Papillae (DP) growth – II : Bulb Matrix Cells envelope DP  Differentiation  Descent of Bulb
  8. 8. Anagen • Stage III – Differentiation (Bulb Matrix Cells  Follicular Cells) • Stage IV – Matrix melanocytes reactivate • Stage V – Hair shaft emerges  Telopstosis • Stage VI – New hair shaft emerges from skin surface • Stage VII – Stable progressive growth
  9. 9. • aa
  10. 10. Bulge hypothesis • Franz Von Leydig • Lower portion of the follicle cyclically regenerates, the upper portion stays constant • The hair bulge harbours stem cells which give rise to all epithelial layers of hair follicle during anagen • Loss of hair follicle stem cells in bulge leads to permanent or cicatricial alopecia
  11. 11. Catagen • Onset is marked by cessation of mitotic activity of matrix cells • There is well coordinated apoptosis in the cyclic portion of hair follicle • Pigment production by melanocytes ceases before matrix cell proliferation, thus leading to the non pigmented proximal end of telogen club hair
  12. 12. Catagen • The lower follicle retracts upwards with dermal papilla • The perifollicular sheath forms a fibrous streamer comprised of fibroblasts,small blood vessels and collagen; Cuts off blood supply • 1 to 2% of follicles are in catagen • Duration is 2-3 weeks approx
  13. 13. Telogen • Stage of rest / QUISCENT • Approximately 10% of scalp hair are in Telogen • Duration is 02-03 months • Shedding is an active process • Formation of Club Root - Fully keratinized, dead hair
  14. 14. Telogen hair
  15. 15. Exogen • Stage of active hair shedding TELOPTOSIS • 1% of telogen hair are in exogen at a given time
  16. 16. Kenogen • Usually whenever a telogen hair is shed, an anagen hair is already present in the follicle to replace it • At times, the follicle stays empty after telogen sheds, this is known as kenogen • May last from weeks to months, seen in patients of androgenetic alopecia, prepubertal children
  17. 17. THANK YOU

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