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Hair follicle (structure)

  • Hair follicles are the structures which contain hairs supplying them with the cells to become hard keratin and melanin.
  • The cells are produced in the matrix which contains stem cells.
    • This area is located just over an area of richly irrigated areas (blood vessels).
  • Associated structures include glands (sebaceous and apocrine) and the arector pili muscles (contraction of these muscles in response to cold for example give rise to “goose bumps”).
  • Hair follicles cause hair to grow. Three phases exist: anagen, catagen and telogen.
    • anagen=growth phase
    • catagen=involuting or regressing phase
    • telogen=resting phase.
    • Hair growth cycle phases vary with the area: for example hairs are longer on the scalp because of a longer anagen phase (years). By contrast the phase is a few months for eyebrows.
  • In scarring alopecia hair follicles are destroyed but in non-scarring alopecia, these structures are mostly intact. In common balding, the topical drug minoxidil aims to dilate the blood vessels, in order to increase the blood supply to hair follicles (this drug was used to treat hypertension).